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, 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::utils::*;
  32 use crate::vertical::rewrite_with_alignment;
  33 use crate::visitor::FmtVisitor;
  34
  35 const DEFAULT_VISIBILITY: ast::Visibility = ast::Visibility {
  36     kind: ast::VisibilityKind::Inherited,
  37     span: DUMMY_SP,
  38     tokens: None,
  39 };
  40
  41 fn type_annotation_separator(config: &Config) -> &str {
  42     colon_spaces(config)
  43 }
  44
  45 // Statements of the form
  46 // let pat: ty = init;
  47 impl Rewrite for ast::Local {
  48     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
  49         debug!(
  50             "Local::rewrite {:?} {} {:?}",
  51             self, shape.width, shape.indent
  52         );
  53
  54         skip_out_of_file_lines_range!(context, self.span);
  55
  56         if contains_skip(&self.attrs) || matches!(self.kind, ast::LocalKind::InitElse(..)) {
  57             return None;
  58         }
  59
  60         let attrs_str = self.attrs.rewrite(context, shape)?;
  61         let mut result = if attrs_str.is_empty() {
  62             "let ".to_owned()
  63         } else {
  64             combine_strs_with_missing_comments(
  65                 context,
  66                 &attrs_str,
  67                 "let ",
  68                 mk_sp(
  69                     self.attrs.last().map(|a| a.span.hi()).unwrap(),
  70                     self.span.lo(),
  71                 ),
  72                 shape,
  73                 false,
  74             )?
  75         };
  76
  77         // 4 = "let ".len()
  78         let pat_shape = shape.offset_left(4)?;
  79         // 1 = ;
  80         let pat_shape = pat_shape.sub_width(1)?;
  81         let pat_str = self.pat.rewrite(context, pat_shape)?;
  82         result.push_str(&pat_str);
  83
  84         // String that is placed within the assignment pattern and expression.
  85         let infix = {
  86             let mut infix = String::with_capacity(32);
  87
  88             if let Some(ref ty) = self.ty {
  89                 let separator = type_annotation_separator(context.config);
  90                 let ty_shape = if pat_str.contains('\n') {
  91                     shape.with_max_width(context.config)
  92                 } else {
  93                     shape
  94                 }
  95                 .offset_left(last_line_width(&result) + separator.len())?
  96                 // 2 = ` =`
  97                 .sub_width(2)?;
  98
  99                 let rewrite = ty.rewrite(context, ty_shape)?;
 100
 101                 infix.push_str(separator);
 102                 infix.push_str(&rewrite);
 103             }
 104
 105             if self.kind.init().is_some() {
 106                 infix.push_str(" =");
 107             }
 108
 109             infix
 110         };
 111
 112         result.push_str(&infix);
 113
 114         if let Some((init, _els)) = self.kind.init_else_opt() {
 115             // 1 = trailing semicolon;
 116             let nested_shape = shape.sub_width(1)?;
 117
 118             result = rewrite_assign_rhs(context, result, init, nested_shape)?;
 119             // todo else
 120         }
 121
 122         result.push(';');
 123         Some(result)
 124     }
 125 }
 126
 127 // FIXME convert to using rewrite style rather than visitor
 128 // FIXME format modules in this style
 129 #[allow(dead_code)]
 130 #[derive(Debug)]
 131 struct Item<'a> {
 132     unsafety: ast::Unsafe,
 133     abi: Cow<'static, str>,
 134     vis: Option<&'a ast::Visibility>,
 135     body: Vec<BodyElement<'a>>,
 136     span: Span,
 137 }
 138
 139 impl<'a> Item<'a> {
 140     fn from_foreign_mod(fm: &'a ast::ForeignMod, span: Span, config: &Config) -> Item<'a> {
 141         Item {
 142             unsafety: fm.unsafety,
 143             abi: format_extern(
 144                 ast::Extern::from_abi(fm.abi),
 145                 config.force_explicit_abi(),
 146                 true,
 147             ),
 148             vis: None,
 149             body: fm
 150                 .items
 151                 .iter()
 152                 .map(|i| BodyElement::ForeignItem(i))
 153                 .collect(),
 154             span,
 155         }
 156     }
 157 }
 158
 159 #[derive(Debug)]
 160 enum BodyElement<'a> {
 161     // Stmt(&'a ast::Stmt),
 162     // Field(&'a ast::ExprField),
 163     // Variant(&'a ast::Variant),
 164     // Item(&'a ast::Item),
 165     ForeignItem(&'a ast::ForeignItem),
 166 }
 167
 168 /// Represents a fn's signature.
 169 pub(crate) struct FnSig<'a> {
 170     decl: &'a ast::FnDecl,
 171     generics: &'a ast::Generics,
 172     ext: ast::Extern,
 173     is_async: Cow<'a, ast::Async>,
 174     constness: ast::Const,
 175     defaultness: ast::Defaultness,
 176     unsafety: ast::Unsafe,
 177     visibility: &'a ast::Visibility,
 178 }
 179
 180 impl<'a> FnSig<'a> {
 181     pub(crate) fn from_method_sig(
 182         method_sig: &'a ast::FnSig,
 183         generics: &'a ast::Generics,
 184         visibility: &'a ast::Visibility,
 185     ) -> FnSig<'a> {
 186         FnSig {
 187             unsafety: method_sig.header.unsafety,
 188             is_async: Cow::Borrowed(&method_sig.header.asyncness),
 189             constness: method_sig.header.constness,
 190             defaultness: ast::Defaultness::Final,
 191             ext: method_sig.header.ext,
 192             decl: &*method_sig.decl,
 193             generics,
 194             visibility,
 195         }
 196     }
 197
 198     pub(crate) fn from_fn_kind(
 199         fn_kind: &'a visit::FnKind<'_>,
 200         generics: &'a ast::Generics,
 201         decl: &'a ast::FnDecl,
 202         defaultness: ast::Defaultness,
 203     ) -> FnSig<'a> {
 204         match *fn_kind {
 205             visit::FnKind::Fn(fn_ctxt, _, fn_sig, vis, _) => match fn_ctxt {
 206                 visit::FnCtxt::Assoc(..) => {
 207                     let mut fn_sig = FnSig::from_method_sig(fn_sig, generics, vis);
 208                     fn_sig.defaultness = defaultness;
 209                     fn_sig
 210                 }
 211                 _ => FnSig {
 212                     decl,
 213                     generics,
 214                     ext: fn_sig.header.ext,
 215                     constness: fn_sig.header.constness,
 216                     is_async: Cow::Borrowed(&fn_sig.header.asyncness),
 217                     defaultness,
 218                     unsafety: fn_sig.header.unsafety,
 219                     visibility: vis,
 220                 },
 221             },
 222             _ => unreachable!(),
 223         }
 224     }
 225
 226     fn to_str(&self, context: &RewriteContext<'_>) -> String {
 227         let mut result = String::with_capacity(128);
 228         // Vis defaultness constness unsafety abi.
 229         result.push_str(&*format_visibility(context, &self.visibility));
 230         result.push_str(format_defaultness(self.defaultness));
 231         result.push_str(format_constness(self.constness));
 232         result.push_str(format_async(&self.is_async));
 233         result.push_str(format_unsafety(self.unsafety));
 234         result.push_str(&format_extern(
 235             self.ext,
 236             context.config.force_explicit_abi(),
 237             false,
 238         ));
 239         result
 240     }
 241 }
 242
 243 impl<'a> FmtVisitor<'a> {
 244     fn format_item(&mut self, item: &Item<'_>) {
 245         self.buffer.push_str(format_unsafety(item.unsafety));
 246         self.buffer.push_str(&item.abi);
 247
 248         let snippet = self.snippet(item.span);
 249         let brace_pos = snippet.find_uncommented("{").unwrap();
 250
 251         self.push_str("{");
 252         if !item.body.is_empty() || contains_comment(&snippet[brace_pos..]) {
 253             // FIXME: this skips comments between the extern keyword and the opening
 254             // brace.
 255             self.last_pos = item.span.lo() + BytePos(brace_pos as u32 + 1);
 256             self.block_indent = self.block_indent.block_indent(self.config);
 257
 258             if !item.body.is_empty() {
 259                 for item in &item.body {
 260                     self.format_body_element(item);
 261                 }
 262             }
 263
 264             self.format_missing_no_indent(item.span.hi() - BytePos(1));
 265             self.block_indent = self.block_indent.block_unindent(self.config);
 266             let indent_str = self.block_indent.to_string(self.config);
 267             self.push_str(&indent_str);
 268         }
 269
 270         self.push_str("}");
 271         self.last_pos = item.span.hi();
 272     }
 273
 274     fn format_body_element(&mut self, element: &BodyElement<'_>) {
 275         match *element {
 276             BodyElement::ForeignItem(item) => self.format_foreign_item(item),
 277         }
 278     }
 279
 280     pub(crate) fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
 281         let item = Item::from_foreign_mod(fm, span, self.config);
 282         self.format_item(&item);
 283     }
 284
 285     fn format_foreign_item(&mut self, item: &ast::ForeignItem) {
 286         let rewrite = item.rewrite(&self.get_context(), self.shape());
 287         let hi = item.span.hi();
 288         let span = if item.attrs.is_empty() {
 289             item.span
 290         } else {
 291             mk_sp(item.attrs[0].span.lo(), hi)
 292         };
 293         self.push_rewrite(span, rewrite);
 294         self.last_pos = hi;
 295     }
 296
 297     pub(crate) fn rewrite_fn_before_block(
 298         &mut self,
 299         indent: Indent,
 300         ident: symbol::Ident,
 301         fn_sig: &FnSig<'_>,
 302         span: Span,
 303     ) -> Option<(String, FnBraceStyle)> {
 304         let context = self.get_context();
 305
 306         let mut fn_brace_style = newline_for_brace(self.config, &fn_sig.generics.where_clause);
 307         let (result, _, force_newline_brace) =
 308             rewrite_fn_base(&context, indent, ident, fn_sig, span, fn_brace_style)?;
 309
 310         // 2 = ` {`
 311         if self.config.brace_style() == BraceStyle::AlwaysNextLine
 312             || force_newline_brace
 313             || last_line_width(&result) + 2 > self.shape().width
 314         {
 315             fn_brace_style = FnBraceStyle::NextLine
 316         }
 317
 318         Some((result, fn_brace_style))
 319     }
 320
 321     pub(crate) fn rewrite_required_fn(
 322         &mut self,
 323         indent: Indent,
 324         ident: symbol::Ident,
 325         sig: &ast::FnSig,
 326         vis: &ast::Visibility,
 327         generics: &ast::Generics,
 328         span: Span,
 329     ) -> Option<String> {
 330         // Drop semicolon or it will be interpreted as comment.
 331         let span = mk_sp(span.lo(), span.hi() - BytePos(1));
 332         let context = self.get_context();
 333
 334         let (mut result, ends_with_comment, _) = rewrite_fn_base(
 335             &context,
 336             indent,
 337             ident,
 338             &FnSig::from_method_sig(sig, generics, vis),
 339             span,
 340             FnBraceStyle::None,
 341         )?;
 342
 343         // If `result` ends with a comment, then remember to add a newline
 344         if ends_with_comment {
 345             result.push_str(&indent.to_string_with_newline(context.config));
 346         }
 347
 348         // Re-attach semicolon
 349         result.push(';');
 350
 351         Some(result)
 352     }
 353
 354     pub(crate) fn single_line_fn(
 355         &self,
 356         fn_str: &str,
 357         block: &ast::Block,
 358         inner_attrs: Option<&[ast::Attribute]>,
 359     ) -> Option<String> {
 360         if fn_str.contains('\n') || inner_attrs.map_or(false, |a| !a.is_empty()) {
 361             return None;
 362         }
 363
 364         let context = self.get_context();
 365
 366         if self.config.empty_item_single_line()
 367             && is_empty_block(&context, block, None)
 368             && self.block_indent.width() + fn_str.len() + 3 <= self.config.max_width()
 369             && !last_line_contains_single_line_comment(fn_str)
 370         {
 371             return Some(format!("{} {{}}", fn_str));
 372         }
 373
 374         if !self.config.fn_single_line() || !is_simple_block_stmt(&context, block, None) {
 375             return None;
 376         }
 377
 378         let res = Stmt::from_ast_node(block.stmts.first()?, true)
 379             .rewrite(&self.get_context(), self.shape())?;
 380
 381         let width = self.block_indent.width() + fn_str.len() + res.len() + 5;
 382         if !res.contains('\n') && width <= self.config.max_width() {
 383             Some(format!("{} {{ {} }}", fn_str, res))
 384         } else {
 385             None
 386         }
 387     }
 388
 389     pub(crate) fn visit_static(&mut self, static_parts: &StaticParts<'_>) {
 390         let rewrite = rewrite_static(&self.get_context(), static_parts, self.block_indent);
 391         self.push_rewrite(static_parts.span, rewrite);
 392     }
 393
 394     pub(crate) fn visit_struct(&mut self, struct_parts: &StructParts<'_>) {
 395         let is_tuple = match struct_parts.def {
 396             ast::VariantData::Tuple(..) => true,
 397             _ => false,
 398         };
 399         let rewrite = format_struct(&self.get_context(), struct_parts, self.block_indent, None)
 400             .map(|s| if is_tuple { s + ";" } else { s });
 401         self.push_rewrite(struct_parts.span, rewrite);
 402     }
 403
 404     pub(crate) fn visit_enum(
 405         &mut self,
 406         ident: symbol::Ident,
 407         vis: &ast::Visibility,
 408         enum_def: &ast::EnumDef,
 409         generics: &ast::Generics,
 410         span: Span,
 411     ) {
 412         let enum_header =
 413             format_header(&self.get_context(), "enum ", ident, vis, self.block_indent);
 414         self.push_str(&enum_header);
 415
 416         let enum_snippet = self.snippet(span);
 417         let brace_pos = enum_snippet.find_uncommented("{").unwrap();
 418         let body_start = span.lo() + BytePos(brace_pos as u32 + 1);
 419         let generics_str = format_generics(
 420             &self.get_context(),
 421             generics,
 422             self.config.brace_style(),
 423             if enum_def.variants.is_empty() {
 424                 BracePos::ForceSameLine
 425             } else {
 426                 BracePos::Auto
 427             },
 428             self.block_indent,
 429             // make a span that starts right after `enum Foo`
 430             mk_sp(ident.span.hi(), body_start),
 431             last_line_width(&enum_header),
 432         )
 433         .unwrap();
 434         self.push_str(&generics_str);
 435
 436         self.last_pos = body_start;
 437
 438         match self.format_variant_list(enum_def, body_start, span.hi()) {
 439             Some(ref s) if enum_def.variants.is_empty() => self.push_str(s),
 440             rw => {
 441                 self.push_rewrite(mk_sp(body_start, span.hi()), rw);
 442                 self.block_indent = self.block_indent.block_unindent(self.config);
 443             }
 444         }
 445     }
 446
 447     // Format the body of an enum definition
 448     fn format_variant_list(
 449         &mut self,
 450         enum_def: &ast::EnumDef,
 451         body_lo: BytePos,
 452         body_hi: BytePos,
 453     ) -> Option<String> {
 454         if enum_def.variants.is_empty() {
 455             let mut buffer = String::with_capacity(128);
 456             // 1 = "}"
 457             let span = mk_sp(body_lo, body_hi - BytePos(1));
 458             format_empty_struct_or_tuple(
 459                 &self.get_context(),
 460                 span,
 461                 self.block_indent,
 462                 &mut buffer,
 463                 "",
 464                 "}",
 465             );
 466             return Some(buffer);
 467         }
 468         let mut result = String::with_capacity(1024);
 469         let original_offset = self.block_indent;
 470         self.block_indent = self.block_indent.block_indent(self.config);
 471
 472         // If enum variants have discriminants, try to vertically align those,
 473         // provided the discrims are not shifted too much  to the right
 474         let align_threshold: usize = self.config.enum_discrim_align_threshold();
 475         let discr_ident_lens: Vec<usize> = enum_def
 476             .variants
 477             .iter()
 478             .filter(|var| var.disr_expr.is_some())
 479             .map(|var| rewrite_ident(&self.get_context(), var.ident).len())
 480             .collect();
 481         // cut the list at the point of longest discrim shorter than the threshold
 482         // All of the discrims under the threshold will get padded, and all above - left as is.
