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.3, &rty.3) || both_opaque(&lty.3, &rty.3) =>
 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.3, &rty.3) || both_opaque(&lty.3, &rty.3) =>
 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.3) => Ordering::Less,
 645                 (_, TyAlias(ty)) if is_type(&ty.3) => 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::ImplKind {
 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::ImplKind {
 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::TraitKind(is_auto, unsafety, ref generics, ref generic_bounds, ref trait_items) =
1033             **trait_kind;
1034         let mut result = String::with_capacity(128);
1035         let header = format!(
1036             "{}{}{}trait ",
1037             format_visibility(context, &item.vis),
1038             format_unsafety(unsafety),
1039             format_auto(is_auto),
1040         );
1041         result.push_str(&header);
1042
1043         let body_lo = context.snippet_provider.span_after(item.span, "{");
1044
1045         let shape = Shape::indented(offset, context.config).offset_left(result.len())?;
1046         let generics_str =
1047             rewrite_generics(context, rewrite_ident(context, item.ident), generics, shape)?;
1048         result.push_str(&generics_str);
1049
1050         // FIXME(#2055): rustfmt fails to format when there are comments between trait bounds.
1051         if !generic_bounds.is_empty() {
1052             let ident_hi = context
1053                 .snippet_provider
1054                 .span_after(item.span, &item.ident.as_str());
1055             let bound_hi = generic_bounds.last().unwrap().span().hi();
1056             let snippet = context.snippet(mk_sp(ident_hi, bound_hi));
1057             if contains_comment(snippet) {
1058                 return None;
1059             }
1060
1061             result = rewrite_assign_rhs_with(
1062                 context,
1063                 result + ":",
1064                 generic_bounds,
1065                 shape,
1066                 RhsTactics::ForceNextLineWithoutIndent,
1067             )?;
1068         }
1069
1070         // Rewrite where-clause.
1071         if !generics.where_clause.predicates.is_empty() {
1072             let where_on_new_line = context.config.indent_style() != IndentStyle::Block;
1073
1074             let where_budget = context.budget(last_line_width(&result));
1075             let pos_before_where = if generic_bounds.is_empty() {
1076                 generics.where_clause.span.lo()
1077             } else {
1078                 generic_bounds[generic_bounds.len() - 1].span().hi()
1079             };
1080             let option = WhereClauseOption::snuggled(&generics_str);
1081             let where_clause_str = rewrite_where_clause(
1082                 context,
1083                 &generics.where_clause,
1084                 context.config.brace_style(),
1085                 Shape::legacy(where_budget, offset.block_only()),
1086                 where_on_new_line,
1087                 "{",
1088                 None,
1089                 pos_before_where,
1090                 option,
1091             )?;
1092             // If the where-clause cannot fit on the same line,
1093             // put the where-clause on a new line
1094             if !where_clause_str.contains('\n')
1095                 && last_line_width(&result) + where_clause_str.len() + offset.width()
1096                     > context.config.comment_width()
1097             {
1098                 let width = offset.block_indent + context.config.tab_spaces() - 1;
1099                 let where_indent = Indent::new(0, width);
1100                 result.push_str(&where_indent.to_string_with_newline(context.config));
1101             }
1102             result.push_str(&where_clause_str);
1103         } else {
1104             let item_snippet = context.snippet(item.span);
1105             if let Some(lo) = item_snippet.find('/') {
1106                 // 1 = `{`
1107                 let comment_hi = body_lo - BytePos(1);
1108                 let comment_lo = item.span.lo() + BytePos(lo as u32);
1109                 if comment_lo < comment_hi {
1110                     match recover_missing_comment_in_span(
1111                         mk_sp(comment_lo, comment_hi),
1112                         Shape::indented(offset, context.config),
1113                         context,
1114                         last_line_width(&result),
1115                     ) {
1116                         Some(ref missing_comment) if !missing_comment.is_empty() => {
1117                             result.push_str(missing_comment);
1118                         }
1119                         _ => (),
1120                     }
1121                 }
1122             }
1123         }
1124
1125         match context.config.brace_style() {
1126             _ if last_line_contains_single_line_comment(&result)
1127                 || last_line_width(&result) + 2 > context.budget(offset.width()) =>
1128             {
1129                 result.push_str(&offset.to_string_with_newline(context.config));
1130             }
1131             BraceStyle::AlwaysNextLine => {
1132                 result.push_str(&offset.to_string_with_newline(context.config));
1133             }
1134             BraceStyle::PreferSameLine => result.push(' '),
1135             BraceStyle::SameLineWhere => {
1136                 if result.contains('\n')
1137                     || (!generics.where_clause.predicates.is_empty() && !trait_items.is_empty())
1138                 {
1139                     result.push_str(&offset.to_string_with_newline(context.config));
1140                 } else {
1141                     result.push(' ');
1142                 }
1143             }
1144         }
1145         result.push('{');
1146
1147         let block_span = mk_sp(generics.where_clause.span.hi(), item.span.hi());
1148         let snippet = context.snippet(block_span);
1149         let open_pos = snippet.find_uncommented("{")? + 1;
1150         let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
1151
1152         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
1153             let mut visitor = FmtVisitor::from_context(context);
1154             visitor.block_indent = offset.block_only().block_indent(context.config);
1155             visitor.last_pos = block_span.lo() + BytePos(open_pos as u32);
1156
1157             for item in trait_items {
1158                 visitor.visit_trait_item(item);
1159             }
1160
1161             visitor.format_missing(item.span.hi() - BytePos(1));
1162
1163             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
1164
1165             result.push_str(&inner_indent_str);
1166             result.push_str(visitor.buffer.trim());
1167             result.push_str(&outer_indent_str);
1168         } else if result.contains('\n') {
1169             result.push_str(&outer_indent_str);
1170         }
1171
1172         result.push('}');
1173         Some(result)
1174     } else {
1175         unreachable!();
1176     }
1177 }
1178
1179 struct OpaqueTypeBounds<'a> {
1180     generic_bounds: &'a ast::GenericBounds,
1181 }
1182
1183 impl<'a> Rewrite for OpaqueTypeBounds<'a> {
1184     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1185         self.generic_bounds
1186             .rewrite(context, shape)
1187             .map(|s| format!("impl {}", s))
1188     }
1189 }
1190
1191 pub(crate) struct TraitAliasBounds<'a> {
1192     generic_bounds: &'a ast::GenericBounds,
1193     generics: &'a ast::Generics,
1194 }
1195
1196 impl<'a> Rewrite for TraitAliasBounds<'a> {
1197     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1198         let generic_bounds_str = self.generic_bounds.rewrite(context, shape)?;
1199
1200         let mut option = WhereClauseOption::new(true, WhereClauseSpace::None);
1201         option.allow_single_line();
1202
1203         let where_str = rewrite_where_clause(
1204             context,
1205             &self.generics.where_clause,
1206             context.config.brace_style(),
1207             shape,
1208             false,
1209             ";",
1210             None,
1211             self.generics.where_clause.span.lo(),
1212             option,
1213         )?;
1214
1215         let fits_single_line = !generic_bounds_str.contains('\n')
1216             && !where_str.contains('\n')
1217             && generic_bounds_str.len() + where_str.len() < shape.width;
1218         let space = if generic_bounds_str.is_empty() || where_str.is_empty() {
1219             Cow::from("")
1220         } else if fits_single_line {
1221             Cow::from(" ")
1222         } else {
1223             shape.indent.to_string_with_newline(&context.config)
1224         };
1225
1226         Some(format!("{}{}{}", generic_bounds_str, space, where_str))
1227     }
1228 }
1229
1230 pub(crate) fn format_trait_alias(
1231     context: &RewriteContext<'_>,
1232     ident: symbol::Ident,
1233     vis: &ast::Visibility,
1234     generics: &ast::Generics,
1235     generic_bounds: &ast::GenericBounds,
1236     shape: Shape,
1237 ) -> Option<String> {
1238     let alias = rewrite_ident(context, ident);
1239     // 6 = "trait ", 2 = " ="
1240     let g_shape = shape.offset_left(6)?.sub_width(2)?;
1241     let generics_str = rewrite_generics(context, &alias, generics, g_shape)?;
1242     let vis_str = format_visibility(context, vis);
1243     let lhs = format!("{}trait {} =", vis_str, generics_str);
1244     // 1 = ";"
1245     let trait_alias_bounds = TraitAliasBounds {
1246         generic_bounds,
1247         generics,
1248     };
1249     rewrite_assign_rhs(context, lhs, &trait_alias_bounds, shape.sub_width(1)?).map(|s| s + ";")
1250 }
1251
1252 fn format_unit_struct(
1253     context: &RewriteContext<'_>,
1254     p: &StructParts<'_>,
1255     offset: Indent,
1256 ) -> Option<String> {
1257     let header_str = format_header(context, p.prefix, p.ident, p.vis, offset);
1258     let generics_str = if let Some(generics) = p.generics {
1259         let hi = context.snippet_provider.span_before(p.span, ";");
1260         format_generics(
1261             context,
1262             generics,
1263             context.config.brace_style(),
1264             BracePos::None,
1265             offset,
1266             // make a span that starts right after `struct Foo`
1267             mk_sp(p.ident.span.hi(), hi),
1268             last_line_width(&header_str),
1269         )?
1270     } else {
1271         String::new()
1272     };
1273     Some(format!("{}{};", header_str, generics_str))
1274 }
1275
1276 pub(crate) fn format_struct_struct(
1277     context: &RewriteContext<'_>,
1278     struct_parts: &StructParts<'_>,
1279     fields: &[ast::FieldDef],
1280     offset: Indent,
1281     one_line_width: Option<usize>,
1282 ) -> Option<String> {
1283     let mut result = String::with_capacity(1024);
1284     let span = struct_parts.span;
1285
1286     let header_str = struct_parts.format_header(context, offset);
1287     result.push_str(&header_str);
1288
1289     let header_hi = struct_parts.ident.span.hi();
1290     let body_lo = context.snippet_provider.span_after(span, "{");
1291
1292     let generics_str = match struct_parts.generics {
1293         Some(g) => format_generics(
1294             context,
1295             g,
1296             context.config.brace_style(),
1297             if fields.is_empty() {
1298                 BracePos::ForceSameLine
1299             } else {
1300                 BracePos::Auto
1301             },
1302             offset,
1303             // make a span that starts right after `struct Foo`
1304             mk_sp(header_hi, body_lo),
1305             last_line_width(&result),
1306         )?,
1307         None => {
1308             // 3 = ` {}`, 2 = ` {`.
