src/tools/rustfmt/src/items.rs

   1 // Formatting top-level items - functions, structs, enums, traits, impls.
   2
   3 use std::borrow::Cow;
   4 use std::cmp::{max, min, Ordering};
   5
   6 use regex::Regex;
   7 use rustc_ast::visit;
   8 use rustc_ast::{ast, ptr};
   9 use rustc_span::{symbol, BytePos, Span, DUMMY_SP};
  10
  11 use crate::attr::filter_inline_attrs;
  12 use crate::comment::{
  13     combine_strs_with_missing_comments, contains_comment, is_last_comment_block,
  14     recover_comment_removed, recover_missing_comment_in_span, rewrite_missing_comment,
  15     FindUncommented,
  16 };
  17 use crate::config::lists::*;
  18 use crate::config::{BraceStyle, Config, IndentStyle, Version};
  19 use crate::expr::{
  20     is_empty_block, is_simple_block_stmt, rewrite_assign_rhs, rewrite_assign_rhs_with,
  21     rewrite_assign_rhs_with_comments, RhsAssignKind, RhsTactics,
  22 };
  23 use crate::lists::{definitive_tactic, itemize_list, write_list, ListFormatting, Separator};
  24 use crate::macros::{rewrite_macro, MacroPosition};
  25 use crate::overflow;
  26 use crate::rewrite::{Rewrite, RewriteContext};
  27 use crate::shape::{Indent, Shape};
  28 use crate::source_map::{LineRangeUtils, SpanUtils};
  29 use crate::spanned::Spanned;
  30 use crate::stmt::Stmt;
  31 use crate::types::opaque_ty;
  32 use crate::utils::*;
  33 use crate::vertical::rewrite_with_alignment;
  34 use crate::visitor::FmtVisitor;
  35
  36 const DEFAULT_VISIBILITY: ast::Visibility = ast::Visibility {
  37     kind: ast::VisibilityKind::Inherited,
  38     span: DUMMY_SP,
  39     tokens: None,
  40 };
  41
  42 fn type_annotation_separator(config: &Config) -> &str {
  43     colon_spaces(config)
  44 }
  45
  46 // Statements of the form
  47 // let pat: ty = init;
  48 impl Rewrite for ast::Local {
  49     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
  50         debug!(
  51             "Local::rewrite {:?} {} {:?}",
  52             self, shape.width, shape.indent
  53         );
  54
  55         skip_out_of_file_lines_range!(context, self.span);
  56
  57         if contains_skip(&self.attrs) || matches!(self.kind, ast::LocalKind::InitElse(..)) {
  58             return None;
  59         }
  60
  61         let attrs_str = self.attrs.rewrite(context, shape)?;
  62         let mut result = if attrs_str.is_empty() {
  63             "let ".to_owned()
  64         } else {
  65             combine_strs_with_missing_comments(
  66                 context,
  67                 &attrs_str,
  68                 "let ",
  69                 mk_sp(
  70                     self.attrs.last().map(|a| a.span.hi()).unwrap(),
  71                     self.span.lo(),
  72                 ),
  73                 shape,
  74                 false,
  75             )?
  76         };
  77
  78         // 4 = "let ".len()
  79         let pat_shape = shape.offset_left(4)?;
  80         // 1 = ;
  81         let pat_shape = pat_shape.sub_width(1)?;
  82         let pat_str = self.pat.rewrite(context, pat_shape)?;
  83         result.push_str(&pat_str);
  84
  85         // String that is placed within the assignment pattern and expression.
  86         let infix = {
  87             let mut infix = String::with_capacity(32);
  88
  89             if let Some(ref ty) = self.ty {
  90                 let separator = type_annotation_separator(context.config);
  91                 let ty_shape = if pat_str.contains('\n') {
  92                     shape.with_max_width(context.config)
  93                 } else {
  94                     shape
  95                 }
  96                 .offset_left(last_line_width(&result) + separator.len())?
  97                 // 2 = ` =`
  98                 .sub_width(2)?;
  99
 100                 let rewrite = ty.rewrite(context, ty_shape)?;
 101
 102                 infix.push_str(separator);
 103                 infix.push_str(&rewrite);
 104             }
 105
 106             if self.kind.init().is_some() {
 107                 infix.push_str(" =");
 108             }
 109
 110             infix
 111         };
 112
 113         result.push_str(&infix);
 114
 115         if let Some((init, _els)) = self.kind.init_else_opt() {
 116             // 1 = trailing semicolon;
 117             let nested_shape = shape.sub_width(1)?;
 118
 119             result = rewrite_assign_rhs(
 120                 context,
 121                 result,
 122                 init,
 123                 &RhsAssignKind::Expr(&init.kind, init.span),
 124                 nested_shape,
 125             )?;
 126             // todo else
 127         }
 128
 129         result.push(';');
 130         Some(result)
 131     }
 132 }
 133
 134 // FIXME convert to using rewrite style rather than visitor
 135 // FIXME format modules in this style
 136 #[allow(dead_code)]
 137 #[derive(Debug)]
 138 struct Item<'a> {
 139     unsafety: ast::Unsafe,
 140     abi: Cow<'static, str>,
 141     vis: Option<&'a ast::Visibility>,
 142     body: Vec<BodyElement<'a>>,
 143     span: Span,
 144 }
 145
 146 impl<'a> Item<'a> {
 147     fn from_foreign_mod(fm: &'a ast::ForeignMod, span: Span, config: &Config) -> Item<'a> {
 148         Item {
 149             unsafety: fm.unsafety,
 150             abi: format_extern(
 151                 ast::Extern::from_abi(fm.abi, DUMMY_SP),
 152                 config.force_explicit_abi(),
 153                 true,
 154             ),
 155             vis: None,
 156             body: fm
 157                 .items
 158                 .iter()
 159                 .map(|i| BodyElement::ForeignItem(i))
 160                 .collect(),
 161             span,
 162         }
 163     }
 164 }
 165
 166 #[derive(Debug)]
 167 enum BodyElement<'a> {
 168     // Stmt(&'a ast::Stmt),
 169     // Field(&'a ast::ExprField),
 170     // Variant(&'a ast::Variant),
 171     // Item(&'a ast::Item),
 172     ForeignItem(&'a ast::ForeignItem),
 173 }
 174
 175 /// Represents a fn's signature.
 176 pub(crate) struct FnSig<'a> {
 177     decl: &'a ast::FnDecl,
 178     generics: &'a ast::Generics,
 179     ext: ast::Extern,
 180     is_async: Cow<'a, ast::Async>,
 181     constness: ast::Const,
 182     defaultness: ast::Defaultness,
 183     unsafety: ast::Unsafe,
 184     visibility: &'a ast::Visibility,
 185 }
 186
 187 impl<'a> FnSig<'a> {
 188     pub(crate) fn from_method_sig(
 189         method_sig: &'a ast::FnSig,
 190         generics: &'a ast::Generics,
 191         visibility: &'a ast::Visibility,
 192     ) -> FnSig<'a> {
 193         FnSig {
 194             unsafety: method_sig.header.unsafety,
 195             is_async: Cow::Borrowed(&method_sig.header.asyncness),
 196             constness: method_sig.header.constness,
 197             defaultness: ast::Defaultness::Final,
 198             ext: method_sig.header.ext,
 199             decl: &*method_sig.decl,
 200             generics,
 201             visibility,
 202         }
 203     }
 204
 205     pub(crate) fn from_fn_kind(
 206         fn_kind: &'a visit::FnKind<'_>,
 207         decl: &'a ast::FnDecl,
 208         defaultness: ast::Defaultness,
 209     ) -> FnSig<'a> {
 210         match *fn_kind {
 211             visit::FnKind::Fn(fn_ctxt, _, fn_sig, vis, generics, _) => match fn_ctxt {
 212                 visit::FnCtxt::Assoc(..) => {
 213                     let mut fn_sig = FnSig::from_method_sig(fn_sig, generics, vis);
 214                     fn_sig.defaultness = defaultness;
 215                     fn_sig
 216                 }
 217                 _ => FnSig {
 218                     decl,
 219                     generics,
 220                     ext: fn_sig.header.ext,
 221                     constness: fn_sig.header.constness,
 222                     is_async: Cow::Borrowed(&fn_sig.header.asyncness),
 223                     defaultness,
 224                     unsafety: fn_sig.header.unsafety,
 225                     visibility: vis,
 226                 },
 227             },
 228             _ => unreachable!(),
 229         }
 230     }
 231
 232     fn to_str(&self, context: &RewriteContext<'_>) -> String {
 233         let mut result = String::with_capacity(128);
 234         // Vis defaultness constness unsafety abi.
 235         result.push_str(&*format_visibility(context, self.visibility));
 236         result.push_str(format_defaultness(self.defaultness));
 237         result.push_str(format_constness(self.constness));
 238         result.push_str(format_async(&self.is_async));
 239         result.push_str(format_unsafety(self.unsafety));
 240         result.push_str(&format_extern(
 241             self.ext,
 242             context.config.force_explicit_abi(),
 243             false,
 244         ));
 245         result
 246     }
 247 }
 248
 249 impl<'a> FmtVisitor<'a> {
 250     fn format_item(&mut self, item: &Item<'_>) {
 251         self.buffer.push_str(format_unsafety(item.unsafety));
 252         self.buffer.push_str(&item.abi);
 253
 254         let snippet = self.snippet(item.span);
 255         let brace_pos = snippet.find_uncommented("{").unwrap();
 256
 257         self.push_str("{");
 258         if !item.body.is_empty() || contains_comment(&snippet[brace_pos..]) {
 259             // FIXME: this skips comments between the extern keyword and the opening
 260             // brace.
 261             self.last_pos = item.span.lo() + BytePos(brace_pos as u32 + 1);
 262             self.block_indent = self.block_indent.block_indent(self.config);
 263
 264             if !item.body.is_empty() {
 265                 for item in &item.body {
 266                     self.format_body_element(item);
 267                 }
 268             }
 269
 270             self.format_missing_no_indent(item.span.hi() - BytePos(1));
 271             self.block_indent = self.block_indent.block_unindent(self.config);
 272             let indent_str = self.block_indent.to_string(self.config);
 273             self.push_str(&indent_str);
 274         }
 275
 276         self.push_str("}");
 277         self.last_pos = item.span.hi();
 278     }
 279
 280     fn format_body_element(&mut self, element: &BodyElement<'_>) {
 281         match *element {
 282             BodyElement::ForeignItem(item) => self.format_foreign_item(item),
 283         }
 284     }
 285
 286     pub(crate) fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
 287         let item = Item::from_foreign_mod(fm, span, self.config);
 288         self.format_item(&item);
 289     }
 290
 291     fn format_foreign_item(&mut self, item: &ast::ForeignItem) {
 292         let rewrite = item.rewrite(&self.get_context(), self.shape());
 293         let hi = item.span.hi();
 294         let span = if item.attrs.is_empty() {
 295             item.span
 296         } else {
 297             mk_sp(item.attrs[0].span.lo(), hi)
 298         };
 299         self.push_rewrite(span, rewrite);
 300         self.last_pos = hi;
 301     }
 302
 303     pub(crate) fn rewrite_fn_before_block(
 304         &mut self,
 305         indent: Indent,
 306         ident: symbol::Ident,
 307         fn_sig: &FnSig<'_>,
 308         span: Span,
 309     ) -> Option<(String, FnBraceStyle)> {
 310         let context = self.get_context();
 311
 312         let mut fn_brace_style = newline_for_brace(self.config, &fn_sig.generics.where_clause);
 313         let (result, _, force_newline_brace) =
 314             rewrite_fn_base(&context, indent, ident, fn_sig, span, fn_brace_style)?;
 315
 316         // 2 = ` {`
 317         if self.config.brace_style() == BraceStyle::AlwaysNextLine
 318             || force_newline_brace
 319             || last_line_width(&result) + 2 > self.shape().width
 320         {
 321             fn_brace_style = FnBraceStyle::NextLine
 322         }
 323
 324         Some((result, fn_brace_style))
 325     }
 326
 327     pub(crate) fn rewrite_required_fn(
 328         &mut self,
 329         indent: Indent,
 330         ident: symbol::Ident,
 331         sig: &ast::FnSig,
 332         vis: &ast::Visibility,
 333         generics: &ast::Generics,
 334         span: Span,
 335     ) -> Option<String> {
 336         // Drop semicolon or it will be interpreted as comment.
 337         let span = mk_sp(span.lo(), span.hi() - BytePos(1));
 338         let context = self.get_context();
 339
 340         let (mut result, ends_with_comment, _) = rewrite_fn_base(
 341             &context,
 342             indent,
 343             ident,
 344             &FnSig::from_method_sig(sig, generics, vis),
 345             span,
 346             FnBraceStyle::None,
 347         )?;
 348
 349         // If `result` ends with a comment, then remember to add a newline
 350         if ends_with_comment {
 351             result.push_str(&indent.to_string_with_newline(context.config));
 352         }
 353
 354         // Re-attach semicolon
 355         result.push(';');
 356
 357         Some(result)
 358     }
 359
 360     pub(crate) fn single_line_fn(
 361         &self,
 362         fn_str: &str,
 363         block: &ast::Block,
 364         inner_attrs: Option<&[ast::Attribute]>,
 365     ) -> Option<String> {
 366         if fn_str.contains('\n') || inner_attrs.map_or(false, |a| !a.is_empty()) {
 367             return None;
 368         }
 369
 370         let context = self.get_context();
 371
 372         if self.config.empty_item_single_line()
 373             && is_empty_block(&context, block, None)
 374             && self.block_indent.width() + fn_str.len() + 3 <= self.config.max_width()
 375             && !last_line_contains_single_line_comment(fn_str)
 376         {
 377             return Some(format!("{} {{}}", fn_str));
 378         }
 379
 380         if !self.config.fn_single_line() || !is_simple_block_stmt(&context, block, None) {
 381             return None;
 382         }
 383
 384         let res = Stmt::from_ast_node(block.stmts.first()?, true)
 385             .rewrite(&self.get_context(), self.shape())?;
 386
 387         let width = self.block_indent.width() + fn_str.len() + res.len() + 5;
 388         if !res.contains('\n') && width <= self.config.max_width() {
 389             Some(format!("{} {{ {} }}", fn_str, res))
 390         } else {
 391             None
 392         }
 393     }
 394
 395     pub(crate) fn visit_static(&mut self, static_parts: &StaticParts<'_>) {
 396         let rewrite = rewrite_static(&self.get_context(), static_parts, self.block_indent);
 397         self.push_rewrite(static_parts.span, rewrite);
 398     }
 399
 400     pub(crate) fn visit_struct(&mut self, struct_parts: &StructParts<'_>) {
 401         let is_tuple = match struct_parts.def {
 402             ast::VariantData::Tuple(..) => true,
 403             _ => false,
 404         };
 405         let rewrite = format_struct(&self.get_context(), struct_parts, self.block_indent, None)
 406             .map(|s| if is_tuple { s + ";" } else { s });
 407         self.push_rewrite(struct_parts.span, rewrite);
 408     }
 409
 410     pub(crate) fn visit_enum(
 411         &mut self,
 412         ident: symbol::Ident,
 413         vis: &ast::Visibility,
 414         enum_def: &ast::EnumDef,
 415         generics: &ast::Generics,
 416         span: Span,
 417     ) {
 418         let enum_header =
 419             format_header(&self.get_context(), "enum ", ident, vis, self.block_indent);
 420         self.push_str(&enum_header);
 421
 422         let enum_snippet = self.snippet(span);
 423         let brace_pos = enum_snippet.find_uncommented("{").unwrap();
 424         let body_start = span.lo() + BytePos(brace_pos as u32 + 1);
 425         let generics_str = format_generics(
 426             &self.get_context(),
 427             generics,
 428             self.config.brace_style(),
 429             if enum_def.variants.is_empty() {
 430                 BracePos::ForceSameLine
 431             } else {
 432                 BracePos::Auto
 433             },
 434             self.block_indent,
 435             // make a span that starts right after `enum Foo`
 436             mk_sp(ident.span.hi(), body_start),
 437             last_line_width(&enum_header),
 438         )
 439         .unwrap();
 440         self.push_str(&generics_str);
 441
 442         self.last_pos = body_start;
 443
 444         match self.format_variant_list(enum_def, body_start, span.hi()) {
 445             Some(ref s) if enum_def.variants.is_empty() => self.push_str(s),
 446             rw => {
 447                 self.push_rewrite(mk_sp(body_start, span.hi()), rw);
 448                 self.block_indent = self.block_indent.block_unindent(self.config);
 449             }
 450         }
 451     }
 452
 453     // Format the body of an enum definition
 454     fn format_variant_list(
 455         &mut self,
 456         enum_def: &ast::EnumDef,
 457         body_lo: BytePos,
 458         body_hi: BytePos,
 459     ) -> Option<String> {
 460         if enum_def.variants.is_empty() {
 461             let mut buffer = String::with_capacity(128);
 462             // 1 = "}"
 463             let span = mk_sp(body_lo, body_hi - BytePos(1));
 464             format_empty_struct_or_tuple(
 465                 &self.get_context(),
 466                 span,
 467                 self.block_indent,
 468                 &mut buffer,
 469                 "",
 470                 "}",
 471             );
 472             return Some(buffer);
 473         }
 474         let mut result = String::with_capacity(1024);
 475         let original_offset = self.block_indent;
 476         self.block_indent = self.block_indent.block_indent(self.config);
 477
 478         // If enum variants have discriminants, try to vertically align those,
 479         // provided the discrims are not shifted too much  to the right
 480         let align_threshold: usize = self.config.enum_discrim_align_threshold();
 481         let discr_ident_lens: Vec<usize> = enum_def
 482             .variants
 483             .iter()
 484             .filter(|var| var.disr_expr.is_some())
 485             .map(|var| rewrite_ident(&self.get_context(), var.ident).len())
 486             .collect();
 487         // cut the list at the point of longest discrim shorter than the threshold
 488         // All of the discrims under the threshold will get padded, and all above - left as is.