 483         let pad_discrim_ident_to = *discr_ident_lens
 484             .iter()
 485             .filter(|&l| *l <= align_threshold)
 486             .max()
 487             .unwrap_or(&0);
 488
 489         let itemize_list_with = |one_line_width: usize| {
 490             itemize_list(
 491                 self.snippet_provider,
 492                 enum_def.variants.iter(),
 493                 "}",
 494                 ",",
 495                 |f| {
 496                     if !f.attrs.is_empty() {
 497                         f.attrs[0].span.lo()
 498                     } else {
 499                         f.span.lo()
 500                     }
 501                 },
 502                 |f| f.span.hi(),
 503                 |f| self.format_variant(f, one_line_width, pad_discrim_ident_to),
 504                 body_lo,
 505                 body_hi,
 506                 false,
 507             )
 508             .collect()
 509         };
 510         let mut items: Vec<_> = itemize_list_with(self.config.struct_variant_width());
 511
 512         // If one of the variants use multiple lines, use multi-lined formatting for all variants.
 513         let has_multiline_variant = items.iter().any(|item| item.inner_as_ref().contains('\n'));
 514         let has_single_line_variant = items.iter().any(|item| !item.inner_as_ref().contains('\n'));
 515         if has_multiline_variant && has_single_line_variant {
 516             items = itemize_list_with(0);
 517         }
 518
 519         let shape = self.shape().sub_width(2)?;
 520         let fmt = ListFormatting::new(shape, self.config)
 521             .trailing_separator(self.config.trailing_comma())
 522             .preserve_newline(true);
 523
 524         let list = write_list(&items, &fmt)?;
 525         result.push_str(&list);
 526         result.push_str(&original_offset.to_string_with_newline(self.config));
 527         result.push('}');
 528         Some(result)
 529     }
 530
 531     // Variant of an enum.
 532     fn format_variant(
 533         &self,
 534         field: &ast::Variant,
 535         one_line_width: usize,
 536         pad_discrim_ident_to: usize,
 537     ) -> Option<String> {
 538         if contains_skip(&field.attrs) {
 539             let lo = field.attrs[0].span.lo();
 540             let span = mk_sp(lo, field.span.hi());
 541             return Some(self.snippet(span).to_owned());
 542         }
 543
 544         let context = self.get_context();
 545         // 1 = ','
 546         let shape = self.shape().sub_width(1)?;
 547         let attrs_str = field.attrs.rewrite(&context, shape)?;
 548         let lo = field
 549             .attrs
 550             .last()
 551             .map_or(field.span.lo(), |attr| attr.span.hi());
 552         let span = mk_sp(lo, field.span.lo());
 553
 554         let variant_body = match field.data {
 555             ast::VariantData::Tuple(..) | ast::VariantData::Struct(..) => format_struct(
 556                 &context,
 557                 &StructParts::from_variant(field),
 558                 self.block_indent,
 559                 Some(one_line_width),
 560             )?,
 561             ast::VariantData::Unit(..) => rewrite_ident(&context, field.ident).to_owned(),
 562         };
 563
 564         let variant_body = if let Some(ref expr) = field.disr_expr {
 565             let lhs = format!("{:1$} =", variant_body, pad_discrim_ident_to);
 566             rewrite_assign_rhs_with(
 567                 &context,
 568                 lhs,
 569                 &*expr.value,
 570                 shape,
 571                 RhsTactics::AllowOverflow,
 572             )?
 573         } else {
 574             variant_body
 575         };
 576
 577         combine_strs_with_missing_comments(&context, &attrs_str, &variant_body, span, shape, false)
 578     }
 579
 580     fn visit_impl_items(&mut self, items: &[ptr::P<ast::AssocItem>]) {
 581         if self.get_context().config.reorder_impl_items() {
 582             // Create visitor for each items, then reorder them.
 583             let mut buffer = vec![];
 584             for item in items {
 585                 self.visit_impl_item(item);
 586                 buffer.push((self.buffer.clone(), item.clone()));
 587                 self.buffer.clear();
 588             }
 589
 590             fn is_type(ty: &Option<rustc_ast::ptr::P<ast::Ty>>) -> bool {
 591                 if let Some(lty) = ty {
 592                     if let ast::TyKind::ImplTrait(..) = lty.kind {
 593                         return false;
 594                     }
 595                 }
 596                 true
 597             }
 598
 599             fn is_opaque(ty: &Option<rustc_ast::ptr::P<ast::Ty>>) -> bool {
 600                 !is_type(ty)
 601             }
 602
 603             fn both_type(
 604                 a: &Option<rustc_ast::ptr::P<ast::Ty>>,
 605                 b: &Option<rustc_ast::ptr::P<ast::Ty>>,
 606             ) -> bool {
 607                 is_type(a) && is_type(b)
 608             }
 609
 610             fn both_opaque(
 611                 a: &Option<rustc_ast::ptr::P<ast::Ty>>,
 612                 b: &Option<rustc_ast::ptr::P<ast::Ty>>,
 613             ) -> bool {
 614                 is_opaque(a) && is_opaque(b)
 615             }
 616
 617             // In rustc-ap-v638 the `OpaqueTy` AssocItemKind variant was removed but
 618             // we still need to differentiate to maintain sorting order.
 619
 620             // type -> opaque -> const -> macro -> method
 621             use crate::ast::AssocItemKind::*;
 622             fn need_empty_line(a: &ast::AssocItemKind, b: &ast::AssocItemKind) -> bool {
 623                 match (a, b) {
 624                     (TyAlias(lty), TyAlias(rty))
 625                         if both_type(&lty.ty, &rty.ty) || both_opaque(&lty.ty, &rty.ty) =>
 626                     {
 627                         false
 628                     }
 629                     (Const(..), Const(..)) => false,
 630                     _ => true,
 631                 }
 632             }
 633
 634             buffer.sort_by(|(_, a), (_, b)| match (&a.kind, &b.kind) {
 635                 (TyAlias(lty), TyAlias(rty))
 636                     if both_type(&lty.ty, &rty.ty) || both_opaque(&lty.ty, &rty.ty) =>
 637                 {
 638                     a.ident.as_str().cmp(&b.ident.as_str())
 639                 }
 640                 (Const(..), Const(..)) | (MacCall(..), MacCall(..)) => {
 641                     a.ident.as_str().cmp(&b.ident.as_str())
 642                 }
 643                 (Fn(..), Fn(..)) => a.span.lo().cmp(&b.span.lo()),
 644                 (TyAlias(ty), _) if is_type(&ty.ty) => Ordering::Less,
 645                 (_, TyAlias(ty)) if is_type(&ty.ty) => Ordering::Greater,
 646                 (TyAlias(..), _) => Ordering::Less,
 647                 (_, TyAlias(..)) => Ordering::Greater,
 648                 (Const(..), _) => Ordering::Less,
 649                 (_, Const(..)) => Ordering::Greater,
 650                 (MacCall(..), _) => Ordering::Less,
 651                 (_, MacCall(..)) => Ordering::Greater,
 652             });
 653             let mut prev_kind = None;
 654             for (buf, item) in buffer {
 655                 // Make sure that there are at least a single empty line between
 656                 // different impl items.
 657                 if prev_kind
 658                     .as_ref()
 659                     .map_or(false, |prev_kind| need_empty_line(prev_kind, &item.kind))
 660                 {
 661                     self.push_str("\n");
 662                 }
 663                 let indent_str = self.block_indent.to_string_with_newline(self.config);
 664                 self.push_str(&indent_str);
 665                 self.push_str(buf.trim());
 666                 prev_kind = Some(item.kind.clone());
 667             }
 668         } else {
 669             for item in items {
 670                 self.visit_impl_item(item);
 671             }
 672         }
 673     }
 674 }
 675
 676 pub(crate) fn format_impl(
 677     context: &RewriteContext<'_>,
 678     item: &ast::Item,
 679     offset: Indent,
 680 ) -> Option<String> {
 681     if let ast::ItemKind::Impl(impl_kind) = &item.kind {
 682         let ast::Impl {
 683             ref generics,
 684             ref self_ty,
 685             ref items,
 686             ..
 687         } = **impl_kind;
 688         let mut result = String::with_capacity(128);
 689         let ref_and_type = format_impl_ref_and_type(context, item, offset)?;
 690         let sep = offset.to_string_with_newline(context.config);
 691         result.push_str(&ref_and_type);
 692
 693         let where_budget = if result.contains('\n') {
 694             context.config.max_width()
 695         } else {
 696             context.budget(last_line_width(&result))
 697         };
 698
 699         let mut option = WhereClauseOption::snuggled(&ref_and_type);
 700         let snippet = context.snippet(item.span);
 701         let open_pos = snippet.find_uncommented("{")? + 1;
 702         if !contains_comment(&snippet[open_pos..])
 703             && items.is_empty()
 704             && generics.where_clause.predicates.len() == 1
 705             && !result.contains('\n')
 706         {
 707             option.suppress_comma();
 708             option.snuggle();
 709             option.allow_single_line();
 710         }
 711
 712         let missing_span = mk_sp(self_ty.span.hi(), item.span.hi());
 713         let where_span_end = context.snippet_provider.opt_span_before(missing_span, "{");
 714         let where_clause_str = rewrite_where_clause(
 715             context,
 716             &generics.where_clause,
 717             context.config.brace_style(),
 718             Shape::legacy(where_budget, offset.block_only()),
 719             false,
 720             "{",
 721             where_span_end,
 722             self_ty.span.hi(),
 723             option,
 724         )?;
 725
 726         // If there is no where-clause, we may have missing comments between the trait name and
 727         // the opening brace.
 728         if generics.where_clause.predicates.is_empty() {
 729             if let Some(hi) = where_span_end {
 730                 match recover_missing_comment_in_span(
 731                     mk_sp(self_ty.span.hi(), hi),
 732                     Shape::indented(offset, context.config),
 733                     context,
 734                     last_line_width(&result),
 735                 ) {
 736                     Some(ref missing_comment) if !missing_comment.is_empty() => {
 737                         result.push_str(missing_comment);
 738                     }
 739                     _ => (),
 740                 }
 741             }
 742         }
 743
 744         if is_impl_single_line(context, items.as_slice(), &result, &where_clause_str, item)? {
 745             result.push_str(&where_clause_str);
 746             if where_clause_str.contains('\n') || last_line_contains_single_line_comment(&result) {
 747                 // if the where_clause contains extra comments AND
 748                 // there is only one where-clause predicate
 749                 // recover the suppressed comma in single line where_clause formatting
 750                 if generics.where_clause.predicates.len() == 1 {
 751                     result.push(',');
 752                 }
 753                 result.push_str(&format!("{}{{{}}}", sep, sep));
 754             } else {
 755                 result.push_str(" {}");
 756             }
 757             return Some(result);
 758         }
 759
 760         result.push_str(&where_clause_str);
 761
 762         let need_newline = last_line_contains_single_line_comment(&result) || result.contains('\n');
 763         match context.config.brace_style() {
 764             _ if need_newline => result.push_str(&sep),
 765             BraceStyle::AlwaysNextLine => result.push_str(&sep),
 766             BraceStyle::PreferSameLine => result.push(' '),
 767             BraceStyle::SameLineWhere => {
 768                 if !where_clause_str.is_empty() {
 769                     result.push_str(&sep);
 770                 } else {
 771                     result.push(' ');
 772                 }
 773             }
 774         }
 775
 776         result.push('{');
 777         // this is an impl body snippet(impl SampleImpl { /* here */ })
 778         let lo = max(self_ty.span.hi(), generics.where_clause.span.hi());
 779         let snippet = context.snippet(mk_sp(lo, item.span.hi()));
 780         let open_pos = snippet.find_uncommented("{")? + 1;
 781
 782         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 783             let mut visitor = FmtVisitor::from_context(context);
 784             let item_indent = offset.block_only().block_indent(context.config);
 785             visitor.block_indent = item_indent;
 786             visitor.last_pos = lo + BytePos(open_pos as u32);
 787
 788             visitor.visit_attrs(&item.attrs, ast::AttrStyle::Inner);
 789             visitor.visit_impl_items(items);
 790
 791             visitor.format_missing(item.span.hi() - BytePos(1));
 792
 793             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
 794             let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
 795
 796             result.push_str(&inner_indent_str);
 797             result.push_str(visitor.buffer.trim());
 798             result.push_str(&outer_indent_str);
 799         } else if need_newline || !context.config.empty_item_single_line() {
 800             result.push_str(&sep);
 801         }
 802
 803         result.push('}');
 804
 805         Some(result)
 806     } else {
 807         unreachable!();
 808     }
 809 }
 810
 811 fn is_impl_single_line(
 812     context: &RewriteContext<'_>,
 813     items: &[ptr::P<ast::AssocItem>],
 814     result: &str,
 815     where_clause_str: &str,
 816     item: &ast::Item,
 817 ) -> Option<bool> {
 818     let snippet = context.snippet(item.span);
 819     let open_pos = snippet.find_uncommented("{")? + 1;
 820
 821     Some(
 822         context.config.empty_item_single_line()
 823             && items.is_empty()
 824             && !result.contains('\n')
 825             && result.len() + where_clause_str.len() <= context.config.max_width()
 826             && !contains_comment(&snippet[open_pos..]),
 827     )
 828 }
 829
 830 fn format_impl_ref_and_type(
 831     context: &RewriteContext<'_>,
 832     item: &ast::Item,
 833     offset: Indent,
 834 ) -> Option<String> {
 835     if let ast::ItemKind::Impl(impl_kind) = &item.kind {
 836         let ast::Impl {
 837             unsafety,
 838             polarity,
 839             defaultness,
 840             constness,
 841             ref generics,
 842             of_trait: ref trait_ref,
 843             ref self_ty,
 844             ..