1309             let overhead = if fields.is_empty() { 3 } else { 2 };
1310             if (context.config.brace_style() == BraceStyle::AlwaysNextLine && !fields.is_empty())
1311                 || context.config.max_width() < overhead + result.len()
1312             {
1313                 format!("\n{}{{", offset.block_only().to_string(context.config))
1314             } else {
1315                 " {".to_owned()
1316             }
1317         }
1318     };
1319     // 1 = `}`
1320     let overhead = if fields.is_empty() { 1 } else { 0 };
1321     let total_width = result.len() + generics_str.len() + overhead;
1322     if !generics_str.is_empty()
1323         && !generics_str.contains('\n')
1324         && total_width > context.config.max_width()
1325     {
1326         result.push('\n');
1327         result.push_str(&offset.to_string(context.config));
1328         result.push_str(generics_str.trim_start());
1329     } else {
1330         result.push_str(&generics_str);
1331     }
1332
1333     if fields.is_empty() {
1334         let inner_span = mk_sp(body_lo, span.hi() - BytePos(1));
1335         format_empty_struct_or_tuple(context, inner_span, offset, &mut result, "", "}");
1336         return Some(result);
1337     }
1338
1339     // 3 = ` ` and ` }`
1340     let one_line_budget = context.budget(result.len() + 3 + offset.width());
1341     let one_line_budget =
1342         one_line_width.map_or(0, |one_line_width| min(one_line_width, one_line_budget));
1343
1344     let items_str = rewrite_with_alignment(
1345         fields,
1346         context,
1347         Shape::indented(offset.block_indent(context.config), context.config).sub_width(1)?,
1348         mk_sp(body_lo, span.hi()),
1349         one_line_budget,
1350     )?;
1351
1352     if !items_str.contains('\n')
1353         && !result.contains('\n')
1354         && items_str.len() <= one_line_budget
1355         && !last_line_contains_single_line_comment(&items_str)
1356     {
1357         Some(format!("{} {} }}", result, items_str))
1358     } else {
1359         Some(format!(
1360             "{}\n{}{}\n{}}}",
1361             result,
1362             offset
1363                 .block_indent(context.config)
1364                 .to_string(context.config),
1365             items_str,
1366             offset.to_string(context.config)
1367         ))
1368     }
1369 }
1370
1371 fn get_bytepos_after_visibility(vis: &ast::Visibility, default_span: Span) -> BytePos {
1372     match vis.kind {
1373         ast::VisibilityKind::Crate(..) | ast::VisibilityKind::Restricted { .. } => vis.span.hi(),
1374         _ => default_span.lo(),
1375     }
1376 }
1377
1378 // Format tuple or struct without any fields. We need to make sure that the comments
1379 // inside the delimiters are preserved.
1380 fn format_empty_struct_or_tuple(
1381     context: &RewriteContext<'_>,
1382     span: Span,
1383     offset: Indent,
1384     result: &mut String,
1385     opener: &str,
1386     closer: &str,
1387 ) {
1388     // 3 = " {}" or "();"
1389     let used_width = last_line_used_width(&result, offset.width()) + 3;
1390     if used_width > context.config.max_width() {
1391         result.push_str(&offset.to_string_with_newline(context.config))
1392     }
1393     result.push_str(opener);
1394     match rewrite_missing_comment(span, Shape::indented(offset, context.config), context) {
1395         Some(ref s) if s.is_empty() => (),
1396         Some(ref s) => {
1397             if !is_single_line(s) || first_line_contains_single_line_comment(s) {
1398                 let nested_indent_str = offset
1399                     .block_indent(context.config)
1400                     .to_string_with_newline(context.config);
1401                 result.push_str(&nested_indent_str);
1402             }
1403             result.push_str(s);
1404             if last_line_contains_single_line_comment(s) {
1405                 result.push_str(&offset.to_string_with_newline(context.config));
1406             }
1407         }
1408         None => result.push_str(context.snippet(span)),
1409     }
1410     result.push_str(closer);
1411 }
1412
1413 fn format_tuple_struct(
1414     context: &RewriteContext<'_>,
1415     struct_parts: &StructParts<'_>,
1416     fields: &[ast::FieldDef],
1417     offset: Indent,
1418 ) -> Option<String> {
1419     let mut result = String::with_capacity(1024);
1420     let span = struct_parts.span;
1421
1422     let header_str = struct_parts.format_header(context, offset);
1423     result.push_str(&header_str);
1424
1425     let body_lo = if fields.is_empty() {
1426         let lo = get_bytepos_after_visibility(struct_parts.vis, span);
1427         context
1428             .snippet_provider
1429             .span_after(mk_sp(lo, span.hi()), "(")
1430     } else {
1431         fields[0].span.lo()
1432     };
1433     let body_hi = if fields.is_empty() {
1434         context
1435             .snippet_provider
1436             .span_after(mk_sp(body_lo, span.hi()), ")")
1437     } else {
1438         // This is a dirty hack to work around a missing `)` from the span of the last field.
1439         let last_arg_span = fields[fields.len() - 1].span;
1440         context
1441             .snippet_provider
1442             .opt_span_after(mk_sp(last_arg_span.hi(), span.hi()), ")")
1443             .unwrap_or_else(|| last_arg_span.hi())
1444     };
1445
1446     let where_clause_str = match struct_parts.generics {
1447         Some(generics) => {
1448             let budget = context.budget(last_line_width(&header_str));
1449             let shape = Shape::legacy(budget, offset);
1450             let generics_str = rewrite_generics(context, "", generics, shape)?;
1451             result.push_str(&generics_str);
1452
1453             let where_budget = context.budget(last_line_width(&result));
1454             let option = WhereClauseOption::new(true, WhereClauseSpace::Newline);
1455             rewrite_where_clause(
1456                 context,
1457                 &generics.where_clause,
1458                 context.config.brace_style(),
1459                 Shape::legacy(where_budget, offset.block_only()),
1460                 false,
1461                 ";",
1462                 None,
1463                 body_hi,
1464                 option,
1465             )?
1466         }
1467         None => "".to_owned(),
1468     };
1469
1470     if fields.is_empty() {
1471         let body_hi = context
1472             .snippet_provider
1473             .span_before(mk_sp(body_lo, span.hi()), ")");
1474         let inner_span = mk_sp(body_lo, body_hi);
1475         format_empty_struct_or_tuple(context, inner_span, offset, &mut result, "(", ")");
1476     } else {
1477         let shape = Shape::indented(offset, context.config).sub_width(1)?;
1478         let lo = if let Some(generics) = struct_parts.generics {
1479             generics.span.hi()
1480         } else {
1481             struct_parts.ident.span.hi()
1482         };
1483         result = overflow::rewrite_with_parens(
1484             context,
1485             &result,
1486             fields.iter(),
1487             shape,
1488             mk_sp(lo, span.hi()),
1489             context.config.fn_call_width(),
1490             None,
1491         )?;
1492     }
1493
1494     if !where_clause_str.is_empty()
1495         && !where_clause_str.contains('\n')
1496         && (result.contains('\n')
1497             || offset.block_indent + result.len() + where_clause_str.len() + 1
1498                 > context.config.max_width())
1499     {
1500         // We need to put the where-clause on a new line, but we didn't
1501         // know that earlier, so the where-clause will not be indented properly.
1502         result.push('\n');
1503         result.push_str(
1504             &(offset.block_only() + (context.config.tab_spaces() - 1)).to_string(context.config),
1505         );
1506     }
1507     result.push_str(&where_clause_str);
1508
1509     Some(result)
1510 }
1511
1512 pub(crate) fn rewrite_type<R: Rewrite>(
1513     context: &RewriteContext<'_>,
1514     indent: Indent,
1515     ident: symbol::Ident,
1516     vis: &ast::Visibility,
1517     generics: &ast::Generics,
1518     generic_bounds_opt: Option<&ast::GenericBounds>,
1519     rhs: Option<&R>,
1520     span: Span,
1521 ) -> Option<String> {
1522     let mut result = String::with_capacity(128);
1523     result.push_str(&format!("{}type ", format_visibility(context, vis)));
1524     let ident_str = rewrite_ident(context, ident);
1525
1526     if generics.params.is_empty() {
1527         result.push_str(ident_str)
1528     } else {
1529         // 2 = `= `
1530         let g_shape = Shape::indented(indent, context.config)
1531             .offset_left(result.len())?
1532             .sub_width(2)?;
1533         let generics_str = rewrite_generics(context, ident_str, generics, g_shape)?;
1534         result.push_str(&generics_str);
1535     }
1536
1537     if let Some(bounds) = generic_bounds_opt {
1538         if !bounds.is_empty() {
1539             // 2 = `: `
1540             let shape = Shape::indented(indent, context.config).offset_left(result.len() + 2)?;
1541             let type_bounds = bounds.rewrite(context, shape).map(|s| format!(": {}", s))?;
1542             result.push_str(&type_bounds);
1543         }
1544     }
1545
1546     let where_budget = context.budget(last_line_width(&result));
1547     let mut option = WhereClauseOption::snuggled(&result);
1548     if rhs.is_none() {
1549         option.suppress_comma();
1550     }
1551     let where_clause_str = rewrite_where_clause(
1552         context,
1553         &generics.where_clause,
1554         context.config.brace_style(),
1555         Shape::legacy(where_budget, indent),
1556         false,
1557         "=",
1558         None,
1559         generics.span.hi(),
1560         option,
1561     )?;
1562     result.push_str(&where_clause_str);
1563
1564     if let Some(ty) = rhs {
1565         // If there's a where clause, add a newline before the assignment. Otherwise just add a
1566         // space.
1567         let has_where = !generics.where_clause.predicates.is_empty();
1568         if has_where {
1569             result.push_str(&indent.to_string_with_newline(context.config));
1570         } else {
1571             result.push(' ');
1572         }
1573
1574         let comment_span = context
1575             .snippet_provider
1576             .opt_span_before(span, "=")
1577             .map(|op_lo| mk_sp(generics.where_clause.span.hi(), op_lo));
1578
1579         let lhs = match comment_span {
1580             Some(comment_span)
1581                 if contains_comment(context.snippet_provider.span_to_snippet(comment_span)?) =>
1582             {
1583                 let comment_shape = if has_where {
1584                     Shape::indented(indent, context.config)
1585                 } else {
1586                     Shape::indented(indent, context.config)
1587                         .block_left(context.config.tab_spaces())?
