src/items.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // Formatting top-level items - functions, structs, enums, traits, impls.
  12
  13 use std::borrow::Cow;
  14 use std::cmp::{min, Ordering};
  15
  16 use config::lists::*;
  17 use regex::Regex;
  18 use rustc_target::spec::abi;
  19 use syntax::codemap::{self, BytePos, Span};
  20 use syntax::visit;
  21 use syntax::{ast, ptr, symbol};
  22
  23 use codemap::{LineRangeUtils, SpanUtils};
  24 use comment::{
  25     combine_strs_with_missing_comments, contains_comment, recover_comment_removed,
  26     recover_missing_comment_in_span, rewrite_missing_comment, FindUncommented,
  27 };
  28 use config::{BraceStyle, Config, Density, IndentStyle};
  29 use expr::{
  30     format_expr, is_empty_block, is_simple_block_stmt, rewrite_assign_rhs, rewrite_assign_rhs_with,
  31     ExprType, RhsTactics,
  32 };
  33 use lists::{definitive_tactic, itemize_list, write_list, ListFormatting, ListItem, Separator};
  34 use macros::{rewrite_macro, MacroPosition};
  35 use overflow;
  36 use rewrite::{Rewrite, RewriteContext};
  37 use shape::{Indent, Shape};
  38 use spanned::Spanned;
  39 use utils::*;
  40 use vertical::rewrite_with_alignment;
  41 use visitor::FmtVisitor;
  42
  43 const DEFAULT_VISIBILITY: ast::Visibility = codemap::Spanned {
  44     node: ast::VisibilityKind::Inherited,
  45     span: codemap::DUMMY_SP,
  46 };
  47
  48 fn type_annotation_separator(config: &Config) -> &str {
  49     colon_spaces(config.space_before_colon(), config.space_after_colon())
  50 }
  51
  52 // Statements of the form
  53 // let pat: ty = init;
  54 impl Rewrite for ast::Local {
  55     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  56         debug!(
  57             "Local::rewrite {:?} {} {:?}",
  58             self, shape.width, shape.indent
  59         );
  60
  61         skip_out_of_file_lines_range!(context, self.span);
  62
  63         if contains_skip(&self.attrs) {
  64             return None;
  65         }
  66
  67         let attrs_str = self.attrs.rewrite(context, shape)?;
  68         let mut result = if attrs_str.is_empty() {
  69             "let ".to_owned()
  70         } else {
  71             combine_strs_with_missing_comments(
  72                 context,
  73                 &attrs_str,
  74                 "let ",
  75                 mk_sp(
  76                     self.attrs.last().map(|a| a.span.hi()).unwrap(),
  77                     self.span.lo(),
  78                 ),
  79                 shape,
  80                 false,
  81             )?
  82         };
  83
  84         // 4 = "let ".len()
  85         let pat_shape = shape.offset_left(4)?;
  86         // 1 = ;
  87         let pat_shape = pat_shape.sub_width(1)?;
  88         let pat_str = self.pat.rewrite(context, pat_shape)?;
  89         result.push_str(&pat_str);
  90
  91         // String that is placed within the assignment pattern and expression.
  92         let infix = {
  93             let mut infix = String::with_capacity(32);
  94
  95             if let Some(ref ty) = self.ty {
  96                 let separator = type_annotation_separator(context.config);
  97                 let indent = shape.indent + last_line_width(&result) + separator.len();
  98                 // 1 = ;
  99                 let budget = shape.width.checked_sub(indent.width() + 1)?;
 100                 let rewrite = ty.rewrite(context, Shape::legacy(budget, indent))?;
 101
 102                 infix.push_str(separator);
 103                 infix.push_str(&rewrite);
 104             }
 105
 106             if self.init.is_some() {
 107                 infix.push_str(" =");
 108             }
 109
 110             infix
 111         };
 112
 113         result.push_str(&infix);
 114
 115         if let Some(ref ex) = self.init {
 116             // 1 = trailing semicolon;
 117             let nested_shape = shape.sub_width(1)?;
 118
 119             result = rewrite_assign_rhs(context, result, &**ex, nested_shape)?;
 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 struct Item<'a> {
 131     keyword: &'static str,
 132     abi: Cow<'static, str>,
 133     vis: Option<&'a ast::Visibility>,
 134     body: Vec<BodyElement<'a>>,
 135     span: Span,
 136 }
 137
 138 impl<'a> Item<'a> {
 139     fn from_foreign_mod(fm: &'a ast::ForeignMod, span: Span, config: &Config) -> Item<'a> {
 140         Item {
 141             keyword: "",
 142             abi: format_abi(fm.abi, config.force_explicit_abi(), true),
 143             vis: None,
 144             body: fm
 145                 .items
 146                 .iter()
 147                 .map(|i| BodyElement::ForeignItem(i))
 148                 .collect(),
 149             span,
 150         }
 151     }
 152 }
 153
 154 enum BodyElement<'a> {
 155     // Stmt(&'a ast::Stmt),
 156     // Field(&'a ast::Field),
 157     // Variant(&'a ast::Variant),
 158     // Item(&'a ast::Item),
 159     ForeignItem(&'a ast::ForeignItem),
 160 }
 161
 162 /// Represents a fn's signature.
 163 pub struct FnSig<'a> {
 164     decl: &'a ast::FnDecl,
 165     generics: &'a ast::Generics,
 166     abi: abi::Abi,
 167     constness: ast::Constness,
 168     defaultness: ast::Defaultness,
 169     unsafety: ast::Unsafety,
 170     visibility: ast::Visibility,
 171 }
 172
 173 impl<'a> FnSig<'a> {
 174     pub fn new(
 175         decl: &'a ast::FnDecl,
 176         generics: &'a ast::Generics,
 177         vis: ast::Visibility,
 178     ) -> FnSig<'a> {
 179         FnSig {
 180             decl,
 181             generics,
 182             abi: abi::Abi::Rust,
 183             constness: ast::Constness::NotConst,
 184             defaultness: ast::Defaultness::Final,
 185             unsafety: ast::Unsafety::Normal,
 186             visibility: vis,
 187         }
 188     }
 189
 190     pub fn from_method_sig(
 191         method_sig: &'a ast::MethodSig,
 192         generics: &'a ast::Generics,
 193     ) -> FnSig<'a> {
 194         FnSig {
 195             unsafety: method_sig.header.unsafety,
 196             constness: method_sig.header.constness.node,
 197             defaultness: ast::Defaultness::Final,
 198             abi: method_sig.header.abi,
 199             decl: &*method_sig.decl,
 200             generics,
 201             visibility: DEFAULT_VISIBILITY,
 202         }
 203     }
 204
 205     pub fn from_fn_kind(
 206         fn_kind: &'a visit::FnKind,
 207         generics: &'a ast::Generics,
 208         decl: &'a ast::FnDecl,
 209         defaultness: ast::Defaultness,
 210     ) -> FnSig<'a> {
 211         match *fn_kind {
 212             visit::FnKind::ItemFn(_, fn_header, visibility, _) => FnSig {
 213                 decl,
 214                 generics,
 215                 abi: fn_header.abi,
 216                 constness: fn_header.constness.node,
 217                 defaultness,
 218                 unsafety: fn_header.unsafety,
 219                 visibility: visibility.clone(),
 220             },
 221             visit::FnKind::Method(_, method_sig, vis, _) => {
 222                 let mut fn_sig = FnSig::from_method_sig(method_sig, generics);
 223                 fn_sig.defaultness = defaultness;
 224                 if let Some(vis) = vis {
 225                     fn_sig.visibility = vis.clone();
 226                 }
 227                 fn_sig
 228             }
 229             _ => unreachable!(),
 230         }
 231     }
 232
 233     fn to_str(&self, context: &RewriteContext) -> String {
 234         let mut result = String::with_capacity(128);
 235         // Vis defaultness constness unsafety abi.
 236         result.push_str(&*format_visibility(context, &self.visibility));
 237         result.push_str(format_defaultness(self.defaultness));
 238         result.push_str(format_constness(self.constness));
 239         result.push_str(format_unsafety(self.unsafety));
 240         result.push_str(&format_abi(
 241             self.abi,
 242             context.config.force_explicit_abi(),
 243             false,
 244         ));
 245         result
 246     }
 247 }
 248
 249 impl<'a> FmtVisitor<'a> {
 250     fn format_item(&mut self, item: &Item) {
 251         self.buffer.push_str(&item.abi);
 252
 253         let snippet = self.snippet(item.span);
 254         let brace_pos = snippet.find_uncommented("{").unwrap();
 255
 256         self.push_str("{");
 257         if !item.body.is_empty() || contains_comment(&snippet[brace_pos..]) {
 258             // FIXME: this skips comments between the extern keyword and the opening
 259             // brace.
 260             self.last_pos = item.span.lo() + BytePos(brace_pos as u32 + 1);
 261             self.block_indent = self.block_indent.block_indent(self.config);
 262
 263             if item.body.is_empty() {
 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             } else {
 269                 for item in &item.body {
 270                     self.format_body_element(item);
 271                 }
 272
 273                 self.block_indent = self.block_indent.block_unindent(self.config);
 274                 self.format_missing_with_indent(item.span.hi() - BytePos(1));
 275             }
 276         }
 277
 278         self.push_str("}");
 279         self.last_pos = item.span.hi();
 280     }
 281
 282     fn format_body_element(&mut self, element: &BodyElement) {
 283         match *element {
 284             BodyElement::ForeignItem(item) => self.format_foreign_item(item),
 285         }
 286     }
 287
 288     pub fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
 289         let item = Item::from_foreign_mod(fm, span, self.config);
 290         self.format_item(&item);
 291     }
 292
 293     fn format_foreign_item(&mut self, item: &ast::ForeignItem) {
 294         let rewrite = item.rewrite(&self.get_context(), self.shape());
 295         self.push_rewrite(item.span(), rewrite);
 296         self.last_pos = item.span.hi();
 297     }
 298
 299     pub fn rewrite_fn(
 300         &mut self,
 301         indent: Indent,
 302         ident: ast::Ident,
 303         fn_sig: &FnSig,
 304         span: Span,
 305         block: &ast::Block,
 306         inner_attrs: Option<&[ast::Attribute]>,
 307     ) -> Option<String> {
 308         let context = self.get_context();
 309
 310         let mut newline_brace = newline_for_brace(self.config, &fn_sig.generics.where_clause);
 311
 312         let (mut result, force_newline_brace) =
 313             rewrite_fn_base(&context, indent, ident, fn_sig, span, newline_brace, true)?;
 314
 315         // 2 = ` {`
 316         if self.config.brace_style() == BraceStyle::AlwaysNextLine
 317             || force_newline_brace
 318             || last_line_width(&result) + 2 > self.shape().width
 319         {
 320             newline_brace = true;
 321         } else if !result.contains('\n') {
 322             newline_brace = false;
 323         }
 324
 325         // Prepare for the function body by possibly adding a newline and
 326         // indent.