 845         } = **impl_kind;
 846         let mut result = String::with_capacity(128);
 847
 848         result.push_str(&format_visibility(context, &item.vis));
 849         result.push_str(format_defaultness(defaultness));
 850         result.push_str(format_unsafety(unsafety));
 851
 852         let shape = if context.config.version() == Version::Two {
 853             Shape::indented(offset + last_line_width(&result), context.config)
 854         } else {
 855             generics_shape_from_config(
 856                 context.config,
 857                 Shape::indented(offset + last_line_width(&result), context.config),
 858                 0,
 859             )?
 860         };
 861         let generics_str = rewrite_generics(context, "impl", generics, shape)?;
 862         result.push_str(&generics_str);
 863         result.push_str(format_constness_right(constness));
 864
 865         let polarity_str = match polarity {
 866             ast::ImplPolarity::Negative(_) => "!",
 867             ast::ImplPolarity::Positive => "",
 868         };
 869
 870         let polarity_overhead;
 871         let trait_ref_overhead;
 872         if let Some(ref trait_ref) = *trait_ref {
 873             let result_len = last_line_width(&result);
 874             result.push_str(&rewrite_trait_ref(
 875                 context,
 876                 trait_ref,
 877                 offset,
 878                 polarity_str,
 879                 result_len,
 880             )?);
 881             polarity_overhead = 0; // already written
 882             trait_ref_overhead = " for".len();
 883         } else {
 884             polarity_overhead = polarity_str.len();
 885             trait_ref_overhead = 0;
 886         }
 887
 888         // Try to put the self type in a single line.
 889         let curly_brace_overhead = if generics.where_clause.predicates.is_empty() {
 890             // If there is no where-clause adapt budget for type formatting to take space and curly
 891             // brace into account.
 892             match context.config.brace_style() {
 893                 BraceStyle::AlwaysNextLine => 0,
 894                 _ => 2,
 895             }
 896         } else {
 897             0
 898         };
 899         let used_space = last_line_width(&result)
 900             + polarity_overhead
 901             + trait_ref_overhead
 902             + curly_brace_overhead;
 903         // 1 = space before the type.
 904         let budget = context.budget(used_space + 1);
 905         if let Some(self_ty_str) = self_ty.rewrite(context, Shape::legacy(budget, offset)) {
 906             if !self_ty_str.contains('\n') {
 907                 if trait_ref.is_some() {
 908                     result.push_str(" for ");
 909                 } else {
 910                     result.push(' ');
 911                     result.push_str(polarity_str);
 912                 }
 913                 result.push_str(&self_ty_str);
 914                 return Some(result);
 915             }
 916         }
 917
 918         // Couldn't fit the self type on a single line, put it on a new line.
 919         result.push('\n');
 920         // Add indentation of one additional tab.
 921         let new_line_offset = offset.block_indent(context.config);
 922         result.push_str(&new_line_offset.to_string(context.config));
 923         if trait_ref.is_some() {
 924             result.push_str("for ");
 925         } else {
 926             result.push_str(polarity_str);
 927         }
 928         let budget = context.budget(last_line_width(&result) + polarity_overhead);
 929         let type_offset = match context.config.indent_style() {
 930             IndentStyle::Visual => new_line_offset + trait_ref_overhead,
 931             IndentStyle::Block => new_line_offset,
 932         };
 933         result.push_str(&*self_ty.rewrite(context, Shape::legacy(budget, type_offset))?);
 934         Some(result)
 935     } else {
 936         unreachable!();
 937     }
 938 }
 939
 940 fn rewrite_trait_ref(
 941     context: &RewriteContext<'_>,
 942     trait_ref: &ast::TraitRef,
 943     offset: Indent,
 944     polarity_str: &str,
 945     result_len: usize,
 946 ) -> Option<String> {
 947     // 1 = space between generics and trait_ref
 948     let used_space = 1 + polarity_str.len() + result_len;
 949     let shape = Shape::indented(offset + used_space, context.config);
 950     if let Some(trait_ref_str) = trait_ref.rewrite(context, shape) {
 951         if !trait_ref_str.contains('\n') {
 952             return Some(format!(" {}{}", polarity_str, trait_ref_str));
 953         }
 954     }
 955     // We could not make enough space for trait_ref, so put it on new line.
 956     let offset = offset.block_indent(context.config);
 957     let shape = Shape::indented(offset, context.config);
 958     let trait_ref_str = trait_ref.rewrite(context, shape)?;
 959     Some(format!(
 960         "{}{}{}",
 961         offset.to_string_with_newline(context.config),
 962         polarity_str,
 963         trait_ref_str
 964     ))
 965 }
 966
 967 pub(crate) struct StructParts<'a> {
 968     prefix: &'a str,
 969     ident: symbol::Ident,
 970     vis: &'a ast::Visibility,
 971     def: &'a ast::VariantData,
 972     generics: Option<&'a ast::Generics>,
 973     span: Span,
 974 }
 975
 976 impl<'a> StructParts<'a> {
 977     fn format_header(&self, context: &RewriteContext<'_>, offset: Indent) -> String {
 978         format_header(context, self.prefix, self.ident, self.vis, offset)
 979     }
 980
 981     fn from_variant(variant: &'a ast::Variant) -> Self {
 982         StructParts {
 983             prefix: "",
 984             ident: variant.ident,
 985             vis: &DEFAULT_VISIBILITY,
 986             def: &variant.data,
 987             generics: None,
 988             span: variant.span,
 989         }
 990     }
 991
 992     pub(crate) fn from_item(item: &'a ast::Item) -> Self {
 993         let (prefix, def, generics) = match item.kind {
 994             ast::ItemKind::Struct(ref def, ref generics) => ("struct ", def, generics),
 995             ast::ItemKind::Union(ref def, ref generics) => ("union ", def, generics),
 996             _ => unreachable!(),
 997         };
 998         StructParts {
 999             prefix,
1000             ident: item.ident,
1001             vis: &item.vis,
1002             def,
1003             generics: Some(generics),
1004             span: item.span,
1005         }
1006     }
1007 }
1008
1009 fn format_struct(
1010     context: &RewriteContext<'_>,
1011     struct_parts: &StructParts<'_>,
1012     offset: Indent,
1013     one_line_width: Option<usize>,
1014 ) -> Option<String> {
1015     match *struct_parts.def {
1016         ast::VariantData::Unit(..) => format_unit_struct(context, struct_parts, offset),
1017         ast::VariantData::Tuple(ref fields, _) => {
1018             format_tuple_struct(context, struct_parts, fields, offset)
1019         }
1020         ast::VariantData::Struct(ref fields, _) => {
1021             format_struct_struct(context, struct_parts, fields, offset, one_line_width)
1022         }
1023     }
1024 }
1025
1026 pub(crate) fn format_trait(
1027     context: &RewriteContext<'_>,
1028     item: &ast::Item,
1029     offset: Indent,
1030 ) -> Option<String> {
1031     if let ast::ItemKind::Trait(trait_kind) = &item.kind {
1032         let ast::Trait {
1033             is_auto,
1034             unsafety,
1035             ref generics,
1036             ref bounds,
1037             ref items,
1038         } = **trait_kind;
1039         let mut result = String::with_capacity(128);
1040         let header = format!(
1041             "{}{}{}trait ",
1042             format_visibility(context, &item.vis),
1043             format_unsafety(unsafety),
1044             format_auto(is_auto),
1045         );
1046         result.push_str(&header);
1047
1048         let body_lo = context.snippet_provider.span_after(item.span, "{");
1049
1050         let shape = Shape::indented(offset, context.config).offset_left(result.len())?;
1051         let generics_str =
1052             rewrite_generics(context, rewrite_ident(context, item.ident), generics, shape)?;
1053         result.push_str(&generics_str);
1054
1055         // FIXME(#2055): rustfmt fails to format when there are comments between trait bounds.
1056         if !bounds.is_empty() {
1057             let ident_hi = context
1058                 .snippet_provider
1059                 .span_after(item.span, &item.ident.as_str());
1060             let bound_hi = bounds.last().unwrap().span().hi();
1061             let snippet = context.snippet(mk_sp(ident_hi, bound_hi));
1062             if contains_comment(snippet) {
1063                 return None;
1064             }
1065
1066             result = rewrite_assign_rhs_with(
1067                 context,
1068                 result + ":",
1069                 bounds,
1070                 shape,
1071                 RhsTactics::ForceNextLineWithoutIndent,
1072             )?;
1073         }
1074
1075         // Rewrite where-clause.
1076         if !generics.where_clause.predicates.is_empty() {
1077             let where_on_new_line = context.config.indent_style() != IndentStyle::Block;
1078
1079             let where_budget = context.budget(last_line_width(&result));
1080             let pos_before_where = if bounds.is_empty() {
1081                 generics.where_clause.span.lo()
1082             } else {
1083                 bounds[bounds.len() - 1].span().hi()
1084             };
1085             let option = WhereClauseOption::snuggled(&generics_str);
1086             let where_clause_str = rewrite_where_clause(
1087                 context,
1088                 &generics.where_clause,
1089                 context.config.brace_style(),
1090                 Shape::legacy(where_budget, offset.block_only()),
1091                 where_on_new_line,
1092                 "{",
1093                 None,
1094                 pos_before_where,
1095                 option,
1096             )?;
1097             // If the where-clause cannot fit on the same line,
1098             // put the where-clause on a new line
1099             if !where_clause_str.contains('\n')
1100                 && last_line_width(&result) + where_clause_str.len() + offset.width()
1101                     > context.config.comment_width()
1102             {
1103                 let width = offset.block_indent + context.config.tab_spaces() - 1;
1104                 let where_indent = Indent::new(0, width);
1105                 result.push_str(&where_indent.to_string_with_newline(context.config));
1106             }
1107             result.push_str(&where_clause_str);
1108         } else {
1109             let item_snippet = context.snippet(item.span);
1110             if let Some(lo) = item_snippet.find('/') {
1111                 // 1 = `{`
1112                 let comment_hi = body_lo - BytePos(1);
1113                 let comment_lo = item.span.lo() + BytePos(lo as u32);
1114                 if comment_lo < comment_hi {
1115                     match recover_missing_comment_in_span(
1116                         mk_sp(comment_lo, comment_hi),
1117                         Shape::indented(offset, context.config),
1118                         context,
1119                         last_line_width(&result),
1120                     ) {
1121                         Some(ref missing_comment) if !missing_comment.is_empty() => {
1122                             result.push_str(missing_comment);
1123                         }
1124                         _ => (),
1125                     }
1126                 }
1127             }
1128         }
1129
1130         match context.config.brace_style() {
1131             _ if last_line_contains_single_line_comment(&result)
1132                 || last_line_width(&result) + 2 > context.budget(offset.width()) =>
1133             {
1134                 result.push_str(&offset.to_string_with_newline(context.config));
1135             }
1136             BraceStyle::AlwaysNextLine => {
1137                 result.push_str(&offset.to_string_with_newline(context.config));
1138             }
1139             BraceStyle::PreferSameLine => result.push(' '),
1140             BraceStyle::SameLineWhere => {
1141                 if result.contains('\n')
1142                     || (!generics.where_clause.predicates.is_empty() && !items.is_empty())
1143                 {
1144                     result.push_str(&offset.to_string_with_newline(context.config));
1145                 } else {
1146                     result.push(' ');
1147                 }
1148             }
1149         }
1150         result.push('{');
1151
1152         let block_span = mk_sp(generics.where_clause.span.hi(), item.span.hi());
1153         let snippet = context.snippet(block_span);
1154         let open_pos = snippet.find_uncommented("{")? + 1;
1155         let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
1156
1157         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
1158             let mut visitor = FmtVisitor::from_context(context);
1159             visitor.block_indent = offset.block_only().block_indent(context.config);
1160             visitor.last_pos = block_span.lo() + BytePos(open_pos as u32);
1161
1162             for item in items {
1163                 visitor.visit_trait_item(item);
1164             }
1165
1166             visitor.format_missing(item.span.hi() - BytePos(1));
1167
1168             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
1169
1170             result.push_str(&inner_indent_str);
1171             result.push_str(visitor.buffer.trim());
1172             result.push_str(&outer_indent_str);
1173         } else if result.contains('\n') {
1174             result.push_str(&outer_indent_str);
1175         }
1176
1177         result.push('}');
1178         Some(result)
1179     } else {
1180         unreachable!();
1181     }
1182 }
1183
1184 struct OpaqueTypeBounds<'a> {
1185     generic_bounds: &'a ast::GenericBounds,
1186 }
1187
1188 impl<'a> Rewrite for OpaqueTypeBounds<'a> {
1189     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1190         self.generic_bounds
1191             .rewrite(context, shape)
1192             .map(|s| format!("impl {}", s))
1193     }
1194 }
1195
1196 pub(crate) struct TraitAliasBounds<'a> {
1197     generic_bounds: &'a ast::GenericBounds,
1198     generics: &'a ast::Generics,
1199 }
1200
1201 impl<'a> Rewrite for TraitAliasBounds<'a> {
1202     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1203         let generic_bounds_str = self.generic_bounds.rewrite(context, shape)?;
1204
1205         let mut option = WhereClauseOption::new(true, WhereClauseSpace::None);
1206         option.allow_single_line();
1207
1208         let where_str = rewrite_where_clause(
1209             context,
1210             &self.generics.where_clause,
1211             context.config.brace_style(),
1212             shape,
1213             false,
1214             ";",
1215             None,
1216             self.generics.where_clause.span.lo(),
1217             option,
1218         )?;
1219
1220         let fits_single_line = !generic_bounds_str.contains('\n')
1221             && !where_str.contains('\n')
1222             && generic_bounds_str.len() + where_str.len() < shape.width;
1223         let space = if generic_bounds_str.is_empty() || where_str.is_empty() {
1224             Cow::from("")
1225         } else if fits_single_line {
1226             Cow::from(" ")
1227         } else {
1228             shape.indent.to_string_with_newline(&context.config)
1229         };
1230
1231         Some(format!("{}{}{}", generic_bounds_str, space, where_str))
1232     }
1233 }
1234
1235 pub(crate) fn format_trait_alias(
1236     context: &RewriteContext<'_>,
1237     ident: symbol::Ident,
1238     vis: &ast::Visibility,
1239     generics: &ast::Generics,
1240     generic_bounds: &ast::GenericBounds,
1241     shape: Shape,
1242 ) -> Option<String> {
1243     let alias = rewrite_ident(context, ident);
1244     // 6 = "trait ", 2 = " ="
1245     let g_shape = shape.offset_left(6)?.sub_width(2)?;
1246     let generics_str = rewrite_generics(context, &alias, generics, g_shape)?;
1247     let vis_str = format_visibility(context, vis);
1248     let lhs = format!("{}trait {} =", vis_str, generics_str);
1249     // 1 = ";"
1250     let trait_alias_bounds = TraitAliasBounds {
1251         generic_bounds,
1252         generics,
1253     };
1254     rewrite_assign_rhs(context, lhs, &trait_alias_bounds, shape.sub_width(1)?).map(|s| s + ";")
1255 }
1256
1257 fn format_unit_struct(
1258     context: &RewriteContext<'_>,
1259     p: &StructParts<'_>,
1260     offset: Indent,
1261 ) -> Option<String> {
1262     let header_str = format_header(context, p.prefix, p.ident, p.vis, offset);
1263     let generics_str = if let Some(generics) = p.generics {
1264         let hi = context.snippet_provider.span_before(p.span, ";");
1265         format_generics(
1266             context,
1267             generics,
1268             context.config.brace_style(),
1269             BracePos::None,
1270             offset,
1271             // make a span that starts right after `struct Foo`
1272             mk_sp(p.ident.span.hi(), hi),
1273             last_line_width(&header_str),
1274         )?