 489         let pad_discrim_ident_to = *discr_ident_lens
 490             .iter()
 491             .filter(|&l| *l <= align_threshold)
 492             .max()
 493             .unwrap_or(&0);
 494
 495         let itemize_list_with = |one_line_width: usize| {
 496             itemize_list(
 497                 self.snippet_provider,
 498                 enum_def.variants.iter(),
 499                 "}",
 500                 ",",
 501                 |f| {
 502                     if !f.attrs.is_empty() {
 503                         f.attrs[0].span.lo()
 504                     } else {
 505                         f.span.lo()
 506                     }
 507                 },
 508                 |f| f.span.hi(),
 509                 |f| self.format_variant(f, one_line_width, pad_discrim_ident_to),
 510                 body_lo,
 511                 body_hi,
 512                 false,
 513             )
 514             .collect()
 515         };
 516         let mut items: Vec<_> = itemize_list_with(self.config.struct_variant_width());
 517
 518         // If one of the variants use multiple lines, use multi-lined formatting for all variants.
 519         let has_multiline_variant = items.iter().any(|item| item.inner_as_ref().contains('\n'));
 520         let has_single_line_variant = items.iter().any(|item| !item.inner_as_ref().contains('\n'));
 521         if has_multiline_variant && has_single_line_variant {
 522             items = itemize_list_with(0);
 523         }
 524
 525         let shape = self.shape().sub_width(2)?;
 526         let fmt = ListFormatting::new(shape, self.config)
 527             .trailing_separator(self.config.trailing_comma())
 528             .preserve_newline(true);
 529
 530         let list = write_list(&items, &fmt)?;
 531         result.push_str(&list);
 532         result.push_str(&original_offset.to_string_with_newline(self.config));
 533         result.push('}');
 534         Some(result)
 535     }
 536
 537     // Variant of an enum.
 538     fn format_variant(
 539         &self,
 540         field: &ast::Variant,
 541         one_line_width: usize,
 542         pad_discrim_ident_to: usize,
 543     ) -> Option<String> {
 544         if contains_skip(&field.attrs) {
 545             let lo = field.attrs[0].span.lo();
 546             let span = mk_sp(lo, field.span.hi());
 547             return Some(self.snippet(span).to_owned());
 548         }
 549
 550         let context = self.get_context();
 551         // 1 = ','
 552         let shape = self.shape().sub_width(1)?;
 553         let attrs_str = field.attrs.rewrite(&context, shape)?;
 554         let lo = field
 555             .attrs
 556             .last()
 557             .map_or(field.span.lo(), |attr| attr.span.hi());
 558         let span = mk_sp(lo, field.span.lo());
 559
 560         let variant_body = match field.data {
 561             ast::VariantData::Tuple(..) | ast::VariantData::Struct(..) => format_struct(
 562                 &context,
 563                 &StructParts::from_variant(field),
 564                 self.block_indent,
 565                 Some(one_line_width),
 566             )?,
 567             ast::VariantData::Unit(..) => rewrite_ident(&context, field.ident).to_owned(),
 568         };
 569
 570         let variant_body = if let Some(ref expr) = field.disr_expr {
 571             let lhs = format!("{:1$} =", variant_body, pad_discrim_ident_to);
 572             let ex = &*expr.value;
 573             rewrite_assign_rhs_with(
 574                 &context,
 575                 lhs,
 576                 ex,
 577                 shape,
 578                 &RhsAssignKind::Expr(&ex.kind, ex.span),
 579                 RhsTactics::AllowOverflow,
 580             )?
 581         } else {
 582             variant_body
 583         };
 584
 585         combine_strs_with_missing_comments(&context, &attrs_str, &variant_body, span, shape, false)
 586     }
 587
 588     fn visit_impl_items(&mut self, items: &[ptr::P<ast::AssocItem>]) {
 589         if self.get_context().config.reorder_impl_items() {
 590             type TyOpt = Option<ptr::P<ast::Ty>>;
 591             use crate::ast::AssocItemKind::*;
 592             let is_type = |ty: &TyOpt| opaque_ty(ty).is_none();
 593             let is_opaque = |ty: &TyOpt| opaque_ty(ty).is_some();
 594             let both_type = |l: &TyOpt, r: &TyOpt| is_type(l) && is_type(r);
 595             let both_opaque = |l: &TyOpt, r: &TyOpt| is_opaque(l) && is_opaque(r);
 596             let need_empty_line = |a: &ast::AssocItemKind, b: &ast::AssocItemKind| match (a, b) {
 597                 (Type(lty), Type(rty))
 598                     if both_type(&lty.ty, &rty.ty) || both_opaque(&lty.ty, &rty.ty) =>
 599                 {
 600                     false
 601                 }
 602                 (Const(..), Const(..)) => false,
 603                 _ => true,
 604             };
 605
 606             // Create visitor for each items, then reorder them.
 607             let mut buffer = vec![];
 608             for item in items {
 609                 self.visit_impl_item(item);
 610                 buffer.push((self.buffer.clone(), item.clone()));
 611                 self.buffer.clear();
 612             }
 613
 614             buffer.sort_by(|(_, a), (_, b)| match (&a.kind, &b.kind) {
 615                 (Type(lty), Type(rty))
 616                     if both_type(&lty.ty, &rty.ty) || both_opaque(&lty.ty, &rty.ty) =>
 617                 {
 618                     a.ident.as_str().cmp(b.ident.as_str())
 619                 }
 620                 (Const(..), Const(..)) | (MacCall(..), MacCall(..)) => {
 621                     a.ident.as_str().cmp(b.ident.as_str())
 622                 }
 623                 (Fn(..), Fn(..)) => a.span.lo().cmp(&b.span.lo()),
 624                 (Type(ty), _) if is_type(&ty.ty) => Ordering::Less,
 625                 (_, Type(ty)) if is_type(&ty.ty) => Ordering::Greater,
 626                 (Type(..), _) => Ordering::Less,
 627                 (_, Type(..)) => Ordering::Greater,
 628                 (Const(..), _) => Ordering::Less,
 629                 (_, Const(..)) => Ordering::Greater,
 630                 (MacCall(..), _) => Ordering::Less,
 631                 (_, MacCall(..)) => Ordering::Greater,
 632             });
 633             let mut prev_kind = None;
 634             for (buf, item) in buffer {
 635                 // Make sure that there are at least a single empty line between
 636                 // different impl items.
 637                 if prev_kind
 638                     .as_ref()
 639                     .map_or(false, |prev_kind| need_empty_line(prev_kind, &item.kind))
 640                 {
 641                     self.push_str("\n");
 642                 }
 643                 let indent_str = self.block_indent.to_string_with_newline(self.config);
 644                 self.push_str(&indent_str);
 645                 self.push_str(buf.trim());
 646                 prev_kind = Some(item.kind.clone());
 647             }
 648         } else {
 649             for item in items {
 650                 self.visit_impl_item(item);
 651             }
 652         }
 653     }
 654 }
 655
 656 pub(crate) fn format_impl(
 657     context: &RewriteContext<'_>,
 658     item: &ast::Item,
 659     iimpl: &ast::Impl,
 660     offset: Indent,
 661 ) -> Option<String> {
 662     let ast::Impl {
 663         generics,
 664         self_ty,
 665         items,
 666         ..
 667     } = iimpl;
 668     let mut result = String::with_capacity(128);
 669     let ref_and_type = format_impl_ref_and_type(context, item, iimpl, offset)?;
 670     let sep = offset.to_string_with_newline(context.config);
 671     result.push_str(&ref_and_type);
 672
 673     let where_budget = if result.contains('\n') {
 674         context.config.max_width()
 675     } else {
 676         context.budget(last_line_width(&result))
 677     };
 678
 679     let mut option = WhereClauseOption::snuggled(&ref_and_type);
 680     let snippet = context.snippet(item.span);
 681     let open_pos = snippet.find_uncommented("{")? + 1;
 682     if !contains_comment(&snippet[open_pos..])
 683         && items.is_empty()
 684         && generics.where_clause.predicates.len() == 1
 685         && !result.contains('\n')
 686     {
 687         option.suppress_comma();
 688         option.snuggle();
 689         option.allow_single_line();
 690     }
 691
 692     let missing_span = mk_sp(self_ty.span.hi(), item.span.hi());
 693     let where_span_end = context.snippet_provider.opt_span_before(missing_span, "{");
 694     let where_clause_str = rewrite_where_clause(
 695         context,
 696         &generics.where_clause.predicates,
 697         generics.where_clause.span,
 698         context.config.brace_style(),
 699         Shape::legacy(where_budget, offset.block_only()),
 700         false,
 701         "{",
 702         where_span_end,
 703         self_ty.span.hi(),
 704         option,
 705     )?;
 706
 707     // If there is no where-clause, we may have missing comments between the trait name and
 708     // the opening brace.
 709     if generics.where_clause.predicates.is_empty() {
 710         if let Some(hi) = where_span_end {
 711             match recover_missing_comment_in_span(
 712                 mk_sp(self_ty.span.hi(), hi),
 713                 Shape::indented(offset, context.config),
 714                 context,
 715                 last_line_width(&result),
 716             ) {
 717                 Some(ref missing_comment) if !missing_comment.is_empty() => {
 718                     result.push_str(missing_comment);
 719                 }
 720                 _ => (),
 721             }
 722         }
 723     }
 724
 725     if is_impl_single_line(context, items.as_slice(), &result, &where_clause_str, item)? {
 726         result.push_str(&where_clause_str);
 727         if where_clause_str.contains('\n') || last_line_contains_single_line_comment(&result) {
 728             // if the where_clause contains extra comments AND
 729             // there is only one where-clause predicate
 730             // recover the suppressed comma in single line where_clause formatting
 731             if generics.where_clause.predicates.len() == 1 {
 732                 result.push(',');
 733             }
 734             result.push_str(&format!("{}{{{}}}", sep, sep));
 735         } else {
 736             result.push_str(" {}");
 737         }
 738         return Some(result);
 739     }
 740
 741     result.push_str(&where_clause_str);
 742
 743     let need_newline = last_line_contains_single_line_comment(&result) || result.contains('\n');
 744     match context.config.brace_style() {
 745         _ if need_newline => result.push_str(&sep),
 746         BraceStyle::AlwaysNextLine => result.push_str(&sep),
 747         BraceStyle::PreferSameLine => result.push(' '),
 748         BraceStyle::SameLineWhere => {
 749             if !where_clause_str.is_empty() {
 750                 result.push_str(&sep);
 751             } else {
 752                 result.push(' ');
 753             }
 754         }
 755     }
 756
 757     result.push('{');
 758     // this is an impl body snippet(impl SampleImpl { /* here */ })
 759     let lo = max(self_ty.span.hi(), generics.where_clause.span.hi());
 760     let snippet = context.snippet(mk_sp(lo, item.span.hi()));
 761     let open_pos = snippet.find_uncommented("{")? + 1;
 762
 763     if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 764         let mut visitor = FmtVisitor::from_context(context);
 765         let item_indent = offset.block_only().block_indent(context.config);
 766         visitor.block_indent = item_indent;
 767         visitor.last_pos = lo + BytePos(open_pos as u32);
 768
 769         visitor.visit_attrs(&item.attrs, ast::AttrStyle::Inner);
 770         visitor.visit_impl_items(items);
 771
 772         visitor.format_missing(item.span.hi() - BytePos(1));
 773
 774         let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
 775         let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
 776
 777         result.push_str(&inner_indent_str);
 778         result.push_str(visitor.buffer.trim());
 779         result.push_str(&outer_indent_str);
 780     } else if need_newline || !context.config.empty_item_single_line() {
 781         result.push_str(&sep);
 782     }
 783
 784     result.push('}');
 785
 786     Some(result)
 787 }
 788
 789 fn is_impl_single_line(
 790     context: &RewriteContext<'_>,
 791     items: &[ptr::P<ast::AssocItem>],
 792     result: &str,
 793     where_clause_str: &str,
 794     item: &ast::Item,
 795 ) -> Option<bool> {
 796     let snippet = context.snippet(item.span);
 797     let open_pos = snippet.find_uncommented("{")? + 1;
 798
 799     Some(
 800         context.config.empty_item_single_line()
 801             && items.is_empty()
 802             && !result.contains('\n')
 803             && result.len() + where_clause_str.len() <= context.config.max_width()
 804             && !contains_comment(&snippet[open_pos..]),
 805     )
 806 }
 807
 808 fn format_impl_ref_and_type(
 809     context: &RewriteContext<'_>,
 810     item: &ast::Item,
 811     iimpl: &ast::Impl,
 812     offset: Indent,
 813 ) -> Option<String> {
 814     let ast::Impl {
 815         unsafety,
 816         polarity,
 817         defaultness,
 818         constness,
 819         ref generics,
 820         of_trait: ref trait_ref,
 821         ref self_ty,
 822         ..