 327         // FIXME we'll miss anything between the end of the signature and the
 328         // start of the body, but we need more spans from the compiler to solve
 329         // this.
 330         if newline_brace {
 331             result.push_str(&indent.to_string_with_newline(self.config));
 332         } else {
 333             result.push(' ');
 334         }
 335
 336         self.single_line_fn(&result, block, inner_attrs)
 337             .or_else(|| Some(result))
 338     }
 339
 340     pub fn rewrite_required_fn(
 341         &mut self,
 342         indent: Indent,
 343         ident: ast::Ident,
 344         sig: &ast::MethodSig,
 345         generics: &ast::Generics,
 346         span: Span,
 347     ) -> Option<String> {
 348         // Drop semicolon or it will be interpreted as comment.
 349         let span = mk_sp(span.lo(), span.hi() - BytePos(1));
 350         let context = self.get_context();
 351
 352         let (mut result, _) = rewrite_fn_base(
 353             &context,
 354             indent,
 355             ident,
 356             &FnSig::from_method_sig(sig, generics),
 357             span,
 358             false,
 359             false,
 360         )?;
 361
 362         // Re-attach semicolon
 363         result.push(';');
 364
 365         Some(result)
 366     }
 367
 368     fn single_line_fn(
 369         &self,
 370         fn_str: &str,
 371         block: &ast::Block,
 372         inner_attrs: Option<&[ast::Attribute]>,
 373     ) -> Option<String> {
 374         if fn_str.contains('\n') || inner_attrs.map_or(false, |a| !a.is_empty()) {
 375             return None;
 376         }
 377
 378         let codemap = self.get_context().codemap;
 379
 380         if self.config.empty_item_single_line()
 381             && is_empty_block(block, None, codemap)
 382             && self.block_indent.width() + fn_str.len() + 2 <= self.config.max_width()
 383         {
 384             return Some(format!("{}{{}}", fn_str));
 385         }
 386
 387         if self.config.fn_single_line() && is_simple_block_stmt(block, None, codemap) {
 388             let rewrite = {
 389                 if let Some(stmt) = block.stmts.first() {
 390                     match stmt_expr(stmt) {
 391                         Some(e) => {
 392                             let suffix = if semicolon_for_expr(&self.get_context(), e) {
 393                                 ";"
 394                             } else {
 395                                 ""
 396                             };
 397
 398                             format_expr(e, ExprType::Statement, &self.get_context(), self.shape())
 399                                 .map(|s| s + suffix)
 400                                 .or_else(|| Some(self.snippet(e.span).to_owned()))
 401                         }
 402                         None => stmt.rewrite(&self.get_context(), self.shape()),
 403                     }
 404                 } else {
 405                     None
 406                 }
 407             };
 408
 409             if let Some(res) = rewrite {
 410                 let width = self.block_indent.width() + fn_str.len() + res.len() + 4;
 411                 if !res.contains('\n') && width <= self.config.max_width() {
 412                     return Some(format!("{}{{ {} }}", fn_str, res));
 413                 }
 414             }
 415         }
 416
 417         None
 418     }
 419
 420     pub fn visit_static(&mut self, static_parts: &StaticParts) {
 421         let rewrite = rewrite_static(&self.get_context(), static_parts, self.block_indent);
 422         self.push_rewrite(static_parts.span, rewrite);
 423     }
 424
 425     pub fn visit_struct(&mut self, struct_parts: &StructParts) {
 426         let is_tuple = struct_parts.def.is_tuple();
 427         let rewrite = format_struct(&self.get_context(), struct_parts, self.block_indent, None)
 428             .map(|s| if is_tuple { s + ";" } else { s });
 429         self.push_rewrite(struct_parts.span, rewrite);
 430     }
 431
 432     pub fn visit_enum(
 433         &mut self,
 434         ident: ast::Ident,
 435         vis: &ast::Visibility,
 436         enum_def: &ast::EnumDef,
 437         generics: &ast::Generics,
 438         span: Span,
 439     ) {
 440         let enum_header = format_header(&self.get_context(), "enum ", ident, vis);
 441         self.push_str(&enum_header);
 442
 443         let enum_snippet = self.snippet(span);
 444         let brace_pos = enum_snippet.find_uncommented("{").unwrap();
 445         let body_start = span.lo() + BytePos(brace_pos as u32 + 1);
 446         let generics_str = format_generics(
 447             &self.get_context(),
 448             generics,
 449             self.config.brace_style(),
 450             if enum_def.variants.is_empty() {
 451                 BracePos::ForceSameLine
 452             } else {
 453                 BracePos::Auto
 454             },
 455             self.block_indent,
 456             mk_sp(span.lo(), body_start),
 457             last_line_width(&enum_header),
 458         ).unwrap();
 459         self.push_str(&generics_str);
 460
 461         self.last_pos = body_start;
 462
 463         match self.format_variant_list(enum_def, body_start, span.hi()) {
 464             Some(ref s) if enum_def.variants.is_empty() => self.push_str(s),
 465             rw => {
 466                 self.push_rewrite(mk_sp(body_start, span.hi()), rw);
 467                 self.block_indent = self.block_indent.block_unindent(self.config);
 468             }
 469         }
 470     }
 471
 472     // Format the body of an enum definition
 473     fn format_variant_list(
 474         &mut self,
 475         enum_def: &ast::EnumDef,
 476         body_lo: BytePos,
 477         body_hi: BytePos,
 478     ) -> Option<String> {
 479         if enum_def.variants.is_empty() {
 480             let mut buffer = String::with_capacity(128);
 481             // 1 = "}"
 482             let span = mk_sp(body_lo, body_hi - BytePos(1));
 483             format_empty_struct_or_tuple(
 484                 &self.get_context(),
 485                 span,
 486                 self.block_indent,
 487                 &mut buffer,
 488                 "",
 489                 "}",
 490             );
 491             return Some(buffer);
 492         }
 493         let mut result = String::with_capacity(1024);
 494         let original_offset = self.block_indent;
 495         self.block_indent = self.block_indent.block_indent(self.config);
 496
 497         let itemize_list_with = |one_line_width: usize| {
 498             itemize_list(
 499                 self.snippet_provider,
 500                 enum_def.variants.iter(),
 501                 "}",
 502                 ",",
 503                 |f| {
 504                     if !f.node.attrs.is_empty() {
 505                         f.node.attrs[0].span.lo()
 506                     } else {
 507                         f.span.lo()
 508                     }
 509                 },
 510                 |f| f.span.hi(),
 511                 |f| self.format_variant(f, one_line_width),
 512                 body_lo,
 513                 body_hi,
 514                 false,
 515             ).collect()
 516         };
 517         let mut items: Vec<_> =
 518             itemize_list_with(self.config.width_heuristics().struct_variant_width);
 519         // If one of the variants use multiple lines, use multi-lined formatting for all variants.
 520         let has_multiline_variant = items.iter().any(|item| item.inner_as_ref().contains('\n'));
 521         let has_single_line_variant = items.iter().any(|item| !item.inner_as_ref().contains('\n'));
 522         if has_multiline_variant && has_single_line_variant {
 523             items = itemize_list_with(0);
 524         }
 525
 526         let shape = self.shape().sub_width(2)?;
 527         let fmt = ListFormatting {
 528             tactic: DefinitiveListTactic::Vertical,
 529             separator: ",",
 530             trailing_separator: self.config.trailing_comma(),
 531             separator_place: SeparatorPlace::Back,
 532             shape,
 533             ends_with_newline: true,
 534             preserve_newline: true,
 535             nested: false,
 536             config: self.config,
 537         };
 538
 539         let list = write_list(&items, &fmt)?;
 540         result.push_str(&list);
 541         result.push_str(&original_offset.to_string_with_newline(self.config));
 542         result.push('}');
 543         Some(result)
 544     }
 545
 546     // Variant of an enum.
 547     fn format_variant(&self, field: &ast::Variant, one_line_width: usize) -> Option<String> {
 548         if contains_skip(&field.node.attrs) {
 549             let lo = field.node.attrs[0].span.lo();
 550             let span = mk_sp(lo, field.span.hi());
 551             return Some(self.snippet(span).to_owned());
 552         }
 553
 554         let context = self.get_context();
 555         // 1 = ','
 556         let shape = self.shape().sub_width(1)?;
 557         let attrs_str = field.node.attrs.rewrite(&context, shape)?;
 558         let lo = field
 559             .node
 560             .attrs
 561             .last()
 562             .map_or(field.span.lo(), |attr| attr.span.hi());
 563         let span = mk_sp(lo, field.span.lo());
 564
 565         let variant_body = match field.node.data {
 566             ast::VariantData::Tuple(..) | ast::VariantData::Struct(..) => format_struct(
 567                 &context,
 568                 &StructParts::from_variant(field),
 569                 self.block_indent,
 570                 Some(one_line_width),
 571             )?,
 572             ast::VariantData::Unit(..) => {
 573                 if let Some(ref expr) = field.node.disr_expr {
 574                     let lhs = format!("{} =", rewrite_ident(&context, field.node.ident));
 575                     rewrite_assign_rhs(&context, lhs, &*expr.value, shape)?