1275     } else {
1276         String::new()
1277     };
1278     Some(format!("{}{};", header_str, generics_str))
1279 }
1280
1281 pub(crate) fn format_struct_struct(
1282     context: &RewriteContext<'_>,
1283     struct_parts: &StructParts<'_>,
1284     fields: &[ast::FieldDef],
1285     offset: Indent,
1286     one_line_width: Option<usize>,
1287 ) -> Option<String> {
1288     let mut result = String::with_capacity(1024);
1289     let span = struct_parts.span;
1290
1291     let header_str = struct_parts.format_header(context, offset);
1292     result.push_str(&header_str);
1293
1294     let header_hi = struct_parts.ident.span.hi();
1295     let body_lo = context.snippet_provider.span_after(span, "{");
1296
1297     let generics_str = match struct_parts.generics {
1298         Some(g) => format_generics(
1299             context,
1300             g,
1301             context.config.brace_style(),
1302             if fields.is_empty() {
1303                 BracePos::ForceSameLine
1304             } else {
1305                 BracePos::Auto
1306             },
1307             offset,
1308             // make a span that starts right after `struct Foo`
1309             mk_sp(header_hi, body_lo),
1310             last_line_width(&result),
1311         )?,
1312         None => {
1313             // 3 = ` {}`, 2 = ` {`.
1314             let overhead = if fields.is_empty() { 3 } else { 2 };
1315             if (context.config.brace_style() == BraceStyle::AlwaysNextLine && !fields.is_empty())
1316                 || context.config.max_width() < overhead + result.len()
1317             {
1318                 format!("\n{}{{", offset.block_only().to_string(context.config))
1319             } else {
1320                 " {".to_owned()
1321             }
1322         }
1323     };
1324     // 1 = `}`
1325     let overhead = if fields.is_empty() { 1 } else { 0 };
1326     let total_width = result.len() + generics_str.len() + overhead;
1327     if !generics_str.is_empty()
1328         && !generics_str.contains('\n')
1329         && total_width > context.config.max_width()
1330     {
1331         result.push('\n');
1332         result.push_str(&offset.to_string(context.config));
1333         result.push_str(generics_str.trim_start());
1334     } else {
1335         result.push_str(&generics_str);
1336     }
1337
1338     if fields.is_empty() {
1339         let inner_span = mk_sp(body_lo, span.hi() - BytePos(1));
1340         format_empty_struct_or_tuple(context, inner_span, offset, &mut result, "", "}");
1341         return Some(result);
1342     }
1343
1344     // 3 = ` ` and ` }`
1345     let one_line_budget = context.budget(result.len() + 3 + offset.width());
1346     let one_line_budget =
1347         one_line_width.map_or(0, |one_line_width| min(one_line_width, one_line_budget));
1348
1349     let items_str = rewrite_with_alignment(
1350         fields,
1351         context,
1352         Shape::indented(offset.block_indent(context.config), context.config).sub_width(1)?,
1353         mk_sp(body_lo, span.hi()),
1354         one_line_budget,
1355     )?;
1356
1357     if !items_str.contains('\n')
1358         && !result.contains('\n')
1359         && items_str.len() <= one_line_budget
1360         && !last_line_contains_single_line_comment(&items_str)
1361     {
1362         Some(format!("{} {} }}", result, items_str))
1363     } else {
1364         Some(format!(
1365             "{}\n{}{}\n{}}}",
1366             result,
1367             offset
1368                 .block_indent(context.config)
1369                 .to_string(context.config),
1370             items_str,
1371             offset.to_string(context.config)
1372         ))
1373     }
1374 }
1375
1376 fn get_bytepos_after_visibility(vis: &ast::Visibility, default_span: Span) -> BytePos {
1377     match vis.kind {
1378         ast::VisibilityKind::Crate(..) | ast::VisibilityKind::Restricted { .. } => vis.span.hi(),
1379         _ => default_span.lo(),
1380     }
1381 }
1382
1383 // Format tuple or struct without any fields. We need to make sure that the comments
1384 // inside the delimiters are preserved.
1385 fn format_empty_struct_or_tuple(
1386     context: &RewriteContext<'_>,
1387     span: Span,
1388     offset: Indent,
1389     result: &mut String,
1390     opener: &str,
1391     closer: &str,
1392 ) {
1393     // 3 = " {}" or "();"
1394     let used_width = last_line_used_width(&result, offset.width()) + 3;
1395     if used_width > context.config.max_width() {
1396         result.push_str(&offset.to_string_with_newline(context.config))
1397     }
1398     result.push_str(opener);
1399     match rewrite_missing_comment(span, Shape::indented(offset, context.config), context) {
1400         Some(ref s) if s.is_empty() => (),
1401         Some(ref s) => {
1402             if !is_single_line(s) || first_line_contains_single_line_comment(s) {
1403                 let nested_indent_str = offset
1404                     .block_indent(context.config)
1405                     .to_string_with_newline(context.config);
1406                 result.push_str(&nested_indent_str);
1407             }
1408             result.push_str(s);
1409             if last_line_contains_single_line_comment(s) {
1410                 result.push_str(&offset.to_string_with_newline(context.config));
1411             }
1412         }
1413         None => result.push_str(context.snippet(span)),
1414     }
1415     result.push_str(closer);
1416 }
1417
1418 fn format_tuple_struct(
1419     context: &RewriteContext<'_>,
1420     struct_parts: &StructParts<'_>,
1421     fields: &[ast::FieldDef],
1422     offset: Indent,
1423 ) -> Option<String> {
1424     let mut result = String::with_capacity(1024);
1425     let span = struct_parts.span;
1426
1427     let header_str = struct_parts.format_header(context, offset);
1428     result.push_str(&header_str);
1429
1430     let body_lo = if fields.is_empty() {
1431         let lo = get_bytepos_after_visibility(struct_parts.vis, span);
1432         context
1433             .snippet_provider
1434             .span_after(mk_sp(lo, span.hi()), "(")
1435     } else {
1436         fields[0].span.lo()
1437     };
1438     let body_hi = if fields.is_empty() {
1439         context
1440             .snippet_provider
1441             .span_after(mk_sp(body_lo, span.hi()), ")")
1442     } else {
1443         // This is a dirty hack to work around a missing `)` from the span of the last field.
1444         let last_arg_span = fields[fields.len() - 1].span;
1445         context
1446             .snippet_provider
1447             .opt_span_after(mk_sp(last_arg_span.hi(), span.hi()), ")")
1448             .unwrap_or_else(|| last_arg_span.hi())
1449     };
1450
1451     let where_clause_str = match struct_parts.generics {
1452         Some(generics) => {
1453             let budget = context.budget(last_line_width(&header_str));
1454             let shape = Shape::legacy(budget, offset);
1455             let generics_str = rewrite_generics(context, "", generics, shape)?;
1456             result.push_str(&generics_str);
1457
1458             let where_budget = context.budget(last_line_width(&result));
1459             let option = WhereClauseOption::new(true, WhereClauseSpace::Newline);
1460             rewrite_where_clause(
1461                 context,
1462                 &generics.where_clause,
1463                 context.config.brace_style(),
1464                 Shape::legacy(where_budget, offset.block_only()),
1465                 false,
1466                 ";",
1467                 None,
1468                 body_hi,
1469                 option,
1470             )?
1471         }
1472         None => "".to_owned(),
1473     };
1474
1475     if fields.is_empty() {
1476         let body_hi = context
1477             .snippet_provider
1478             .span_before(mk_sp(body_lo, span.hi()), ")");
1479         let inner_span = mk_sp(body_lo, body_hi);
1480         format_empty_struct_or_tuple(context, inner_span, offset, &mut result, "(", ")");
1481     } else {
1482         let shape = Shape::indented(offset, context.config).sub_width(1)?;
1483         let lo = if let Some(generics) = struct_parts.generics {
1484             generics.span.hi()
1485         } else {
1486             struct_parts.ident.span.hi()
1487         };
1488         result = overflow::rewrite_with_parens(
1489             context,
1490             &result,
1491             fields.iter(),
1492             shape,
1493             mk_sp(lo, span.hi()),
1494             context.config.fn_call_width(),
1495             None,
1496         )?;
1497     }
1498
1499     if !where_clause_str.is_empty()
1500         && !where_clause_str.contains('\n')
1501         && (result.contains('\n')
1502             || offset.block_indent + result.len() + where_clause_str.len() + 1
1503                 > context.config.max_width())
1504     {
1505         // We need to put the where-clause on a new line, but we didn't
1506         // know that earlier, so the where-clause will not be indented properly.
1507         result.push('\n');
1508         result.push_str(
1509             &(offset.block_only() + (context.config.tab_spaces() - 1)).to_string(context.config),
1510         );
1511     }
1512     result.push_str(&where_clause_str);
1513
1514     Some(result)
1515 }
1516
1517 pub(crate) fn rewrite_type<R: Rewrite>(
1518     context: &RewriteContext<'_>,
1519     indent: Indent,
1520     ident: symbol::Ident,
1521     vis: &ast::Visibility,
1522     generics: &ast::Generics,
1523     generic_bounds_opt: Option<&ast::GenericBounds>,
1524     rhs: Option<&R>,
1525     span: Span,
1526 ) -> Option<String> {
1527     let mut result = String::with_capacity(128);
1528     result.push_str(&format!("{}type ", format_visibility(context, vis)));
1529     let ident_str = rewrite_ident(context, ident);
1530
1531     if generics.params.is_empty() {
1532         result.push_str(ident_str)
1533     } else {
1534         // 2 = `= `
1535         let g_shape = Shape::indented(indent, context.config)
1536             .offset_left(result.len())?
1537             .sub_width(2)?;
1538         let generics_str = rewrite_generics(context, ident_str, generics, g_shape)?;
1539         result.push_str(&generics_str);
1540     }
1541
1542     if let Some(bounds) = generic_bounds_opt {
1543         if !bounds.is_empty() {
1544             // 2 = `: `
1545             let shape = Shape::indented(indent, context.config).offset_left(result.len() + 2)?;
1546             let type_bounds = bounds.rewrite(context, shape).map(|s| format!(": {}", s))?;
1547             result.push_str(&type_bounds);
1548         }
1549     }
1550
1551     let where_budget = context.budget(last_line_width(&result));
1552     let mut option = WhereClauseOption::snuggled(&result);
1553     if rhs.is_none() {
1554         option.suppress_comma();
1555     }
1556     let where_clause_str = rewrite_where_clause(
1557         context,
1558         &generics.where_clause,
1559         context.config.brace_style(),
1560         Shape::legacy(where_budget, indent),
1561         false,
1562         "=",
1563         None,
1564         generics.span.hi(),
1565         option,
1566     )?;
1567     result.push_str(&where_clause_str);
1568
1569     if let Some(ty) = rhs {
1570         // If there's a where clause, add a newline before the assignment. Otherwise just add a
1571         // space.
1572         let has_where = !generics.where_clause.predicates.is_empty();
1573         if has_where {
1574             result.push_str(&indent.to_string_with_newline(context.config));
1575         } else {
1576             result.push(' ');
1577         }
1578
1579         let comment_span = context
1580             .snippet_provider
1581             .opt_span_before(span, "=")
1582             .map(|op_lo| mk_sp(generics.where_clause.span.hi(), op_lo));
1583
1584         let lhs = match comment_span {
1585             Some(comment_span)
1586                 if contains_comment(context.snippet_provider.span_to_snippet(comment_span)?) =>
1587             {
1588                 let comment_shape = if has_where {
1589                     Shape::indented(indent, context.config)
1590                 } else {
1591                     Shape::indented(indent, context.config)
1592                         .block_left(context.config.tab_spaces())?
1593                 };
1594
1595                 combine_strs_with_missing_comments(
1596                     context,
1597                     result.trim_end(),
1598                     "=",
1599                     comment_span,
1600                     comment_shape,
1601                     true,
1602                 )?
1603             }
1604             _ => format!("{}=", result),
1605         };
1606
1607         // 1 = `;`
1608         let shape = Shape::indented(indent, context.config).sub_width(1)?;
1609         rewrite_assign_rhs(context, lhs, &*ty, shape).map(|s| s + ";")
1610     } else {
1611         Some(format!("{};", result))
1612     }
1613 }
1614
1615 pub(crate) fn rewrite_opaque_type(
1616     context: &RewriteContext<'_>,
1617     indent: Indent,
1618     ident: symbol::Ident,
1619     generic_bounds: &ast::GenericBounds,
1620     generics: &ast::Generics,
1621     vis: &ast::Visibility,
1622     span: Span,
1623 ) -> Option<String> {
1624     let opaque_type_bounds = OpaqueTypeBounds { generic_bounds };
1625     rewrite_type(
1626         context,
1627         indent,
1628         ident,
1629         vis,
1630         generics,
1631         Some(generic_bounds),
1632         Some(&opaque_type_bounds),
1633         span,
1634     )
1635 }
1636
1637 fn type_annotation_spacing(config: &Config) -> (&str, &str) {
1638     (
1639         if config.space_before_colon() { " " } else { "" },
1640         if config.space_after_colon() { " " } else { "" },
1641     )
1642 }
1643
1644 pub(crate) fn rewrite_struct_field_prefix(
1645     context: &RewriteContext<'_>,
1646     field: &ast::FieldDef,
1647 ) -> Option<String> {
1648     let vis = format_visibility(context, &field.vis);
1649     let type_annotation_spacing = type_annotation_spacing(context.config);
1650     Some(match field.ident {
1651         Some(name) => format!(
1652             "{}{}{}:",
1653             vis,
1654             rewrite_ident(context, name),
1655             type_annotation_spacing.0
1656         ),
1657         None => vis.to_string(),
1658     })
1659 }
1660
1661 impl Rewrite for ast::FieldDef {
1662     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1663         rewrite_struct_field(context, self, shape, 0)
1664     }
1665 }
1666
1667 pub(crate) fn rewrite_struct_field(
1668     context: &RewriteContext<'_>,
1669     field: &ast::FieldDef,
1670     shape: Shape,
1671     lhs_max_width: usize,
1672 ) -> Option<String> {
1673     if contains_skip(&field.attrs) {
1674         return Some(context.snippet(field.span()).to_owned());
1675     }
1676
1677     let type_annotation_spacing = type_annotation_spacing(context.config);
1678     let prefix = rewrite_struct_field_prefix(context, field)?;
1679
1680     let attrs_str = field.attrs.rewrite(context, shape)?;
1681     let attrs_extendable = field.ident.is_none() && is_attributes_extendable(&attrs_str);
1682     let missing_span = if field.attrs.is_empty() {
1683         mk_sp(field.span.lo(), field.span.lo())
1684     } else {
1685         mk_sp(field.attrs.last().unwrap().span.hi(), field.span.lo())
1686     };
1687     let mut spacing = String::from(if field.ident.is_some() {
1688         type_annotation_spacing.1
1689     } else {
1690         ""
1691     });
1692     // Try to put everything on a single line.