 823     } = *iimpl;
 824     let mut result = String::with_capacity(128);
 825
 826     result.push_str(&format_visibility(context, &item.vis));
 827     result.push_str(format_defaultness(defaultness));
 828     result.push_str(format_unsafety(unsafety));
 829
 830     let shape = if context.config.version() == Version::Two {
 831         Shape::indented(offset + last_line_width(&result), context.config)
 832     } else {
 833         generics_shape_from_config(
 834             context.config,
 835             Shape::indented(offset + last_line_width(&result), context.config),
 836             0,
 837         )?
 838     };
 839     let generics_str = rewrite_generics(context, "impl", generics, shape)?;
 840     result.push_str(&generics_str);
 841     result.push_str(format_constness_right(constness));
 842
 843     let polarity_str = match polarity {
 844         ast::ImplPolarity::Negative(_) => "!",
 845         ast::ImplPolarity::Positive => "",
 846     };
 847
 848     let polarity_overhead;
 849     let trait_ref_overhead;
 850     if let Some(ref trait_ref) = *trait_ref {
 851         let result_len = last_line_width(&result);
 852         result.push_str(&rewrite_trait_ref(
 853             context,
 854             trait_ref,
 855             offset,
 856             polarity_str,
 857             result_len,
 858         )?);
 859         polarity_overhead = 0; // already written
 860         trait_ref_overhead = " for".len();
 861     } else {
 862         polarity_overhead = polarity_str.len();
 863         trait_ref_overhead = 0;
 864     }
 865
 866     // Try to put the self type in a single line.
 867     let curly_brace_overhead = if generics.where_clause.predicates.is_empty() {
 868         // If there is no where-clause adapt budget for type formatting to take space and curly
 869         // brace into account.
 870         match context.config.brace_style() {
 871             BraceStyle::AlwaysNextLine => 0,
 872             _ => 2,
 873         }
 874     } else {
 875         0
 876     };
 877     let used_space =
 878         last_line_width(&result) + polarity_overhead + trait_ref_overhead + curly_brace_overhead;
 879     // 1 = space before the type.
 880     let budget = context.budget(used_space + 1);
 881     if let Some(self_ty_str) = self_ty.rewrite(context, Shape::legacy(budget, offset)) {
 882         if !self_ty_str.contains('\n') {
 883             if trait_ref.is_some() {
 884                 result.push_str(" for ");
 885             } else {
 886                 result.push(' ');
 887                 result.push_str(polarity_str);
 888             }
 889             result.push_str(&self_ty_str);
 890             return Some(result);
 891         }
 892     }
 893
 894     // Couldn't fit the self type on a single line, put it on a new line.
 895     result.push('\n');
 896     // Add indentation of one additional tab.
 897     let new_line_offset = offset.block_indent(context.config);
 898     result.push_str(&new_line_offset.to_string(context.config));
 899     if trait_ref.is_some() {
 900         result.push_str("for ");
 901     } else {
 902         result.push_str(polarity_str);
 903     }
 904     let budget = context.budget(last_line_width(&result) + polarity_overhead);
 905     let type_offset = match context.config.indent_style() {
 906         IndentStyle::Visual => new_line_offset + trait_ref_overhead,
 907         IndentStyle::Block => new_line_offset,
 908     };
 909     result.push_str(&*self_ty.rewrite(context, Shape::legacy(budget, type_offset))?);
 910     Some(result)
 911 }
 912
 913 fn rewrite_trait_ref(
 914     context: &RewriteContext<'_>,
 915     trait_ref: &ast::TraitRef,
 916     offset: Indent,
 917     polarity_str: &str,
 918     result_len: usize,
 919 ) -> Option<String> {
 920     // 1 = space between generics and trait_ref
 921     let used_space = 1 + polarity_str.len() + result_len;
 922     let shape = Shape::indented(offset + used_space, context.config);
 923     if let Some(trait_ref_str) = trait_ref.rewrite(context, shape) {
 924         if !trait_ref_str.contains('\n') {
 925             return Some(format!(" {}{}", polarity_str, trait_ref_str));
 926         }
 927     }
 928     // We could not make enough space for trait_ref, so put it on new line.
 929     let offset = offset.block_indent(context.config);
 930     let shape = Shape::indented(offset, context.config);
 931     let trait_ref_str = trait_ref.rewrite(context, shape)?;
 932     Some(format!(
 933         "{}{}{}",
 934         offset.to_string_with_newline(context.config),
 935         polarity_str,
 936         trait_ref_str
 937     ))
 938 }
 939
 940 pub(crate) struct StructParts<'a> {
 941     prefix: &'a str,
 942     ident: symbol::Ident,
 943     vis: &'a ast::Visibility,
 944     def: &'a ast::VariantData,
 945     generics: Option<&'a ast::Generics>,
 946     span: Span,
 947 }
 948
 949 impl<'a> StructParts<'a> {
 950     fn format_header(&self, context: &RewriteContext<'_>, offset: Indent) -> String {
 951         format_header(context, self.prefix, self.ident, self.vis, offset)
 952     }
 953
 954     fn from_variant(variant: &'a ast::Variant) -> Self {
 955         StructParts {
 956             prefix: "",
 957             ident: variant.ident,
 958             vis: &DEFAULT_VISIBILITY,
 959             def: &variant.data,
 960             generics: None,
 961             span: variant.span,
 962         }
 963     }
 964
 965     pub(crate) fn from_item(item: &'a ast::Item) -> Self {
 966         let (prefix, def, generics) = match item.kind {
 967             ast::ItemKind::Struct(ref def, ref generics) => ("struct ", def, generics),
 968             ast::ItemKind::Union(ref def, ref generics) => ("union ", def, generics),
 969             _ => unreachable!(),
 970         };
 971         StructParts {
 972             prefix,
 973             ident: item.ident,
 974             vis: &item.vis,
 975             def,
 976             generics: Some(generics),
 977             span: item.span,
 978         }
 979     }
 980 }
 981
 982 fn format_struct(
 983     context: &RewriteContext<'_>,
 984     struct_parts: &StructParts<'_>,
 985     offset: Indent,
 986     one_line_width: Option<usize>,
 987 ) -> Option<String> {
 988     match *struct_parts.def {
 989         ast::VariantData::Unit(..) => format_unit_struct(context, struct_parts, offset),
 990         ast::VariantData::Tuple(ref fields, _) => {
 991             format_tuple_struct(context, struct_parts, fields, offset)
 992         }
 993         ast::VariantData::Struct(ref fields, _) => {
 994             format_struct_struct(context, struct_parts, fields, offset, one_line_width)
 995         }
 996     }
 997 }
 998
 999 pub(crate) fn format_trait(
1000     context: &RewriteContext<'_>,
1001     item: &ast::Item,
1002     offset: Indent,
1003 ) -> Option<String> {
1004     if let ast::ItemKind::Trait(trait_kind) = &item.kind {
1005         let ast::Trait {
1006             is_auto,
1007             unsafety,
1008             ref generics,
1009             ref bounds,
1010             ref items,
1011         } = **trait_kind;
1012         let mut result = String::with_capacity(128);
1013         let header = format!(
1014             "{}{}{}trait ",
1015             format_visibility(context, &item.vis),
1016             format_unsafety(unsafety),
1017             format_auto(is_auto),
1018         );
1019         result.push_str(&header);
1020
1021         let body_lo = context.snippet_provider.span_after(item.span, "{");
1022
1023         let shape = Shape::indented(offset, context.config).offset_left(result.len())?;
1024         let generics_str =
1025             rewrite_generics(context, rewrite_ident(context, item.ident), generics, shape)?;
1026         result.push_str(&generics_str);
1027
1028         // FIXME(#2055): rustfmt fails to format when there are comments between trait bounds.
1029         if !bounds.is_empty() {
1030             let ident_hi = context
1031                 .snippet_provider
1032                 .span_after(item.span, item.ident.as_str());
1033             let bound_hi = bounds.last().unwrap().span().hi();
1034             let snippet = context.snippet(mk_sp(ident_hi, bound_hi));
1035             if contains_comment(snippet) {
1036                 return None;
1037             }
1038
1039             result = rewrite_assign_rhs_with(
1040                 context,
1041                 result + ":",
1042                 bounds,
1043                 shape,
1044                 &RhsAssignKind::Bounds,
1045                 RhsTactics::ForceNextLineWithoutIndent,
1046             )?;
1047         }
1048
1049         // Rewrite where-clause.
1050         if !generics.where_clause.predicates.is_empty() {
1051             let where_on_new_line = context.config.indent_style() != IndentStyle::Block;
1052
1053             let where_budget = context.budget(last_line_width(&result));
1054             let pos_before_where = if bounds.is_empty() {
1055                 generics.where_clause.span.lo()
1056             } else {
1057                 bounds[bounds.len() - 1].span().hi()
1058             };
1059             let option = WhereClauseOption::snuggled(&generics_str);
1060             let where_clause_str = rewrite_where_clause(
1061                 context,
1062                 &generics.where_clause.predicates,
1063                 generics.where_clause.span,
1064                 context.config.brace_style(),
1065                 Shape::legacy(where_budget, offset.block_only()),
1066                 where_on_new_line,
1067                 "{",
1068                 None,
1069                 pos_before_where,
1070                 option,
1071             )?;
1072             // If the where-clause cannot fit on the same line,
1073             // put the where-clause on a new line
1074             if !where_clause_str.contains('\n')
1075                 && last_line_width(&result) + where_clause_str.len() + offset.width()
1076                     > context.config.comment_width()
1077             {
1078                 let width = offset.block_indent + context.config.tab_spaces() - 1;
1079                 let where_indent = Indent::new(0, width);
1080                 result.push_str(&where_indent.to_string_with_newline(context.config));
1081             }
1082             result.push_str(&where_clause_str);
1083         } else {
1084             let item_snippet = context.snippet(item.span);
1085             if let Some(lo) = item_snippet.find('/') {
1086                 // 1 = `{`
1087                 let comment_hi = body_lo - BytePos(1);
1088                 let comment_lo = item.span.lo() + BytePos(lo as u32);
1089                 if comment_lo < comment_hi {
1090                     match recover_missing_comment_in_span(
1091                         mk_sp(comment_lo, comment_hi),
1092                         Shape::indented(offset, context.config),
1093                         context,
1094                         last_line_width(&result),
1095                     ) {
1096                         Some(ref missing_comment) if !missing_comment.is_empty() => {
1097                             result.push_str(missing_comment);
1098                         }
1099                         _ => (),
1100                     }
1101                 }
1102             }
1103         }
1104
1105         let block_span = mk_sp(generics.where_clause.span.hi(), item.span.hi());
1106         let snippet = context.snippet(block_span);
1107         let open_pos = snippet.find_uncommented("{")? + 1;
1108
1109         match context.config.brace_style() {
1110             _ if last_line_contains_single_line_comment(&result)
1111                 || last_line_width(&result) + 2 > context.budget(offset.width()) =>
1112             {
1113                 result.push_str(&offset.to_string_with_newline(context.config));
1114             }
1115             _ if context.config.empty_item_single_line()
1116                 && items.is_empty()
1117                 && !result.contains('\n')
1118                 && !contains_comment(&snippet[open_pos..]) =>
1119             {
1120                 result.push_str(" {}");
1121                 return Some(result);
1122             }
1123             BraceStyle::AlwaysNextLine => {
1124                 result.push_str(&offset.to_string_with_newline(context.config));
1125             }
1126             BraceStyle::PreferSameLine => result.push(' '),
1127             BraceStyle::SameLineWhere => {
1128                 if result.contains('\n')
1129                     || (!generics.where_clause.predicates.is_empty() && !items.is_empty())
1130                 {
1131                     result.push_str(&offset.to_string_with_newline(context.config));
1132                 } else {
1133                     result.push(' ');
1134                 }
1135             }
1136         }
1137         result.push('{');
1138
1139         let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
1140
1141         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
1142             let mut visitor = FmtVisitor::from_context(context);
1143             visitor.block_indent = offset.block_only().block_indent(context.config);
1144             visitor.last_pos = block_span.lo() + BytePos(open_pos as u32);
1145
1146             for item in items {
1147                 visitor.visit_trait_item(item);
1148             }
1149
1150             visitor.format_missing(item.span.hi() - BytePos(1));
1151
1152             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
1153
1154             result.push_str(&inner_indent_str);
1155             result.push_str(visitor.buffer.trim());
1156             result.push_str(&outer_indent_str);
1157         } else if result.contains('\n') {
1158             result.push_str(&outer_indent_str);
1159         }
1160
1161         result.push('}');
1162         Some(result)
1163     } else {
1164         unreachable!();
1165     }
1166 }
1167
1168 pub(crate) struct TraitAliasBounds<'a> {
1169     generic_bounds: &'a ast::GenericBounds,
1170     generics: &'a ast::Generics,
1171 }
1172
1173 impl<'a> Rewrite for TraitAliasBounds<'a> {
1174     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1175         let generic_bounds_str = self.generic_bounds.rewrite(context, shape)?;
1176
1177         let mut option = WhereClauseOption::new(true, WhereClauseSpace::None);
1178         option.allow_single_line();
1179
1180         let where_str = rewrite_where_clause(
1181             context,
1182             &self.generics.where_clause.predicates,
1183             self.generics.where_clause.span,
1184             context.config.brace_style(),
1185             shape,
1186             false,
1187             ";",
1188             None,
1189             self.generics.where_clause.span.lo(),
1190             option,
1191         )?;
1192
1193         let fits_single_line = !generic_bounds_str.contains('\n')
1194             && !where_str.contains('\n')
1195             && generic_bounds_str.len() + where_str.len() < shape.width;
1196         let space = if generic_bounds_str.is_empty() || where_str.is_empty() {
1197             Cow::from("")
1198         } else if fits_single_line {
1199             Cow::from(" ")
1200         } else {
1201             shape.indent.to_string_with_newline(context.config)
1202         };
1203
1204         Some(format!("{}{}{}", generic_bounds_str, space, where_str))
1205     }
1206 }
1207
1208 pub(crate) fn format_trait_alias(
1209     context: &RewriteContext<'_>,
1210     ident: symbol::Ident,
1211     vis: &ast::Visibility,
1212     generics: &ast::Generics,
1213     generic_bounds: &ast::GenericBounds,
1214     shape: Shape,
1215 ) -> Option<String> {
1216     let alias = rewrite_ident(context, ident);
1217     // 6 = "trait ", 2 = " ="
1218     let g_shape = shape.offset_left(6)?.sub_width(2)?;
1219     let generics_str = rewrite_generics(context, alias, generics, g_shape)?;
1220     let vis_str = format_visibility(context, vis);
1221     let lhs = format!("{}trait {} =", vis_str, generics_str);
1222     // 1 = ";"
1223     let trait_alias_bounds = TraitAliasBounds {
1224         generic_bounds,
1225         generics,
1226     };
1227     rewrite_assign_rhs(
1228         context,
1229         lhs,
1230         &trait_alias_bounds,
1231         &RhsAssignKind::Bounds,
1232         shape.sub_width(1)?,
1233     )
1234     .map(|s| s + ";")
1235 }
1236
1237 fn format_unit_struct(
1238     context: &RewriteContext<'_>,
1239     p: &StructParts<'_>,
1240     offset: Indent,
1241 ) -> Option<String> {
1242     let header_str = format_header(context, p.prefix, p.ident, p.vis, offset);
1243     let generics_str = if let Some(generics) = p.generics {
1244         let hi = context.snippet_provider.span_before(p.span, ";");
1245         format_generics(
1246             context,
1247             generics,
1248             context.config.brace_style(),
1249             BracePos::None,
1250             offset,
1251             // make a span that starts right after `struct Foo`
1252             mk_sp(p.ident.span.hi(), hi),
1253             last_line_width(&header_str),
1254         )?