 576                 } else {
 577                     rewrite_ident(&context, field.node.ident).to_owned()
 578                 }
 579             }
 580         };
 581
 582         combine_strs_with_missing_comments(&context, &attrs_str, &variant_body, span, shape, false)
 583     }
 584
 585     fn visit_impl_items(&mut self, items: &[ast::ImplItem]) {
 586         if self.get_context().config.reorder_impl_items() {
 587             // Create visitor for each items, then reorder them.
 588             let mut buffer = vec![];
 589             for item in items {
 590                 self.visit_impl_item(item);
 591                 buffer.push((self.buffer.clone(), item.clone()));
 592                 self.buffer.clear();
 593             }
 594             // type -> const -> macro -> method
 595             use ast::ImplItemKind::*;
 596             fn need_empty_line(a: &ast::ImplItemKind, b: &ast::ImplItemKind) -> bool {
 597                 match (a, b) {
 598                     (Type(..), Type(..)) | (Const(..), Const(..)) => false,
 599                     _ => true,
 600                 }
 601             }
 602
 603             buffer.sort_by(|(_, a), (_, b)| match (&a.node, &b.node) {
 604                 (Type(..), _) => Ordering::Less,
 605                 (_, Type(..)) => Ordering::Greater,
 606                 (Const(..), _) => Ordering::Less,
 607                 (_, Const(..)) => Ordering::Greater,
 608                 (Macro(..), _) => Ordering::Less,
 609                 (_, Macro(..)) => Ordering::Greater,
 610                 _ => a.span.lo().cmp(&b.span.lo()),
 611             });
 612             let mut prev_kind = None;
 613             for (buf, item) in buffer {
 614                 // Make sure that there are at least a single empty line between
 615                 // different impl items.
 616                 if prev_kind
 617                     .as_ref()
 618                     .map_or(false, |prev_kind| need_empty_line(prev_kind, &item.node))
 619                 {
 620                     self.push_str("\n");
 621                 }
 622                 let indent_str = self.block_indent.to_string_with_newline(self.config);
 623                 self.push_str(&indent_str);
 624                 self.push_str(buf.trim());
 625                 prev_kind = Some(item.node.clone());
 626             }
 627         } else {
 628             for item in items {
 629                 self.visit_impl_item(item);
 630             }
 631         }
 632     }
 633 }
 634
 635 pub fn format_impl(
 636     context: &RewriteContext,
 637     item: &ast::Item,
 638     offset: Indent,
 639     where_span_end: Option<BytePos>,
 640 ) -> Option<String> {
 641     if let ast::ItemKind::Impl(_, _, _, ref generics, _, ref self_ty, ref items) = item.node {
 642         let mut result = String::with_capacity(128);
 643         let ref_and_type = format_impl_ref_and_type(context, item, offset)?;
 644         let sep = offset.to_string_with_newline(context.config);
 645         result.push_str(&ref_and_type);
 646
 647         let where_budget = if result.contains('\n') {
 648             context.config.max_width()
 649         } else {
 650             context.budget(last_line_width(&result))
 651         };
 652
 653         let mut option = WhereClauseOption::snuggled(&ref_and_type);
 654         let snippet = context.snippet(item.span);
 655         let open_pos = snippet.find_uncommented("{")? + 1;
 656         if !contains_comment(&snippet[open_pos..])
 657             && items.is_empty()
 658             && generics.where_clause.predicates.len() == 1
 659             && !result.contains('\n')
 660         {
 661             option.suppress_comma();
 662             option.snuggle();
 663             option.compress_where();
 664         }
 665
 666         let where_clause_str = rewrite_where_clause(
 667             context,
 668             &generics.where_clause,
 669             context.config.brace_style(),
 670             Shape::legacy(where_budget, offset.block_only()),
 671             Density::Vertical,
 672             "{",
 673             where_span_end,
 674             self_ty.span.hi(),
 675             option,
 676             false,
 677         )?;
 678
 679         // If there is no where clause, we may have missing comments between the trait name and
 680         // the opening brace.
 681         if generics.where_clause.predicates.is_empty() {
 682             if let Some(hi) = where_span_end {
 683                 match recover_missing_comment_in_span(
 684                     mk_sp(self_ty.span.hi(), hi),
 685                     Shape::indented(offset, context.config),
 686                     context,
 687                     last_line_width(&result),
 688                 ) {
 689                     Some(ref missing_comment) if !missing_comment.is_empty() => {
 690                         result.push_str(missing_comment);
 691                     }
 692                     _ => (),
 693                 }
 694             }
 695         }
 696
 697         if is_impl_single_line(context, items, &result, &where_clause_str, item)? {
 698             result.push_str(&where_clause_str);
 699             if where_clause_str.contains('\n') || last_line_contains_single_line_comment(&result) {
 700                 // if the where_clause contains extra comments AND
 701                 // there is only one where clause predicate
 702                 // recover the suppressed comma in single line where_clause formatting
 703                 if generics.where_clause.predicates.len() == 1 {
 704                     result.push_str(",");
 705                 }
 706                 result.push_str(&format!("{}{{{}}}", &sep, &sep));
 707             } else {
 708                 result.push_str(" {}");
 709             }
 710             return Some(result);
 711         }
 712
 713         result.push_str(&where_clause_str);
 714
 715         let need_newline = last_line_contains_single_line_comment(&result) || result.contains('\n');
 716         match context.config.brace_style() {
 717             _ if need_newline => result.push_str(&sep),
 718             BraceStyle::AlwaysNextLine => result.push_str(&sep),
 719             BraceStyle::PreferSameLine => result.push(' '),
 720             BraceStyle::SameLineWhere => {
 721                 if !where_clause_str.is_empty() {
 722                     result.push_str(&sep);
 723                 } else {
 724                     result.push(' ');
 725                 }
 726             }
 727         }
 728
 729         result.push('{');
 730
 731         let snippet = context.snippet(item.span);
 732         let open_pos = snippet.find_uncommented("{")? + 1;
 733
 734         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 735             let mut visitor = FmtVisitor::from_context(context);
 736             let item_indent = offset.block_only().block_indent(context.config);
 737             visitor.block_indent = item_indent;
 738             visitor.last_pos = item.span.lo() + BytePos(open_pos as u32);
 739
 740             visitor.visit_attrs(&item.attrs, ast::AttrStyle::Inner);
 741             visitor.visit_impl_items(items);
 742
 743             visitor.format_missing(item.span.hi() - BytePos(1));
 744
 745             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
 746             let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
 747
 748             result.push_str(&inner_indent_str);
 749             result.push_str(visitor.buffer.to_string().trim());
 750             result.push_str(&outer_indent_str);
 751         }
 752
 753         if result.ends_with('{') && !context.config.empty_item_single_line() {
 754             result.push_str(&sep);
 755         }
 756         result.push('}');
 757
 758         Some(result)
 759     } else {
 760         unreachable!();
 761     }
 762 }
 763
 764 fn is_impl_single_line(
 765     context: &RewriteContext,
 766     items: &[ast::ImplItem],
 767     result: &str,
 768     where_clause_str: &str,
 769     item: &ast::Item,
 770 ) -> Option<bool> {
 771     let snippet = context.snippet(item.span);
 772     let open_pos = snippet.find_uncommented("{")? + 1;
 773
 774     Some(
 775         context.config.empty_item_single_line()
 776             && items.is_empty()
 777             && !result.contains('\n')
 778             && result.len() + where_clause_str.len() <= context.config.max_width()
 779             && !contains_comment(&snippet[open_pos..]),
 780     )
 781 }
 782
 783 fn format_impl_ref_and_type(
 784     context: &RewriteContext,
 785     item: &ast::Item,
 786     offset: Indent,
 787 ) -> Option<String> {
 788     if let ast::ItemKind::Impl(
 789         unsafety,
 790         polarity,
 791         defaultness,
 792         ref generics,
 793         ref trait_ref,
 794         ref self_ty,
 795         _,
 796     ) = item.node
 797     {
 798         let mut result = String::with_capacity(128);
 799
 800         result.push_str(&format_visibility(context, &item.vis));
 801         result.push_str(format_defaultness(defaultness));
 802         result.push_str(format_unsafety(unsafety));
 803
 804         let lo = context.snippet_provider.span_after(item.span, "impl");
 805         let hi = match *trait_ref {
 806             Some(ref tr) => tr.path.span.lo(),
 807             None => self_ty.span.lo(),
 808         };
 809         let shape = generics_shape_from_config(
 810             context.config,
 811             Shape::indented(offset + last_line_width(&result), context.config),
 812             0,
 813         )?;
 814         let generics_str = rewrite_generics(context, "impl", generics, shape, mk_sp(lo, hi))?;
 815         result.push_str(&generics_str);
 816
 817         let polarity_str = if polarity == ast::ImplPolarity::Negative {
 818             "!"
 819         } else {
 820             ""
 821         };
 822
 823         if let Some(ref trait_ref) = *trait_ref {
 824             let result_len = last_line_width(&result);
 825             result.push_str(&rewrite_trait_ref(
 826                 context,
 827                 trait_ref,
 828                 offset,
 829                 polarity_str,
 830                 result_len,
 831             )?);
 832         }
 833
 834         // Try to put the self type in a single line.
 835         // ` for`
 836         let trait_ref_overhead = if trait_ref.is_some() { 4 } else { 0 };
 837         let curly_brace_overhead = if generics.where_clause.predicates.is_empty() {
 838             // If there is no where clause adapt budget for type formatting to take space and curly
 839             // brace into account.
 840             match context.config.brace_style() {
 841                 BraceStyle::AlwaysNextLine => 0,
 842                 _ => 2,
 843             }
 844         } else {
 845             0
 846         };
 847         let used_space = last_line_width(&result) + trait_ref_overhead + curly_brace_overhead;
 848         // 1 = space before the type.