1693     let attr_prefix = combine_strs_with_missing_comments(
1694         context,
1695         &attrs_str,
1696         &prefix,
1697         missing_span,
1698         shape,
1699         attrs_extendable,
1700     )?;
1701     let overhead = trimmed_last_line_width(&attr_prefix);
1702     let lhs_offset = lhs_max_width.saturating_sub(overhead);
1703     for _ in 0..lhs_offset {
1704         spacing.push(' ');
1705     }
1706     // In this extreme case we will be missing a space between an attribute and a field.
1707     if prefix.is_empty() && !attrs_str.is_empty() && attrs_extendable && spacing.is_empty() {
1708         spacing.push(' ');
1709     }
1710     let orig_ty = shape
1711         .offset_left(overhead + spacing.len())
1712         .and_then(|ty_shape| field.ty.rewrite(context, ty_shape));
1713     if let Some(ref ty) = orig_ty {
1714         if !ty.contains('\n') {
1715             return Some(attr_prefix + &spacing + ty);
1716         }
1717     }
1718
1719     let is_prefix_empty = prefix.is_empty();
1720     // We must use multiline. We are going to put attributes and a field on different lines.
1721     let field_str = rewrite_assign_rhs(context, prefix, &*field.ty, shape)?;
1722     // Remove a leading white-space from `rewrite_assign_rhs()` when rewriting a tuple struct.
1723     let field_str = if is_prefix_empty {
1724         field_str.trim_start()
1725     } else {
1726         &field_str
1727     };
1728     combine_strs_with_missing_comments(context, &attrs_str, field_str, missing_span, shape, false)
1729 }
1730
1731 pub(crate) struct StaticParts<'a> {
1732     prefix: &'a str,
1733     vis: &'a ast::Visibility,
1734     ident: symbol::Ident,
1735     ty: &'a ast::Ty,
1736     mutability: ast::Mutability,
1737     expr_opt: Option<&'a ptr::P<ast::Expr>>,
1738     defaultness: Option<ast::Defaultness>,
1739     span: Span,
1740 }
1741
1742 impl<'a> StaticParts<'a> {
1743     pub(crate) fn from_item(item: &'a ast::Item) -> Self {
1744         let (defaultness, prefix, ty, mutability, expr) = match item.kind {
1745             ast::ItemKind::Static(ref ty, mutability, ref expr) => {
1746                 (None, "static", ty, mutability, expr)
1747             }
1748             ast::ItemKind::Const(defaultness, ref ty, ref expr) => {
1749                 (Some(defaultness), "const", ty, ast::Mutability::Not, expr)
1750             }
1751             _ => unreachable!(),
1752         };
1753         StaticParts {
1754             prefix,
1755             vis: &item.vis,
1756             ident: item.ident,
1757             ty,
1758             mutability,
1759             expr_opt: expr.as_ref(),
1760             defaultness,
1761             span: item.span,
1762         }
1763     }
1764
1765     pub(crate) fn from_trait_item(ti: &'a ast::AssocItem) -> Self {
1766         let (defaultness, ty, expr_opt) = match ti.kind {
1767             ast::AssocItemKind::Const(defaultness, ref ty, ref expr_opt) => {
1768                 (defaultness, ty, expr_opt)
1769             }
1770             _ => unreachable!(),
1771         };
1772         StaticParts {
1773             prefix: "const",
1774             vis: &ti.vis,
1775             ident: ti.ident,
1776             ty,
1777             mutability: ast::Mutability::Not,
1778             expr_opt: expr_opt.as_ref(),
1779             defaultness: Some(defaultness),
1780             span: ti.span,
1781         }
1782     }
1783
1784     pub(crate) fn from_impl_item(ii: &'a ast::AssocItem) -> Self {
1785         let (defaultness, ty, expr) = match ii.kind {
1786             ast::AssocItemKind::Const(defaultness, ref ty, ref expr) => (defaultness, ty, expr),
1787             _ => unreachable!(),
1788         };
1789         StaticParts {
1790             prefix: "const",
1791             vis: &ii.vis,
1792             ident: ii.ident,
1793             ty,
1794             mutability: ast::Mutability::Not,
1795             expr_opt: expr.as_ref(),
1796             defaultness: Some(defaultness),
1797             span: ii.span,
1798         }
1799     }
1800 }
1801
1802 fn rewrite_static(
1803     context: &RewriteContext<'_>,
1804     static_parts: &StaticParts<'_>,
1805     offset: Indent,
1806 ) -> Option<String> {
1807     let colon = colon_spaces(context.config);
1808     let mut prefix = format!(
1809         "{}{}{} {}{}{}",
1810         format_visibility(context, static_parts.vis),
1811         static_parts.defaultness.map_or("", format_defaultness),
1812         static_parts.prefix,
1813         format_mutability(static_parts.mutability),
1814         rewrite_ident(context, static_parts.ident),
1815         colon,
1816     );
1817     // 2 = " =".len()
1818     let ty_shape =
1819         Shape::indented(offset.block_only(), context.config).offset_left(prefix.len() + 2)?;
1820     let ty_str = match static_parts.ty.rewrite(context, ty_shape) {
1821         Some(ty_str) => ty_str,
1822         None => {
1823             if prefix.ends_with(' ') {
1824                 prefix.pop();
1825             }
1826             let nested_indent = offset.block_indent(context.config);
1827             let nested_shape = Shape::indented(nested_indent, context.config);
1828             let ty_str = static_parts.ty.rewrite(context, nested_shape)?;
1829             format!(
1830                 "{}{}",
1831                 nested_indent.to_string_with_newline(context.config),
1832                 ty_str
1833             )
1834         }
1835     };
1836
1837     if let Some(expr) = static_parts.expr_opt {
1838         let comments_lo = context.snippet_provider.span_after(static_parts.span, "=");
1839         let expr_lo = expr.span.lo();
1840         let comments_span = mk_sp(comments_lo, expr_lo);
1841
1842         let lhs = format!("{}{} =", prefix, ty_str);
1843
1844         // 1 = ;
1845         let remaining_width = context.budget(offset.block_indent + 1);
1846         rewrite_assign_rhs_with_comments(
1847             context,
1848             &lhs,
1849             &**expr,
1850             Shape::legacy(remaining_width, offset.block_only()),
1851             RhsTactics::Default,
1852             comments_span,
1853             true,
1854         )
1855         .and_then(|res| recover_comment_removed(res, static_parts.span, context))
1856         .map(|s| if s.ends_with(';') { s } else { s + ";" })
1857     } else {
1858         Some(format!("{}{};", prefix, ty_str))
1859     }
1860 }
1861 struct OpaqueType<'a> {
1862     bounds: &'a ast::GenericBounds,
1863 }
1864
1865 impl<'a> Rewrite for OpaqueType<'a> {
1866     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1867         let shape = shape.offset_left(5)?; // `impl `
1868         self.bounds
1869             .rewrite(context, shape)
1870             .map(|s| format!("impl {}", s))
1871     }
1872 }
1873
1874 pub(crate) fn rewrite_impl_type(
1875     ident: symbol::Ident,
1876     vis: &ast::Visibility,
1877     defaultness: ast::Defaultness,
1878     ty_opt: Option<&ptr::P<ast::Ty>>,
1879     generics: &ast::Generics,
1880     context: &RewriteContext<'_>,
1881     indent: Indent,
1882     span: Span,
1883 ) -> Option<String> {
1884     // Opaque type
1885     let result = if let Some(rustc_ast::ast::Ty {
1886         kind: ast::TyKind::ImplTrait(_, ref bounds),
1887         ..
1888     }) = ty_opt.map(|t| &**t)
1889     {
1890         rewrite_type(
1891             context,
1892             indent,
1893             ident,
1894             &DEFAULT_VISIBILITY,
1895             generics,
1896             None,
1897             Some(&OpaqueType { bounds }),
1898             span,
1899         )
1900     } else {
1901         rewrite_type(context, indent, ident, vis, generics, None, ty_opt, span)
1902     }?;
1903
1904     match defaultness {
1905         ast::Defaultness::Default(..) => Some(format!("default {}", result)),
1906         _ => Some(result),
1907     }
1908 }
1909
1910 impl Rewrite for ast::FnRetTy {
1911     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1912         match *self {
1913             ast::FnRetTy::Default(_) => Some(String::new()),
1914             ast::FnRetTy::Ty(ref ty) => {
1915                 if context.config.version() == Version::One
1916                     || context.config.indent_style() == IndentStyle::Visual
1917                 {
1918                     let inner_width = shape.width.checked_sub(3)?;
1919                     return ty
1920                         .rewrite(context, Shape::legacy(inner_width, shape.indent + 3))
1921                         .map(|r| format!("-> {}", r));
1922                 }
1923
1924                 ty.rewrite(context, shape.offset_left(3)?)
1925                     .map(|s| format!("-> {}", s))
1926             }
1927         }
1928     }
1929 }
1930
1931 fn is_empty_infer(ty: &ast::Ty, pat_span: Span) -> bool {
1932     match ty.kind {
1933         ast::TyKind::Infer => ty.span.hi() == pat_span.hi(),
1934         _ => false,
1935     }
1936 }
1937
1938 /// Recover any missing comments between the param and the type.
1939 ///
1940 /// # Returns
1941 ///
1942 /// A 2-len tuple with the comment before the colon in first position, and the comment after the
1943 /// colon in second position.
1944 fn get_missing_param_comments(
1945     context: &RewriteContext<'_>,
1946     pat_span: Span,
1947     ty_span: Span,
1948     shape: Shape,
1949 ) -> (String, String) {
1950     let missing_comment_span = mk_sp(pat_span.hi(), ty_span.lo());
1951
1952     let span_before_colon = {
1953         let missing_comment_span_hi = context
1954             .snippet_provider
1955             .span_before(missing_comment_span, ":");
1956         mk_sp(pat_span.hi(), missing_comment_span_hi)
1957     };
1958     let span_after_colon = {
1959         let missing_comment_span_lo = context
1960             .snippet_provider
1961             .span_after(missing_comment_span, ":");
1962         mk_sp(missing_comment_span_lo, ty_span.lo())
1963     };
1964
1965     let comment_before_colon = rewrite_missing_comment(span_before_colon, shape, context)
1966         .filter(|comment| !comment.is_empty())
1967         .map_or(String::new(), |comment| format!(" {}", comment));
1968     let comment_after_colon = rewrite_missing_comment(span_after_colon, shape, context)
1969         .filter(|comment| !comment.is_empty())
1970         .map_or(String::new(), |comment| format!("{} ", comment));
1971     (comment_before_colon, comment_after_colon)
1972 }
1973
1974 impl Rewrite for ast::Param {
1975     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1976         let param_attrs_result = self
1977             .attrs
1978             .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
1979         // N.B. Doc comments aren't typically valid syntax, but could appear
1980         // in the presence of certain macros - https://github.com/rust-lang/rustfmt/issues/4936
1981         let (span, has_multiple_attr_lines, has_doc_comments) = if !self.attrs.is_empty() {
1982             let num_attrs = self.attrs.len();
1983             (
1984                 mk_sp(self.attrs[num_attrs - 1].span.hi(), self.pat.span.lo()),
1985                 param_attrs_result.contains('\n'),
1986                 self.attrs.iter().any(|a| a.is_doc_comment()),
1987             )
1988         } else {
1989             (mk_sp(self.span.lo(), self.span.lo()), false, false)
1990         };
1991
1992         if let Some(ref explicit_self) = self.to_self() {
1993             rewrite_explicit_self(
1994                 context,
1995                 explicit_self,
1996                 &param_attrs_result,
1997                 span,
1998                 shape,
1999                 has_multiple_attr_lines,
2000             )
2001         } else if is_named_param(self) {
2002             let param_name = &self
2003                 .pat
2004                 .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
2005             let mut result = combine_strs_with_missing_comments(
2006                 context,
2007                 &param_attrs_result,
2008                 param_name,
2009                 span,
2010                 shape,
2011                 !has_multiple_attr_lines && !has_doc_comments,
2012             )?;
2013
2014             if !is_empty_infer(&*self.ty, self.pat.span) {
2015                 let (before_comment, after_comment) =
2016                     get_missing_param_comments(context, self.pat.span, self.ty.span, shape);
2017                 result.push_str(&before_comment);
2018                 result.push_str(colon_spaces(context.config));
2019                 result.push_str(&after_comment);
2020                 let overhead = last_line_width(&result);
2021                 let max_width = shape.width.checked_sub(overhead)?;
2022                 if let Some(ty_str) = self
2023                     .ty
2024                     .rewrite(context, Shape::legacy(max_width, shape.indent))
2025                 {
2026                     result.push_str(&ty_str);
2027                 } else {
2028                     result = combine_strs_with_missing_comments(
2029                         context,
2030                         &(param_attrs_result + &shape.to_string_with_newline(context.config)),
2031                         param_name,
2032                         span,
2033                         shape,
2034                         !has_multiple_attr_lines,
2035                     )?;
2036                     result.push_str(&before_comment);
2037                     result.push_str(colon_spaces(context.config));
2038                     result.push_str(&after_comment);
2039                     let overhead = last_line_width(&result);
2040                     let max_width = shape.width.checked_sub(overhead)?;
2041                     let ty_str = self
2042                         .ty
2043                         .rewrite(context, Shape::legacy(max_width, shape.indent))?;
2044                     result.push_str(&ty_str);
2045                 }
2046             }
2047
2048             Some(result)
2049         } else {
2050             self.ty.rewrite(context, shape)
2051         }
2052     }
2053 }
2054
2055 fn rewrite_explicit_self(
2056     context: &RewriteContext<'_>,
2057     explicit_self: &ast::ExplicitSelf,
2058     param_attrs: &str,
2059     span: Span,
2060     shape: Shape,
2061     has_multiple_attr_lines: bool,
2062 ) -> Option<String> {
2063     match explicit_self.node {
2064         ast::SelfKind::Region(lt, m) => {
2065             let mut_str = format_mutability(m);
2066             match lt {
2067                 Some(ref l) => {
2068                     let lifetime_str = l.rewrite(
2069                         context,
2070                         Shape::legacy(context.config.max_width(), Indent::empty()),
2071                     )?;
2072                     Some(combine_strs_with_missing_comments(
2073                         context,
2074                         &param_attrs,
2075                         &format!("&{} {}self", lifetime_str, mut_str),
2076                         span,
2077                         shape,
2078                         !has_multiple_attr_lines,
2079                     )?)