1255     } else {
1256         String::new()
1257     };
1258     Some(format!("{}{};", header_str, generics_str))
1259 }
1260
1261 pub(crate) fn format_struct_struct(
1262     context: &RewriteContext<'_>,
1263     struct_parts: &StructParts<'_>,
1264     fields: &[ast::FieldDef],
1265     offset: Indent,
1266     one_line_width: Option<usize>,
1267 ) -> Option<String> {
1268     let mut result = String::with_capacity(1024);
1269     let span = struct_parts.span;
1270
1271     let header_str = struct_parts.format_header(context, offset);
1272     result.push_str(&header_str);
1273
1274     let header_hi = struct_parts.ident.span.hi();
1275     let body_lo = if let Some(generics) = struct_parts.generics {
1276         // Adjust the span to start at the end of the generic arguments before searching for the '{'
1277         let span = span.with_lo(generics.span.hi());
1278         context.snippet_provider.span_after(span, "{")
1279     } else {
1280         context.snippet_provider.span_after(span, "{")
1281     };
1282
1283     let generics_str = match struct_parts.generics {
1284         Some(g) => format_generics(
1285             context,
1286             g,
1287             context.config.brace_style(),
1288             if fields.is_empty() {
1289                 BracePos::ForceSameLine
1290             } else {
1291                 BracePos::Auto
1292             },
1293             offset,
1294             // make a span that starts right after `struct Foo`
1295             mk_sp(header_hi, body_lo),
1296             last_line_width(&result),
1297         )?,
1298         None => {
1299             // 3 = ` {}`, 2 = ` {`.
1300             let overhead = if fields.is_empty() { 3 } else { 2 };
1301             if (context.config.brace_style() == BraceStyle::AlwaysNextLine && !fields.is_empty())
1302                 || context.config.max_width() < overhead + result.len()
1303             {
1304                 format!("\n{}{{", offset.block_only().to_string(context.config))
1305             } else {
1306                 " {".to_owned()
1307             }
1308         }
1309     };
1310     // 1 = `}`
1311     let overhead = if fields.is_empty() { 1 } else { 0 };
1312     let total_width = result.len() + generics_str.len() + overhead;
1313     if !generics_str.is_empty()
1314         && !generics_str.contains('\n')
1315         && total_width > context.config.max_width()
1316     {
1317         result.push('\n');
1318         result.push_str(&offset.to_string(context.config));
1319         result.push_str(generics_str.trim_start());
1320     } else {
1321         result.push_str(&generics_str);
1322     }
1323
1324     if fields.is_empty() {
1325         let inner_span = mk_sp(body_lo, span.hi() - BytePos(1));
1326         format_empty_struct_or_tuple(context, inner_span, offset, &mut result, "", "}");
1327         return Some(result);
1328     }
1329
1330     // 3 = ` ` and ` }`
1331     let one_line_budget = context.budget(result.len() + 3 + offset.width());
1332     let one_line_budget =
1333         one_line_width.map_or(0, |one_line_width| min(one_line_width, one_line_budget));
1334
1335     let items_str = rewrite_with_alignment(
1336         fields,
1337         context,
1338         Shape::indented(offset.block_indent(context.config), context.config).sub_width(1)?,
1339         mk_sp(body_lo, span.hi()),
1340         one_line_budget,
1341     )?;
1342
1343     if !items_str.contains('\n')
1344         && !result.contains('\n')
1345         && items_str.len() <= one_line_budget
1346         && !last_line_contains_single_line_comment(&items_str)
1347     {
1348         Some(format!("{} {} }}", result, items_str))
1349     } else {
1350         Some(format!(
1351             "{}\n{}{}\n{}}}",
1352             result,
1353             offset
1354                 .block_indent(context.config)
1355                 .to_string(context.config),
1356             items_str,
1357             offset.to_string(context.config)
1358         ))
1359     }
1360 }
1361
1362 fn get_bytepos_after_visibility(vis: &ast::Visibility, default_span: Span) -> BytePos {
1363     match vis.kind {
1364         ast::VisibilityKind::Restricted { .. } => vis.span.hi(),
1365         _ => default_span.lo(),
1366     }
1367 }
1368
1369 // Format tuple or struct without any fields. We need to make sure that the comments
1370 // inside the delimiters are preserved.
1371 fn format_empty_struct_or_tuple(
1372     context: &RewriteContext<'_>,
1373     span: Span,
1374     offset: Indent,
1375     result: &mut String,
1376     opener: &str,
1377     closer: &str,
1378 ) {
1379     // 3 = " {}" or "();"
1380     let used_width = last_line_used_width(result, offset.width()) + 3;
1381     if used_width > context.config.max_width() {
1382         result.push_str(&offset.to_string_with_newline(context.config))
1383     }
1384     result.push_str(opener);
1385
1386     // indented shape for proper indenting of multi-line comments
1387     let shape = Shape::indented(offset.block_indent(context.config), context.config);
1388     match rewrite_missing_comment(span, shape, context) {
1389         Some(ref s) if s.is_empty() => (),
1390         Some(ref s) => {
1391             let is_multi_line = !is_single_line(s);
1392             if is_multi_line || first_line_contains_single_line_comment(s) {
1393                 let nested_indent_str = offset
1394                     .block_indent(context.config)
1395                     .to_string_with_newline(context.config);
1396                 result.push_str(&nested_indent_str);
1397             }
1398             result.push_str(s);
1399             if is_multi_line || last_line_contains_single_line_comment(s) {
1400                 result.push_str(&offset.to_string_with_newline(context.config));
1401             }
1402         }
1403         None => result.push_str(context.snippet(span)),
1404     }
1405     result.push_str(closer);
1406 }
1407
1408 fn format_tuple_struct(
1409     context: &RewriteContext<'_>,
1410     struct_parts: &StructParts<'_>,
1411     fields: &[ast::FieldDef],
1412     offset: Indent,
1413 ) -> Option<String> {
1414     let mut result = String::with_capacity(1024);
1415     let span = struct_parts.span;
1416
1417     let header_str = struct_parts.format_header(context, offset);
1418     result.push_str(&header_str);
1419
1420     let body_lo = if fields.is_empty() {
1421         let lo = get_bytepos_after_visibility(struct_parts.vis, span);
1422         context
1423             .snippet_provider
1424             .span_after(mk_sp(lo, span.hi()), "(")
1425     } else {
1426         fields[0].span.lo()
1427     };
1428     let body_hi = if fields.is_empty() {
1429         context
1430             .snippet_provider
1431             .span_after(mk_sp(body_lo, span.hi()), ")")
1432     } else {
1433         // This is a dirty hack to work around a missing `)` from the span of the last field.
1434         let last_arg_span = fields[fields.len() - 1].span;
1435         context
1436             .snippet_provider
1437             .opt_span_after(mk_sp(last_arg_span.hi(), span.hi()), ")")
1438             .unwrap_or_else(|| last_arg_span.hi())
1439     };
1440
1441     let where_clause_str = match struct_parts.generics {
1442         Some(generics) => {
1443             let budget = context.budget(last_line_width(&header_str));
1444             let shape = Shape::legacy(budget, offset);
1445             let generics_str = rewrite_generics(context, "", generics, shape)?;
1446             result.push_str(&generics_str);
1447
1448             let where_budget = context.budget(last_line_width(&result));
1449             let option = WhereClauseOption::new(true, WhereClauseSpace::Newline);
1450             rewrite_where_clause(
1451                 context,
1452                 &generics.where_clause.predicates,
1453                 generics.where_clause.span,
1454                 context.config.brace_style(),
1455                 Shape::legacy(where_budget, offset.block_only()),
1456                 false,
1457                 ";",
1458                 None,
1459                 body_hi,
1460                 option,
1461             )?
1462         }
1463         None => "".to_owned(),
1464     };
1465
1466     if fields.is_empty() {
1467         let body_hi = context
1468             .snippet_provider
1469             .span_before(mk_sp(body_lo, span.hi()), ")");
1470         let inner_span = mk_sp(body_lo, body_hi);
1471         format_empty_struct_or_tuple(context, inner_span, offset, &mut result, "(", ")");
1472     } else {
1473         let shape = Shape::indented(offset, context.config).sub_width(1)?;
1474         let lo = if let Some(generics) = struct_parts.generics {
1475             generics.span.hi()
1476         } else {
1477             struct_parts.ident.span.hi()
1478         };
1479         result = overflow::rewrite_with_parens(
1480             context,
1481             &result,
1482             fields.iter(),
1483             shape,
1484             mk_sp(lo, span.hi()),
1485             context.config.fn_call_width(),
1486             None,
1487         )?;
1488     }
1489
1490     if !where_clause_str.is_empty()
1491         && !where_clause_str.contains('\n')
1492         && (result.contains('\n')
1493             || offset.block_indent + result.len() + where_clause_str.len() + 1
1494                 > context.config.max_width())
1495     {
1496         // We need to put the where-clause on a new line, but we didn't
1497         // know that earlier, so the where-clause will not be indented properly.
1498         result.push('\n');
1499         result.push_str(
1500             &(offset.block_only() + (context.config.tab_spaces() - 1)).to_string(context.config),
1501         );
1502     }
1503     result.push_str(&where_clause_str);
1504
1505     Some(result)
1506 }
1507
1508 pub(crate) enum ItemVisitorKind<'a> {
1509     Item(&'a ast::Item),
1510     AssocTraitItem(&'a ast::AssocItem),
1511     AssocImplItem(&'a ast::AssocItem),
1512     ForeignItem(&'a ast::ForeignItem),
1513 }
1514
1515 struct TyAliasRewriteInfo<'c, 'g>(
1516     &'c RewriteContext<'c>,
1517     Indent,
1518     &'g ast::Generics,
1519     (ast::TyAliasWhereClause, ast::TyAliasWhereClause),
1520     usize,
1521     symbol::Ident,
1522     Span,
1523 );
1524
1525 pub(crate) fn rewrite_type_alias<'a, 'b>(
1526     ty_alias_kind: &ast::TyAlias,
1527     context: &RewriteContext<'a>,
1528     indent: Indent,
1529     visitor_kind: &ItemVisitorKind<'b>,
1530     span: Span,
1531 ) -> Option<String> {
1532     use ItemVisitorKind::*;
1533
1534     let ast::TyAlias {
1535         defaultness,
1536         ref generics,
1537         ref bounds,
1538         ref ty,
1539         where_clauses,
1540         where_predicates_split,
1541     } = *ty_alias_kind;
1542     let ty_opt = ty.as_ref();
1543     let (ident, vis) = match visitor_kind {
1544         Item(i) => (i.ident, &i.vis),
1545         AssocTraitItem(i) | AssocImplItem(i) => (i.ident, &i.vis),
1546         ForeignItem(i) => (i.ident, &i.vis),
1547     };
1548     let rw_info = &TyAliasRewriteInfo(
1549         context,
1550         indent,
1551         generics,
1552         where_clauses,
1553         where_predicates_split,
1554         ident,
1555         span,
1556     );
1557     let op_ty = opaque_ty(ty);
1558     // Type Aliases are formatted slightly differently depending on the context
1559     // in which they appear, whether they are opaque, and whether they are associated.
1560     // https://rustc-dev-guide.rust-lang.org/opaque-types-type-alias-impl-trait.html
1561     // https://github.com/rust-dev-tools/fmt-rfcs/blob/master/guide/items.md#type-aliases
1562     match (visitor_kind, &op_ty) {
1563         (Item(_) | AssocTraitItem(_) | ForeignItem(_), Some(op_bounds)) => {
1564             let op = OpaqueType { bounds: op_bounds };
1565             rewrite_ty(rw_info, Some(bounds), Some(&op), vis)
1566         }
1567         (Item(_) | AssocTraitItem(_) | ForeignItem(_), None) => {
1568             rewrite_ty(rw_info, Some(bounds), ty_opt, vis)
1569         }
1570         (AssocImplItem(_), _) => {
1571             let result = if let Some(op_bounds) = op_ty {
1572                 let op = OpaqueType { bounds: op_bounds };
1573                 rewrite_ty(rw_info, Some(bounds), Some(&op), &DEFAULT_VISIBILITY)
1574             } else {
1575                 rewrite_ty(rw_info, Some(bounds), ty_opt, vis)
1576             }?;
1577             match defaultness {
1578                 ast::Defaultness::Default(..) => Some(format!("default {}", result)),
1579                 _ => Some(result),
1580             }
1581         }
1582     }
1583 }
1584
1585 fn rewrite_ty<R: Rewrite>(
1586     rw_info: &TyAliasRewriteInfo<'_, '_>,
1587     generic_bounds_opt: Option<&ast::GenericBounds>,
1588     rhs: Option<&R>,
1589     vis: &ast::Visibility,
1590 ) -> Option<String> {
1591     let mut result = String::with_capacity(128);
1592     let TyAliasRewriteInfo(
1593         context,
1594         indent,
1595         generics,
1596         where_clauses,
1597         where_predicates_split,
1598         ident,
1599         span,
1600     ) = *rw_info;
1601     let (before_where_predicates, after_where_predicates) = generics
1602         .where_clause
1603         .predicates
1604         .split_at(where_predicates_split);
1605     if !after_where_predicates.is_empty() {
1606         return None;
1607     }
1608     result.push_str(&format!("{}type ", format_visibility(context, vis)));
1609     let ident_str = rewrite_ident(context, ident);
1610
1611     if generics.params.is_empty() {
1612         result.push_str(ident_str)
1613     } else {
1614         // 2 = `= `
1615         let g_shape = Shape::indented(indent, context.config)
1616             .offset_left(result.len())?
1617             .sub_width(2)?;
1618         let generics_str = rewrite_generics(context, ident_str, generics, g_shape)?;
1619         result.push_str(&generics_str);
1620     }
1621
1622     if let Some(bounds) = generic_bounds_opt {
1623         if !bounds.is_empty() {
1624             // 2 = `: `
1625             let shape = Shape::indented(indent, context.config).offset_left(result.len() + 2)?;
1626             let type_bounds = bounds.rewrite(context, shape).map(|s| format!(": {}", s))?;
1627             result.push_str(&type_bounds);
1628         }
1629     }
1630
1631     let where_budget = context.budget(last_line_width(&result));
1632     let mut option = WhereClauseOption::snuggled(&result);
1633     if rhs.is_none() {
1634         option.suppress_comma();
1635     }
1636     let where_clause_str = rewrite_where_clause(
1637         context,
1638         before_where_predicates,
1639         where_clauses.0.1,
1640         context.config.brace_style(),
1641         Shape::legacy(where_budget, indent),
1642         false,
1643         "=",
1644         None,
1645         generics.span.hi(),
1646         option,
1647     )?;
1648     result.push_str(&where_clause_str);
1649
1650     if let Some(ty) = rhs {
1651         // If there's a where clause, add a newline before the assignment. Otherwise just add a
1652         // space.