 849         let budget = context.budget(used_space + 1);
 850         if let Some(self_ty_str) = self_ty.rewrite(context, Shape::legacy(budget, offset)) {
 851             if !self_ty_str.contains('\n') {
 852                 if trait_ref.is_some() {
 853                     result.push_str(" for ");
 854                 } else {
 855                     result.push(' ');
 856                 }
 857                 result.push_str(&self_ty_str);
 858                 return Some(result);
 859             }
 860         }
 861
 862         // Couldn't fit the self type on a single line, put it on a new line.
 863         result.push('\n');
 864         // Add indentation of one additional tab.
 865         let new_line_offset = offset.block_indent(context.config);
 866         result.push_str(&new_line_offset.to_string(context.config));
 867         if trait_ref.is_some() {
 868             result.push_str("for ");
 869         }
 870         let budget = context.budget(last_line_width(&result));
 871         let type_offset = match context.config.indent_style() {
 872             IndentStyle::Visual => new_line_offset + trait_ref_overhead,
 873             IndentStyle::Block => new_line_offset,
 874         };
 875         result.push_str(&*self_ty.rewrite(context, Shape::legacy(budget, type_offset))?);
 876         Some(result)
 877     } else {
 878         unreachable!();
 879     }
 880 }
 881
 882 fn rewrite_trait_ref(
 883     context: &RewriteContext,
 884     trait_ref: &ast::TraitRef,
 885     offset: Indent,
 886     polarity_str: &str,
 887     result_len: usize,
 888 ) -> Option<String> {
 889     // 1 = space between generics and trait_ref
 890     let used_space = 1 + polarity_str.len() + result_len;
 891     let shape = Shape::indented(offset + used_space, context.config);
 892     if let Some(trait_ref_str) = trait_ref.rewrite(context, shape) {
 893         if !trait_ref_str.contains('\n') {
 894             return Some(format!(" {}{}", polarity_str, &trait_ref_str));
 895         }
 896     }
 897     // We could not make enough space for trait_ref, so put it on new line.
 898     let offset = offset.block_indent(context.config);
 899     let shape = Shape::indented(offset, context.config);
 900     let trait_ref_str = trait_ref.rewrite(context, shape)?;
 901     Some(format!(
 902         "{}{}{}",
 903         &offset.to_string_with_newline(context.config),
 904         polarity_str,
 905         &trait_ref_str
 906     ))
 907 }
 908
 909 pub struct StructParts<'a> {
 910     prefix: &'a str,
 911     ident: ast::Ident,
 912     vis: &'a ast::Visibility,
 913     def: &'a ast::VariantData,
 914     generics: Option<&'a ast::Generics>,
 915     span: Span,
 916 }
 917
 918 impl<'a> StructParts<'a> {
 919     fn format_header(&self, context: &RewriteContext) -> String {
 920         format_header(context, self.prefix, self.ident, self.vis)
 921     }
 922
 923     fn from_variant(variant: &'a ast::Variant) -> Self {
 924         StructParts {
 925             prefix: "",
 926             ident: variant.node.ident,
 927             vis: &DEFAULT_VISIBILITY,
 928             def: &variant.node.data,
 929             generics: None,
 930             span: variant.span,
 931         }
 932     }
 933
 934     pub fn from_item(item: &'a ast::Item) -> Self {
 935         let (prefix, def, generics) = match item.node {
 936             ast::ItemKind::Struct(ref def, ref generics) => ("struct ", def, generics),
 937             ast::ItemKind::Union(ref def, ref generics) => ("union ", def, generics),
 938             _ => unreachable!(),
 939         };
 940         StructParts {
 941             prefix,
 942             ident: item.ident,
 943             vis: &item.vis,
 944             def,
 945             generics: Some(generics),
 946             span: item.span,
 947         }
 948     }
 949 }
 950
 951 fn format_struct(
 952     context: &RewriteContext,
 953     struct_parts: &StructParts,
 954     offset: Indent,
 955     one_line_width: Option<usize>,
 956 ) -> Option<String> {
 957     match *struct_parts.def {
 958         ast::VariantData::Unit(..) => format_unit_struct(context, struct_parts, offset),
 959         ast::VariantData::Tuple(ref fields, _) => {
 960             format_tuple_struct(context, struct_parts, fields, offset)
 961         }
 962         ast::VariantData::Struct(ref fields, _) => {
 963             format_struct_struct(context, struct_parts, fields, offset, one_line_width)
 964         }
 965     }
 966 }
 967
 968 pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 969     if let ast::ItemKind::Trait(
 970         is_auto,
 971         unsafety,
 972         ref generics,
 973         ref generic_bounds,
 974         ref trait_items,
 975     ) = item.node
 976     {
 977         let mut result = String::with_capacity(128);
 978         let header = format!(
 979             "{}{}{}trait ",
 980             format_visibility(context, &item.vis),
 981             format_unsafety(unsafety),
 982             format_auto(is_auto),
 983         );
 984         result.push_str(&header);
 985
 986         let body_lo = context.snippet_provider.span_after(item.span, "{");
 987
 988         let shape = Shape::indented(offset, context.config).offset_left(result.len())?;
 989         let generics_str = rewrite_generics(
 990             context,
 991             rewrite_ident(context, item.ident),
 992             generics,
 993             shape,
 994             mk_sp(item.span.lo(), body_lo),
 995         )?;
 996         result.push_str(&generics_str);
 997
 998         // FIXME(#2055): rustfmt fails to format when there are comments between trait bounds.
 999         if !generic_bounds.is_empty() {
1000             let ident_hi = context
1001                 .snippet_provider
1002                 .span_after(item.span, &item.ident.as_str());
1003             let bound_hi = generic_bounds.last().unwrap().span().hi();
1004             let snippet = context.snippet(mk_sp(ident_hi, bound_hi));
1005             if contains_comment(snippet) {
1006                 return None;
1007             }
1008
1009             result = rewrite_assign_rhs_with(
1010                 context,
1011                 result + ":",
1012                 generic_bounds,
1013                 shape,
1014                 RhsTactics::ForceNextLineWithoutIndent,
1015             )?;
1016         }
1017
1018         // Rewrite where clause.
1019         if !generics.where_clause.predicates.is_empty() {
1020             let where_density = if context.config.indent_style() == IndentStyle::Block {
1021                 Density::Compressed
1022             } else {
1023                 Density::Tall
1024             };
1025
1026             let where_budget = context.budget(last_line_width(&result));
1027             let pos_before_where = if generic_bounds.is_empty() {
1028                 generics.where_clause.span.lo()
1029             } else {
1030                 generic_bounds[generic_bounds.len() - 1].span().hi()
1031             };
1032             let option = WhereClauseOption::snuggled(&generics_str);
1033             let where_clause_str = rewrite_where_clause(
1034                 context,
1035                 &generics.where_clause,
1036                 context.config.brace_style(),
1037                 Shape::legacy(where_budget, offset.block_only()),
1038                 where_density,
1039                 "{",
1040                 None,
1041                 pos_before_where,
1042                 option,
1043                 false,
1044             )?;
1045             // If the where clause cannot fit on the same line,
1046             // put the where clause on a new line
1047             if !where_clause_str.contains('\n')
1048                 && last_line_width(&result) + where_clause_str.len() + offset.width()
1049                     > context.config.comment_width()
1050             {
1051                 let width = offset.block_indent + context.config.tab_spaces() - 1;
1052                 let where_indent = Indent::new(0, width);
1053                 result.push_str(&where_indent.to_string_with_newline(context.config));
1054             }
1055             result.push_str(&where_clause_str);
1056         } else {
1057             let item_snippet = context.snippet(item.span);
1058             if let Some(lo) = item_snippet.find('/') {
1059                 // 1 = `{`
1060                 let comment_hi = body_lo - BytePos(1);
1061                 let comment_lo = item.span.lo() + BytePos(lo as u32);
1062                 if comment_lo < comment_hi {
1063                     match recover_missing_comment_in_span(
1064                         mk_sp(comment_lo, comment_hi),
1065                         Shape::indented(offset, context.config),
1066                         context,
1067                         last_line_width(&result),
1068                     ) {
1069                         Some(ref missing_comment) if !missing_comment.is_empty() => {
1070                             result.push_str(missing_comment);
1071                         }
1072                         _ => (),
1073                     }
1074                 }
1075             }
1076         }
1077
1078         match context.config.brace_style() {
1079             _ if last_line_contains_single_line_comment(&result)
1080                 || last_line_width(&result) + 2 > context.budget(offset.width()) =>
1081             {
1082                 result.push_str(&offset.to_string_with_newline(context.config));
1083             }
1084             BraceStyle::AlwaysNextLine => {
1085                 result.push_str(&offset.to_string_with_newline(context.config));
1086             }
1087             BraceStyle::PreferSameLine => result.push(' '),
1088             BraceStyle::SameLineWhere => {
1089                 if result.contains('\n')
1090                     || (!generics.where_clause.predicates.is_empty() && !trait_items.is_empty())
1091                 {
1092                     result.push_str(&offset.to_string_with_newline(context.config));
1093                 } else {
1094                     result.push(' ');
1095                 }
1096             }
1097         }
1098         result.push('{');
1099
1100         let snippet = context.snippet(item.span);
1101         let open_pos = snippet.find_uncommented("{")? + 1;
1102
1103         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
1104             let mut visitor = FmtVisitor::from_context(context);
1105             visitor.block_indent = offset.block_only().block_indent(context.config);
1106             visitor.last_pos = item.span.lo() + BytePos(open_pos as u32);
1107
1108             for item in trait_items {
1109                 visitor.visit_trait_item(item);
1110             }
1111
1112             visitor.format_missing(item.span.hi() - BytePos(1));
1113
1114             let inner_indent_str = visitor.block_indent.to_string_with_newline(context.config);
1115             let outer_indent_str = offset.block_only().to_string_with_newline(context.config);
1116
1117             result.push_str(&inner_indent_str);
1118             result.push_str(visitor.buffer.to_string().trim());
1119             result.push_str(&outer_indent_str);
1120         } else if result.contains('\n') {
1121             result.push('\n');
1122         }
1123
1124         result.push('}');
1125         Some(result)
1126     } else {
1127         unreachable!();
1128     }
1129 }
1130
1131 pub fn format_trait_alias(
1132     context: &RewriteContext,
1133     ident: ast::Ident,
1134     generics: &ast::Generics,
1135     generic_bounds: &ast::GenericBounds,
1136     shape: Shape,
1137 ) -> Option<String> {
1138     let alias = rewrite_ident(context, ident);
1139     // 6 = "trait ", 2 = " ="
1140     let g_shape = shape.offset_left(6)?.sub_width(2)?;
1141     let generics_str = rewrite_generics(context, &alias, generics, g_shape, generics.span)?;
1142     let lhs = format!("trait {} =", generics_str);
1143     // 1 = ";"
1144     rewrite_assign_rhs(context, lhs, generic_bounds, shape.sub_width(1)?).map(|s| s + ";")
1145 }
1146
1147 fn format_unit_struct(context: &RewriteContext, p: &StructParts, offset: Indent) -> Option<String> {
1148     let header_str = format_header(context, p.prefix, p.ident, p.vis);
1149     let generics_str = if let Some(generics) = p.generics {
1150         let hi = if generics.where_clause.predicates.is_empty() {
1151             generics.span.hi()
1152         } else {
1153             generics.where_clause.span.hi()
1154         };
1155         format_generics(
1156             context,
1157             generics,
1158             context.config.brace_style(),
1159             BracePos::None,
1160             offset,
1161             mk_sp(generics.span.lo(), hi),
1162             last_line_width(&header_str),
1163         )?