2080                 }
2081                 None => Some(combine_strs_with_missing_comments(
2082                     context,
2083                     &param_attrs,
2084                     &format!("&{}self", mut_str),
2085                     span,
2086                     shape,
2087                     !has_multiple_attr_lines,
2088                 )?),
2089             }
2090         }
2091         ast::SelfKind::Explicit(ref ty, mutability) => {
2092             let type_str = ty.rewrite(
2093                 context,
2094                 Shape::legacy(context.config.max_width(), Indent::empty()),
2095             )?;
2096
2097             Some(combine_strs_with_missing_comments(
2098                 context,
2099                 &param_attrs,
2100                 &format!("{}self: {}", format_mutability(mutability), type_str),
2101                 span,
2102                 shape,
2103                 !has_multiple_attr_lines,
2104             )?)
2105         }
2106         ast::SelfKind::Value(mutability) => Some(combine_strs_with_missing_comments(
2107             context,
2108             &param_attrs,
2109             &format!("{}self", format_mutability(mutability)),
2110             span,
2111             shape,
2112             !has_multiple_attr_lines,
2113         )?),
2114     }
2115 }
2116
2117 pub(crate) fn span_lo_for_param(param: &ast::Param) -> BytePos {
2118     if param.attrs.is_empty() {
2119         if is_named_param(param) {
2120             param.pat.span.lo()
2121         } else {
2122             param.ty.span.lo()
2123         }
2124     } else {
2125         param.attrs[0].span.lo()
2126     }
2127 }
2128
2129 pub(crate) fn span_hi_for_param(context: &RewriteContext<'_>, param: &ast::Param) -> BytePos {
2130     match param.ty.kind {
2131         ast::TyKind::Infer if context.snippet(param.ty.span) == "_" => param.ty.span.hi(),
2132         ast::TyKind::Infer if is_named_param(param) => param.pat.span.hi(),
2133         _ => param.ty.span.hi(),
2134     }
2135 }
2136
2137 pub(crate) fn is_named_param(param: &ast::Param) -> bool {
2138     if let ast::PatKind::Ident(_, ident, _) = param.pat.kind {
2139         ident.name != symbol::kw::Empty
2140     } else {
2141         true
2142     }
2143 }
2144
2145 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
2146 pub(crate) enum FnBraceStyle {
2147     SameLine,
2148     NextLine,
2149     None,
2150 }
2151
2152 // Return type is (result, force_new_line_for_brace)
2153 fn rewrite_fn_base(
2154     context: &RewriteContext<'_>,
2155     indent: Indent,
2156     ident: symbol::Ident,
2157     fn_sig: &FnSig<'_>,
2158     span: Span,
2159     fn_brace_style: FnBraceStyle,
2160 ) -> Option<(String, bool, bool)> {
2161     let mut force_new_line_for_brace = false;
2162
2163     let where_clause = &fn_sig.generics.where_clause;
2164
2165     let mut result = String::with_capacity(1024);
2166     result.push_str(&fn_sig.to_str(context));
2167
2168     // fn foo
2169     result.push_str("fn ");
2170
2171     // Generics.
2172     let overhead = if let FnBraceStyle::SameLine = fn_brace_style {
2173         // 4 = `() {`
2174         4
2175     } else {
2176         // 2 = `()`
2177         2
2178     };
2179     let used_width = last_line_used_width(&result, indent.width());
2180     let one_line_budget = context.budget(used_width + overhead);
2181     let shape = Shape {
2182         width: one_line_budget,
2183         indent,
2184         offset: used_width,
2185     };
2186     let fd = fn_sig.decl;
2187     let generics_str = rewrite_generics(
2188         context,
2189         rewrite_ident(context, ident),
2190         fn_sig.generics,
2191         shape,
2192     )?;
2193     result.push_str(&generics_str);
2194
2195     let snuggle_angle_bracket = generics_str
2196         .lines()
2197         .last()
2198         .map_or(false, |l| l.trim_start().len() == 1);
2199
2200     // Note that the width and indent don't really matter, we'll re-layout the
2201     // return type later anyway.
2202     let ret_str = fd
2203         .output
2204         .rewrite(context, Shape::indented(indent, context.config))?;
2205
2206     let multi_line_ret_str = ret_str.contains('\n');
2207     let ret_str_len = if multi_line_ret_str { 0 } else { ret_str.len() };
2208
2209     // Params.
2210     let (one_line_budget, multi_line_budget, mut param_indent) = compute_budgets_for_params(
2211         context,
2212         &result,
2213         indent,
2214         ret_str_len,
2215         fn_brace_style,
2216         multi_line_ret_str,
2217     )?;
2218
2219     debug!(
2220         "rewrite_fn_base: one_line_budget: {}, multi_line_budget: {}, param_indent: {:?}",
2221         one_line_budget, multi_line_budget, param_indent
2222     );
2223
2224     result.push('(');
2225     // Check if vertical layout was forced.
2226     if one_line_budget == 0
2227         && !snuggle_angle_bracket
2228         && context.config.indent_style() == IndentStyle::Visual
2229     {
2230         result.push_str(&param_indent.to_string_with_newline(context.config));
2231     }
2232
2233     // Skip `pub(crate)`.
2234     let lo_after_visibility = get_bytepos_after_visibility(&fn_sig.visibility, span);
2235     // A conservative estimation, the goal is to be over all parens in generics
2236     let params_start = fn_sig
2237         .generics
2238         .params
2239         .last()
2240         .map_or(lo_after_visibility, |param| param.span().hi());
2241     let params_end = if fd.inputs.is_empty() {
2242         context
2243             .snippet_provider
2244             .span_after(mk_sp(params_start, span.hi()), ")")
2245     } else {
2246         let last_span = mk_sp(fd.inputs[fd.inputs.len() - 1].span().hi(), span.hi());
2247         context.snippet_provider.span_after(last_span, ")")
2248     };
2249     let params_span = mk_sp(
2250         context
2251             .snippet_provider
2252             .span_after(mk_sp(params_start, span.hi()), "("),
2253         params_end,
2254     );
2255     let param_str = rewrite_params(
2256         context,
2257         &fd.inputs,
2258         one_line_budget,
2259         multi_line_budget,
2260         indent,
2261         param_indent,
2262         params_span,
2263         fd.c_variadic(),
2264     )?;
2265
2266     let put_params_in_block = match context.config.indent_style() {
2267         IndentStyle::Block => param_str.contains('\n') || param_str.len() > one_line_budget,
2268         _ => false,
2269     } && !fd.inputs.is_empty();
2270
2271     let mut params_last_line_contains_comment = false;
2272     let mut no_params_and_over_max_width = false;
2273
2274     if put_params_in_block {
2275         param_indent = indent.block_indent(context.config);
2276         result.push_str(&param_indent.to_string_with_newline(context.config));
2277         result.push_str(&param_str);
2278         result.push_str(&indent.to_string_with_newline(context.config));
2279         result.push(')');
2280     } else {
2281         result.push_str(&param_str);
2282         let used_width = last_line_used_width(&result, indent.width()) + first_line_width(&ret_str);
2283         // Put the closing brace on the next line if it overflows the max width.
2284         // 1 = `)`
2285         let closing_paren_overflow_max_width =
2286             fd.inputs.is_empty() && used_width + 1 > context.config.max_width();
2287         // If the last line of params contains comment, we cannot put the closing paren
2288         // on the same line.
2289         params_last_line_contains_comment = param_str
2290             .lines()
2291             .last()
2292             .map_or(false, |last_line| last_line.contains("//"));
2293
2294         if context.config.version() == Version::Two {
2295             if closing_paren_overflow_max_width {
2296                 result.push(')');
2297                 result.push_str(&indent.to_string_with_newline(context.config));
2298                 no_params_and_over_max_width = true;
2299             } else if params_last_line_contains_comment {
2300                 result.push_str(&indent.to_string_with_newline(context.config));
2301                 result.push(')');
2302                 no_params_and_over_max_width = true;
2303             } else {
2304                 result.push(')');
2305             }
2306         } else {
2307             if closing_paren_overflow_max_width || params_last_line_contains_comment {
2308                 result.push_str(&indent.to_string_with_newline(context.config));
2309             }
2310             result.push(')');
2311         }
2312     }
2313
2314     // Return type.
2315     if let ast::FnRetTy::Ty(..) = fd.output {
2316         let ret_should_indent = match context.config.indent_style() {
2317             // If our params are block layout then we surely must have space.
2318             IndentStyle::Block if put_params_in_block || fd.inputs.is_empty() => false,
2319             _ if params_last_line_contains_comment => false,
2320             _ if result.contains('\n') || multi_line_ret_str => true,
2321             _ => {
2322                 // If the return type would push over the max width, then put the return type on
2323                 // a new line. With the +1 for the signature length an additional space between
2324                 // the closing parenthesis of the param and the arrow '->' is considered.
2325                 let mut sig_length = result.len() + indent.width() + ret_str_len + 1;
2326
2327                 // If there is no where-clause, take into account the space after the return type
2328                 // and the brace.
2329                 if where_clause.predicates.is_empty() {
2330                     sig_length += 2;
2331                 }
2332
2333                 sig_length > context.config.max_width()
2334             }
2335         };
2336         let ret_shape = if ret_should_indent {
2337             if context.config.version() == Version::One
2338                 || context.config.indent_style() == IndentStyle::Visual
2339             {
2340                 let indent = if param_str.is_empty() {
2341                     // Aligning with non-existent params looks silly.
2342                     force_new_line_for_brace = true;
2343                     indent + 4
2344                 } else {
2345                     // FIXME: we might want to check that using the param indent
2346                     // doesn't blow our budget, and if it does, then fallback to
2347                     // the where-clause indent.
2348                     param_indent
2349                 };
2350
2351                 result.push_str(&indent.to_string_with_newline(context.config));
2352                 Shape::indented(indent, context.config)
2353             } else {
2354                 let mut ret_shape = Shape::indented(indent, context.config);
2355                 if param_str.is_empty() {
2356                     // Aligning with non-existent params looks silly.
2357                     force_new_line_for_brace = true;
2358                     ret_shape = if context.use_block_indent() {
2359                         ret_shape.offset_left(4).unwrap_or(ret_shape)
2360                     } else {
2361                         ret_shape.indent = ret_shape.indent + 4;
2362                         ret_shape
2363                     };
2364                 }
2365
2366                 result.push_str(&ret_shape.indent.to_string_with_newline(context.config));
2367                 ret_shape
2368             }
2369         } else {
2370             if context.config.version() == Version::Two {
2371                 if !param_str.is_empty() || !no_params_and_over_max_width {
2372                     result.push(' ');
2373                 }
2374             } else {
2375                 result.push(' ');
2376             }
2377
2378             let ret_shape = Shape::indented(indent, context.config);
2379             ret_shape
2380                 .offset_left(last_line_width(&result))
2381                 .unwrap_or(ret_shape)
2382         };
2383
2384         if multi_line_ret_str || ret_should_indent {
2385             // Now that we know the proper indent and width, we need to
2386             // re-layout the return type.
2387             let ret_str = fd.output.rewrite(context, ret_shape)?;
2388             result.push_str(&ret_str);
2389         } else {
2390             result.push_str(&ret_str);
2391         }
2392
2393         // Comment between return type and the end of the decl.
2394         let snippet_lo = fd.output.span().hi();
2395         if where_clause.predicates.is_empty() {
2396             let snippet_hi = span.hi();
2397             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
2398             // Try to preserve the layout of the original snippet.
2399             let original_starts_with_newline = snippet
2400                 .find(|c| c != ' ')
2401                 .map_or(false, |i| starts_with_newline(&snippet[i..]));
2402             let original_ends_with_newline = snippet
2403                 .rfind(|c| c != ' ')
2404                 .map_or(false, |i| snippet[i..].ends_with('\n'));
2405             let snippet = snippet.trim();
2406             if !snippet.is_empty() {
2407                 result.push(if original_starts_with_newline {
2408                     '\n'
2409                 } else {
2410                     ' '
2411                 });
2412                 result.push_str(snippet);
2413                 if original_ends_with_newline {
2414                     force_new_line_for_brace = true;
2415                 }
2416             }
2417         }
2418     }
2419
2420     let pos_before_where = match fd.output {
2421         ast::FnRetTy::Default(..) => params_span.hi(),
2422         ast::FnRetTy::Ty(ref ty) => ty.span.hi(),
2423     };
2424
2425     let is_params_multi_lined = param_str.contains('\n');
2426
2427     let space = if put_params_in_block && ret_str.is_empty() {
2428         WhereClauseSpace::Space
2429     } else {
2430         WhereClauseSpace::Newline
2431     };
2432     let mut option = WhereClauseOption::new(fn_brace_style == FnBraceStyle::None, space);
2433     if is_params_multi_lined {
2434         option.veto_single_line();
2435     }
2436     let where_clause_str = rewrite_where_clause(
2437         context,
2438         where_clause,
2439         context.config.brace_style(),
2440         Shape::indented(indent, context.config),
2441         true,
2442         "{",
2443         Some(span.hi()),
2444         pos_before_where,
2445         option,
2446     )?;
2447     // If there are neither where-clause nor return type, we may be missing comments between
2448     // params and `{`.
2449     if where_clause_str.is_empty() {
2450         if let ast::FnRetTy::Default(ret_span) = fd.output {
2451             match recover_missing_comment_in_span(
2452                 mk_sp(params_span.hi(), ret_span.hi()),
2453                 shape,
2454                 context,
2455                 last_line_width(&result),
2456             ) {
2457                 Some(ref missing_comment) if !missing_comment.is_empty() => {
2458                     result.push_str(missing_comment);
2459                     force_new_line_for_brace = true;
2460                 }
2461                 _ => (),
2462             }
2463         }
2464     }
2465
2466     result.push_str(&where_clause_str);
2467
2468     let ends_with_comment = last_line_contains_single_line_comment(&result);
2469     force_new_line_for_brace |= ends_with_comment;
2470     force_new_line_for_brace |=
2471         is_params_multi_lined && context.config.where_single_line() && !where_clause_str.is_empty();
2472     Some((result, ends_with_comment, force_new_line_for_brace))
2473 }
2474
2475 /// Kind of spaces to put before `where`.