1653         let has_where = !before_where_predicates.is_empty();
1654         if has_where {
1655             result.push_str(&indent.to_string_with_newline(context.config));
1656         } else {
1657             result.push(' ');
1658         }
1659
1660         let comment_span = context
1661             .snippet_provider
1662             .opt_span_before(span, "=")
1663             .map(|op_lo| mk_sp(where_clauses.0.1.hi(), op_lo));
1664
1665         let lhs = match comment_span {
1666             Some(comment_span)
1667                 if contains_comment(context.snippet_provider.span_to_snippet(comment_span)?) =>
1668             {
1669                 let comment_shape = if has_where {
1670                     Shape::indented(indent, context.config)
1671                 } else {
1672                     Shape::indented(indent, context.config)
1673                         .block_left(context.config.tab_spaces())?
1674                 };
1675
1676                 combine_strs_with_missing_comments(
1677                     context,
1678                     result.trim_end(),
1679                     "=",
1680                     comment_span,
1681                     comment_shape,
1682                     true,
1683                 )?
1684             }
1685             _ => format!("{}=", result),
1686         };
1687
1688         // 1 = `;`
1689         let shape = Shape::indented(indent, context.config).sub_width(1)?;
1690         rewrite_assign_rhs(context, lhs, &*ty, &RhsAssignKind::Ty, shape).map(|s| s + ";")
1691     } else {
1692         Some(format!("{};", result))
1693     }
1694 }
1695
1696 fn type_annotation_spacing(config: &Config) -> (&str, &str) {
1697     (
1698         if config.space_before_colon() { " " } else { "" },
1699         if config.space_after_colon() { " " } else { "" },
1700     )
1701 }
1702
1703 pub(crate) fn rewrite_struct_field_prefix(
1704     context: &RewriteContext<'_>,
1705     field: &ast::FieldDef,
1706 ) -> Option<String> {
1707     let vis = format_visibility(context, &field.vis);
1708     let type_annotation_spacing = type_annotation_spacing(context.config);
1709     Some(match field.ident {
1710         Some(name) => format!(
1711             "{}{}{}:",
1712             vis,
1713             rewrite_ident(context, name),
1714             type_annotation_spacing.0
1715         ),
1716         None => vis.to_string(),
1717     })
1718 }
1719
1720 impl Rewrite for ast::FieldDef {
1721     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1722         rewrite_struct_field(context, self, shape, 0)
1723     }
1724 }
1725
1726 pub(crate) fn rewrite_struct_field(
1727     context: &RewriteContext<'_>,
1728     field: &ast::FieldDef,
1729     shape: Shape,
1730     lhs_max_width: usize,
1731 ) -> Option<String> {
1732     if contains_skip(&field.attrs) {
1733         return Some(context.snippet(field.span()).to_owned());
1734     }
1735
1736     let type_annotation_spacing = type_annotation_spacing(context.config);
1737     let prefix = rewrite_struct_field_prefix(context, field)?;
1738
1739     let attrs_str = field.attrs.rewrite(context, shape)?;
1740     let attrs_extendable = field.ident.is_none() && is_attributes_extendable(&attrs_str);
1741     let missing_span = if field.attrs.is_empty() {
1742         mk_sp(field.span.lo(), field.span.lo())
1743     } else {
1744         mk_sp(field.attrs.last().unwrap().span.hi(), field.span.lo())
1745     };
1746     let mut spacing = String::from(if field.ident.is_some() {
1747         type_annotation_spacing.1
1748     } else {
1749         ""
1750     });
1751     // Try to put everything on a single line.
1752     let attr_prefix = combine_strs_with_missing_comments(
1753         context,
1754         &attrs_str,
1755         &prefix,
1756         missing_span,
1757         shape,
1758         attrs_extendable,
1759     )?;
1760     let overhead = trimmed_last_line_width(&attr_prefix);
1761     let lhs_offset = lhs_max_width.saturating_sub(overhead);
1762     for _ in 0..lhs_offset {
1763         spacing.push(' ');
1764     }
1765     // In this extreme case we will be missing a space between an attribute and a field.
1766     if prefix.is_empty() && !attrs_str.is_empty() && attrs_extendable && spacing.is_empty() {
1767         spacing.push(' ');
1768     }
1769     let orig_ty = shape
1770         .offset_left(overhead + spacing.len())
1771         .and_then(|ty_shape| field.ty.rewrite(context, ty_shape));
1772     if let Some(ref ty) = orig_ty {
1773         if !ty.contains('\n') && !contains_comment(context.snippet(missing_span)) {
1774             return Some(attr_prefix + &spacing + ty);
1775         }
1776     }
1777
1778     let is_prefix_empty = prefix.is_empty();
1779     // We must use multiline. We are going to put attributes and a field on different lines.
1780     let field_str = rewrite_assign_rhs(context, prefix, &*field.ty, &RhsAssignKind::Ty, shape)?;
1781     // Remove a leading white-space from `rewrite_assign_rhs()` when rewriting a tuple struct.
1782     let field_str = if is_prefix_empty {
1783         field_str.trim_start()
1784     } else {
1785         &field_str
1786     };
1787     combine_strs_with_missing_comments(context, &attrs_str, field_str, missing_span, shape, false)
1788 }
1789
1790 pub(crate) struct StaticParts<'a> {
1791     prefix: &'a str,
1792     vis: &'a ast::Visibility,
1793     ident: symbol::Ident,
1794     ty: &'a ast::Ty,
1795     mutability: ast::Mutability,
1796     expr_opt: Option<&'a ptr::P<ast::Expr>>,
1797     defaultness: Option<ast::Defaultness>,
1798     span: Span,
1799 }
1800
1801 impl<'a> StaticParts<'a> {
1802     pub(crate) fn from_item(item: &'a ast::Item) -> Self {
1803         let (defaultness, prefix, ty, mutability, expr) = match item.kind {
1804             ast::ItemKind::Static(ref ty, mutability, ref expr) => {
1805                 (None, "static", ty, mutability, expr)
1806             }
1807             ast::ItemKind::Const(defaultness, ref ty, ref expr) => {
1808                 (Some(defaultness), "const", ty, ast::Mutability::Not, expr)
1809             }
1810             _ => unreachable!(),
1811         };
1812         StaticParts {
1813             prefix,
1814             vis: &item.vis,
1815             ident: item.ident,
1816             ty,
1817             mutability,
1818             expr_opt: expr.as_ref(),
1819             defaultness,
1820             span: item.span,
1821         }
1822     }
1823
1824     pub(crate) fn from_trait_item(ti: &'a ast::AssocItem) -> Self {
1825         let (defaultness, ty, expr_opt) = match ti.kind {
1826             ast::AssocItemKind::Const(defaultness, ref ty, ref expr_opt) => {
1827                 (defaultness, ty, expr_opt)
1828             }
1829             _ => unreachable!(),
1830         };
1831         StaticParts {
1832             prefix: "const",
1833             vis: &ti.vis,
1834             ident: ti.ident,
1835             ty,
1836             mutability: ast::Mutability::Not,
1837             expr_opt: expr_opt.as_ref(),
1838             defaultness: Some(defaultness),
1839             span: ti.span,
1840         }
1841     }
1842
1843     pub(crate) fn from_impl_item(ii: &'a ast::AssocItem) -> Self {
1844         let (defaultness, ty, expr) = match ii.kind {
1845             ast::AssocItemKind::Const(defaultness, ref ty, ref expr) => (defaultness, ty, expr),
1846             _ => unreachable!(),
1847         };
1848         StaticParts {
1849             prefix: "const",
1850             vis: &ii.vis,
1851             ident: ii.ident,
1852             ty,
1853             mutability: ast::Mutability::Not,
1854             expr_opt: expr.as_ref(),
1855             defaultness: Some(defaultness),
1856             span: ii.span,
1857         }
1858     }
1859 }
1860
1861 fn rewrite_static(
1862     context: &RewriteContext<'_>,
1863     static_parts: &StaticParts<'_>,
1864     offset: Indent,
1865 ) -> Option<String> {
1866     let colon = colon_spaces(context.config);
1867     let mut prefix = format!(
1868         "{}{}{} {}{}{}",
1869         format_visibility(context, static_parts.vis),
1870         static_parts.defaultness.map_or("", format_defaultness),
1871         static_parts.prefix,
1872         format_mutability(static_parts.mutability),
1873         rewrite_ident(context, static_parts.ident),
1874         colon,
1875     );
1876     // 2 = " =".len()
1877     let ty_shape =
1878         Shape::indented(offset.block_only(), context.config).offset_left(prefix.len() + 2)?;
1879     let ty_str = match static_parts.ty.rewrite(context, ty_shape) {
1880         Some(ty_str) => ty_str,
1881         None => {
1882             if prefix.ends_with(' ') {
1883                 prefix.pop();
1884             }
1885             let nested_indent = offset.block_indent(context.config);
1886             let nested_shape = Shape::indented(nested_indent, context.config);
1887             let ty_str = static_parts.ty.rewrite(context, nested_shape)?;
1888             format!(
1889                 "{}{}",
1890                 nested_indent.to_string_with_newline(context.config),
1891                 ty_str
1892             )
1893         }
1894     };
1895
1896     if let Some(expr) = static_parts.expr_opt {
1897         let comments_lo = context.snippet_provider.span_after(static_parts.span, "=");
1898         let expr_lo = expr.span.lo();
1899         let comments_span = mk_sp(comments_lo, expr_lo);
1900
1901         let lhs = format!("{}{} =", prefix, ty_str);
1902
1903         // 1 = ;
1904         let remaining_width = context.budget(offset.block_indent + 1);
1905         rewrite_assign_rhs_with_comments(
1906             context,
1907             &lhs,
1908             &**expr,
1909             Shape::legacy(remaining_width, offset.block_only()),
1910             &RhsAssignKind::Expr(&expr.kind, expr.span),
1911             RhsTactics::Default,
1912             comments_span,
1913             true,
1914         )
1915         .and_then(|res| recover_comment_removed(res, static_parts.span, context))
1916         .map(|s| if s.ends_with(';') { s } else { s + ";" })
1917     } else {
1918         Some(format!("{}{};", prefix, ty_str))
1919     }
1920 }
1921
1922 // FIXME(calebcartwright) - This is a hack around a bug in the handling of TyKind::ImplTrait.
1923 // This should be removed once that bug is resolved, with the type alias formatting using the
1924 // defined Ty for the RHS directly.
1925 // https://github.com/rust-lang/rustfmt/issues/4373
1926 // https://github.com/rust-lang/rustfmt/issues/5027
1927 struct OpaqueType<'a> {
1928     bounds: &'a ast::GenericBounds,
1929 }
1930
1931 impl<'a> Rewrite for OpaqueType<'a> {
1932     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1933         let shape = shape.offset_left(5)?; // `impl `
1934         self.bounds
1935             .rewrite(context, shape)
1936             .map(|s| format!("impl {}", s))
1937     }
1938 }
1939
1940 impl Rewrite for ast::FnRetTy {
1941     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1942         match *self {
1943             ast::FnRetTy::Default(_) => Some(String::new()),
1944             ast::FnRetTy::Ty(ref ty) => {
1945                 if context.config.version() == Version::One
1946                     || context.config.indent_style() == IndentStyle::Visual
1947                 {
1948                     let inner_width = shape.width.checked_sub(3)?;
1949                     return ty
1950                         .rewrite(context, Shape::legacy(inner_width, shape.indent + 3))
1951                         .map(|r| format!("-> {}", r));
1952                 }
1953
1954                 ty.rewrite(context, shape.offset_left(3)?)
1955                     .map(|s| format!("-> {}", s))
1956             }
1957         }
1958     }
1959 }
1960
1961 fn is_empty_infer(ty: &ast::Ty, pat_span: Span) -> bool {
1962     match ty.kind {
1963         ast::TyKind::Infer => ty.span.hi() == pat_span.hi(),
1964         _ => false,
1965     }
1966 }
1967
1968 /// Recover any missing comments between the param and the type.
1969 ///
1970 /// # Returns
1971 ///
1972 /// A 2-len tuple with the comment before the colon in first position, and the comment after the
1973 /// colon in second position.
1974 fn get_missing_param_comments(
1975     context: &RewriteContext<'_>,
1976     pat_span: Span,
1977     ty_span: Span,
1978     shape: Shape,
1979 ) -> (String, String) {
1980     let missing_comment_span = mk_sp(pat_span.hi(), ty_span.lo());
1981
1982     let span_before_colon = {
1983         let missing_comment_span_hi = context
1984             .snippet_provider
1985             .span_before(missing_comment_span, ":");
1986         mk_sp(pat_span.hi(), missing_comment_span_hi)
1987     };
1988     let span_after_colon = {
1989         let missing_comment_span_lo = context
1990             .snippet_provider
1991             .span_after(missing_comment_span, ":");
1992         mk_sp(missing_comment_span_lo, ty_span.lo())
1993     };
1994
1995     let comment_before_colon = rewrite_missing_comment(span_before_colon, shape, context)
1996         .filter(|comment| !comment.is_empty())
1997         .map_or(String::new(), |comment| format!(" {}", comment));
1998     let comment_after_colon = rewrite_missing_comment(span_after_colon, shape, context)
1999         .filter(|comment| !comment.is_empty())
2000         .map_or(String::new(), |comment| format!("{} ", comment));
2001     (comment_before_colon, comment_after_colon)
2002 }
2003
2004 impl Rewrite for ast::Param {
2005     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
2006         let param_attrs_result = self
2007             .attrs
2008             .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
2009         // N.B. Doc comments aren't typically valid syntax, but could appear
2010         // in the presence of certain macros - https://github.com/rust-lang/rustfmt/issues/4936
2011         let (span, has_multiple_attr_lines, has_doc_comments) = if !self.attrs.is_empty() {
2012             let num_attrs = self.attrs.len();
2013             (
2014                 mk_sp(self.attrs[num_attrs - 1].span.hi(), self.pat.span.lo()),
2015                 param_attrs_result.contains('\n'),
2016                 self.attrs.iter().any(|a| a.is_doc_comment()),
2017             )
2018         } else {
2019             (mk_sp(self.span.lo(), self.span.lo()), false, false)
2020         };
2021
2022         if let Some(ref explicit_self) = self.to_self() {
2023             rewrite_explicit_self(
2024                 context,
2025                 explicit_self,
2026                 &param_attrs_result,
2027                 span,
2028                 shape,
2029                 has_multiple_attr_lines,
2030             )
2031         } else if is_named_param(self) {
2032             let param_name = &self
2033                 .pat
2034                 .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
2035             let mut result = combine_strs_with_missing_comments(
2036                 context,
2037                 &param_attrs_result,
2038                 param_name,
2039                 span,
2040                 shape,
2041                 !has_multiple_attr_lines && !has_doc_comments,
2042             )?;
2043
2044             if !is_empty_infer(&*self.ty, self.pat.span) {
2045                 let (before_comment, after_comment) =
2046                     get_missing_param_comments(context, self.pat.span, self.ty.span, shape);
2047                 result.push_str(&before_comment);
2048                 result.push_str(colon_spaces(context.config));
2049                 result.push_str(&after_comment);
2050                 let overhead = last_line_width(&result);
2051                 let max_width = shape.width.checked_sub(overhead)?;
2052                 if let Some(ty_str) = self
2053                     .ty
2054                     .rewrite(context, Shape::legacy(max_width, shape.indent))
2055                 {
2056                     result.push_str(&ty_str);
2057                 } else {
2058                     let prev_str = if param_attrs_result.is_empty() {
2059                         param_attrs_result
2060                     } else {
2061                         param_attrs_result + &shape.to_string_with_newline(context.config)
2062                     };
2063
2064                     result = combine_strs_with_missing_comments(
2065                         context,
2066                         &prev_str,
2067                         param_name,
2068                         span,
2069                         shape,
2070                         !has_multiple_attr_lines,
2071                     )?;
2072                     result.push_str(&before_comment);
2073                     result.push_str(colon_spaces(context.config));
2074                     result.push_str(&after_comment);
2075                     let overhead = last_line_width(&result);
2076                     let max_width = shape.width.checked_sub(overhead)?;
2077                     let ty_str = self
2078                         .ty
2079                         .rewrite(context, Shape::legacy(max_width, shape.indent))?;
2080                     result.push_str(&ty_str);
2081                 }
2082             }
2083
2084             Some(result)
2085         } else {
2086             self.ty.rewrite(context, shape)
2087         }
2088     }
2089 }
2090
2091 fn rewrite_explicit_self(
2092     context: &RewriteContext<'_>,
2093     explicit_self: &ast::ExplicitSelf,
2094     param_attrs: &str,
2095     span: Span,
2096     shape: Shape,
2097     has_multiple_attr_lines: bool,
2098 ) -> Option<String> {
2099     match explicit_self.node {
2100         ast::SelfKind::Region(lt, m) => {
2101             let mut_str = format_mutability(m);
2102             match lt {
2103                 Some(ref l) => {
2104                     let lifetime_str = l.rewrite(
2105                         context,
2106                         Shape::legacy(context.config.max_width(), Indent::empty()),
2107                     )?;
2108                     Some(combine_strs_with_missing_comments(
2109                         context,
2110                         param_attrs,
2111                         &format!("&{} {}self", lifetime_str, mut_str),
2112                         span,
2113                         shape,
2114                         !has_multiple_attr_lines,
2115                     )?)