1588                 };
1589
1590                 combine_strs_with_missing_comments(
1591                     context,
1592                     result.trim_end(),
1593                     "=",
1594                     comment_span,
1595                     comment_shape,
1596                     true,
1597                 )?
1598             }
1599             _ => format!("{}=", result),
1600         };
1601
1602         // 1 = `;`
1603         let shape = Shape::indented(indent, context.config).sub_width(1)?;
1604         rewrite_assign_rhs(context, lhs, &*ty, shape).map(|s| s + ";")
1605     } else {
1606         Some(format!("{};", result))
1607     }
1608 }
1609
1610 pub(crate) fn rewrite_opaque_type(
1611     context: &RewriteContext<'_>,
1612     indent: Indent,
1613     ident: symbol::Ident,
1614     generic_bounds: &ast::GenericBounds,
1615     generics: &ast::Generics,
1616     vis: &ast::Visibility,
1617     span: Span,
1618 ) -> Option<String> {
1619     let opaque_type_bounds = OpaqueTypeBounds { generic_bounds };
1620     rewrite_type(
1621         context,
1622         indent,
1623         ident,
1624         vis,
1625         generics,
1626         Some(generic_bounds),
1627         Some(&opaque_type_bounds),
1628         span,
1629     )
1630 }
1631
1632 fn type_annotation_spacing(config: &Config) -> (&str, &str) {
1633     (
1634         if config.space_before_colon() { " " } else { "" },
1635         if config.space_after_colon() { " " } else { "" },
1636     )
1637 }
1638
1639 pub(crate) fn rewrite_struct_field_prefix(
1640     context: &RewriteContext<'_>,
1641     field: &ast::FieldDef,
1642 ) -> Option<String> {
1643     let vis = format_visibility(context, &field.vis);
1644     let type_annotation_spacing = type_annotation_spacing(context.config);
1645     Some(match field.ident {
1646         Some(name) => format!(
1647             "{}{}{}:",
1648             vis,
1649             rewrite_ident(context, name),
1650             type_annotation_spacing.0
1651         ),
1652         None => vis.to_string(),
1653     })
1654 }
1655
1656 impl Rewrite for ast::FieldDef {
1657     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1658         rewrite_struct_field(context, self, shape, 0)
1659     }
1660 }
1661
1662 pub(crate) fn rewrite_struct_field(
1663     context: &RewriteContext<'_>,
1664     field: &ast::FieldDef,
1665     shape: Shape,
1666     lhs_max_width: usize,
1667 ) -> Option<String> {
1668     if contains_skip(&field.attrs) {
1669         return Some(context.snippet(field.span()).to_owned());
1670     }
1671
1672     let type_annotation_spacing = type_annotation_spacing(context.config);
1673     let prefix = rewrite_struct_field_prefix(context, field)?;
1674
1675     let attrs_str = field.attrs.rewrite(context, shape)?;
1676     let attrs_extendable = field.ident.is_none() && is_attributes_extendable(&attrs_str);
1677     let missing_span = if field.attrs.is_empty() {
1678         mk_sp(field.span.lo(), field.span.lo())
1679     } else {
1680         mk_sp(field.attrs.last().unwrap().span.hi(), field.span.lo())
1681     };
1682     let mut spacing = String::from(if field.ident.is_some() {
1683         type_annotation_spacing.1
1684     } else {
1685         ""
1686     });
1687     // Try to put everything on a single line.
1688     let attr_prefix = combine_strs_with_missing_comments(
1689         context,
1690         &attrs_str,
1691         &prefix,
1692         missing_span,
1693         shape,
1694         attrs_extendable,
1695     )?;
1696     let overhead = trimmed_last_line_width(&attr_prefix);
1697     let lhs_offset = lhs_max_width.saturating_sub(overhead);
1698     for _ in 0..lhs_offset {
1699         spacing.push(' ');
1700     }
1701     // In this extreme case we will be missing a space between an attribute and a field.
1702     if prefix.is_empty() && !attrs_str.is_empty() && attrs_extendable && spacing.is_empty() {
1703         spacing.push(' ');
1704     }
1705     let orig_ty = shape
1706         .offset_left(overhead + spacing.len())
1707         .and_then(|ty_shape| field.ty.rewrite(context, ty_shape));
1708     if let Some(ref ty) = orig_ty {
1709         if !ty.contains('\n') {
1710             return Some(attr_prefix + &spacing + ty);
1711         }
1712     }
1713
1714     let is_prefix_empty = prefix.is_empty();
1715     // We must use multiline. We are going to put attributes and a field on different lines.
1716     let field_str = rewrite_assign_rhs(context, prefix, &*field.ty, shape)?;
1717     // Remove a leading white-space from `rewrite_assign_rhs()` when rewriting a tuple struct.
1718     let field_str = if is_prefix_empty {
1719         field_str.trim_start()
1720     } else {
1721         &field_str
1722     };
1723     combine_strs_with_missing_comments(context, &attrs_str, field_str, missing_span, shape, false)
1724 }
1725
1726 pub(crate) struct StaticParts<'a> {
1727     prefix: &'a str,
1728     vis: &'a ast::Visibility,
1729     ident: symbol::Ident,
1730     ty: &'a ast::Ty,
1731     mutability: ast::Mutability,
1732     expr_opt: Option<&'a ptr::P<ast::Expr>>,
1733     defaultness: Option<ast::Defaultness>,
1734     span: Span,
1735 }
1736
1737 impl<'a> StaticParts<'a> {
1738     pub(crate) fn from_item(item: &'a ast::Item) -> Self {
1739         let (defaultness, prefix, ty, mutability, expr) = match item.kind {
1740             ast::ItemKind::Static(ref ty, mutability, ref expr) => {
1741                 (None, "static", ty, mutability, expr)
1742             }
1743             ast::ItemKind::Const(defaultness, ref ty, ref expr) => {
1744                 (Some(defaultness), "const", ty, ast::Mutability::Not, expr)
1745             }
1746             _ => unreachable!(),
1747         };
1748         StaticParts {
1749             prefix,
1750             vis: &item.vis,
1751             ident: item.ident,
1752             ty,
1753             mutability,
1754             expr_opt: expr.as_ref(),
1755             defaultness,
1756             span: item.span,
1757         }
1758     }
1759
1760     pub(crate) fn from_trait_item(ti: &'a ast::AssocItem) -> Self {
1761         let (defaultness, ty, expr_opt) = match ti.kind {
1762             ast::AssocItemKind::Const(defaultness, ref ty, ref expr_opt) => {
1763                 (defaultness, ty, expr_opt)
1764             }
1765             _ => unreachable!(),
1766         };
1767         StaticParts {
1768             prefix: "const",
1769             vis: &ti.vis,
1770             ident: ti.ident,
1771             ty,
1772             mutability: ast::Mutability::Not,
1773             expr_opt: expr_opt.as_ref(),
1774             defaultness: Some(defaultness),
1775             span: ti.span,
1776         }
1777     }
1778
1779     pub(crate) fn from_impl_item(ii: &'a ast::AssocItem) -> Self {
1780         let (defaultness, ty, expr) = match ii.kind {
1781             ast::AssocItemKind::Const(defaultness, ref ty, ref expr) => (defaultness, ty, expr),
1782             _ => unreachable!(),
1783         };
1784         StaticParts {
1785             prefix: "const",
1786             vis: &ii.vis,
1787             ident: ii.ident,
1788             ty,
1789             mutability: ast::Mutability::Not,
1790             expr_opt: expr.as_ref(),
1791             defaultness: Some(defaultness),
1792             span: ii.span,
1793         }
1794     }
1795 }
1796
1797 fn rewrite_static(
1798     context: &RewriteContext<'_>,
1799     static_parts: &StaticParts<'_>,
1800     offset: Indent,
1801 ) -> Option<String> {
1802     let colon = colon_spaces(context.config);
1803     let mut prefix = format!(
1804         "{}{}{} {}{}{}",
1805         format_visibility(context, static_parts.vis),
1806         static_parts.defaultness.map_or("", format_defaultness),
1807         static_parts.prefix,
1808         format_mutability(static_parts.mutability),
1809         rewrite_ident(context, static_parts.ident),
1810         colon,
1811     );
1812     // 2 = " =".len()
1813     let ty_shape =
1814         Shape::indented(offset.block_only(), context.config).offset_left(prefix.len() + 2)?;
1815     let ty_str = match static_parts.ty.rewrite(context, ty_shape) {
1816         Some(ty_str) => ty_str,
1817         None => {
1818             if prefix.ends_with(' ') {
1819                 prefix.pop();
1820             }
1821             let nested_indent = offset.block_indent(context.config);
1822             let nested_shape = Shape::indented(nested_indent, context.config);
1823             let ty_str = static_parts.ty.rewrite(context, nested_shape)?;
1824             format!(
1825                 "{}{}",
1826                 nested_indent.to_string_with_newline(context.config),
1827                 ty_str
1828             )
1829         }
1830     };
1831
1832     if let Some(expr) = static_parts.expr_opt {
1833         let comments_lo = context.snippet_provider.span_after(static_parts.span, "=");
1834         let expr_lo = expr.span.lo();
1835         let comments_span = mk_sp(comments_lo, expr_lo);
1836
1837         let lhs = format!("{}{} =", prefix, ty_str);
1838
1839         // 1 = ;
1840         let remaining_width = context.budget(offset.block_indent + 1);
1841         rewrite_assign_rhs_with_comments(
1842             context,
1843             &lhs,
1844             &**expr,
1845             Shape::legacy(remaining_width, offset.block_only()),
1846             RhsTactics::Default,
1847             comments_span,
1848             true,
1849         )
1850         .and_then(|res| recover_comment_removed(res, static_parts.span, context))
1851         .map(|s| if s.ends_with(';') { s } else { s + ";" })
1852     } else {
1853         Some(format!("{}{};", prefix, ty_str))
1854     }
1855 }
1856 struct OpaqueType<'a> {
1857     bounds: &'a ast::GenericBounds,
1858 }
1859
1860 impl<'a> Rewrite for OpaqueType<'a> {
1861     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1862         let shape = shape.offset_left(5)?; // `impl `
1863         self.bounds
1864             .rewrite(context, shape)
1865             .map(|s| format!("impl {}", s))
1866     }
1867 }
1868
1869 pub(crate) fn rewrite_impl_type(
1870     ident: symbol::Ident,
1871     vis: &ast::Visibility,
1872     defaultness: ast::Defaultness,
1873     ty_opt: Option<&ptr::P<ast::Ty>>,
1874     generics: &ast::Generics,
1875     context: &RewriteContext<'_>,
1876     indent: Indent,
1877     span: Span,
1878 ) -> Option<String> {
1879     // Opaque type
1880     let result = if let Some(rustc_ast::ast::Ty {
1881         kind: ast::TyKind::ImplTrait(_, ref bounds),
1882         ..