1164     } else {
1165         String::new()
1166     };
1167     Some(format!("{}{};", header_str, generics_str))
1168 }
1169
1170 pub fn format_struct_struct(
1171     context: &RewriteContext,
1172     struct_parts: &StructParts,
1173     fields: &[ast::StructField],
1174     offset: Indent,
1175     one_line_width: Option<usize>,
1176 ) -> Option<String> {
1177     let mut result = String::with_capacity(1024);
1178     let span = struct_parts.span;
1179
1180     let header_str = struct_parts.format_header(context);
1181     result.push_str(&header_str);
1182
1183     let header_hi = span.lo() + BytePos(header_str.len() as u32);
1184     let body_lo = context.snippet_provider.span_after(span, "{");
1185
1186     let generics_str = match struct_parts.generics {
1187         Some(g) => format_generics(
1188             context,
1189             g,
1190             context.config.brace_style(),
1191             if fields.is_empty() {
1192                 BracePos::ForceSameLine
1193             } else {
1194                 BracePos::Auto
1195             },
1196             offset,
1197             mk_sp(header_hi, body_lo),
1198             last_line_width(&result),
1199         )?,
1200         None => {
1201             // 3 = ` {}`, 2 = ` {`.
1202             let overhead = if fields.is_empty() { 3 } else { 2 };
1203             if (context.config.brace_style() == BraceStyle::AlwaysNextLine && !fields.is_empty())
1204                 || context.config.max_width() < overhead + result.len()
1205             {
1206                 format!("\n{}{{", offset.block_only().to_string(context.config))
1207             } else {
1208                 " {".to_owned()
1209             }
1210         }
1211     };
1212     // 1 = `}`
1213     let overhead = if fields.is_empty() { 1 } else { 0 };
1214     let total_width = result.len() + generics_str.len() + overhead;
1215     if !generics_str.is_empty()
1216         && !generics_str.contains('\n')
1217         && total_width > context.config.max_width()
1218     {
1219         result.push('\n');
1220         result.push_str(&offset.to_string(context.config));
1221         result.push_str(generics_str.trim_left());
1222     } else {
1223         result.push_str(&generics_str);
1224     }
1225
1226     if fields.is_empty() {
1227         let inner_span = mk_sp(body_lo, span.hi() - BytePos(1));
1228         format_empty_struct_or_tuple(context, inner_span, offset, &mut result, "", "}");
1229         return Some(result);
1230     }
1231
1232     // 3 = ` ` and ` }`
1233     let one_line_budget = context.budget(result.len() + 3 + offset.width());
1234     let one_line_budget =
1235         one_line_width.map_or(0, |one_line_width| min(one_line_width, one_line_budget));
1236
1237     let items_str = rewrite_with_alignment(
1238         fields,
1239         context,
1240         Shape::indented(offset, context.config).sub_width(1)?,
1241         mk_sp(body_lo, span.hi()),
1242         one_line_budget,
1243     )?;
1244
1245     if !items_str.contains('\n')
1246         && !result.contains('\n')
1247         && items_str.len() <= one_line_budget
1248         && !last_line_contains_single_line_comment(&items_str)
1249     {
1250         Some(format!("{} {} }}", result, items_str))
1251     } else {
1252         Some(format!(
1253             "{}\n{}{}\n{}}}",
1254             result,
1255             offset
1256                 .block_indent(context.config)
1257                 .to_string(context.config),
1258             items_str,
1259             offset.to_string(context.config)
1260         ))
1261     }
1262 }
1263
1264 fn get_bytepos_after_visibility(vis: &ast::Visibility, default_span: Span) -> BytePos {
1265     match vis.node {
1266         ast::VisibilityKind::Crate(..) | ast::VisibilityKind::Restricted { .. } => vis.span.hi(),
1267         _ => default_span.lo(),
1268     }
1269 }
1270
1271 // Format tuple or struct without any fields. We need to make sure that the comments
1272 // inside the delimiters are preserved.
1273 fn format_empty_struct_or_tuple(
1274     context: &RewriteContext,
1275     span: Span,
1276     offset: Indent,
1277     result: &mut String,
1278     opener: &str,
1279     closer: &str,
1280 ) {
1281     // 3 = " {}" or "();"
1282     let used_width = last_line_used_width(&result, offset.width()) + 3;
1283     if used_width > context.config.max_width() {
1284         result.push_str(&offset.to_string_with_newline(context.config))
1285     }
1286     result.push_str(opener);
1287     match rewrite_missing_comment(span, Shape::indented(offset, context.config), context) {
1288         Some(ref s) if s.is_empty() => (),
1289         Some(ref s) => {
1290             if !is_single_line(s) || first_line_contains_single_line_comment(s) {
1291                 let nested_indent_str = offset
1292                     .block_indent(context.config)
1293                     .to_string_with_newline(context.config);
1294                 result.push_str(&nested_indent_str);
1295             }
1296             result.push_str(s);
1297             if last_line_contains_single_line_comment(s) {
1298                 result.push_str(&offset.to_string_with_newline(context.config));
1299             }
1300         }
1301         None => result.push_str(context.snippet(span)),
1302     }
1303     result.push_str(closer);
1304 }
1305
1306 fn format_tuple_struct(
1307     context: &RewriteContext,
1308     struct_parts: &StructParts,
1309     fields: &[ast::StructField],
1310     offset: Indent,
1311 ) -> Option<String> {
1312     let mut result = String::with_capacity(1024);
1313     let span = struct_parts.span;
1314
1315     let header_str = struct_parts.format_header(context);
1316     result.push_str(&header_str);
1317
1318     let body_lo = if fields.is_empty() {
1319         let lo = get_bytepos_after_visibility(struct_parts.vis, span);
1320         context
1321             .snippet_provider
1322             .span_after(mk_sp(lo, span.hi()), "(")
1323     } else {
1324         fields[0].span.lo()
1325     };
1326     let body_hi = if fields.is_empty() {
1327         context
1328             .snippet_provider
1329             .span_after(mk_sp(body_lo, span.hi()), ")")
1330     } else {
1331         // This is a dirty hack to work around a missing `)` from the span of the last field.
1332         let last_arg_span = fields[fields.len() - 1].span;
1333         context
1334             .snippet_provider
1335             .opt_span_after(mk_sp(last_arg_span.hi(), span.hi()), ")")
1336             .unwrap_or(last_arg_span.hi())
1337     };
1338
1339     let where_clause_str = match struct_parts.generics {
1340         Some(generics) => {
1341             let budget = context.budget(last_line_width(&header_str));
1342             let shape = Shape::legacy(budget, offset);
1343             let g_span = mk_sp(span.lo(), body_lo);
1344             let generics_str = rewrite_generics(context, "", generics, shape, g_span)?;
1345             result.push_str(&generics_str);
1346
1347             let where_budget = context.budget(last_line_width(&result));
1348             let option = WhereClauseOption::new(true, false);
1349             rewrite_where_clause(
1350                 context,
1351                 &generics.where_clause,
1352                 context.config.brace_style(),
1353                 Shape::legacy(where_budget, offset.block_only()),
1354                 Density::Compressed,
1355                 ";",
1356                 None,
1357                 body_hi,
1358                 option,
1359                 false,
1360             )?
1361         }
1362         None => "".to_owned(),
1363     };
1364
1365     if fields.is_empty() {
1366         let body_hi = context
1367             .snippet_provider
1368             .span_before(mk_sp(body_lo, span.hi()), ")");
1369         let inner_span = mk_sp(body_lo, body_hi);
1370         format_empty_struct_or_tuple(context, inner_span, offset, &mut result, "(", ")");
1371     } else {
1372         let shape = Shape::indented(offset, context.config).sub_width(1)?;
1373         let fields = &fields.iter().collect::<Vec<_>>();
1374         result = overflow::rewrite_with_parens(
1375             context,
1376             &result,
1377             fields,
1378             shape,
1379             span,
1380             context.config.width_heuristics().fn_call_width,
1381             None,
1382         )?;
1383     }
1384
1385     if !where_clause_str.is_empty()
1386         && !where_clause_str.contains('\n')
1387         && (result.contains('\n')
1388             || offset.block_indent + result.len() + where_clause_str.len() + 1
1389                 > context.config.max_width())
1390     {
1391         // We need to put the where clause on a new line, but we didn't
1392         // know that earlier, so the where clause will not be indented properly.