2116                 }
2117                 None => Some(combine_strs_with_missing_comments(
2118                     context,
2119                     param_attrs,
2120                     &format!("&{}self", mut_str),
2121                     span,
2122                     shape,
2123                     !has_multiple_attr_lines,
2124                 )?),
2125             }
2126         }
2127         ast::SelfKind::Explicit(ref ty, mutability) => {
2128             let type_str = ty.rewrite(
2129                 context,
2130                 Shape::legacy(context.config.max_width(), Indent::empty()),
2131             )?;
2132
2133             Some(combine_strs_with_missing_comments(
2134                 context,
2135                 param_attrs,
2136                 &format!("{}self: {}", format_mutability(mutability), type_str),
2137                 span,
2138                 shape,
2139                 !has_multiple_attr_lines,
2140             )?)
2141         }
2142         ast::SelfKind::Value(mutability) => Some(combine_strs_with_missing_comments(
2143             context,
2144             param_attrs,
2145             &format!("{}self", format_mutability(mutability)),
2146             span,
2147             shape,
2148             !has_multiple_attr_lines,
2149         )?),
2150     }
2151 }
2152
2153 pub(crate) fn span_lo_for_param(param: &ast::Param) -> BytePos {
2154     if param.attrs.is_empty() {
2155         if is_named_param(param) {
2156             param.pat.span.lo()
2157         } else {
2158             param.ty.span.lo()
2159         }
2160     } else {
2161         param.attrs[0].span.lo()
2162     }
2163 }
2164
2165 pub(crate) fn span_hi_for_param(context: &RewriteContext<'_>, param: &ast::Param) -> BytePos {
2166     match param.ty.kind {
2167         ast::TyKind::Infer if context.snippet(param.ty.span) == "_" => param.ty.span.hi(),
2168         ast::TyKind::Infer if is_named_param(param) => param.pat.span.hi(),
2169         _ => param.ty.span.hi(),
2170     }
2171 }
2172
2173 pub(crate) fn is_named_param(param: &ast::Param) -> bool {
2174     if let ast::PatKind::Ident(_, ident, _) = param.pat.kind {
2175         ident.name != symbol::kw::Empty
2176     } else {
2177         true
2178     }
2179 }
2180
2181 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
2182 pub(crate) enum FnBraceStyle {
2183     SameLine,
2184     NextLine,
2185     None,
2186 }
2187
2188 // Return type is (result, force_new_line_for_brace)
2189 fn rewrite_fn_base(
2190     context: &RewriteContext<'_>,
2191     indent: Indent,
2192     ident: symbol::Ident,
2193     fn_sig: &FnSig<'_>,
2194     span: Span,
2195     fn_brace_style: FnBraceStyle,
2196 ) -> Option<(String, bool, bool)> {
2197     let mut force_new_line_for_brace = false;
2198
2199     let where_clause = &fn_sig.generics.where_clause;
2200
2201     let mut result = String::with_capacity(1024);
2202     result.push_str(&fn_sig.to_str(context));
2203
2204     // fn foo
2205     result.push_str("fn ");
2206
2207     // Generics.
2208     let overhead = if let FnBraceStyle::SameLine = fn_brace_style {
2209         // 4 = `() {`
2210         4
2211     } else {
2212         // 2 = `()`
2213         2
2214     };
2215     let used_width = last_line_used_width(&result, indent.width());
2216     let one_line_budget = context.budget(used_width + overhead);
2217     let shape = Shape {
2218         width: one_line_budget,
2219         indent,
2220         offset: used_width,
2221     };
2222     let fd = fn_sig.decl;
2223     let generics_str = rewrite_generics(
2224         context,
2225         rewrite_ident(context, ident),
2226         &fn_sig.generics,
2227         shape,
2228     )?;
2229     result.push_str(&generics_str);
2230
2231     let snuggle_angle_bracket = generics_str
2232         .lines()
2233         .last()
2234         .map_or(false, |l| l.trim_start().len() == 1);
2235
2236     // Note that the width and indent don't really matter, we'll re-layout the
2237     // return type later anyway.
2238     let ret_str = fd
2239         .output
2240         .rewrite(context, Shape::indented(indent, context.config))?;
2241
2242     let multi_line_ret_str = ret_str.contains('\n');
2243     let ret_str_len = if multi_line_ret_str { 0 } else { ret_str.len() };
2244
2245     // Params.
2246     let (one_line_budget, multi_line_budget, mut param_indent) = compute_budgets_for_params(
2247         context,
2248         &result,
2249         indent,
2250         ret_str_len,
2251         fn_brace_style,
2252         multi_line_ret_str,
2253     )?;
2254
2255     debug!(
2256         "rewrite_fn_base: one_line_budget: {}, multi_line_budget: {}, param_indent: {:?}",
2257         one_line_budget, multi_line_budget, param_indent
2258     );
2259
2260     result.push('(');
2261     // Check if vertical layout was forced.
2262     if one_line_budget == 0
2263         && !snuggle_angle_bracket
2264         && context.config.indent_style() == IndentStyle::Visual
2265     {
2266         result.push_str(&param_indent.to_string_with_newline(context.config));
2267     }
2268
2269     let params_end = if fd.inputs.is_empty() {
2270         context
2271             .snippet_provider
2272             .span_after(mk_sp(fn_sig.generics.span.hi(), span.hi()), ")")
2273     } else {
2274         let last_span = mk_sp(fd.inputs[fd.inputs.len() - 1].span().hi(), span.hi());
2275         context.snippet_provider.span_after(last_span, ")")
2276     };
2277     let params_span = mk_sp(
2278         context
2279             .snippet_provider
2280             .span_after(mk_sp(fn_sig.generics.span.hi(), span.hi()), "("),
2281         params_end,
2282     );
2283     let param_str = rewrite_params(
2284         context,
2285         &fd.inputs,
2286         one_line_budget,
2287         multi_line_budget,
2288         indent,
2289         param_indent,
2290         params_span,
2291         fd.c_variadic(),
2292     )?;
2293
2294     let put_params_in_block = match context.config.indent_style() {
2295         IndentStyle::Block => param_str.contains('\n') || param_str.len() > one_line_budget,
2296         _ => false,
2297     } && !fd.inputs.is_empty();
2298
2299     let mut params_last_line_contains_comment = false;
2300     let mut no_params_and_over_max_width = false;
2301
2302     if put_params_in_block {
2303         param_indent = indent.block_indent(context.config);
2304         result.push_str(&param_indent.to_string_with_newline(context.config));
2305         result.push_str(&param_str);
2306         result.push_str(&indent.to_string_with_newline(context.config));
2307         result.push(')');
2308     } else {
2309         result.push_str(&param_str);
2310         let used_width = last_line_used_width(&result, indent.width()) + first_line_width(&ret_str);
2311         // Put the closing brace on the next line if it overflows the max width.
2312         // 1 = `)`
2313         let closing_paren_overflow_max_width =
2314             fd.inputs.is_empty() && used_width + 1 > context.config.max_width();
2315         // If the last line of params contains comment, we cannot put the closing paren
2316         // on the same line.
2317         params_last_line_contains_comment = param_str
2318             .lines()
2319             .last()
2320             .map_or(false, |last_line| last_line.contains("//"));
2321
2322         if context.config.version() == Version::Two {
2323             if closing_paren_overflow_max_width {
2324                 result.push(')');
2325                 result.push_str(&indent.to_string_with_newline(context.config));
2326                 no_params_and_over_max_width = true;
2327             } else if params_last_line_contains_comment {
2328                 result.push_str(&indent.to_string_with_newline(context.config));
2329                 result.push(')');
2330                 no_params_and_over_max_width = true;
2331             } else {
2332                 result.push(')');
2333             }
2334         } else {
2335             if closing_paren_overflow_max_width || params_last_line_contains_comment {
2336                 result.push_str(&indent.to_string_with_newline(context.config));
2337             }
2338             result.push(')');
2339         }
2340     }
2341
2342     // Return type.
2343     if let ast::FnRetTy::Ty(..) = fd.output {
2344         let ret_should_indent = match context.config.indent_style() {
2345             // If our params are block layout then we surely must have space.
2346             IndentStyle::Block if put_params_in_block || fd.inputs.is_empty() => false,
2347             _ if params_last_line_contains_comment => false,
2348             _ if result.contains('\n') || multi_line_ret_str => true,
2349             _ => {
2350                 // If the return type would push over the max width, then put the return type on
2351                 // a new line. With the +1 for the signature length an additional space between
2352                 // the closing parenthesis of the param and the arrow '->' is considered.
2353                 let mut sig_length = result.len() + indent.width() + ret_str_len + 1;
2354
2355                 // If there is no where-clause, take into account the space after the return type
2356                 // and the brace.
2357                 if where_clause.predicates.is_empty() {
2358                     sig_length += 2;
2359                 }
2360
2361                 sig_length > context.config.max_width()
2362             }
2363         };
2364         let ret_shape = if ret_should_indent {
2365             if context.config.version() == Version::One
2366                 || context.config.indent_style() == IndentStyle::Visual
2367             {
2368                 let indent = if param_str.is_empty() {
2369                     // Aligning with non-existent params looks silly.
2370                     force_new_line_for_brace = true;
2371                     indent + 4
2372                 } else {
2373                     // FIXME: we might want to check that using the param indent
2374                     // doesn't blow our budget, and if it does, then fallback to
2375                     // the where-clause indent.
2376                     param_indent
2377                 };
2378
2379                 result.push_str(&indent.to_string_with_newline(context.config));
2380                 Shape::indented(indent, context.config)
2381             } else {
2382                 let mut ret_shape = Shape::indented(indent, context.config);
2383                 if param_str.is_empty() {
2384                     // Aligning with non-existent params looks silly.
2385                     force_new_line_for_brace = true;
2386                     ret_shape = if context.use_block_indent() {
2387                         ret_shape.offset_left(4).unwrap_or(ret_shape)
2388                     } else {
2389                         ret_shape.indent = ret_shape.indent + 4;
2390                         ret_shape
2391                     };
2392                 }
2393
2394                 result.push_str(&ret_shape.indent.to_string_with_newline(context.config));
2395                 ret_shape
2396             }
2397         } else {
2398             if context.config.version() == Version::Two {
2399                 if !param_str.is_empty() || !no_params_and_over_max_width {
2400                     result.push(' ');
2401                 }
2402             } else {
2403                 result.push(' ');
2404             }
2405
2406             let ret_shape = Shape::indented(indent, context.config);
2407             ret_shape
2408                 .offset_left(last_line_width(&result))
2409                 .unwrap_or(ret_shape)
2410         };
2411
2412         if multi_line_ret_str || ret_should_indent {
2413             // Now that we know the proper indent and width, we need to
2414             // re-layout the return type.
2415             let ret_str = fd.output.rewrite(context, ret_shape)?;
2416             result.push_str(&ret_str);
2417         } else {
2418             result.push_str(&ret_str);
2419         }
2420
2421         // Comment between return type and the end of the decl.
2422         let snippet_lo = fd.output.span().hi();
2423         if where_clause.predicates.is_empty() {
2424             let snippet_hi = span.hi();
2425             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
2426             // Try to preserve the layout of the original snippet.
2427             let original_starts_with_newline = snippet
2428                 .find(|c| c != ' ')
2429                 .map_or(false, |i| starts_with_newline(&snippet[i..]));
2430             let original_ends_with_newline = snippet
2431                 .rfind(|c| c != ' ')
2432                 .map_or(false, |i| snippet[i..].ends_with('\n'));
2433             let snippet = snippet.trim();
2434             if !snippet.is_empty() {
2435                 result.push(if original_starts_with_newline {
2436                     '\n'
2437                 } else {
2438                     ' '
2439                 });
2440                 result.push_str(snippet);
2441                 if original_ends_with_newline {
2442                     force_new_line_for_brace = true;
2443                 }
2444             }
2445         }
2446     }
2447
2448     let pos_before_where = match fd.output {
2449         ast::FnRetTy::Default(..) => params_span.hi(),
2450         ast::FnRetTy::Ty(ref ty) => ty.span.hi(),
2451     };
2452
2453     let is_params_multi_lined = param_str.contains('\n');
2454
2455     let space = if put_params_in_block && ret_str.is_empty() {
2456         WhereClauseSpace::Space
2457     } else {
2458         WhereClauseSpace::Newline
2459     };
2460     let mut option = WhereClauseOption::new(fn_brace_style == FnBraceStyle::None, space);
2461     if is_params_multi_lined {
2462         option.veto_single_line();
2463     }
2464     let where_clause_str = rewrite_where_clause(
2465         context,
2466         &where_clause.predicates,
2467         where_clause.span,
2468         context.config.brace_style(),
2469         Shape::indented(indent, context.config),
2470         true,
2471         "{",
2472         Some(span.hi()),
2473         pos_before_where,
2474         option,
2475     )?;
2476     // If there are neither where-clause nor return type, we may be missing comments between
2477     // params and `{`.