1883     }) = ty_opt.map(|t| &**t)
1884     {
1885         rewrite_type(
1886             context,
1887             indent,
1888             ident,
1889             &DEFAULT_VISIBILITY,
1890             generics,
1891             None,
1892             Some(&OpaqueType { bounds }),
1893             span,
1894         )
1895     } else {
1896         rewrite_type(context, indent, ident, vis, generics, None, ty_opt, span)
1897     }?;
1898
1899     match defaultness {
1900         ast::Defaultness::Default(..) => Some(format!("default {}", result)),
1901         _ => Some(result),
1902     }
1903 }
1904
1905 impl Rewrite for ast::FnRetTy {
1906     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1907         match *self {
1908             ast::FnRetTy::Default(_) => Some(String::new()),
1909             ast::FnRetTy::Ty(ref ty) => {
1910                 if context.config.version() == Version::One
1911                     || context.config.indent_style() == IndentStyle::Visual
1912                 {
1913                     let inner_width = shape.width.checked_sub(3)?;
1914                     return ty
1915                         .rewrite(context, Shape::legacy(inner_width, shape.indent + 3))
1916                         .map(|r| format!("-> {}", r));
1917                 }
1918
1919                 ty.rewrite(context, shape.offset_left(3)?)
1920                     .map(|s| format!("-> {}", s))
1921             }
1922         }
1923     }
1924 }
1925
1926 fn is_empty_infer(ty: &ast::Ty, pat_span: Span) -> bool {
1927     match ty.kind {
1928         ast::TyKind::Infer => ty.span.hi() == pat_span.hi(),
1929         _ => false,
1930     }
1931 }
1932
1933 /// Recover any missing comments between the param and the type.
1934 ///
1935 /// # Returns
1936 ///
1937 /// A 2-len tuple with the comment before the colon in first position, and the comment after the
1938 /// colon in second position.
1939 fn get_missing_param_comments(
1940     context: &RewriteContext<'_>,
1941     pat_span: Span,
1942     ty_span: Span,
1943     shape: Shape,
1944 ) -> (String, String) {
1945     let missing_comment_span = mk_sp(pat_span.hi(), ty_span.lo());
1946
1947     let span_before_colon = {
1948         let missing_comment_span_hi = context
1949             .snippet_provider
1950             .span_before(missing_comment_span, ":");
1951         mk_sp(pat_span.hi(), missing_comment_span_hi)
1952     };
1953     let span_after_colon = {
1954         let missing_comment_span_lo = context
1955             .snippet_provider
1956             .span_after(missing_comment_span, ":");
1957         mk_sp(missing_comment_span_lo, ty_span.lo())
1958     };
1959
1960     let comment_before_colon = rewrite_missing_comment(span_before_colon, shape, context)
1961         .filter(|comment| !comment.is_empty())
1962         .map_or(String::new(), |comment| format!(" {}", comment));
1963     let comment_after_colon = rewrite_missing_comment(span_after_colon, shape, context)
1964         .filter(|comment| !comment.is_empty())
1965         .map_or(String::new(), |comment| format!("{} ", comment));
1966     (comment_before_colon, comment_after_colon)
1967 }
1968
1969 impl Rewrite for ast::Param {
1970     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
1971         let param_attrs_result = self
1972             .attrs
1973             .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
1974         // N.B. Doc comments aren't typically valid syntax, but could appear
1975         // in the presence of certain macros - https://github.com/rust-lang/rustfmt/issues/4936
1976         let (span, has_multiple_attr_lines, has_doc_comments) = if !self.attrs.is_empty() {
1977             let num_attrs = self.attrs.len();
1978             (
1979                 mk_sp(self.attrs[num_attrs - 1].span.hi(), self.pat.span.lo()),
1980                 param_attrs_result.contains('\n'),
1981                 self.attrs.iter().any(|a| a.is_doc_comment()),
1982             )
1983         } else {
1984             (mk_sp(self.span.lo(), self.span.lo()), false, false)
1985         };
1986
1987         if let Some(ref explicit_self) = self.to_self() {
1988             rewrite_explicit_self(
1989                 context,
1990                 explicit_self,
1991                 &param_attrs_result,
1992                 span,
1993                 shape,
1994                 has_multiple_attr_lines,
1995             )
1996         } else if is_named_param(self) {
1997             let param_name = &self
1998                 .pat
1999                 .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
2000             let mut result = combine_strs_with_missing_comments(
2001                 context,
2002                 &param_attrs_result,
2003                 param_name,
2004                 span,
2005                 shape,
2006                 !has_multiple_attr_lines && !has_doc_comments,
2007             )?;
2008
2009             if !is_empty_infer(&*self.ty, self.pat.span) {
2010                 let (before_comment, after_comment) =
2011                     get_missing_param_comments(context, self.pat.span, self.ty.span, shape);
2012                 result.push_str(&before_comment);
2013                 result.push_str(colon_spaces(context.config));
2014                 result.push_str(&after_comment);
2015                 let overhead = last_line_width(&result);
2016                 let max_width = shape.width.checked_sub(overhead)?;
2017                 if let Some(ty_str) = self
2018                     .ty
2019                     .rewrite(context, Shape::legacy(max_width, shape.indent))
2020                 {
2021                     result.push_str(&ty_str);
2022                 } else {
2023                     result = combine_strs_with_missing_comments(
2024                         context,
2025                         &(param_attrs_result + &shape.to_string_with_newline(context.config)),
2026                         param_name,
2027                         span,
2028                         shape,
2029                         !has_multiple_attr_lines,
2030                     )?;
2031                     result.push_str(&before_comment);
2032                     result.push_str(colon_spaces(context.config));
2033                     result.push_str(&after_comment);
2034                     let overhead = last_line_width(&result);
2035                     let max_width = shape.width.checked_sub(overhead)?;
2036                     let ty_str = self
2037                         .ty
2038                         .rewrite(context, Shape::legacy(max_width, shape.indent))?;
2039                     result.push_str(&ty_str);
2040                 }
2041             }
2042
2043             Some(result)
2044         } else {
2045             self.ty.rewrite(context, shape)
2046         }
2047     }
2048 }
2049
2050 fn rewrite_explicit_self(
2051     context: &RewriteContext<'_>,
2052     explicit_self: &ast::ExplicitSelf,
2053     param_attrs: &str,
2054     span: Span,
2055     shape: Shape,
2056     has_multiple_attr_lines: bool,
2057 ) -> Option<String> {
2058     match explicit_self.node {
2059         ast::SelfKind::Region(lt, m) => {
2060             let mut_str = format_mutability(m);
2061             match lt {
2062                 Some(ref l) => {
2063                     let lifetime_str = l.rewrite(
2064                         context,
2065                         Shape::legacy(context.config.max_width(), Indent::empty()),
2066                     )?;
2067                     Some(combine_strs_with_missing_comments(
2068                         context,
2069                         &param_attrs,
2070                         &format!("&{} {}self", lifetime_str, mut_str),
2071                         span,
2072                         shape,
2073                         !has_multiple_attr_lines,
2074                     )?)
2075                 }
2076                 None => Some(combine_strs_with_missing_comments(
2077                     context,
2078                     &param_attrs,
2079                     &format!("&{}self", mut_str),
2080                     span,
2081                     shape,
2082                     !has_multiple_attr_lines,
2083                 )?),
2084             }
2085         }
2086         ast::SelfKind::Explicit(ref ty, mutability) => {
2087             let type_str = ty.rewrite(
2088                 context,
2089                 Shape::legacy(context.config.max_width(), Indent::empty()),
2090             )?;
2091
2092             Some(combine_strs_with_missing_comments(
2093                 context,
2094                 &param_attrs,
2095                 &format!("{}self: {}", format_mutability(mutability), type_str),
2096                 span,
2097                 shape,
2098                 !has_multiple_attr_lines,
2099             )?)
2100         }
2101         ast::SelfKind::Value(mutability) => Some(combine_strs_with_missing_comments(
2102             context,
2103             &param_attrs,
2104             &format!("{}self", format_mutability(mutability)),
2105             span,
2106             shape,
2107             !has_multiple_attr_lines,
2108         )?),
2109     }
2110 }
2111
2112 pub(crate) fn span_lo_for_param(param: &ast::Param) -> BytePos {
2113     if param.attrs.is_empty() {
2114         if is_named_param(param) {
2115             param.pat.span.lo()
2116         } else {
2117             param.ty.span.lo()
2118         }
2119     } else {
2120         param.attrs[0].span.lo()
2121     }
2122 }
2123
2124 pub(crate) fn span_hi_for_param(context: &RewriteContext<'_>, param: &ast::Param) -> BytePos {
2125     match param.ty.kind {
2126         ast::TyKind::Infer if context.snippet(param.ty.span) == "_" => param.ty.span.hi(),
2127         ast::TyKind::Infer if is_named_param(param) => param.pat.span.hi(),
2128         _ => param.ty.span.hi(),
2129     }
2130 }
2131
2132 pub(crate) fn is_named_param(param: &ast::Param) -> bool {
2133     if let ast::PatKind::Ident(_, ident, _) = param.pat.kind {
2134         ident.name != symbol::kw::Empty
2135     } else {
2136         true
2137     }
2138 }
2139
2140 #[derive(Copy, Clone, Debug, PartialEq, Eq)]
2141 pub(crate) enum FnBraceStyle {
2142     SameLine,
2143     NextLine,
2144     None,
2145 }
2146
2147 // Return type is (result, force_new_line_for_brace)
2148 fn rewrite_fn_base(
2149     context: &RewriteContext<'_>,
2150     indent: Indent,
2151     ident: symbol::Ident,
2152     fn_sig: &FnSig<'_>,
2153     span: Span,
2154     fn_brace_style: FnBraceStyle,
2155 ) -> Option<(String, bool, bool)> {
2156     let mut force_new_line_for_brace = false;
2157
2158     let where_clause = &fn_sig.generics.where_clause;
2159
2160     let mut result = String::with_capacity(1024);
2161     result.push_str(&fn_sig.to_str(context));
2162
2163     // fn foo
2164     result.push_str("fn ");
2165
2166     // Generics.