1393         result.push('\n');
1394         result.push_str(
1395             &(offset.block_only() + (context.config.tab_spaces() - 1)).to_string(context.config),
1396         );
1397     }
1398     result.push_str(&where_clause_str);
1399
1400     Some(result)
1401 }
1402
1403 fn rewrite_type_prefix(
1404     context: &RewriteContext,
1405     indent: Indent,
1406     prefix: &str,
1407     ident: ast::Ident,
1408     generics: &ast::Generics,
1409 ) -> Option<String> {
1410     let mut result = String::with_capacity(128);
1411     result.push_str(prefix);
1412     let ident_str = rewrite_ident(context, ident);
1413
1414     // 2 = `= `
1415     if generics.params.is_empty() {
1416         result.push_str(ident_str)
1417     } else {
1418         let g_shape = Shape::indented(indent, context.config)
1419             .offset_left(result.len())?
1420             .sub_width(2)?;
1421         let generics_str = rewrite_generics(context, ident_str, generics, g_shape, generics.span)?;
1422         result.push_str(&generics_str);
1423     }
1424
1425     let where_budget = context.budget(last_line_width(&result));
1426     let option = WhereClauseOption::snuggled(&result);
1427     let where_clause_str = rewrite_where_clause(
1428         context,
1429         &generics.where_clause,
1430         context.config.brace_style(),
1431         Shape::legacy(where_budget, indent),
1432         Density::Vertical,
1433         "=",
1434         None,
1435         generics.span.hi(),
1436         option,
1437         false,
1438     )?;
1439     result.push_str(&where_clause_str);
1440
1441     Some(result)
1442 }
1443
1444 fn rewrite_type_item<R: Rewrite>(
1445     context: &RewriteContext,
1446     indent: Indent,
1447     prefix: &str,
1448     suffix: &str,
1449     ident: ast::Ident,
1450     rhs: &R,
1451     generics: &ast::Generics,
1452     vis: &ast::Visibility,
1453 ) -> Option<String> {
1454     let mut result = String::with_capacity(128);
1455     result.push_str(&rewrite_type_prefix(
1456         context,
1457         indent,
1458         &format!("{}{} ", format_visibility(context, vis), prefix),
1459         ident,
1460         generics,
1461     )?);
1462
1463     if generics.where_clause.predicates.is_empty() {
1464         result.push_str(suffix);
1465     } else {
1466         result.push_str(&indent.to_string_with_newline(context.config));
1467         result.push_str(suffix.trim_left());
1468     }
1469
1470     // 1 = ";"
1471     let rhs_shape = Shape::indented(indent, context.config).sub_width(1)?;
1472     rewrite_assign_rhs(context, result, rhs, rhs_shape).map(|s| s + ";")
1473 }
1474
1475 pub fn rewrite_type_alias(
1476     context: &RewriteContext,
1477     indent: Indent,
1478     ident: ast::Ident,
1479     ty: &ast::Ty,
1480     generics: &ast::Generics,
1481     vis: &ast::Visibility,
1482 ) -> Option<String> {
1483     rewrite_type_item(context, indent, "type", " =", ident, ty, generics, vis)
1484 }
1485
1486 pub fn rewrite_existential_type(
1487     context: &RewriteContext,
1488     indent: Indent,
1489     ident: ast::Ident,
1490     generic_bounds: &ast::GenericBounds,
1491     generics: &ast::Generics,
1492     vis: &ast::Visibility,
1493 ) -> Option<String> {
1494     rewrite_type_item(
1495         context,
1496         indent,
1497         "existential type",
1498         ":",
1499         ident,
1500         generic_bounds,
1501         generics,
1502         vis,
1503     )
1504 }
1505
1506 fn type_annotation_spacing(config: &Config) -> (&str, &str) {
1507     (
1508         if config.space_before_colon() { " " } else { "" },
1509         if config.space_after_colon() { " " } else { "" },
1510     )
1511 }
1512
1513 pub fn rewrite_struct_field_prefix(
1514     context: &RewriteContext,
1515     field: &ast::StructField,
1516 ) -> Option<String> {
1517     let vis = format_visibility(context, &field.vis);
1518     let type_annotation_spacing = type_annotation_spacing(context.config);
1519     Some(match field.ident {
1520         Some(name) => format!(
1521             "{}{}{}:",
1522             vis,
1523             rewrite_ident(context, name),
1524             type_annotation_spacing.0
1525         ),
1526         None => format!("{}", vis),
1527     })
1528 }
1529
1530 impl Rewrite for ast::StructField {
1531     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1532         rewrite_struct_field(context, self, shape, 0)
1533     }
1534 }
1535
1536 pub fn rewrite_struct_field(
1537     context: &RewriteContext,
1538     field: &ast::StructField,
1539     shape: Shape,
1540     lhs_max_width: usize,
1541 ) -> Option<String> {
1542     if contains_skip(&field.attrs) {
1543         return Some(context.snippet(field.span()).to_owned());
1544     }
1545
1546     let type_annotation_spacing = type_annotation_spacing(context.config);
1547     let prefix = rewrite_struct_field_prefix(context, field)?;
1548
1549     let attrs_str = field.attrs.rewrite(context, shape)?;
1550     let attrs_extendable = field.ident.is_none() && is_attributes_extendable(&attrs_str);
1551     let missing_span = if field.attrs.is_empty() {
1552         mk_sp(field.span.lo(), field.span.lo())
1553     } else {
1554         mk_sp(field.attrs.last().unwrap().span.hi(), field.span.lo())
1555     };
1556     let mut spacing = String::from(if field.ident.is_some() {
1557         type_annotation_spacing.1
1558     } else {
1559         ""
1560     });
1561     // Try to put everything on a single line.
1562     let attr_prefix = combine_strs_with_missing_comments(
1563         context,
1564         &attrs_str,
1565         &prefix,
1566         missing_span,
1567         shape,
1568         attrs_extendable,
1569     )?;
1570     let overhead = last_line_width(&attr_prefix);
1571     let lhs_offset = lhs_max_width.saturating_sub(overhead);
1572     for _ in 0..lhs_offset {
1573         spacing.push(' ');
1574     }
1575     // In this extreme case we will be missing a space betweeen an attribute and a field.
1576     if prefix.is_empty() && !attrs_str.is_empty() && attrs_extendable && spacing.is_empty() {
1577         spacing.push(' ');
1578     }
1579     let orig_ty = shape
1580         .offset_left(overhead + spacing.len())
1581         .and_then(|ty_shape| field.ty.rewrite(context, ty_shape));
1582     if let Some(ref ty) = orig_ty {
1583         if !ty.contains('\n') {
1584             return Some(attr_prefix + &spacing + ty);
1585         }
1586     }
1587
1588     let is_prefix_empty = prefix.is_empty();
1589     // We must use multiline. We are going to put attributes and a field on different lines.
1590     let field_str = rewrite_assign_rhs(context, prefix, &*field.ty, shape)?;
1591     // Remove a leading white-space from `rewrite_assign_rhs()` when rewriting a tuple struct.
1592     let field_str = if is_prefix_empty {
1593         field_str.trim_left()
1594     } else {
1595         &field_str
1596     };
1597     combine_strs_with_missing_comments(context, &attrs_str, field_str, missing_span, shape, false)
1598 }
1599
1600 pub struct StaticParts<'a> {
1601     prefix: &'a str,
1602     vis: &'a ast::Visibility,
1603     ident: ast::Ident,
1604     ty: &'a ast::Ty,
1605     mutability: ast::Mutability,
1606     expr_opt: Option<&'a ptr::P<ast::Expr>>,
1607     defaultness: Option<ast::Defaultness>,
1608     span: Span,
1609 }
1610
1611 impl<'a> StaticParts<'a> {
1612     pub fn from_item(item: &'a ast::Item) -> Self {
1613         let (prefix, ty, mutability, expr) = match item.node {
1614             ast::ItemKind::Static(ref ty, mutability, ref expr) => ("static", ty, mutability, expr),
1615             ast::ItemKind::Const(ref ty, ref expr) => {
1616                 ("const", ty, ast::Mutability::Immutable, expr)
1617             }
1618             _ => unreachable!(),
1619         };
1620         StaticParts {
1621             prefix,
1622             vis: &item.vis,
1623             ident: item.ident,
1624             ty,
1625             mutability,
1626             expr_opt: Some(expr),
1627             defaultness: None,
1628             span: item.span,
1629         }
1630     }
1631
1632     pub fn from_trait_item(ti: &'a ast::TraitItem) -> Self {
1633         let (ty, expr_opt) = match ti.node {
1634             ast::TraitItemKind::Const(ref ty, ref expr_opt) => (ty, expr_opt),
1635             _ => unreachable!(),
1636         };
1637         StaticParts {
1638             prefix: "const",
1639             vis: &DEFAULT_VISIBILITY,
1640             ident: ti.ident,
1641             ty,
1642             mutability: ast::Mutability::Immutable,
1643             expr_opt: expr_opt.as_ref(),
1644             defaultness: None,
1645             span: ti.span,
1646         }
1647     }
1648
1649     pub fn from_impl_item(ii: &'a ast::ImplItem) -> Self {
1650         let (ty, expr) = match ii.node {
1651             ast::ImplItemKind::Const(ref ty, ref expr) => (ty, expr),
1652             _ => unreachable!(),
1653         };
1654         StaticParts {
1655             prefix: "const",
1656             vis: &ii.vis,
1657             ident: ii.ident,
1658             ty,
1659             mutability: ast::Mutability::Immutable,
1660             expr_opt: Some(expr),
1661             defaultness: Some(ii.defaultness),
1662             span: ii.span,
1663         }
1664     }
1665 }
1666
1667 fn rewrite_static(
1668     context: &RewriteContext,
1669     static_parts: &StaticParts,
1670     offset: Indent,
1671 ) -> Option<String> {
1672     let colon = colon_spaces(
1673         context.config.space_before_colon(),
1674         context.config.space_after_colon(),
1675     );
1676     let mut prefix = format!(
1677         "{}{}{} {}{}{}",
1678         format_visibility(context, static_parts.vis),
1679         static_parts.defaultness.map_or("", format_defaultness),
1680         static_parts.prefix,
1681         format_mutability(static_parts.mutability),
1682         static_parts.ident,
1683         colon,
1684     );
1685     // 2 = " =".len()
1686     let ty_shape =
1687         Shape::indented(offset.block_only(), context.config).offset_left(prefix.len() + 2)?;
1688     let ty_str = match static_parts.ty.rewrite(context, ty_shape) {
1689         Some(ty_str) => ty_str,
1690         None => {
1691             if prefix.ends_with(' ') {
1692                 prefix.pop();
1693             }
1694             let nested_indent = offset.block_indent(context.config);
1695             let nested_shape = Shape::indented(nested_indent, context.config);
1696             let ty_str = static_parts.ty.rewrite(context, nested_shape)?;
1697             format!(
1698                 "{}{}",
1699                 nested_indent.to_string_with_newline(context.config),
1700                 ty_str
1701             )
1702         }
1703     };
1704
1705     if let Some(expr) = static_parts.expr_opt {
1706         let lhs = format!("{}{} =", prefix, ty_str);
1707         // 1 = ;
1708         let remaining_width = context.budget(offset.block_indent + 1);
1709         rewrite_assign_rhs(
1710             context,
1711             lhs,
1712             &**expr,
1713             Shape::legacy(remaining_width, offset.block_only()),
1714         ).and_then(|res| recover_comment_removed(res, static_parts.span, context))
1715         .map(|s| if s.ends_with(';') { s } else { s + ";" })
1716     } else {
1717         Some(format!("{}{};", prefix, ty_str))
1718     }
1719 }
1720
1721 pub fn rewrite_associated_type(
1722     ident: ast::Ident,
1723     ty_opt: Option<&ptr::P<ast::Ty>>,
1724     generic_bounds_opt: Option<&ast::GenericBounds>,
1725     context: &RewriteContext,
1726     indent: Indent,
1727 ) -> Option<String> {
1728     let prefix = format!("type {}", rewrite_ident(context, ident));
1729
1730     let type_bounds_str = if let Some(bounds) = generic_bounds_opt {
1731         if bounds.is_empty() {
1732             String::new()
1733         } else {
1734             // 2 = ": ".len()
1735             let shape = Shape::indented(indent, context.config).offset_left(prefix.len() + 2)?;
1736             bounds.rewrite(context, shape).map(|s| format!(": {}", s))?