2476 #[derive(Copy, Clone)]
2477 enum WhereClauseSpace {
2478     /// A single space.
2479     Space,
2480     /// A new line.
2481     Newline,
2482     /// Nothing.
2483     None,
2484 }
2485
2486 #[derive(Copy, Clone)]
2487 struct WhereClauseOption {
2488     suppress_comma: bool, // Force no trailing comma
2489     snuggle: WhereClauseSpace,
2490     allow_single_line: bool, // Try single line where-clause instead of vertical layout
2491     veto_single_line: bool,  // Disallow a single-line where-clause.
2492 }
2493
2494 impl WhereClauseOption {
2495     fn new(suppress_comma: bool, snuggle: WhereClauseSpace) -> WhereClauseOption {
2496         WhereClauseOption {
2497             suppress_comma,
2498             snuggle,
2499             allow_single_line: false,
2500             veto_single_line: false,
2501         }
2502     }
2503
2504     fn snuggled(current: &str) -> WhereClauseOption {
2505         WhereClauseOption {
2506             suppress_comma: false,
2507             snuggle: if last_line_width(current) == 1 {
2508                 WhereClauseSpace::Space
2509             } else {
2510                 WhereClauseSpace::Newline
2511             },
2512             allow_single_line: false,
2513             veto_single_line: false,
2514         }
2515     }
2516
2517     fn suppress_comma(&mut self) {
2518         self.suppress_comma = true
2519     }
2520
2521     fn allow_single_line(&mut self) {
2522         self.allow_single_line = true
2523     }
2524
2525     fn snuggle(&mut self) {
2526         self.snuggle = WhereClauseSpace::Space
2527     }
2528
2529     fn veto_single_line(&mut self) {
2530         self.veto_single_line = true;
2531     }
2532 }
2533
2534 fn rewrite_params(
2535     context: &RewriteContext<'_>,
2536     params: &[ast::Param],
2537     one_line_budget: usize,
2538     multi_line_budget: usize,
2539     indent: Indent,
2540     param_indent: Indent,
2541     span: Span,
2542     variadic: bool,
2543 ) -> Option<String> {
2544     if params.is_empty() {
2545         let comment = context
2546             .snippet(mk_sp(
2547                 span.lo(),
2548                 // to remove ')'
2549                 span.hi() - BytePos(1),
2550             ))
2551             .trim();
2552         return Some(comment.to_owned());
2553     }
2554     let param_items: Vec<_> = itemize_list(
2555         context.snippet_provider,
2556         params.iter(),
2557         ")",
2558         ",",
2559         |param| span_lo_for_param(param),
2560         |param| param.ty.span.hi(),
2561         |param| {
2562             param
2563                 .rewrite(context, Shape::legacy(multi_line_budget, param_indent))
2564                 .or_else(|| Some(context.snippet(param.span()).to_owned()))
2565         },
2566         span.lo(),
2567         span.hi(),
2568         false,
2569     )
2570     .collect();
2571
2572     let tactic = definitive_tactic(
2573         &param_items,
2574         context
2575             .config
2576             .fn_args_layout()
2577             .to_list_tactic(param_items.len()),
2578         Separator::Comma,
2579         one_line_budget,
2580     );
2581     let budget = match tactic {
2582         DefinitiveListTactic::Horizontal => one_line_budget,
2583         _ => multi_line_budget,
2584     };
2585     let indent = match context.config.indent_style() {
2586         IndentStyle::Block => indent.block_indent(context.config),
2587         IndentStyle::Visual => param_indent,
2588     };
2589     let trailing_separator = if variadic {
2590         SeparatorTactic::Never
2591     } else {
2592         match context.config.indent_style() {
2593             IndentStyle::Block => context.config.trailing_comma(),
2594             IndentStyle::Visual => SeparatorTactic::Never,
2595         }
2596     };
2597     let fmt = ListFormatting::new(Shape::legacy(budget, indent), context.config)
2598         .tactic(tactic)
2599         .trailing_separator(trailing_separator)
2600         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
2601         .preserve_newline(true);
2602     write_list(&param_items, &fmt)
2603 }
2604
2605 fn compute_budgets_for_params(
2606     context: &RewriteContext<'_>,
2607     result: &str,
2608     indent: Indent,
2609     ret_str_len: usize,
2610     fn_brace_style: FnBraceStyle,
2611     force_vertical_layout: bool,
2612 ) -> Option<(usize, usize, Indent)> {
2613     debug!(
2614         "compute_budgets_for_params {} {:?}, {}, {:?}",
2615         result.len(),
2616         indent,
2617         ret_str_len,
2618         fn_brace_style,
2619     );
2620     // Try keeping everything on the same line.
2621     if !result.contains('\n') && !force_vertical_layout {
2622         // 2 = `()`, 3 = `() `, space is before ret_string.
2623         let overhead = if ret_str_len == 0 { 2 } else { 3 };
2624         let mut used_space = indent.width() + result.len() + ret_str_len + overhead;
2625         match fn_brace_style {
2626             FnBraceStyle::None => used_space += 1,     // 1 = `;`
2627             FnBraceStyle::SameLine => used_space += 2, // 2 = `{}`
2628             FnBraceStyle::NextLine => (),
2629         }
2630         let one_line_budget = context.budget(used_space);
2631
2632         if one_line_budget > 0 {
2633             // 4 = "() {".len()
2634             let (indent, multi_line_budget) = match context.config.indent_style() {
2635                 IndentStyle::Block => {
2636                     let indent = indent.block_indent(context.config);
2637                     (indent, context.budget(indent.width() + 1))
2638                 }
2639                 IndentStyle::Visual => {
2640                     let indent = indent + result.len() + 1;
2641                     let multi_line_overhead = match fn_brace_style {
2642                         FnBraceStyle::SameLine => 4,
2643                         _ => 2,
2644                     } + indent.width();
2645                     (indent, context.budget(multi_line_overhead))
2646                 }
2647             };
2648
2649             return Some((one_line_budget, multi_line_budget, indent));
2650         }
2651     }
2652
2653     // Didn't work. we must force vertical layout and put params on a newline.
2654     let new_indent = indent.block_indent(context.config);
2655     let used_space = match context.config.indent_style() {
2656         // 1 = `,`
2657         IndentStyle::Block => new_indent.width() + 1,
2658         // Account for `)` and possibly ` {`.
2659         IndentStyle::Visual => new_indent.width() + if ret_str_len == 0 { 1 } else { 3 },
2660     };
2661     Some((0, context.budget(used_space), new_indent))
2662 }
2663
2664 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> FnBraceStyle {
2665     let predicate_count = where_clause.predicates.len();
2666
2667     if config.where_single_line() && predicate_count == 1 {
2668         return FnBraceStyle::SameLine;
2669     }
2670     let brace_style = config.brace_style();
2671
2672     let use_next_line = brace_style == BraceStyle::AlwaysNextLine
2673         || (brace_style == BraceStyle::SameLineWhere && predicate_count > 0);
2674     if use_next_line {
2675         FnBraceStyle::NextLine
2676     } else {
2677         FnBraceStyle::SameLine
2678     }
2679 }
2680
2681 fn rewrite_generics(
2682     context: &RewriteContext<'_>,
2683     ident: &str,
2684     generics: &ast::Generics,
2685     shape: Shape,
2686 ) -> Option<String> {
2687     // FIXME: convert bounds to where-clauses where they get too big or if
2688     // there is a where-clause at all.
2689
2690     if generics.params.is_empty() {
2691         return Some(ident.to_owned());
2692     }
2693
2694     let params = generics.params.iter();
2695     overflow::rewrite_with_angle_brackets(context, ident, params, shape, generics.span)
2696 }
2697
2698 fn generics_shape_from_config(config: &Config, shape: Shape, offset: usize) -> Option<Shape> {
2699     match config.indent_style() {
2700         IndentStyle::Visual => shape.visual_indent(1 + offset).sub_width(offset + 2),
2701         IndentStyle::Block => {
2702             // 1 = ","
2703             shape
2704                 .block()
2705                 .block_indent(config.tab_spaces())
2706                 .with_max_width(config)
2707                 .sub_width(1)
2708         }
2709     }
2710 }
2711
2712 fn rewrite_where_clause_rfc_style(
2713     context: &RewriteContext<'_>,
2714     where_clause: &ast::WhereClause,
2715     shape: Shape,
2716     terminator: &str,
2717     span_end: Option<BytePos>,
2718     span_end_before_where: BytePos,
2719     where_clause_option: WhereClauseOption,
2720 ) -> Option<String> {
2721     let (where_keyword, allow_single_line) = rewrite_where_keyword(
2722         context,
2723         where_clause,
2724         shape,
2725         span_end_before_where,
2726         where_clause_option,
2727     )?;
2728
2729     // 1 = `,`
2730     let clause_shape = shape
2731         .block()
2732         .with_max_width(context.config)
2733         .block_left(context.config.tab_spaces())?
2734         .sub_width(1)?;
2735     let force_single_line = context.config.where_single_line()
2736         && where_clause.predicates.len() == 1
2737         && !where_clause_option.veto_single_line;
2738
2739     let preds_str = rewrite_bounds_on_where_clause(
2740         context,
2741         where_clause,
2742         clause_shape,
2743         terminator,
2744         span_end,
2745         where_clause_option,
2746         force_single_line,
2747     )?;
2748
2749     // 6 = `where `
2750     let clause_sep =
2751         if allow_single_line && !preds_str.contains('\n') && 6 + preds_str.len() <= shape.width
2752             || force_single_line
2753         {
2754             Cow::from(" ")
2755         } else {
2756             clause_shape.indent.to_string_with_newline(context.config)
2757         };
2758
2759     Some(format!("{}{}{}", where_keyword, clause_sep, preds_str))
2760 }
2761
2762 /// Rewrite `where` and comment around it.
2763 fn rewrite_where_keyword(
2764     context: &RewriteContext<'_>,
2765     where_clause: &ast::WhereClause,
2766     shape: Shape,
2767     span_end_before_where: BytePos,
2768     where_clause_option: WhereClauseOption,
2769 ) -> Option<(String, bool)> {
2770     let block_shape = shape.block().with_max_width(context.config);
2771     // 1 = `,`
2772     let clause_shape = block_shape
2773         .block_left(context.config.tab_spaces())?
2774         .sub_width(1)?;
2775
2776     let comment_separator = |comment: &str, shape: Shape| {
2777         if comment.is_empty() {
2778             Cow::from("")
2779         } else {
2780             shape.indent.to_string_with_newline(context.config)
2781         }
2782     };
2783
2784     let (span_before, span_after) =
2785         missing_span_before_after_where(span_end_before_where, where_clause);
2786     let (comment_before, comment_after) =
2787         rewrite_comments_before_after_where(context, span_before, span_after, shape)?;
2788
2789     let starting_newline = match where_clause_option.snuggle {
2790         WhereClauseSpace::Space if comment_before.is_empty() => Cow::from(" "),
2791         WhereClauseSpace::None => Cow::from(""),
2792         _ => block_shape.indent.to_string_with_newline(context.config),
2793     };
2794
2795     let newline_before_where = comment_separator(&comment_before, shape);
2796     let newline_after_where = comment_separator(&comment_after, clause_shape);
2797     let result = format!(
2798         "{}{}{}where{}{}",
2799         starting_newline, comment_before, newline_before_where, newline_after_where, comment_after
2800     );
2801     let allow_single_line = where_clause_option.allow_single_line
2802         && comment_before.is_empty()
2803         && comment_after.is_empty();
2804
2805     Some((result, allow_single_line))
2806 }
2807
2808 /// Rewrite bounds on a where clause.
2809 fn rewrite_bounds_on_where_clause(
2810     context: &RewriteContext<'_>,
2811     where_clause: &ast::WhereClause,
2812     shape: Shape,
2813     terminator: &str,
2814     span_end: Option<BytePos>,
2815     where_clause_option: WhereClauseOption,
2816     force_single_line: bool,
2817 ) -> Option<String> {
2818     let span_start = where_clause.predicates[0].span().lo();
2819     // If we don't have the start of the next span, then use the end of the
2820     // predicates, but that means we miss comments.
2821     let len = where_clause.predicates.len();
2822     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2823     let span_end = span_end.unwrap_or(end_of_preds);
2824     let items = itemize_list(
2825         context.snippet_provider,
2826         where_clause.predicates.iter(),
2827         terminator,
2828         ",",
2829         |pred| pred.span().lo(),
2830         |pred| pred.span().hi(),
2831         |pred| pred.rewrite(context, shape),
2832         span_start,
2833         span_end,
2834         false,
2835     );
2836     let comma_tactic = if where_clause_option.suppress_comma || force_single_line {
2837         SeparatorTactic::Never
2838     } else {
2839         context.config.trailing_comma()
2840     };
2841
2842     // shape should be vertical only and only if we have `force_single_line` option enabled
2843     // and the number of items of the where-clause is equal to 1
2844     let shape_tactic = if force_single_line {
2845         DefinitiveListTactic::Horizontal
2846     } else {
2847         DefinitiveListTactic::Vertical
2848     };
2849
2850     let fmt = ListFormatting::new(shape, context.config)
2851         .tactic(shape_tactic)
2852         .trailing_separator(comma_tactic)
2853         .preserve_newline(true);
2854     write_list(&items.collect::<Vec<_>>(), &fmt)
2855 }
2856
2857 fn rewrite_where_clause(
2858     context: &RewriteContext<'_>,
2859     where_clause: &ast::WhereClause,
2860     brace_style: BraceStyle,
2861     shape: Shape,
2862     on_new_line: bool,
2863     terminator: &str,
2864     span_end: Option<BytePos>,
2865     span_end_before_where: BytePos,
2866     where_clause_option: WhereClauseOption,
2867 ) -> Option<String> {
2868     if where_clause.predicates.is_empty() {
2869         return Some(String::new());
2870     }
2871
2872     if context.config.indent_style() == IndentStyle::Block {
2873         return rewrite_where_clause_rfc_style(
2874             context,
2875             where_clause,
2876             shape,
2877             terminator,
2878             span_end,
2879             span_end_before_where,
2880             where_clause_option,
2881         );
2882     }
2883
2884     let extra_indent = Indent::new(context.config.tab_spaces(), 0);
2885
2886     let offset = match context.config.indent_style() {
2887         IndentStyle::Block => shape.indent + extra_indent.block_indent(context.config),
2888         // 6 = "where ".len()
2889         IndentStyle::Visual => shape.indent + extra_indent + 6,
2890     };
2891     // FIXME: if indent_style != Visual, then the budgets below might
2892     // be out by a char or two.
2893
2894     let budget = context.config.max_width() - offset.width();
2895     let span_start = where_clause.predicates[0].span().lo();
2896     // If we don't have the start of the next span, then use the end of the
2897     // predicates, but that means we miss comments.