2167     let overhead = if let FnBraceStyle::SameLine = fn_brace_style {
2168         // 4 = `() {`
2169         4
2170     } else {
2171         // 2 = `()`
2172         2
2173     };
2174     let used_width = last_line_used_width(&result, indent.width());
2175     let one_line_budget = context.budget(used_width + overhead);
2176     let shape = Shape {
2177         width: one_line_budget,
2178         indent,
2179         offset: used_width,
2180     };
2181     let fd = fn_sig.decl;
2182     let generics_str = rewrite_generics(
2183         context,
2184         rewrite_ident(context, ident),
2185         fn_sig.generics,
2186         shape,
2187     )?;
2188     result.push_str(&generics_str);
2189
2190     let snuggle_angle_bracket = generics_str
2191         .lines()
2192         .last()
2193         .map_or(false, |l| l.trim_start().len() == 1);
2194
2195     // Note that the width and indent don't really matter, we'll re-layout the
2196     // return type later anyway.
2197     let ret_str = fd
2198         .output
2199         .rewrite(context, Shape::indented(indent, context.config))?;
2200
2201     let multi_line_ret_str = ret_str.contains('\n');
2202     let ret_str_len = if multi_line_ret_str { 0 } else { ret_str.len() };
2203
2204     // Params.
2205     let (one_line_budget, multi_line_budget, mut param_indent) = compute_budgets_for_params(
2206         context,
2207         &result,
2208         indent,
2209         ret_str_len,
2210         fn_brace_style,
2211         multi_line_ret_str,
2212     )?;
2213
2214     debug!(
2215         "rewrite_fn_base: one_line_budget: {}, multi_line_budget: {}, param_indent: {:?}",
2216         one_line_budget, multi_line_budget, param_indent
2217     );
2218
2219     result.push('(');
2220     // Check if vertical layout was forced.
2221     if one_line_budget == 0
2222         && !snuggle_angle_bracket
2223         && context.config.indent_style() == IndentStyle::Visual
2224     {
2225         result.push_str(&param_indent.to_string_with_newline(context.config));
2226     }
2227
2228     // Skip `pub(crate)`.
2229     let lo_after_visibility = get_bytepos_after_visibility(&fn_sig.visibility, span);
2230     // A conservative estimation, the goal is to be over all parens in generics
2231     let params_start = fn_sig
2232         .generics
2233         .params
2234         .last()
2235         .map_or(lo_after_visibility, |param| param.span().hi());
2236     let params_end = if fd.inputs.is_empty() {
2237         context
2238             .snippet_provider
2239             .span_after(mk_sp(params_start, span.hi()), ")")
2240     } else {
2241         let last_span = mk_sp(fd.inputs[fd.inputs.len() - 1].span().hi(), span.hi());
2242         context.snippet_provider.span_after(last_span, ")")
2243     };
2244     let params_span = mk_sp(
2245         context
2246             .snippet_provider
2247             .span_after(mk_sp(params_start, span.hi()), "("),
2248         params_end,
2249     );
2250     let param_str = rewrite_params(
2251         context,
2252         &fd.inputs,
2253         one_line_budget,
2254         multi_line_budget,
2255         indent,
2256         param_indent,
2257         params_span,
2258         fd.c_variadic(),
2259     )?;
2260
2261     let put_params_in_block = match context.config.indent_style() {
2262         IndentStyle::Block => param_str.contains('\n') || param_str.len() > one_line_budget,
2263         _ => false,
2264     } && !fd.inputs.is_empty();
2265
2266     let mut params_last_line_contains_comment = false;
2267     let mut no_params_and_over_max_width = false;
2268
2269     if put_params_in_block {
2270         param_indent = indent.block_indent(context.config);
2271         result.push_str(&param_indent.to_string_with_newline(context.config));
2272         result.push_str(&param_str);
2273         result.push_str(&indent.to_string_with_newline(context.config));
2274         result.push(')');
2275     } else {
2276         result.push_str(&param_str);
2277         let used_width = last_line_used_width(&result, indent.width()) + first_line_width(&ret_str);
2278         // Put the closing brace on the next line if it overflows the max width.
2279         // 1 = `)`
2280         let closing_paren_overflow_max_width =
2281             fd.inputs.is_empty() && used_width + 1 > context.config.max_width();
2282         // If the last line of params contains comment, we cannot put the closing paren
2283         // on the same line.
2284         params_last_line_contains_comment = param_str
2285             .lines()
2286             .last()
2287             .map_or(false, |last_line| last_line.contains("//"));
2288
2289         if context.config.version() == Version::Two {
2290             if closing_paren_overflow_max_width {
2291                 result.push(')');
2292                 result.push_str(&indent.to_string_with_newline(context.config));
2293                 no_params_and_over_max_width = true;
2294             } else if params_last_line_contains_comment {
2295                 result.push_str(&indent.to_string_with_newline(context.config));
2296                 result.push(')');
2297                 no_params_and_over_max_width = true;
2298             } else {
2299                 result.push(')');
2300             }
2301         } else {
2302             if closing_paren_overflow_max_width || params_last_line_contains_comment {
2303                 result.push_str(&indent.to_string_with_newline(context.config));
2304             }
2305             result.push(')');
2306         }
2307     }
2308
2309     // Return type.
2310     if let ast::FnRetTy::Ty(..) = fd.output {
2311         let ret_should_indent = match context.config.indent_style() {
2312             // If our params are block layout then we surely must have space.
2313             IndentStyle::Block if put_params_in_block || fd.inputs.is_empty() => false,
2314             _ if params_last_line_contains_comment => false,
2315             _ if result.contains('\n') || multi_line_ret_str => true,
2316             _ => {
2317                 // If the return type would push over the max width, then put the return type on
2318                 // a new line. With the +1 for the signature length an additional space between
2319                 // the closing parenthesis of the param and the arrow '->' is considered.
2320                 let mut sig_length = result.len() + indent.width() + ret_str_len + 1;
2321
2322                 // If there is no where-clause, take into account the space after the return type
2323                 // and the brace.
2324                 if where_clause.predicates.is_empty() {
2325                     sig_length += 2;
2326                 }
2327
2328                 sig_length > context.config.max_width()
2329             }
2330         };
2331         let ret_shape = if ret_should_indent {
2332             if context.config.version() == Version::One
2333                 || context.config.indent_style() == IndentStyle::Visual
2334             {
2335                 let indent = if param_str.is_empty() {
2336                     // Aligning with non-existent params looks silly.
2337                     force_new_line_for_brace = true;
2338                     indent + 4
2339                 } else {
2340                     // FIXME: we might want to check that using the param indent
2341                     // doesn't blow our budget, and if it does, then fallback to
2342                     // the where-clause indent.
2343                     param_indent
2344                 };
2345
2346                 result.push_str(&indent.to_string_with_newline(context.config));
2347                 Shape::indented(indent, context.config)
2348             } else {
2349                 let mut ret_shape = Shape::indented(indent, context.config);
2350                 if param_str.is_empty() {
2351                     // Aligning with non-existent params looks silly.
2352                     force_new_line_for_brace = true;
2353                     ret_shape = if context.use_block_indent() {
2354                         ret_shape.offset_left(4).unwrap_or(ret_shape)
2355                     } else {
2356                         ret_shape.indent = ret_shape.indent + 4;
2357                         ret_shape
2358                     };
2359                 }
2360
2361                 result.push_str(&ret_shape.indent.to_string_with_newline(context.config));
2362                 ret_shape
2363             }
2364         } else {
2365             if context.config.version() == Version::Two {
2366                 if !param_str.is_empty() || !no_params_and_over_max_width {
2367                     result.push(' ');
2368                 }
2369             } else {
2370                 result.push(' ');
2371             }
2372
2373             let ret_shape = Shape::indented(indent, context.config);
2374             ret_shape
2375                 .offset_left(last_line_width(&result))
2376                 .unwrap_or(ret_shape)
2377         };
2378
2379         if multi_line_ret_str || ret_should_indent {
2380             // Now that we know the proper indent and width, we need to
2381             // re-layout the return type.
2382             let ret_str = fd.output.rewrite(context, ret_shape)?;
2383             result.push_str(&ret_str);
2384         } else {
2385             result.push_str(&ret_str);
2386         }
2387
2388         // Comment between return type and the end of the decl.
2389         let snippet_lo = fd.output.span().hi();
2390         if where_clause.predicates.is_empty() {
2391             let snippet_hi = span.hi();
2392             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
2393             // Try to preserve the layout of the original snippet.
2394             let original_starts_with_newline = snippet
2395                 .find(|c| c != ' ')
2396                 .map_or(false, |i| starts_with_newline(&snippet[i..]));
2397             let original_ends_with_newline = snippet
2398                 .rfind(|c| c != ' ')
2399                 .map_or(false, |i| snippet[i..].ends_with('\n'));
2400             let snippet = snippet.trim();
2401             if !snippet.is_empty() {
2402                 result.push(if original_starts_with_newline {
2403                     '\n'
2404                 } else {
2405                     ' '
2406                 });
2407                 result.push_str(snippet);
2408                 if original_ends_with_newline {
2409                     force_new_line_for_brace = true;
2410                 }
2411             }
2412         }
2413     }
2414
2415     let pos_before_where = match fd.output {
2416         ast::FnRetTy::Default(..) => params_span.hi(),
2417         ast::FnRetTy::Ty(ref ty) => ty.span.hi(),
2418     };
2419
2420     let is_params_multi_lined = param_str.contains('\n');
2421
2422     let space = if put_params_in_block && ret_str.is_empty() {
2423         WhereClauseSpace::Space
2424     } else {
2425         WhereClauseSpace::Newline
2426     };
2427     let mut option = WhereClauseOption::new(fn_brace_style == FnBraceStyle::None, space);
2428     if is_params_multi_lined {
2429         option.veto_single_line();
2430     }
2431     let where_clause_str = rewrite_where_clause(
2432         context,
2433         where_clause,
2434         context.config.brace_style(),
2435         Shape::indented(indent, context.config),
2436         true,
2437         "{",
2438         Some(span.hi()),
2439         pos_before_where,
2440         option,
2441     )?;
2442     // If there are neither where-clause nor return type, we may be missing comments between
2443     // params and `{`.