1737         }
1738     } else {
1739         String::new()
1740     };
1741
1742     if let Some(ty) = ty_opt {
1743         // 1 = `;`
1744         let shape = Shape::indented(indent, context.config).sub_width(1)?;
1745         let lhs = format!("{}{} =", prefix, type_bounds_str);
1746         rewrite_assign_rhs(context, lhs, &**ty, shape).map(|s| s + ";")
1747     } else {
1748         Some(format!("{}{};", prefix, type_bounds_str))
1749     }
1750 }
1751
1752 pub fn rewrite_existential_impl_type(
1753     context: &RewriteContext,
1754     ident: ast::Ident,
1755     generic_bounds: &ast::GenericBounds,
1756     indent: Indent,
1757 ) -> Option<String> {
1758     rewrite_associated_type(ident, None, Some(generic_bounds), context, indent)
1759         .map(|s| format!("existential {}", s))
1760 }
1761
1762 pub fn rewrite_associated_impl_type(
1763     ident: ast::Ident,
1764     defaultness: ast::Defaultness,
1765     ty_opt: Option<&ptr::P<ast::Ty>>,
1766     generic_bounds_opt: Option<&ast::GenericBounds>,
1767     context: &RewriteContext,
1768     indent: Indent,
1769 ) -> Option<String> {
1770     let result = rewrite_associated_type(ident, ty_opt, generic_bounds_opt, context, indent)?;
1771
1772     match defaultness {
1773         ast::Defaultness::Default => Some(format!("default {}", result)),
1774         _ => Some(result),
1775     }
1776 }
1777
1778 impl Rewrite for ast::FunctionRetTy {
1779     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1780         match *self {
1781             ast::FunctionRetTy::Default(_) => Some(String::new()),
1782             ast::FunctionRetTy::Ty(ref ty) => {
1783                 let inner_width = shape.width.checked_sub(3)?;
1784                 ty.rewrite(context, Shape::legacy(inner_width, shape.indent + 3))
1785                     .map(|r| format!("-> {}", r))
1786             }
1787         }
1788     }
1789 }
1790
1791 fn is_empty_infer(context: &RewriteContext, ty: &ast::Ty) -> bool {
1792     match ty.node {
1793         ast::TyKind::Infer => {
1794             let original = context.snippet(ty.span);
1795             original != "_"
1796         }
1797         _ => false,
1798     }
1799 }
1800
1801 impl Rewrite for ast::Arg {
1802     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1803         if is_named_arg(self) {
1804             let mut result = self
1805                 .pat
1806                 .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
1807
1808             if !is_empty_infer(context, &*self.ty) {
1809                 if context.config.space_before_colon() {
1810                     result.push_str(" ");
1811                 }
1812                 result.push_str(":");
1813                 if context.config.space_after_colon() {
1814                     result.push_str(" ");
1815                 }
1816                 let overhead = last_line_width(&result);
1817                 let max_width = shape.width.checked_sub(overhead)?;
1818                 let ty_str = self
1819                     .ty
1820                     .rewrite(context, Shape::legacy(max_width, shape.indent))?;
1821                 result.push_str(&ty_str);
1822             }
1823
1824             Some(result)
1825         } else {
1826             self.ty.rewrite(context, shape)
1827         }
1828     }
1829 }
1830
1831 fn rewrite_explicit_self(
1832     explicit_self: &ast::ExplicitSelf,
1833     args: &[ast::Arg],
1834     context: &RewriteContext,
1835 ) -> Option<String> {
1836     match explicit_self.node {
1837         ast::SelfKind::Region(lt, m) => {
1838             let mut_str = format_mutability(m);
1839             match lt {
1840                 Some(ref l) => {
1841                     let lifetime_str = l.rewrite(
1842                         context,
1843                         Shape::legacy(context.config.max_width(), Indent::empty()),
1844                     )?;
1845                     Some(format!("&{} {}self", lifetime_str, mut_str))
1846                 }
1847                 None => Some(format!("&{}self", mut_str)),
1848             }
1849         }
1850         ast::SelfKind::Explicit(ref ty, _) => {
1851             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1852
1853             let mutability = explicit_self_mutability(&args[0]);
1854             let type_str = ty.rewrite(
1855                 context,
1856                 Shape::legacy(context.config.max_width(), Indent::empty()),
1857             )?;
1858
1859             Some(format!(
1860                 "{}self: {}",
1861                 format_mutability(mutability),
1862                 type_str
1863             ))
1864         }
1865         ast::SelfKind::Value(_) => {
1866             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1867
1868             let mutability = explicit_self_mutability(&args[0]);
1869
1870             Some(format!("{}self", format_mutability(mutability)))
1871         }
1872     }
1873 }
1874
1875 // Hacky solution caused by absence of `Mutability` in `SelfValue` and
1876 // `SelfExplicit` variants of `ast::ExplicitSelf_`.
1877 fn explicit_self_mutability(arg: &ast::Arg) -> ast::Mutability {
1878     if let ast::PatKind::Ident(ast::BindingMode::ByValue(mutability), _, _) = arg.pat.node {
1879         mutability
1880     } else {
1881         unreachable!()
1882     }
1883 }
1884
1885 pub fn span_lo_for_arg(arg: &ast::Arg) -> BytePos {
1886     if is_named_arg(arg) {
1887         arg.pat.span.lo()
1888     } else {
1889         arg.ty.span.lo()
1890     }
1891 }
1892
1893 pub fn span_hi_for_arg(context: &RewriteContext, arg: &ast::Arg) -> BytePos {
1894     match arg.ty.node {
1895         ast::TyKind::Infer if context.snippet(arg.ty.span) == "_" => arg.ty.span.hi(),
1896         ast::TyKind::Infer if is_named_arg(arg) => arg.pat.span.hi(),
1897         _ => arg.ty.span.hi(),
1898     }
1899 }
1900
1901 pub fn is_named_arg(arg: &ast::Arg) -> bool {
1902     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
1903         ident != symbol::keywords::Invalid.ident()
1904     } else {
1905         true
1906     }
1907 }
1908
1909 // Return type is (result, force_new_line_for_brace)
1910 fn rewrite_fn_base(
1911     context: &RewriteContext,
1912     indent: Indent,
1913     ident: ast::Ident,
1914     fn_sig: &FnSig,
1915     span: Span,
1916     newline_brace: bool,
1917     has_body: bool,
1918 ) -> Option<(String, bool)> {
1919     let mut force_new_line_for_brace = false;
1920
1921     let where_clause = &fn_sig.generics.where_clause;
1922
1923     let mut result = String::with_capacity(1024);
1924     result.push_str(&fn_sig.to_str(context));
1925
1926     // fn foo
1927     result.push_str("fn ");
1928
1929     // Generics.
1930     let overhead = if has_body && !newline_brace {
1931         // 4 = `() {`
1932         4
1933     } else {
1934         // 2 = `()`
1935         2
1936     };
1937     let used_width = last_line_used_width(&result, indent.width());
1938     let one_line_budget = context.budget(used_width + overhead);
1939     let shape = Shape {
1940         width: one_line_budget,
1941         indent,
1942         offset: used_width,
1943     };
1944     let fd = fn_sig.decl;
1945     let g_span = mk_sp(span.lo(), fd.output.span().lo());
1946     let generics_str = rewrite_generics(
1947         context,
1948         rewrite_ident(context, ident),
1949         fn_sig.generics,
1950         shape,
1951         g_span,
1952     )?;
1953     result.push_str(&generics_str);
1954
1955     let snuggle_angle_bracket = generics_str
1956         .lines()
1957         .last()
1958         .map_or(false, |l| l.trim_left().len() == 1);
1959
1960     // Note that the width and indent don't really matter, we'll re-layout the
1961     // return type later anyway.
1962     let ret_str = fd
1963         .output
1964         .rewrite(context, Shape::indented(indent, context.config))?;
1965
1966     let multi_line_ret_str = ret_str.contains('\n');
1967     let ret_str_len = if multi_line_ret_str { 0 } else { ret_str.len() };
1968
1969     // Args.