2478     if where_clause_str.is_empty() {
2479         if let ast::FnRetTy::Default(ret_span) = fd.output {
2480             match recover_missing_comment_in_span(
2481                 mk_sp(params_span.hi(), ret_span.hi()),
2482                 shape,
2483                 context,
2484                 last_line_width(&result),
2485             ) {
2486                 Some(ref missing_comment) if !missing_comment.is_empty() => {
2487                     result.push_str(missing_comment);
2488                     force_new_line_for_brace = true;
2489                 }
2490                 _ => (),
2491             }
2492         }
2493     }
2494
2495     result.push_str(&where_clause_str);
2496
2497     let ends_with_comment = last_line_contains_single_line_comment(&result);
2498     force_new_line_for_brace |= ends_with_comment;
2499     force_new_line_for_brace |=
2500         is_params_multi_lined && context.config.where_single_line() && !where_clause_str.is_empty();
2501     Some((result, ends_with_comment, force_new_line_for_brace))
2502 }
2503
2504 /// Kind of spaces to put before `where`.
2505 #[derive(Copy, Clone)]
2506 enum WhereClauseSpace {
2507     /// A single space.
2508     Space,
2509     /// A new line.
2510     Newline,
2511     /// Nothing.
2512     None,
2513 }
2514
2515 #[derive(Copy, Clone)]
2516 struct WhereClauseOption {
2517     suppress_comma: bool, // Force no trailing comma
2518     snuggle: WhereClauseSpace,
2519     allow_single_line: bool, // Try single line where-clause instead of vertical layout
2520     veto_single_line: bool,  // Disallow a single-line where-clause.
2521 }
2522
2523 impl WhereClauseOption {
2524     fn new(suppress_comma: bool, snuggle: WhereClauseSpace) -> WhereClauseOption {
2525         WhereClauseOption {
2526             suppress_comma,
2527             snuggle,
2528             allow_single_line: false,
2529             veto_single_line: false,
2530         }
2531     }
2532
2533     fn snuggled(current: &str) -> WhereClauseOption {
2534         WhereClauseOption {
2535             suppress_comma: false,
2536             snuggle: if last_line_width(current) == 1 {
2537                 WhereClauseSpace::Space
2538             } else {
2539                 WhereClauseSpace::Newline
2540             },
2541             allow_single_line: false,
2542             veto_single_line: false,
2543         }
2544     }
2545
2546     fn suppress_comma(&mut self) {
2547         self.suppress_comma = true
2548     }
2549
2550     fn allow_single_line(&mut self) {
2551         self.allow_single_line = true
2552     }
2553
2554     fn snuggle(&mut self) {
2555         self.snuggle = WhereClauseSpace::Space
2556     }
2557
2558     fn veto_single_line(&mut self) {
2559         self.veto_single_line = true;
2560     }
2561 }
2562
2563 fn rewrite_params(
2564     context: &RewriteContext<'_>,
2565     params: &[ast::Param],
2566     one_line_budget: usize,
2567     multi_line_budget: usize,
2568     indent: Indent,
2569     param_indent: Indent,
2570     span: Span,
2571     variadic: bool,
2572 ) -> Option<String> {
2573     if params.is_empty() {
2574         let comment = context
2575             .snippet(mk_sp(
2576                 span.lo(),
2577                 // to remove ')'
2578                 span.hi() - BytePos(1),
2579             ))
2580             .trim();
2581         return Some(comment.to_owned());
2582     }
2583     let param_items: Vec<_> = itemize_list(
2584         context.snippet_provider,
2585         params.iter(),
2586         ")",
2587         ",",
2588         |param| span_lo_for_param(param),
2589         |param| param.ty.span.hi(),
2590         |param| {
2591             param
2592                 .rewrite(context, Shape::legacy(multi_line_budget, param_indent))
2593                 .or_else(|| Some(context.snippet(param.span()).to_owned()))
2594         },
2595         span.lo(),
2596         span.hi(),
2597         false,
2598     )
2599     .collect();
2600
2601     let tactic = definitive_tactic(
2602         &param_items,
2603         context
2604             .config
2605             .fn_args_layout()
2606             .to_list_tactic(param_items.len()),
2607         Separator::Comma,
2608         one_line_budget,
2609     );
2610     let budget = match tactic {
2611         DefinitiveListTactic::Horizontal => one_line_budget,
2612         _ => multi_line_budget,
2613     };
2614     let indent = match context.config.indent_style() {
2615         IndentStyle::Block => indent.block_indent(context.config),
2616         IndentStyle::Visual => param_indent,
2617     };
2618     let trailing_separator = if variadic {
2619         SeparatorTactic::Never
2620     } else {
2621         match context.config.indent_style() {
2622             IndentStyle::Block => context.config.trailing_comma(),
2623             IndentStyle::Visual => SeparatorTactic::Never,
2624         }
2625     };
2626     let fmt = ListFormatting::new(Shape::legacy(budget, indent), context.config)
2627         .tactic(tactic)
2628         .trailing_separator(trailing_separator)
2629         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
2630         .preserve_newline(true);
2631     write_list(&param_items, &fmt)
2632 }
2633
2634 fn compute_budgets_for_params(
2635     context: &RewriteContext<'_>,
2636     result: &str,
2637     indent: Indent,
2638     ret_str_len: usize,
2639     fn_brace_style: FnBraceStyle,
2640     force_vertical_layout: bool,
2641 ) -> Option<(usize, usize, Indent)> {
2642     debug!(
2643         "compute_budgets_for_params {} {:?}, {}, {:?}",
2644         result.len(),
2645         indent,
2646         ret_str_len,
2647         fn_brace_style,
2648     );
2649     // Try keeping everything on the same line.
2650     if !result.contains('\n') && !force_vertical_layout {
2651         // 2 = `()`, 3 = `() `, space is before ret_string.
2652         let overhead = if ret_str_len == 0 { 2 } else { 3 };
2653         let mut used_space = indent.width() + result.len() + ret_str_len + overhead;
2654         match fn_brace_style {
2655             FnBraceStyle::None => used_space += 1,     // 1 = `;`
2656             FnBraceStyle::SameLine => used_space += 2, // 2 = `{}`
2657             FnBraceStyle::NextLine => (),
2658         }
2659         let one_line_budget = context.budget(used_space);
2660
2661         if one_line_budget > 0 {
2662             // 4 = "() {".len()
2663             let (indent, multi_line_budget) = match context.config.indent_style() {
2664                 IndentStyle::Block => {
2665                     let indent = indent.block_indent(context.config);
2666                     (indent, context.budget(indent.width() + 1))
2667                 }
2668                 IndentStyle::Visual => {
2669                     let indent = indent + result.len() + 1;
2670                     let multi_line_overhead = match fn_brace_style {
2671                         FnBraceStyle::SameLine => 4,
2672                         _ => 2,
2673                     } + indent.width();
2674                     (indent, context.budget(multi_line_overhead))
2675                 }
2676             };
2677
2678             return Some((one_line_budget, multi_line_budget, indent));
2679         }
2680     }
2681
2682     // Didn't work. we must force vertical layout and put params on a newline.
2683     let new_indent = indent.block_indent(context.config);
2684     let used_space = match context.config.indent_style() {
2685         // 1 = `,`
2686         IndentStyle::Block => new_indent.width() + 1,
2687         // Account for `)` and possibly ` {`.
2688         IndentStyle::Visual => new_indent.width() + if ret_str_len == 0 { 1 } else { 3 },
2689     };
2690     Some((0, context.budget(used_space), new_indent))
2691 }
2692
2693 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> FnBraceStyle {
2694     let predicate_count = where_clause.predicates.len();
2695
2696     if config.where_single_line() && predicate_count == 1 {
2697         return FnBraceStyle::SameLine;
2698     }
2699     let brace_style = config.brace_style();
2700
2701     let use_next_line = brace_style == BraceStyle::AlwaysNextLine
2702         || (brace_style == BraceStyle::SameLineWhere && predicate_count > 0);
2703     if use_next_line {
2704         FnBraceStyle::NextLine
2705     } else {
2706         FnBraceStyle::SameLine
2707     }
2708 }
2709
2710 fn rewrite_generics(
2711     context: &RewriteContext<'_>,
2712     ident: &str,
2713     generics: &ast::Generics,
2714     shape: Shape,
2715 ) -> Option<String> {
2716     // FIXME: convert bounds to where-clauses where they get too big or if
2717     // there is a where-clause at all.
2718
2719     if generics.params.is_empty() {
2720         return Some(ident.to_owned());
2721     }
2722
2723     let params = generics.params.iter();
2724     overflow::rewrite_with_angle_brackets(context, ident, params, shape, generics.span)
2725 }
2726
2727 fn generics_shape_from_config(config: &Config, shape: Shape, offset: usize) -> Option<Shape> {
2728     match config.indent_style() {
2729         IndentStyle::Visual => shape.visual_indent(1 + offset).sub_width(offset + 2),
2730         IndentStyle::Block => {
2731             // 1 = ","
2732             shape
2733                 .block()
2734                 .block_indent(config.tab_spaces())
2735                 .with_max_width(config)
2736                 .sub_width(1)
2737         }
2738     }
2739 }
2740
2741 fn rewrite_where_clause_rfc_style(
2742     context: &RewriteContext<'_>,
2743     predicates: &[ast::WherePredicate],
2744     where_span: Span,
2745     shape: Shape,
2746     terminator: &str,
2747     span_end: Option<BytePos>,
2748     span_end_before_where: BytePos,
2749     where_clause_option: WhereClauseOption,
2750 ) -> Option<String> {
2751     let (where_keyword, allow_single_line) = rewrite_where_keyword(
2752         context,
2753         predicates,
2754         where_span,
2755         shape,
2756         span_end_before_where,
2757         where_clause_option,
2758     )?;
2759
2760     // 1 = `,`
2761     let clause_shape = shape
2762         .block()
2763         .with_max_width(context.config)
2764         .block_left(context.config.tab_spaces())?
2765         .sub_width(1)?;
2766     let force_single_line = context.config.where_single_line()
2767         && predicates.len() == 1
2768         && !where_clause_option.veto_single_line;
2769
2770     let preds_str = rewrite_bounds_on_where_clause(
2771         context,
2772         predicates,
2773         clause_shape,
2774         terminator,
2775         span_end,
2776         where_clause_option,
2777         force_single_line,
2778     )?;
2779
2780     // 6 = `where `
2781     let clause_sep =
2782         if allow_single_line && !preds_str.contains('\n') && 6 + preds_str.len() <= shape.width
2783             || force_single_line
2784         {
2785             Cow::from(" ")
2786         } else {
2787             clause_shape.indent.to_string_with_newline(context.config)
2788         };
2789
2790     Some(format!("{}{}{}", where_keyword, clause_sep, preds_str))
2791 }
2792
2793 /// Rewrite `where` and comment around it.
2794 fn rewrite_where_keyword(
2795     context: &RewriteContext<'_>,
2796     predicates: &[ast::WherePredicate],
2797     where_span: Span,
2798     shape: Shape,
2799     span_end_before_where: BytePos,
2800     where_clause_option: WhereClauseOption,
2801 ) -> Option<(String, bool)> {
2802     let block_shape = shape.block().with_max_width(context.config);
2803     // 1 = `,`
2804     let clause_shape = block_shape
2805         .block_left(context.config.tab_spaces())?
2806         .sub_width(1)?;
2807
2808     let comment_separator = |comment: &str, shape: Shape| {
2809         if comment.is_empty() {
2810             Cow::from("")
2811         } else {
2812             shape.indent.to_string_with_newline(context.config)
2813         }
2814     };
2815
2816     let (span_before, span_after) =
2817         missing_span_before_after_where(span_end_before_where, predicates, where_span);
2818     let (comment_before, comment_after) =
2819         rewrite_comments_before_after_where(context, span_before, span_after, shape)?;
2820
2821     let starting_newline = match where_clause_option.snuggle {
2822         WhereClauseSpace::Space if comment_before.is_empty() => Cow::from(" "),
2823         WhereClauseSpace::None => Cow::from(""),
2824         _ => block_shape.indent.to_string_with_newline(context.config),
2825     };
2826
2827     let newline_before_where = comment_separator(&comment_before, shape);
2828     let newline_after_where = comment_separator(&comment_after, clause_shape);
2829     let result = format!(
2830         "{}{}{}where{}{}",
2831         starting_newline, comment_before, newline_before_where, newline_after_where, comment_after
2832     );
2833     let allow_single_line = where_clause_option.allow_single_line
2834         && comment_before.is_empty()
2835         && comment_after.is_empty();
2836
2837     Some((result, allow_single_line))
2838 }
2839
2840 /// Rewrite bounds on a where clause.
2841 fn rewrite_bounds_on_where_clause(
2842     context: &RewriteContext<'_>,
2843     predicates: &[ast::WherePredicate],
2844     shape: Shape,
2845     terminator: &str,
2846     span_end: Option<BytePos>,
2847     where_clause_option: WhereClauseOption,
2848     force_single_line: bool,
2849 ) -> Option<String> {
2850     let span_start = predicates[0].span().lo();
2851     // If we don't have the start of the next span, then use the end of the
2852     // predicates, but that means we miss comments.
2853     let len = predicates.len();
2854     let end_of_preds = predicates[len - 1].span().hi();
2855     let span_end = span_end.unwrap_or(end_of_preds);
2856     let items = itemize_list(
2857         context.snippet_provider,
2858         predicates.iter(),
2859         terminator,
2860         ",",
2861         |pred| pred.span().lo(),
2862         |pred| pred.span().hi(),
2863         |pred| pred.rewrite(context, shape),
2864         span_start,
2865         span_end,
2866         false,
2867     );
2868     let comma_tactic = if where_clause_option.suppress_comma || force_single_line {
2869         SeparatorTactic::Never
2870     } else {
2871         context.config.trailing_comma()
2872     };
2873
2874     // shape should be vertical only and only if we have `force_single_line` option enabled
2875     // and the number of items of the where-clause is equal to 1
2876     let shape_tactic = if force_single_line {
2877         DefinitiveListTactic::Horizontal
2878     } else {
2879         DefinitiveListTactic::Vertical
2880     };
2881
2882     let fmt = ListFormatting::new(shape, context.config)
2883         .tactic(shape_tactic)
2884         .trailing_separator(comma_tactic)
2885         .preserve_newline(true);
2886     write_list(&items.collect::<Vec<_>>(), &fmt)
2887 }
2888
2889 fn rewrite_where_clause(
2890     context: &RewriteContext<'_>,
2891     predicates: &[ast::WherePredicate],
2892     where_span: Span,
2893     brace_style: BraceStyle,
2894     shape: Shape,
2895     on_new_line: bool,
2896     terminator: &str,
2897     span_end: Option<BytePos>,
2898     span_end_before_where: BytePos,
2899     where_clause_option: WhereClauseOption,
2900 ) -> Option<String> {
2901     if predicates.is_empty() {
2902         return Some(String::new());
2903     }
2904
2905     if context.config.indent_style() == IndentStyle::Block {
2906         return rewrite_where_clause_rfc_style(
2907             context,
2908             predicates,
2909             where_span,
2910             shape,
2911             terminator,
2912             span_end,
2913             span_end_before_where,
2914             where_clause_option,
2915         );
2916     }
2917
2918     let extra_indent = Indent::new(context.config.tab_spaces(), 0);
2919
2920     let offset = match context.config.indent_style() {
2921         IndentStyle::Block => shape.indent + extra_indent.block_indent(context.config),
2922         // 6 = "where ".len()
2923         IndentStyle::Visual => shape.indent + extra_indent + 6,
2924     };
2925     // FIXME: if indent_style != Visual, then the budgets below might
2926     // be out by a char or two.