2444     if where_clause_str.is_empty() {
2445         if let ast::FnRetTy::Default(ret_span) = fd.output {
2446             match recover_missing_comment_in_span(
2447                 mk_sp(params_span.hi(), ret_span.hi()),
2448                 shape,
2449                 context,
2450                 last_line_width(&result),
2451             ) {
2452                 Some(ref missing_comment) if !missing_comment.is_empty() => {
2453                     result.push_str(missing_comment);
2454                     force_new_line_for_brace = true;
2455                 }
2456                 _ => (),
2457             }
2458         }
2459     }
2460
2461     result.push_str(&where_clause_str);
2462
2463     let ends_with_comment = last_line_contains_single_line_comment(&result);
2464     force_new_line_for_brace |= ends_with_comment;
2465     force_new_line_for_brace |=
2466         is_params_multi_lined && context.config.where_single_line() && !where_clause_str.is_empty();
2467     Some((result, ends_with_comment, force_new_line_for_brace))
2468 }
2469
2470 /// Kind of spaces to put before `where`.
2471 #[derive(Copy, Clone)]
2472 enum WhereClauseSpace {
2473     /// A single space.
2474     Space,
2475     /// A new line.
2476     Newline,
2477     /// Nothing.
2478     None,
2479 }
2480
2481 #[derive(Copy, Clone)]
2482 struct WhereClauseOption {
2483     suppress_comma: bool, // Force no trailing comma
2484     snuggle: WhereClauseSpace,
2485     allow_single_line: bool, // Try single line where-clause instead of vertical layout
2486     veto_single_line: bool,  // Disallow a single-line where-clause.
2487 }
2488
2489 impl WhereClauseOption {
2490     fn new(suppress_comma: bool, snuggle: WhereClauseSpace) -> WhereClauseOption {
2491         WhereClauseOption {
2492             suppress_comma,
2493             snuggle,
2494             allow_single_line: false,
2495             veto_single_line: false,
2496         }
2497     }
2498
2499     fn snuggled(current: &str) -> WhereClauseOption {
2500         WhereClauseOption {
2501             suppress_comma: false,
2502             snuggle: if last_line_width(current) == 1 {
2503                 WhereClauseSpace::Space
2504             } else {
2505                 WhereClauseSpace::Newline
2506             },
2507             allow_single_line: false,
2508             veto_single_line: false,
2509         }
2510     }
2511
2512     fn suppress_comma(&mut self) {
2513         self.suppress_comma = true
2514     }
2515
2516     fn allow_single_line(&mut self) {
2517         self.allow_single_line = true
2518     }
2519
2520     fn snuggle(&mut self) {
2521         self.snuggle = WhereClauseSpace::Space
2522     }
2523
2524     fn veto_single_line(&mut self) {
2525         self.veto_single_line = true;
2526     }
2527 }
2528
2529 fn rewrite_params(
2530     context: &RewriteContext<'_>,
2531     params: &[ast::Param],
2532     one_line_budget: usize,
2533     multi_line_budget: usize,
2534     indent: Indent,
2535     param_indent: Indent,
2536     span: Span,
2537     variadic: bool,
2538 ) -> Option<String> {
2539     if params.is_empty() {
2540         let comment = context
2541             .snippet(mk_sp(
2542                 span.lo(),
2543                 // to remove ')'
2544                 span.hi() - BytePos(1),
2545             ))
2546             .trim();
2547         return Some(comment.to_owned());
2548     }
2549     let param_items: Vec<_> = itemize_list(
2550         context.snippet_provider,
2551         params.iter(),
2552         ")",
2553         ",",
2554         |param| span_lo_for_param(param),
2555         |param| param.ty.span.hi(),
2556         |param| {
2557             param
2558                 .rewrite(context, Shape::legacy(multi_line_budget, param_indent))
2559                 .or_else(|| Some(context.snippet(param.span()).to_owned()))
2560         },
2561         span.lo(),
2562         span.hi(),
2563         false,
2564     )
2565     .collect();
2566
2567     let tactic = definitive_tactic(
2568         &param_items,
2569         context
2570             .config
2571             .fn_args_layout()
2572             .to_list_tactic(param_items.len()),
2573         Separator::Comma,
2574         one_line_budget,
2575     );
2576     let budget = match tactic {
2577         DefinitiveListTactic::Horizontal => one_line_budget,
2578         _ => multi_line_budget,
2579     };
2580     let indent = match context.config.indent_style() {
2581         IndentStyle::Block => indent.block_indent(context.config),
2582         IndentStyle::Visual => param_indent,
2583     };
2584     let trailing_separator = if variadic {
2585         SeparatorTactic::Never
2586     } else {
2587         match context.config.indent_style() {
2588             IndentStyle::Block => context.config.trailing_comma(),
2589             IndentStyle::Visual => SeparatorTactic::Never,
2590         }
2591     };
2592     let fmt = ListFormatting::new(Shape::legacy(budget, indent), context.config)
2593         .tactic(tactic)
2594         .trailing_separator(trailing_separator)
2595         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
2596         .preserve_newline(true);
2597     write_list(&param_items, &fmt)
2598 }
2599
2600 fn compute_budgets_for_params(
2601     context: &RewriteContext<'_>,
2602     result: &str,
2603     indent: Indent,
2604     ret_str_len: usize,
2605     fn_brace_style: FnBraceStyle,
2606     force_vertical_layout: bool,
2607 ) -> Option<(usize, usize, Indent)> {
2608     debug!(
2609         "compute_budgets_for_params {} {:?}, {}, {:?}",
2610         result.len(),
2611         indent,
2612         ret_str_len,
2613         fn_brace_style,
2614     );
2615     // Try keeping everything on the same line.
2616     if !result.contains('\n') && !force_vertical_layout {
2617         // 2 = `()`, 3 = `() `, space is before ret_string.
2618         let overhead = if ret_str_len == 0 { 2 } else { 3 };
2619         let mut used_space = indent.width() + result.len() + ret_str_len + overhead;
2620         match fn_brace_style {
2621             FnBraceStyle::None => used_space += 1,     // 1 = `;`
2622             FnBraceStyle::SameLine => used_space += 2, // 2 = `{}`
2623             FnBraceStyle::NextLine => (),
2624         }
2625         let one_line_budget = context.budget(used_space);
2626
2627         if one_line_budget > 0 {
2628             // 4 = "() {".len()
2629             let (indent, multi_line_budget) = match context.config.indent_style() {
2630                 IndentStyle::Block => {
2631                     let indent = indent.block_indent(context.config);
2632                     (indent, context.budget(indent.width() + 1))
2633                 }
2634                 IndentStyle::Visual => {
2635                     let indent = indent + result.len() + 1;
2636                     let multi_line_overhead = match fn_brace_style {
2637                         FnBraceStyle::SameLine => 4,
2638                         _ => 2,
2639                     } + indent.width();
2640                     (indent, context.budget(multi_line_overhead))
2641                 }
2642             };
2643
2644             return Some((one_line_budget, multi_line_budget, indent));
2645         }
2646     }
2647
2648     // Didn't work. we must force vertical layout and put params on a newline.
2649     let new_indent = indent.block_indent(context.config);
2650     let used_space = match context.config.indent_style() {
2651         // 1 = `,`
2652         IndentStyle::Block => new_indent.width() + 1,
2653         // Account for `)` and possibly ` {`.
2654         IndentStyle::Visual => new_indent.width() + if ret_str_len == 0 { 1 } else { 3 },
2655     };
2656     Some((0, context.budget(used_space), new_indent))
2657 }
2658
2659 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> FnBraceStyle {
2660     let predicate_count = where_clause.predicates.len();
2661
2662     if config.where_single_line() && predicate_count == 1 {
2663         return FnBraceStyle::SameLine;
2664     }
2665     let brace_style = config.brace_style();
2666
2667     let use_next_line = brace_style == BraceStyle::AlwaysNextLine
2668         || (brace_style == BraceStyle::SameLineWhere && predicate_count > 0);
2669     if use_next_line {
2670         FnBraceStyle::NextLine
2671     } else {
2672         FnBraceStyle::SameLine
2673     }
2674 }
2675
2676 fn rewrite_generics(
2677     context: &RewriteContext<'_>,
2678     ident: &str,
2679     generics: &ast::Generics,
2680     shape: Shape,
2681 ) -> Option<String> {
2682     // FIXME: convert bounds to where-clauses where they get too big or if
2683     // there is a where-clause at all.
2684
2685     if generics.params.is_empty() {
2686         return Some(ident.to_owned());
2687     }
2688
2689     let params = generics.params.iter();
2690     overflow::rewrite_with_angle_brackets(context, ident, params, shape, generics.span)
2691 }
2692
2693 fn generics_shape_from_config(config: &Config, shape: Shape, offset: usize) -> Option<Shape> {
2694     match config.indent_style() {
2695         IndentStyle::Visual => shape.visual_indent(1 + offset).sub_width(offset + 2),
2696         IndentStyle::Block => {
2697             // 1 = ","
2698             shape
2699                 .block()
2700                 .block_indent(config.tab_spaces())
2701                 .with_max_width(config)
2702                 .sub_width(1)
2703         }
2704     }
2705 }
2706
2707 fn rewrite_where_clause_rfc_style(
2708     context: &RewriteContext<'_>,
2709     where_clause: &ast::WhereClause,
2710     shape: Shape,
2711     terminator: &str,
2712     span_end: Option<BytePos>,
2713     span_end_before_where: BytePos,
2714     where_clause_option: WhereClauseOption,
2715 ) -> Option<String> {
2716     let (where_keyword, allow_single_line) = rewrite_where_keyword(
2717         context,
2718         where_clause,
2719         shape,
2720         span_end_before_where,
2721         where_clause_option,
2722     )?;
2723
2724     // 1 = `,`
2725     let clause_shape = shape
2726         .block()
2727         .with_max_width(context.config)
2728         .block_left(context.config.tab_spaces())?