2898     let len = where_clause.predicates.len();
2899     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2900     let span_end = span_end.unwrap_or(end_of_preds);
2901     let items = itemize_list(
2902         context.snippet_provider,
2903         where_clause.predicates.iter(),
2904         terminator,
2905         ",",
2906         |pred| pred.span().lo(),
2907         |pred| pred.span().hi(),
2908         |pred| pred.rewrite(context, Shape::legacy(budget, offset)),
2909         span_start,
2910         span_end,
2911         false,
2912     );
2913     let item_vec = items.collect::<Vec<_>>();
2914     // FIXME: we don't need to collect here
2915     let tactic = definitive_tactic(&item_vec, ListTactic::Vertical, Separator::Comma, budget);
2916
2917     let mut comma_tactic = context.config.trailing_comma();
2918     // Kind of a hack because we don't usually have trailing commas in where-clauses.
2919     if comma_tactic == SeparatorTactic::Vertical || where_clause_option.suppress_comma {
2920         comma_tactic = SeparatorTactic::Never;
2921     }
2922
2923     let fmt = ListFormatting::new(Shape::legacy(budget, offset), context.config)
2924         .tactic(tactic)
2925         .trailing_separator(comma_tactic)
2926         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
2927         .preserve_newline(true);
2928     let preds_str = write_list(&item_vec, &fmt)?;
2929
2930     let end_length = if terminator == "{" {
2931         // If the brace is on the next line we don't need to count it otherwise it needs two
2932         // characters " {"
2933         match brace_style {
2934             BraceStyle::AlwaysNextLine | BraceStyle::SameLineWhere => 0,
2935             BraceStyle::PreferSameLine => 2,
2936         }
2937     } else if terminator == "=" {
2938         2
2939     } else {
2940         terminator.len()
2941     };
2942     if on_new_line
2943         || preds_str.contains('\n')
2944         || shape.indent.width() + " where ".len() + preds_str.len() + end_length > shape.width
2945     {
2946         Some(format!(
2947             "\n{}where {}",
2948             (shape.indent + extra_indent).to_string(context.config),
2949             preds_str
2950         ))
2951     } else {
2952         Some(format!(" where {}", preds_str))
2953     }
2954 }
2955
2956 fn missing_span_before_after_where(
2957     before_item_span_end: BytePos,
2958     where_clause: &ast::WhereClause,
2959 ) -> (Span, Span) {
2960     let missing_span_before = mk_sp(before_item_span_end, where_clause.span.lo());
2961     // 5 = `where`
2962     let pos_after_where = where_clause.span.lo() + BytePos(5);
2963     let missing_span_after = mk_sp(pos_after_where, where_clause.predicates[0].span().lo());
2964     (missing_span_before, missing_span_after)
2965 }
2966
2967 fn rewrite_comments_before_after_where(
2968     context: &RewriteContext<'_>,
2969     span_before_where: Span,
2970     span_after_where: Span,
2971     shape: Shape,
2972 ) -> Option<(String, String)> {
2973     let before_comment = rewrite_missing_comment(span_before_where, shape, context)?;
2974     let after_comment = rewrite_missing_comment(
2975         span_after_where,
2976         shape.block_indent(context.config.tab_spaces()),
2977         context,
2978     )?;
2979     Some((before_comment, after_comment))
2980 }
2981
2982 fn format_header(
2983     context: &RewriteContext<'_>,
2984     item_name: &str,
2985     ident: symbol::Ident,
2986     vis: &ast::Visibility,
2987     offset: Indent,
2988 ) -> String {
2989     let mut result = String::with_capacity(128);
2990     let shape = Shape::indented(offset, context.config);
2991
2992     result.push_str(&format_visibility(context, vis).trim());
2993
2994     // Check for a missing comment between the visibility and the item name.
2995     let after_vis = vis.span.hi();
2996     if let Some(before_item_name) = context
2997         .snippet_provider
2998         .opt_span_before(mk_sp(vis.span.lo(), ident.span.hi()), item_name.trim())
2999     {
3000         let missing_span = mk_sp(after_vis, before_item_name);
3001         if let Some(result_with_comment) = combine_strs_with_missing_comments(
3002             context,
3003             &result,
3004             item_name,
3005             missing_span,
3006             shape,
3007             /* allow_extend */ true,
3008         ) {
3009             result = result_with_comment;
3010         }
3011     }
3012
3013     result.push_str(&rewrite_ident(context, ident));
3014
3015     result
3016 }
3017
3018 #[derive(PartialEq, Eq, Clone, Copy)]
3019 enum BracePos {
3020     None,
3021     Auto,
3022     ForceSameLine,
3023 }
3024
3025 fn format_generics(
3026     context: &RewriteContext<'_>,
3027     generics: &ast::Generics,
3028     brace_style: BraceStyle,
3029     brace_pos: BracePos,
3030     offset: Indent,
3031     span: Span,
3032     used_width: usize,
3033 ) -> Option<String> {
3034     let shape = Shape::legacy(context.budget(used_width + offset.width()), offset);
3035     let mut result = rewrite_generics(context, "", generics, shape)?;
3036
3037     // If the generics are not parameterized then generics.span.hi() == 0,
3038     // so we use span.lo(), which is the position after `struct Foo`.
3039     let span_end_before_where = if !generics.params.is_empty() {
3040         generics.span.hi()
3041     } else {
3042         span.lo()
3043     };
3044     let (same_line_brace, missed_comments) = if !generics.where_clause.predicates.is_empty() {
3045         let budget = context.budget(last_line_used_width(&result, offset.width()));
3046         let mut option = WhereClauseOption::snuggled(&result);
3047         if brace_pos == BracePos::None {
3048             option.suppress_comma = true;
3049         }
3050         let where_clause_str = rewrite_where_clause(
3051             context,
3052             &generics.where_clause,
3053             brace_style,
3054             Shape::legacy(budget, offset.block_only()),
3055             true,
3056             "{",
3057             Some(span.hi()),
3058             span_end_before_where,
3059             option,
3060         )?;
3061         result.push_str(&where_clause_str);
3062         (
3063             brace_pos == BracePos::ForceSameLine || brace_style == BraceStyle::PreferSameLine,
3064             // missed comments are taken care of in #rewrite_where_clause
3065             None,
3066         )
3067     } else {
3068         (
3069             brace_pos == BracePos::ForceSameLine
3070                 || (result.contains('\n') && brace_style == BraceStyle::PreferSameLine
3071                     || brace_style != BraceStyle::AlwaysNextLine)
3072                 || trimmed_last_line_width(&result) == 1,
3073             rewrite_missing_comment(
3074                 mk_sp(
3075                     span_end_before_where,
3076                     if brace_pos == BracePos::None {
3077                         span.hi()
3078                     } else {
3079                         context.snippet_provider.span_before(span, "{")
3080                     },
3081                 ),
3082                 shape,
3083                 context,
3084             ),
3085         )
3086     };
3087     // add missing comments
3088     let missed_line_comments = missed_comments
3089         .filter(|missed_comments| !missed_comments.is_empty())
3090         .map_or(false, |missed_comments| {
3091             let is_block = is_last_comment_block(&missed_comments);
3092             let sep = if is_block { " " } else { "\n" };
3093             result.push_str(sep);
3094             result.push_str(&missed_comments);
3095             !is_block
3096         });
3097     if brace_pos == BracePos::None {
3098         return Some(result);
3099     }
3100     let total_used_width = last_line_used_width(&result, used_width);
3101     let remaining_budget = context.budget(total_used_width);
3102     // If the same line brace if forced, it indicates that we are rewriting an item with empty body,
3103     // and hence we take the closer into account as well for one line budget.
3104     // We assume that the closer has the same length as the opener.
3105     let overhead = if brace_pos == BracePos::ForceSameLine {
3106         // 3 = ` {}`
3107         3
3108     } else {
3109         // 2 = ` {`
3110         2
3111     };
3112     let forbid_same_line_brace = missed_line_comments || overhead > remaining_budget;
3113     if !forbid_same_line_brace && same_line_brace {
3114         result.push(' ');
3115     } else {
3116         result.push('\n');
3117         result.push_str(&offset.block_only().to_string(context.config));
3118     }
3119     result.push('{');
3120
3121     Some(result)
3122 }
3123
3124 impl Rewrite for ast::ForeignItem {
3125     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
3126         let attrs_str = self.attrs.rewrite(context, shape)?;
3127         // Drop semicolon or it will be interpreted as comment.
3128         // FIXME: this may be a faulty span from libsyntax.
3129         let span = mk_sp(self.span.lo(), self.span.hi() - BytePos(1));
3130
3131         let item_str = match self.kind {
3132             ast::ForeignItemKind::Fn(ref fn_kind) => {
3133                 let ast::Fn {
3134                     defaultness,
3135                     ref sig,
3136                     ref generics,
3137                     ref body,
3138                 } = **fn_kind;
3139                 if let Some(ref body) = body {
3140                     let mut visitor = FmtVisitor::from_context(context);
3141                     visitor.block_indent = shape.indent;
3142                     visitor.last_pos = self.span.lo();
3143                     let inner_attrs = inner_attributes(&self.attrs);
3144                     let fn_ctxt = visit::FnCtxt::Foreign;
3145                     visitor.visit_fn(
3146                         visit::FnKind::Fn(fn_ctxt, self.ident, &sig, &self.vis, Some(body)),
3147                         generics,
3148                         &sig.decl,
3149                         self.span,
3150                         defaultness,
3151                         Some(&inner_attrs),
3152                     );
3153                     Some(visitor.buffer.to_owned())
3154                 } else {
3155                     rewrite_fn_base(
3156                         context,
3157                         shape.indent,
3158                         self.ident,
3159                         &FnSig::from_method_sig(&sig, generics, &self.vis),
3160                         span,
3161                         FnBraceStyle::None,
3162                     )
3163                     .map(|(s, _, _)| format!("{};", s))
3164                 }
3165             }
3166             ast::ForeignItemKind::Static(ref ty, mutability, _) => {
3167                 // FIXME(#21): we're dropping potential comments in between the
3168                 // function kw here.
3169                 let vis = format_visibility(context, &self.vis);
3170                 let mut_str = format_mutability(mutability);
3171                 let prefix = format!(
3172                     "{}static {}{}:",
3173                     vis,
3174                     mut_str,
3175                     rewrite_ident(context, self.ident)
3176                 );
3177                 // 1 = ;
3178                 rewrite_assign_rhs(context, prefix, &**ty, shape.sub_width(1)?).map(|s| s + ";")
3179             }
3180             ast::ForeignItemKind::TyAlias(ref ty_alias_kind) => {
3181                 let ast::TyAlias {
3182                     ref generics,
3183                     ref bounds,
3184                     ref ty,
3185                     ..
3186                 } = **ty_alias_kind;
3187                 rewrite_type(
3188                     &context,
3189                     shape.indent,
3190                     self.ident,
3191                     &self.vis,
3192                     generics,
3193                     Some(bounds),
3194                     ty.as_ref(),
3195                     self.span,
3196                 )
3197             }
3198             ast::ForeignItemKind::MacCall(ref mac) => {
3199                 rewrite_macro(mac, None, context, shape, MacroPosition::Item)
3200             }
3201         }?;
3202
3203         let missing_span = if self.attrs.is_empty() {
3204             mk_sp(self.span.lo(), self.span.lo())
3205         } else {
3206             mk_sp(self.attrs[self.attrs.len() - 1].span.hi(), self.span.lo())
3207         };
3208         combine_strs_with_missing_comments(
3209             context,
3210             &attrs_str,
3211             &item_str,
3212             missing_span,
3213             shape,
3214             false,
3215         )
3216     }
3217 }
3218
3219 /// Rewrite the attributes of an item.
3220 fn rewrite_attrs(
3221     context: &RewriteContext<'_>,
3222     item: &ast::Item,
3223     item_str: &str,
3224     shape: Shape,
3225 ) -> Option<String> {
3226     let attrs = filter_inline_attrs(&item.attrs, item.span());
3227     let attrs_str = attrs.rewrite(context, shape)?;
3228
3229     let missed_span = if attrs.is_empty() {
3230         mk_sp(item.span.lo(), item.span.lo())
3231     } else {
3232         mk_sp(attrs[attrs.len() - 1].span.hi(), item.span.lo())
3233     };
3234
3235     let allow_extend = if attrs.len() == 1 {
3236         let line_len = attrs_str.len() + 1 + item_str.len();
3237         !attrs.first().unwrap().is_doc_comment()
3238             && context.config.inline_attribute_width() >= line_len
3239     } else {
3240         false
3241     };
3242
3243     combine_strs_with_missing_comments(
3244         context,
3245         &attrs_str,
3246         &item_str,
3247         missed_span,
3248         shape,
3249         allow_extend,
3250     )
3251 }
3252
3253 /// Rewrite an inline mod.
3254 /// The given shape is used to format the mod's attributes.
3255 pub(crate) fn rewrite_mod(
3256     context: &RewriteContext<'_>,
3257     item: &ast::Item,
3258     attrs_shape: Shape,
3259 ) -> Option<String> {
3260     let mut result = String::with_capacity(32);
3261     result.push_str(&*format_visibility(context, &item.vis));
3262     result.push_str("mod ");
3263     result.push_str(rewrite_ident(context, item.ident));
3264     result.push(';');
3265     rewrite_attrs(context, item, &result, attrs_shape)
3266 }
3267
3268 /// Rewrite `extern crate foo;`.
3269 /// The given shape is used to format the extern crate's attributes.
3270 pub(crate) fn rewrite_extern_crate(
3271     context: &RewriteContext<'_>,
3272     item: &ast::Item,
3273     attrs_shape: Shape,
3274 ) -> Option<String> {
3275     assert!(is_extern_crate(item));
3276     let new_str = context.snippet(item.span);
3277     let item_str = if contains_comment(new_str) {
3278         new_str.to_owned()
3279     } else {
3280         let no_whitespace = &new_str.split_whitespace().collect::<Vec<&str>>().join(" ");
3281         String::from(&*Regex::new(r"\s;").unwrap().replace(no_whitespace, ";"))
3282     };
3283     rewrite_attrs(context, item, &item_str, attrs_shape)
3284 }
3285
3286 /// Returns `true` for `mod foo;`, false for `mod foo { .. }`.
3287 pub(crate) fn is_mod_decl(item: &ast::Item) -> bool {
3288     !matches!(
3289         item.kind,
3290         ast::ItemKind::Mod(_, ast::ModKind::Loaded(_, ast::Inline::Yes, _))
3291     )
3292 }
3293
3294 pub(crate) fn is_use_item(item: &ast::Item) -> bool {
3295     matches!(item.kind, ast::ItemKind::Use(_))
3296 }
3297
3298 pub(crate) fn is_extern_crate(item: &ast::Item) -> bool {
3299     matches!(item.kind, ast::ItemKind::ExternCrate(..))
3300 }