2927
2928     let budget = context.config.max_width() - offset.width();
2929     let span_start = predicates[0].span().lo();
2930     // If we don't have the start of the next span, then use the end of the
2931     // predicates, but that means we miss comments.
2932     let len = predicates.len();
2933     let end_of_preds = predicates[len - 1].span().hi();
2934     let span_end = span_end.unwrap_or(end_of_preds);
2935     let items = itemize_list(
2936         context.snippet_provider,
2937         predicates.iter(),
2938         terminator,
2939         ",",
2940         |pred| pred.span().lo(),
2941         |pred| pred.span().hi(),
2942         |pred| pred.rewrite(context, Shape::legacy(budget, offset)),
2943         span_start,
2944         span_end,
2945         false,
2946     );
2947     let item_vec = items.collect::<Vec<_>>();
2948     // FIXME: we don't need to collect here
2949     let tactic = definitive_tactic(&item_vec, ListTactic::Vertical, Separator::Comma, budget);
2950
2951     let mut comma_tactic = context.config.trailing_comma();
2952     // Kind of a hack because we don't usually have trailing commas in where-clauses.
2953     if comma_tactic == SeparatorTactic::Vertical || where_clause_option.suppress_comma {
2954         comma_tactic = SeparatorTactic::Never;
2955     }
2956
2957     let fmt = ListFormatting::new(Shape::legacy(budget, offset), context.config)
2958         .tactic(tactic)
2959         .trailing_separator(comma_tactic)
2960         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
2961         .preserve_newline(true);
2962     let preds_str = write_list(&item_vec, &fmt)?;
2963
2964     let end_length = if terminator == "{" {
2965         // If the brace is on the next line we don't need to count it otherwise it needs two
2966         // characters " {"
2967         match brace_style {
2968             BraceStyle::AlwaysNextLine | BraceStyle::SameLineWhere => 0,
2969             BraceStyle::PreferSameLine => 2,
2970         }
2971     } else if terminator == "=" {
2972         2
2973     } else {
2974         terminator.len()
2975     };
2976     if on_new_line
2977         || preds_str.contains('\n')
2978         || shape.indent.width() + " where ".len() + preds_str.len() + end_length > shape.width
2979     {
2980         Some(format!(
2981             "\n{}where {}",
2982             (shape.indent + extra_indent).to_string(context.config),
2983             preds_str
2984         ))
2985     } else {
2986         Some(format!(" where {}", preds_str))
2987     }
2988 }
2989
2990 fn missing_span_before_after_where(
2991     before_item_span_end: BytePos,
2992     predicates: &[ast::WherePredicate],
2993     where_span: Span,
2994 ) -> (Span, Span) {
2995     let missing_span_before = mk_sp(before_item_span_end, where_span.lo());
2996     // 5 = `where`
2997     let pos_after_where = where_span.lo() + BytePos(5);
2998     let missing_span_after = mk_sp(pos_after_where, predicates[0].span().lo());
2999     (missing_span_before, missing_span_after)
3000 }
3001
3002 fn rewrite_comments_before_after_where(
3003     context: &RewriteContext<'_>,
3004     span_before_where: Span,
3005     span_after_where: Span,
3006     shape: Shape,
3007 ) -> Option<(String, String)> {
3008     let before_comment = rewrite_missing_comment(span_before_where, shape, context)?;
3009     let after_comment = rewrite_missing_comment(
3010         span_after_where,
3011         shape.block_indent(context.config.tab_spaces()),
3012         context,
3013     )?;
3014     Some((before_comment, after_comment))
3015 }
3016
3017 fn format_header(
3018     context: &RewriteContext<'_>,
3019     item_name: &str,
3020     ident: symbol::Ident,
3021     vis: &ast::Visibility,
3022     offset: Indent,
3023 ) -> String {
3024     let mut result = String::with_capacity(128);
3025     let shape = Shape::indented(offset, context.config);
3026
3027     result.push_str(format_visibility(context, vis).trim());
3028
3029     // Check for a missing comment between the visibility and the item name.
3030     let after_vis = vis.span.hi();
3031     if let Some(before_item_name) = context
3032         .snippet_provider
3033         .opt_span_before(mk_sp(vis.span.lo(), ident.span.hi()), item_name.trim())
3034     {
3035         let missing_span = mk_sp(after_vis, before_item_name);
3036         if let Some(result_with_comment) = combine_strs_with_missing_comments(
3037             context,
3038             &result,
3039             item_name,
3040             missing_span,
3041             shape,
3042             /* allow_extend */ true,
3043         ) {
3044             result = result_with_comment;
3045         }
3046     }
3047
3048     result.push_str(rewrite_ident(context, ident));
3049
3050     result
3051 }
3052
3053 #[derive(PartialEq, Eq, Clone, Copy)]
3054 enum BracePos {
3055     None,
3056     Auto,
3057     ForceSameLine,
3058 }
3059
3060 fn format_generics(
3061     context: &RewriteContext<'_>,
3062     generics: &ast::Generics,
3063     brace_style: BraceStyle,
3064     brace_pos: BracePos,
3065     offset: Indent,
3066     span: Span,
3067     used_width: usize,
3068 ) -> Option<String> {
3069     let shape = Shape::legacy(context.budget(used_width + offset.width()), offset);
3070     let mut result = rewrite_generics(context, "", generics, shape)?;
3071
3072     // If the generics are not parameterized then generics.span.hi() == 0,
3073     // so we use span.lo(), which is the position after `struct Foo`.
3074     let span_end_before_where = if !generics.params.is_empty() {
3075         generics.span.hi()
3076     } else {
3077         span.lo()
3078     };
3079     let (same_line_brace, missed_comments) = if !generics.where_clause.predicates.is_empty() {
3080         let budget = context.budget(last_line_used_width(&result, offset.width()));
3081         let mut option = WhereClauseOption::snuggled(&result);
3082         if brace_pos == BracePos::None {
3083             option.suppress_comma = true;
3084         }
3085         let where_clause_str = rewrite_where_clause(
3086             context,
3087             &generics.where_clause.predicates,
3088             generics.where_clause.span,
3089             brace_style,
3090             Shape::legacy(budget, offset.block_only()),
3091             true,
3092             "{",
3093             Some(span.hi()),
3094             span_end_before_where,
3095             option,
3096         )?;
3097         result.push_str(&where_clause_str);
3098         (
3099             brace_pos == BracePos::ForceSameLine || brace_style == BraceStyle::PreferSameLine,
3100             // missed comments are taken care of in #rewrite_where_clause
3101             None,
3102         )
3103     } else {
3104         (
3105             brace_pos == BracePos::ForceSameLine
3106                 || (result.contains('\n') && brace_style == BraceStyle::PreferSameLine
3107                     || brace_style != BraceStyle::AlwaysNextLine)
3108                 || trimmed_last_line_width(&result) == 1,
3109             rewrite_missing_comment(
3110                 mk_sp(
3111                     span_end_before_where,
3112                     if brace_pos == BracePos::None {
3113                         span.hi()
3114                     } else {
3115                         context.snippet_provider.span_before(span, "{")
3116                     },
3117                 ),
3118                 shape,
3119                 context,
3120             ),
3121         )
3122     };
3123     // add missing comments
3124     let missed_line_comments = missed_comments
3125         .filter(|missed_comments| !missed_comments.is_empty())
3126         .map_or(false, |missed_comments| {
3127             let is_block = is_last_comment_block(&missed_comments);
3128             let sep = if is_block { " " } else { "\n" };
3129             result.push_str(sep);
3130             result.push_str(&missed_comments);
3131             !is_block
3132         });
3133     if brace_pos == BracePos::None {
3134         return Some(result);
3135     }
3136     let total_used_width = last_line_used_width(&result, used_width);
3137     let remaining_budget = context.budget(total_used_width);
3138     // If the same line brace if forced, it indicates that we are rewriting an item with empty body,
3139     // and hence we take the closer into account as well for one line budget.
3140     // We assume that the closer has the same length as the opener.
3141     let overhead = if brace_pos == BracePos::ForceSameLine {
3142         // 3 = ` {}`
3143         3
3144     } else {
3145         // 2 = ` {`
3146         2
3147     };
3148     let forbid_same_line_brace = missed_line_comments || overhead > remaining_budget;
3149     if !forbid_same_line_brace && same_line_brace {
3150         result.push(' ');
3151     } else {
3152         result.push('\n');
3153         result.push_str(&offset.block_only().to_string(context.config));
3154     }
3155     result.push('{');
3156
3157     Some(result)
3158 }
3159
3160 impl Rewrite for ast::ForeignItem {
3161     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
3162         let attrs_str = self.attrs.rewrite(context, shape)?;
3163         // Drop semicolon or it will be interpreted as comment.
3164         // FIXME: this may be a faulty span from libsyntax.
3165         let span = mk_sp(self.span.lo(), self.span.hi() - BytePos(1));
3166
3167         let item_str = match self.kind {
3168             ast::ForeignItemKind::Fn(ref fn_kind) => {
3169                 let ast::Fn {
3170                     defaultness,
3171                     ref sig,
3172                     ref generics,
3173                     ref body,
3174                 } = **fn_kind;
3175                 if let Some(ref body) = body {
3176                     let mut visitor = FmtVisitor::from_context(context);
3177                     visitor.block_indent = shape.indent;
3178                     visitor.last_pos = self.span.lo();
3179                     let inner_attrs = inner_attributes(&self.attrs);
3180                     let fn_ctxt = visit::FnCtxt::Foreign;
3181                     visitor.visit_fn(
3182                         visit::FnKind::Fn(
3183                             fn_ctxt,
3184                             self.ident,
3185                             sig,
3186                             &self.vis,
3187                             generics,
3188                             Some(body),
3189                         ),
3190                         &sig.decl,
3191                         self.span,
3192                         defaultness,
3193                         Some(&inner_attrs),
3194                     );
3195                     Some(visitor.buffer.to_owned())
3196                 } else {
3197                     rewrite_fn_base(
3198                         context,
3199                         shape.indent,
3200                         self.ident,
3201                         &FnSig::from_method_sig(sig, generics, &self.vis),
3202                         span,
3203                         FnBraceStyle::None,
3204                     )
3205                     .map(|(s, _, _)| format!("{};", s))
3206                 }
3207             }
3208             ast::ForeignItemKind::Static(ref ty, mutability, _) => {
3209                 // FIXME(#21): we're dropping potential comments in between the
3210                 // function kw here.
3211                 let vis = format_visibility(context, &self.vis);
3212                 let mut_str = format_mutability(mutability);
3213                 let prefix = format!(
3214                     "{}static {}{}:",
3215                     vis,
3216                     mut_str,
3217                     rewrite_ident(context, self.ident)
3218                 );
3219                 // 1 = ;
3220                 rewrite_assign_rhs(
3221                     context,
3222                     prefix,
3223                     &**ty,
3224                     &RhsAssignKind::Ty,
3225                     shape.sub_width(1)?,
3226                 )
3227                 .map(|s| s + ";")
3228             }
3229             ast::ForeignItemKind::TyAlias(ref ty_alias) => {
3230                 let (kind, span) = (&ItemVisitorKind::ForeignItem(self), self.span);
3231                 rewrite_type_alias(ty_alias, context, shape.indent, kind, span)
3232             }
3233             ast::ForeignItemKind::MacCall(ref mac) => {
3234                 rewrite_macro(mac, None, context, shape, MacroPosition::Item)
3235             }
3236         }?;
3237
3238         let missing_span = if self.attrs.is_empty() {
3239             mk_sp(self.span.lo(), self.span.lo())
3240         } else {
3241             mk_sp(self.attrs[self.attrs.len() - 1].span.hi(), self.span.lo())
3242         };
3243         combine_strs_with_missing_comments(
3244             context,
3245             &attrs_str,
3246             &item_str,
3247             missing_span,
3248             shape,
3249             false,
3250         )
3251     }
3252 }
3253
3254 /// Rewrite the attributes of an item.
3255 fn rewrite_attrs(
3256     context: &RewriteContext<'_>,
3257     item: &ast::Item,
3258     item_str: &str,
3259     shape: Shape,
3260 ) -> Option<String> {
3261     let attrs = filter_inline_attrs(&item.attrs, item.span());
3262     let attrs_str = attrs.rewrite(context, shape)?;
3263
3264     let missed_span = if attrs.is_empty() {
3265         mk_sp(item.span.lo(), item.span.lo())
3266     } else {
3267         mk_sp(attrs[attrs.len() - 1].span.hi(), item.span.lo())
3268     };
3269
3270     let allow_extend = if attrs.len() == 1 {
3271         let line_len = attrs_str.len() + 1 + item_str.len();
3272         !attrs.first().unwrap().is_doc_comment()
3273             && context.config.inline_attribute_width() >= line_len
3274     } else {
3275         false
3276     };
3277
3278     combine_strs_with_missing_comments(
3279         context,
3280         &attrs_str,
3281         item_str,
3282         missed_span,
3283         shape,
3284         allow_extend,
3285     )
3286 }
3287
3288 /// Rewrite an inline mod.
3289 /// The given shape is used to format the mod's attributes.
3290 pub(crate) fn rewrite_mod(
3291     context: &RewriteContext<'_>,
3292     item: &ast::Item,
3293     attrs_shape: Shape,
3294 ) -> Option<String> {
3295     let mut result = String::with_capacity(32);
3296     result.push_str(&*format_visibility(context, &item.vis));
3297     result.push_str("mod ");
3298     result.push_str(rewrite_ident(context, item.ident));
3299     result.push(';');
3300     rewrite_attrs(context, item, &result, attrs_shape)
3301 }
3302
3303 /// Rewrite `extern crate foo;`.
3304 /// The given shape is used to format the extern crate's attributes.
3305 pub(crate) fn rewrite_extern_crate(
3306     context: &RewriteContext<'_>,
3307     item: &ast::Item,
3308     attrs_shape: Shape,
3309 ) -> Option<String> {
3310     assert!(is_extern_crate(item));
3311     let new_str = context.snippet(item.span);
3312     let item_str = if contains_comment(new_str) {
3313         new_str.to_owned()
3314     } else {
3315         let no_whitespace = &new_str.split_whitespace().collect::<Vec<&str>>().join(" ");
3316         String::from(&*Regex::new(r"\s;").unwrap().replace(no_whitespace, ";"))
3317     };
3318     rewrite_attrs(context, item, &item_str, attrs_shape)
3319 }
3320
3321 /// Returns `true` for `mod foo;`, false for `mod foo { .. }`.
3322 pub(crate) fn is_mod_decl(item: &ast::Item) -> bool {
3323     !matches!(
3324         item.kind,
3325         ast::ItemKind::Mod(_, ast::ModKind::Loaded(_, ast::Inline::Yes, _))
3326     )
3327 }
3328
3329 pub(crate) fn is_use_item(item: &ast::Item) -> bool {
3330     matches!(item.kind, ast::ItemKind::Use(_))
3331 }
3332
3333 pub(crate) fn is_extern_crate(item: &ast::Item) -> bool {
3334     matches!(item.kind, ast::ItemKind::ExternCrate(..))
3335 }