2729         .sub_width(1)?;
2730     let force_single_line = context.config.where_single_line()
2731         && where_clause.predicates.len() == 1
2732         && !where_clause_option.veto_single_line;
2733
2734     let preds_str = rewrite_bounds_on_where_clause(
2735         context,
2736         where_clause,
2737         clause_shape,
2738         terminator,
2739         span_end,
2740         where_clause_option,
2741         force_single_line,
2742     )?;
2743
2744     // 6 = `where `
2745     let clause_sep =
2746         if allow_single_line && !preds_str.contains('\n') && 6 + preds_str.len() <= shape.width
2747             || force_single_line
2748         {
2749             Cow::from(" ")
2750         } else {
2751             clause_shape.indent.to_string_with_newline(context.config)
2752         };
2753
2754     Some(format!("{}{}{}", where_keyword, clause_sep, preds_str))
2755 }
2756
2757 /// Rewrite `where` and comment around it.
2758 fn rewrite_where_keyword(
2759     context: &RewriteContext<'_>,
2760     where_clause: &ast::WhereClause,
2761     shape: Shape,
2762     span_end_before_where: BytePos,
2763     where_clause_option: WhereClauseOption,
2764 ) -> Option<(String, bool)> {
2765     let block_shape = shape.block().with_max_width(context.config);
2766     // 1 = `,`
2767     let clause_shape = block_shape
2768         .block_left(context.config.tab_spaces())?
2769         .sub_width(1)?;
2770
2771     let comment_separator = |comment: &str, shape: Shape| {
2772         if comment.is_empty() {
2773             Cow::from("")
2774         } else {
2775             shape.indent.to_string_with_newline(context.config)
2776         }
2777     };
2778
2779     let (span_before, span_after) =
2780         missing_span_before_after_where(span_end_before_where, where_clause);
2781     let (comment_before, comment_after) =
2782         rewrite_comments_before_after_where(context, span_before, span_after, shape)?;
2783
2784     let starting_newline = match where_clause_option.snuggle {
2785         WhereClauseSpace::Space if comment_before.is_empty() => Cow::from(" "),
2786         WhereClauseSpace::None => Cow::from(""),
2787         _ => block_shape.indent.to_string_with_newline(context.config),
2788     };
2789
2790     let newline_before_where = comment_separator(&comment_before, shape);
2791     let newline_after_where = comment_separator(&comment_after, clause_shape);
2792     let result = format!(
2793         "{}{}{}where{}{}",
2794         starting_newline, comment_before, newline_before_where, newline_after_where, comment_after
2795     );
2796     let allow_single_line = where_clause_option.allow_single_line
2797         && comment_before.is_empty()
2798         && comment_after.is_empty();
2799
2800     Some((result, allow_single_line))
2801 }
2802
2803 /// Rewrite bounds on a where clause.
2804 fn rewrite_bounds_on_where_clause(
2805     context: &RewriteContext<'_>,
2806     where_clause: &ast::WhereClause,
2807     shape: Shape,
2808     terminator: &str,
2809     span_end: Option<BytePos>,
2810     where_clause_option: WhereClauseOption,
2811     force_single_line: bool,
2812 ) -> Option<String> {
2813     let span_start = where_clause.predicates[0].span().lo();
2814     // If we don't have the start of the next span, then use the end of the
2815     // predicates, but that means we miss comments.
2816     let len = where_clause.predicates.len();
2817     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2818     let span_end = span_end.unwrap_or(end_of_preds);
2819     let items = itemize_list(
2820         context.snippet_provider,
2821         where_clause.predicates.iter(),
2822         terminator,
2823         ",",
2824         |pred| pred.span().lo(),
2825         |pred| pred.span().hi(),
2826         |pred| pred.rewrite(context, shape),
2827         span_start,
2828         span_end,
2829         false,
2830     );
2831     let comma_tactic = if where_clause_option.suppress_comma || force_single_line {
2832         SeparatorTactic::Never
2833     } else {
2834         context.config.trailing_comma()
2835     };
2836
2837     // shape should be vertical only and only if we have `force_single_line` option enabled
2838     // and the number of items of the where-clause is equal to 1
2839     let shape_tactic = if force_single_line {
2840         DefinitiveListTactic::Horizontal
2841     } else {
2842         DefinitiveListTactic::Vertical
2843     };
2844
2845     let fmt = ListFormatting::new(shape, context.config)
2846         .tactic(shape_tactic)
2847         .trailing_separator(comma_tactic)
2848         .preserve_newline(true);
2849     write_list(&items.collect::<Vec<_>>(), &fmt)
2850 }
2851
2852 fn rewrite_where_clause(
2853     context: &RewriteContext<'_>,
2854     where_clause: &ast::WhereClause,
2855     brace_style: BraceStyle,
2856     shape: Shape,
2857     on_new_line: bool,
2858     terminator: &str,
2859     span_end: Option<BytePos>,
2860     span_end_before_where: BytePos,
2861     where_clause_option: WhereClauseOption,
2862 ) -> Option<String> {
2863     if where_clause.predicates.is_empty() {
2864         return Some(String::new());
2865     }
2866
2867     if context.config.indent_style() == IndentStyle::Block {
2868         return rewrite_where_clause_rfc_style(
2869             context,
2870             where_clause,
2871             shape,
2872             terminator,
2873             span_end,
2874             span_end_before_where,
2875             where_clause_option,
2876         );
2877     }
2878
2879     let extra_indent = Indent::new(context.config.tab_spaces(), 0);
2880
2881     let offset = match context.config.indent_style() {
2882         IndentStyle::Block => shape.indent + extra_indent.block_indent(context.config),
2883         // 6 = "where ".len()
2884         IndentStyle::Visual => shape.indent + extra_indent + 6,
2885     };
2886     // FIXME: if indent_style != Visual, then the budgets below might
2887     // be out by a char or two.
2888
2889     let budget = context.config.max_width() - offset.width();
2890     let span_start = where_clause.predicates[0].span().lo();
2891     // If we don't have the start of the next span, then use the end of the
2892     // predicates, but that means we miss comments.
2893     let len = where_clause.predicates.len();
2894     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2895     let span_end = span_end.unwrap_or(end_of_preds);
2896     let items = itemize_list(
2897         context.snippet_provider,
2898         where_clause.predicates.iter(),
2899         terminator,
2900         ",",
2901         |pred| pred.span().lo(),
2902         |pred| pred.span().hi(),
2903         |pred| pred.rewrite(context, Shape::legacy(budget, offset)),
2904         span_start,
2905         span_end,
2906         false,
2907     );
2908     let item_vec = items.collect::<Vec<_>>();
2909     // FIXME: we don't need to collect here
2910     let tactic = definitive_tactic(&item_vec, ListTactic::Vertical, Separator::Comma, budget);
2911
2912     let mut comma_tactic = context.config.trailing_comma();
2913     // Kind of a hack because we don't usually have trailing commas in where-clauses.
2914     if comma_tactic == SeparatorTactic::Vertical || where_clause_option.suppress_comma {
2915         comma_tactic = SeparatorTactic::Never;
2916     }
2917
2918     let fmt = ListFormatting::new(Shape::legacy(budget, offset), context.config)
2919         .tactic(tactic)
2920         .trailing_separator(comma_tactic)
2921         .ends_with_newline(tactic.ends_with_newline(context.config.indent_style()))
2922         .preserve_newline(true);
2923     let preds_str = write_list(&item_vec, &fmt)?;
2924
2925     let end_length = if terminator == "{" {
2926         // If the brace is on the next line we don't need to count it otherwise it needs two
2927         // characters " {"
2928         match brace_style {
2929             BraceStyle::AlwaysNextLine | BraceStyle::SameLineWhere => 0,
2930             BraceStyle::PreferSameLine => 2,
2931         }
2932     } else if terminator == "=" {
2933         2
2934     } else {
2935         terminator.len()
2936     };
2937     if on_new_line
2938         || preds_str.contains('\n')
2939         || shape.indent.width() + " where ".len() + preds_str.len() + end_length > shape.width
2940     {
2941         Some(format!(
2942             "\n{}where {}",
2943             (shape.indent + extra_indent).to_string(context.config),
2944             preds_str
2945         ))
2946     } else {
2947         Some(format!(" where {}", preds_str))
2948     }
2949 }
2950
2951 fn missing_span_before_after_where(
2952     before_item_span_end: BytePos,
2953     where_clause: &ast::WhereClause,
2954 ) -> (Span, Span) {
2955     let missing_span_before = mk_sp(before_item_span_end, where_clause.span.lo());
2956     // 5 = `where`
2957     let pos_after_where = where_clause.span.lo() + BytePos(5);
2958     let missing_span_after = mk_sp(pos_after_where, where_clause.predicates[0].span().lo());
2959     (missing_span_before, missing_span_after)
2960 }
2961
2962 fn rewrite_comments_before_after_where(
2963     context: &RewriteContext<'_>,
2964     span_before_where: Span,
2965     span_after_where: Span,
2966     shape: Shape,
2967 ) -> Option<(String, String)> {
2968     let before_comment = rewrite_missing_comment(span_before_where, shape, context)?;
2969     let after_comment = rewrite_missing_comment(
2970         span_after_where,
2971         shape.block_indent(context.config.tab_spaces()),
2972         context,
2973     )?;
2974     Some((before_comment, after_comment))
2975 }
2976
2977 fn format_header(
2978     context: &RewriteContext<'_>,
2979     item_name: &str,
2980     ident: symbol::Ident,
2981     vis: &ast::Visibility,
2982     offset: Indent,
2983 ) -> String {
2984     let mut result = String::with_capacity(128);
2985     let shape = Shape::indented(offset, context.config);
2986
2987     result.push_str(&format_visibility(context, vis).trim());
2988
2989     // Check for a missing comment between the visibility and the item name.
2990     let after_vis = vis.span.hi();
2991     if let Some(before_item_name) = context
2992         .snippet_provider
2993         .opt_span_before(mk_sp(vis.span.lo(), ident.span.hi()), item_name.trim())
2994     {
2995         let missing_span = mk_sp(after_vis, before_item_name);
2996         if let Some(result_with_comment) = combine_strs_with_missing_comments(
2997             context,
2998             &result,
2999             item_name,
3000             missing_span,
3001             shape,
3002             /* allow_extend */ true,
3003         ) {
3004             result = result_with_comment;
3005         }
3006     }
3007
3008     result.push_str(&rewrite_ident(context, ident));
3009
3010     result
3011 }
3012
3013 #[derive(PartialEq, Eq, Clone, Copy)]
3014 enum BracePos {
3015     None,
3016     Auto,
3017     ForceSameLine,
3018 }
3019
3020 fn format_generics(
3021     context: &RewriteContext<'_>,
3022     generics: &ast::Generics,
3023     brace_style: BraceStyle,
3024     brace_pos: BracePos,
3025     offset: Indent,
3026     span: Span,
3027     used_width: usize,
3028 ) -> Option<String> {
3029     let shape = Shape::legacy(context.budget(used_width + offset.width()), offset);
3030     let mut result = rewrite_generics(context, "", generics, shape)?;
3031
3032     // If the generics are not parameterized then generics.span.hi() == 0,
3033     // so we use span.lo(), which is the position after `struct Foo`.
3034     let span_end_before_where = if !generics.params.is_empty() {
3035         generics.span.hi()
3036     } else {
3037         span.lo()
3038     };
3039     let (same_line_brace, missed_comments) = if !generics.where_clause.predicates.is_empty() {
3040         let budget = context.budget(last_line_used_width(&result, offset.width()));
3041         let mut option = WhereClauseOption::snuggled(&result);
3042         if brace_pos == BracePos::None {
3043             option.suppress_comma = true;
3044         }
3045         let where_clause_str = rewrite_where_clause(
3046             context,
3047             &generics.where_clause,
3048             brace_style,
3049             Shape::legacy(budget, offset.block_only()),
3050             true,
3051             "{",
3052             Some(span.hi()),
3053             span_end_before_where,
3054             option,
3055         )?;
3056         result.push_str(&where_clause_str);
3057         (
3058             brace_pos == BracePos::ForceSameLine || brace_style == BraceStyle::PreferSameLine,
3059             // missed comments are taken care of in #rewrite_where_clause
3060             None,
3061         )
3062     } else {
3063         (
3064             brace_pos == BracePos::ForceSameLine
3065                 || (result.contains('\n') && brace_style == BraceStyle::PreferSameLine
3066                     || brace_style != BraceStyle::AlwaysNextLine)
3067                 || trimmed_last_line_width(&result) == 1,
3068             rewrite_missing_comment(
3069                 mk_sp(
3070                     span_end_before_where,
3071                     if brace_pos == BracePos::None {
3072                         span.hi()
3073                     } else {
3074                         context.snippet_provider.span_before(span, "{")
3075                     },
3076                 ),
3077                 shape,
3078                 context,
3079             ),
3080         )
3081     };
3082     // add missing comments
3083     let missed_line_comments = missed_comments
3084         .filter(|missed_comments| !missed_comments.is_empty())
3085         .map_or(false, |missed_comments| {
3086             let is_block = is_last_comment_block(&missed_comments);
3087             let sep = if is_block { " " } else { "\n" };
3088             result.push_str(sep);
3089             result.push_str(&missed_comments);
3090             !is_block
3091         });
3092     if brace_pos == BracePos::None {
3093         return Some(result);
3094     }
3095     let total_used_width = last_line_used_width(&result, used_width);
3096     let remaining_budget = context.budget(total_used_width);
3097     // If the same line brace if forced, it indicates that we are rewriting an item with empty body,
3098     // and hence we take the closer into account as well for one line budget.
3099     // We assume that the closer has the same length as the opener.
3100     let overhead = if brace_pos == BracePos::ForceSameLine {
3101         // 3 = ` {}`
3102         3
3103     } else {
3104         // 2 = ` {`
3105         2
3106     };
3107     let forbid_same_line_brace = missed_line_comments || overhead > remaining_budget;
3108     if !forbid_same_line_brace && same_line_brace {
3109         result.push(' ');
3110     } else {
3111         result.push('\n');
3112         result.push_str(&offset.block_only().to_string(context.config));
3113     }
3114     result.push('{');
3115
3116     Some(result)
3117 }
3118
3119 impl Rewrite for ast::ForeignItem {
3120     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
3121         let attrs_str = self.attrs.rewrite(context, shape)?;
3122         // Drop semicolon or it will be interpreted as comment.
3123         // FIXME: this may be a faulty span from libsyntax.
3124         let span = mk_sp(self.span.lo(), self.span.hi() - BytePos(1));
3125
3126         let item_str = match self.kind {
3127             ast::ForeignItemKind::Fn(ref fn_kind) => {
3128                 let ast::FnKind(defaultness, ref fn_sig, ref generics, ref block) = **fn_kind;
3129                 if let Some(ref body) = block {
3130                     let mut visitor = FmtVisitor::from_context(context);
3131                     visitor.block_indent = shape.indent;
3132                     visitor.last_pos = self.span.lo();
3133                     let inner_attrs = inner_attributes(&self.attrs);
3134                     let fn_ctxt = visit::FnCtxt::Foreign;
3135                     visitor.visit_fn(
3136                         visit::FnKind::Fn(fn_ctxt, self.ident, &fn_sig, &self.vis, Some(body)),
3137                         generics,
3138                         &fn_sig.decl,
3139                         self.span,
3140                         defaultness,
3141                         Some(&inner_attrs),
3142                     );
3143                     Some(visitor.buffer.to_owned())
3144                 } else {
3145                     rewrite_fn_base(
3146                         context,
3147                         shape.indent,
3148                         self.ident,
3149                         &FnSig::from_method_sig(&fn_sig, generics, &self.vis),
3150                         span,
3151                         FnBraceStyle::None,
3152                     )
3153                     .map(|(s, _, _)| format!("{};", s))
3154                 }
3155             }
3156             ast::ForeignItemKind::Static(ref ty, mutability, _) => {
3157                 // FIXME(#21): we're dropping potential comments in between the
3158                 // function kw here.
3159                 let vis = format_visibility(context, &self.vis);
3160                 let mut_str = format_mutability(mutability);
3161                 let prefix = format!(
3162                     "{}static {}{}:",
3163                     vis,
3164                     mut_str,
3165                     rewrite_ident(context, self.ident)
3166                 );
3167                 // 1 = ;
3168                 rewrite_assign_rhs(context, prefix, &**ty, shape.sub_width(1)?).map(|s| s + ";")
3169             }
3170             ast::ForeignItemKind::TyAlias(ref ty_alias_kind) => {
3171                 let ast::TyAliasKind(_, ref generics, ref generic_bounds, ref type_default) =
3172                     **ty_alias_kind;
3173                 rewrite_type(
3174                     &context,
3175                     shape.indent,
3176                     self.ident,
3177                     &self.vis,
3178                     generics,
3179                     Some(generic_bounds),
3180                     type_default.as_ref(),
3181                     self.span,
3182                 )
3183             }
3184             ast::ForeignItemKind::MacCall(ref mac) => {
3185                 rewrite_macro(mac, None, context, shape, MacroPosition::Item)
3186             }
3187         }?;
3188
3189         let missing_span = if self.attrs.is_empty() {
3190             mk_sp(self.span.lo(), self.span.lo())
3191         } else {
3192             mk_sp(self.attrs[self.attrs.len() - 1].span.hi(), self.span.lo())
3193         };
3194         combine_strs_with_missing_comments(
3195             context,
3196             &attrs_str,
3197             &item_str,
3198             missing_span,
3199             shape,
3200             false,
3201         )
3202     }
3203 }
3204
3205 /// Rewrite the attributes of an item.
3206 fn rewrite_attrs(
3207     context: &RewriteContext<'_>,
3208     item: &ast::Item,
3209     item_str: &str,
3210     shape: Shape,
3211 ) -> Option<String> {
3212     let attrs = filter_inline_attrs(&item.attrs, item.span());
3213     let attrs_str = attrs.rewrite(context, shape)?;
3214
3215     let missed_span = if attrs.is_empty() {
3216         mk_sp(item.span.lo(), item.span.lo())
3217     } else {
3218         mk_sp(attrs[attrs.len() - 1].span.hi(), item.span.lo())
3219     };
3220
3221     let allow_extend = if attrs.len() == 1 {
3222         let line_len = attrs_str.len() + 1 + item_str.len();
3223         !attrs.first().unwrap().is_doc_comment()
3224             && context.config.inline_attribute_width() >= line_len
3225     } else {
3226         false
3227     };
3228
3229     combine_strs_with_missing_comments(
3230         context,
3231         &attrs_str,
3232         &item_str,
3233         missed_span,
3234         shape,
3235         allow_extend,
3236     )
3237 }
3238
3239 /// Rewrite an inline mod.
3240 /// The given shape is used to format the mod's attributes.
3241 pub(crate) fn rewrite_mod(
3242     context: &RewriteContext<'_>,
3243     item: &ast::Item,
3244     attrs_shape: Shape,
3245 ) -> Option<String> {
3246     let mut result = String::with_capacity(32);
3247     result.push_str(&*format_visibility(context, &item.vis));
3248     result.push_str("mod ");
3249     result.push_str(rewrite_ident(context, item.ident));
3250     result.push(';');
3251     rewrite_attrs(context, item, &result, attrs_shape)
3252 }
3253
3254 /// Rewrite `extern crate foo;`.
3255 /// The given shape is used to format the extern crate's attributes.
3256 pub(crate) fn rewrite_extern_crate(
3257     context: &RewriteContext<'_>,
3258     item: &ast::Item,
3259     attrs_shape: Shape,
3260 ) -> Option<String> {
3261     assert!(is_extern_crate(item));
3262     let new_str = context.snippet(item.span);
3263     let item_str = if contains_comment(new_str) {
3264         new_str.to_owned()
3265     } else {
3266         let no_whitespace = &new_str.split_whitespace().collect::<Vec<&str>>().join(" ");
3267         String::from(&*Regex::new(r"\s;").unwrap().replace(no_whitespace, ";"))
3268     };
3269     rewrite_attrs(context, item, &item_str, attrs_shape)
3270 }
3271
3272 /// Returns `true` for `mod foo;`, false for `mod foo { .. }`.
3273 pub(crate) fn is_mod_decl(item: &ast::Item) -> bool {
3274     !matches!(
3275         item.kind,
3276         ast::ItemKind::Mod(_, ast::ModKind::Loaded(_, ast::Inline::Yes, _))
3277     )
3278 }
3279
3280 pub(crate) fn is_use_item(item: &ast::Item) -> bool {
3281     matches!(item.kind, ast::ItemKind::Use(_))
3282 }
3283
3284 pub(crate) fn is_extern_crate(item: &ast::Item) -> bool {
3285     matches!(item.kind, ast::ItemKind::ExternCrate(..))
3286 }