1970     let (one_line_budget, multi_line_budget, mut arg_indent) = compute_budgets_for_args(
1971         context,
1972         &result,
1973         indent,
1974         ret_str_len,
1975         newline_brace,
1976         has_body,
1977         multi_line_ret_str,
1978     )?;
1979
1980     debug!(
1981         "rewrite_fn_base: one_line_budget: {}, multi_line_budget: {}, arg_indent: {:?}",
1982         one_line_budget, multi_line_budget, arg_indent
1983     );
1984
1985     // Check if vertical layout was forced.
1986     if one_line_budget == 0 {
1987         if snuggle_angle_bracket {
1988             result.push('(');
1989         } else {
1990             result.push_str("(");
1991             if context.config.indent_style() == IndentStyle::Visual {
1992                 result.push_str(&arg_indent.to_string_with_newline(context.config));
1993             }
1994         }
1995     } else {
1996         result.push('(');
1997     }
1998
1999     // Skip `pub(crate)`.
2000     let lo_after_visibility = get_bytepos_after_visibility(&fn_sig.visibility, span);
2001     // A conservative estimation, to goal is to be over all parens in generics
2002     let args_start = fn_sig
2003         .generics
2004         .params
2005         .iter()
2006         .last()
2007         .map_or(lo_after_visibility, |param| param.span().hi());
2008     let args_end = if fd.inputs.is_empty() {
2009         context
2010             .snippet_provider
2011             .span_after(mk_sp(args_start, span.hi()), ")")
2012     } else {
2013         let last_span = mk_sp(fd.inputs[fd.inputs.len() - 1].span().hi(), span.hi());
2014         context.snippet_provider.span_after(last_span, ")")
2015     };
2016     let args_span = mk_sp(
2017         context
2018             .snippet_provider
2019             .span_after(mk_sp(args_start, span.hi()), "("),
2020         args_end,
2021     );
2022     let arg_str = rewrite_args(
2023         context,
2024         &fd.inputs,
2025         fd.get_self().as_ref(),
2026         one_line_budget,
2027         multi_line_budget,
2028         indent,
2029         arg_indent,
2030         args_span,
2031         fd.variadic,
2032         generics_str.contains('\n'),
2033     )?;
2034
2035     let put_args_in_block = match context.config.indent_style() {
2036         IndentStyle::Block => arg_str.contains('\n') || arg_str.len() > one_line_budget,
2037         _ => false,
2038     } && !fd.inputs.is_empty();
2039
2040     let mut args_last_line_contains_comment = false;
2041     if put_args_in_block {
2042         arg_indent = indent.block_indent(context.config);
2043         result.push_str(&arg_indent.to_string_with_newline(context.config));
2044         result.push_str(&arg_str);
2045         result.push_str(&indent.to_string_with_newline(context.config));
2046         result.push(')');
2047     } else {
2048         result.push_str(&arg_str);
2049         let used_width = last_line_used_width(&result, indent.width()) + first_line_width(&ret_str);
2050         // Put the closing brace on the next line if it overflows the max width.
2051         // 1 = `)`
2052         if fd.inputs.is_empty() && used_width + 1 > context.config.max_width() {
2053             result.push('\n');
2054         }
2055         // If the last line of args contains comment, we cannot put the closing paren
2056         // on the same line.
2057         if arg_str
2058             .lines()
2059             .last()
2060             .map_or(false, |last_line| last_line.contains("//"))
2061         {
2062             args_last_line_contains_comment = true;
2063             result.push_str(&arg_indent.to_string_with_newline(context.config));
2064         }
2065         result.push(')');
2066     }
2067
2068     // Return type.
2069     if let ast::FunctionRetTy::Ty(..) = fd.output {
2070         let ret_should_indent = match context.config.indent_style() {
2071             // If our args are block layout then we surely must have space.
2072             IndentStyle::Block if put_args_in_block || fd.inputs.is_empty() => false,
2073             _ if args_last_line_contains_comment => false,
2074             _ if result.contains('\n') || multi_line_ret_str => true,
2075             _ => {
2076                 // If the return type would push over the max width, then put the return type on
2077                 // a new line. With the +1 for the signature length an additional space between
2078                 // the closing parenthesis of the argument and the arrow '->' is considered.
2079                 let mut sig_length = result.len() + indent.width() + ret_str_len + 1;
2080
2081                 // If there is no where clause, take into account the space after the return type
2082                 // and the brace.
2083                 if where_clause.predicates.is_empty() {
2084                     sig_length += 2;
2085                 }
2086
2087                 sig_length > context.config.max_width()
2088             }
2089         };
2090         let ret_indent = if ret_should_indent {
2091             let indent = if arg_str.is_empty() {
2092                 // Aligning with non-existent args looks silly.
2093                 force_new_line_for_brace = true;
2094                 indent + 4
2095             } else {
2096                 // FIXME: we might want to check that using the arg indent
2097                 // doesn't blow our budget, and if it does, then fallback to
2098                 // the where clause indent.
2099                 arg_indent
2100             };
2101
2102             result.push_str(&indent.to_string_with_newline(context.config));
2103             indent
2104         } else {
2105             result.push(' ');
2106             Indent::new(indent.block_indent, last_line_width(&result))
2107         };
2108
2109         if multi_line_ret_str || ret_should_indent {
2110             // Now that we know the proper indent and width, we need to
2111             // re-layout the return type.
2112             let ret_str = fd
2113                 .output
2114                 .rewrite(context, Shape::indented(ret_indent, context.config))?;
2115             result.push_str(&ret_str);
2116         } else {
2117             result.push_str(&ret_str);
2118         }
2119
2120         // Comment between return type and the end of the decl.
2121         let snippet_lo = fd.output.span().hi();
2122         if where_clause.predicates.is_empty() {
2123             let snippet_hi = span.hi();
2124             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
2125             // Try to preserve the layout of the original snippet.
2126             let original_starts_with_newline = snippet
2127                 .find(|c| c != ' ')
2128                 .map_or(false, |i| starts_with_newline(&snippet[i..]));
2129             let original_ends_with_newline = snippet
2130                 .rfind(|c| c != ' ')
2131                 .map_or(false, |i| snippet[i..].ends_with('\n'));
2132             let snippet = snippet.trim();
2133             if !snippet.is_empty() {
2134                 result.push(if original_starts_with_newline {
2135                     '\n'
2136                 } else {
2137                     ' '
2138                 });
2139                 result.push_str(snippet);
2140                 if original_ends_with_newline {
2141                     force_new_line_for_brace = true;
2142                 }
2143             }
2144         }
2145     }
2146
2147     let pos_before_where = match fd.output {
2148         ast::FunctionRetTy::Default(..) => args_span.hi(),
2149         ast::FunctionRetTy::Ty(ref ty) => ty.span.hi(),
2150     };
2151
2152     let is_args_multi_lined = arg_str.contains('\n');
2153
2154     let option = WhereClauseOption::new(!has_body, put_args_in_block && ret_str.is_empty());
2155     let where_clause_str = rewrite_where_clause(
2156         context,
2157         where_clause,
2158         context.config.brace_style(),
2159         Shape::indented(indent, context.config),
2160         Density::Tall,
2161         "{",
2162         Some(span.hi()),
2163         pos_before_where,
2164         option,
2165         is_args_multi_lined,
2166     )?;
2167     // If there are neither where clause nor return type, we may be missing comments between
2168     // args and `{`.
2169     if where_clause_str.is_empty() {
2170         if let ast::FunctionRetTy::Default(ret_span) = fd.output {
2171             match recover_missing_comment_in_span(
2172                 mk_sp(args_span.hi(), ret_span.hi()),
2173                 shape,
2174                 context,
2175                 last_line_width(&result),
2176             ) {
2177                 Some(ref missing_comment) if !missing_comment.is_empty() => {
2178                     result.push_str(missing_comment);
2179                     force_new_line_for_brace = true;
2180                 }
2181                 _ => (),
2182             }
2183         }
2184     }
2185
2186     result.push_str(&where_clause_str);
2187
2188     force_new_line_for_brace |= last_line_contains_single_line_comment(&result);
2189     force_new_line_for_brace |= is_args_multi_lined && context.config.where_single_line();
2190     Some((result, force_new_line_for_brace))
2191 }
2192
2193 #[derive(Copy, Clone)]
2194 struct WhereClauseOption {
2195     suppress_comma: bool, // Force no trailing comma
2196     snuggle: bool,        // Do not insert newline before `where`
2197     compress_where: bool, // Try single line where clause instead of vertical layout
2198 }
2199
2200 impl WhereClauseOption {
2201     pub fn new(suppress_comma: bool, snuggle: bool) -> WhereClauseOption {
2202         WhereClauseOption {
2203             suppress_comma,
2204             snuggle,
2205             compress_where: false,
2206         }
2207     }
2208
2209     pub fn snuggled(current: &str) -> WhereClauseOption {
2210         WhereClauseOption {
2211             suppress_comma: false,
2212             snuggle: last_line_width(current) == 1,
2213             compress_where: false,
2214         }
2215     }
2216
2217     pub fn suppress_comma(&mut self) {
2218         self.suppress_comma = true
2219     }
2220
2221     pub fn compress_where(&mut self) {
2222         self.compress_where = true
2223     }
2224
2225     pub fn snuggle(&mut self) {
2226         self.snuggle = true
2227     }
2228 }
2229
2230 fn rewrite_args(
2231     context: &RewriteContext,
2232     args: &[ast::Arg],
2233     explicit_self: Option<&ast::ExplicitSelf>,
2234     one_line_budget: usize,
2235     multi_line_budget: usize,
2236     indent: Indent,
2237     arg_indent: Indent,
2238     span: Span,
2239     variadic: bool,
2240     generics_str_contains_newline: bool,
2241 ) -> Option<String> {
2242     let mut arg_item_strs = args
2243         .iter()
2244         .map(|arg| arg.rewrite(context, Shape::legacy(multi_line_budget, arg_indent)))
2245         .collect::<Option<Vec<_>>>()?;
2246
2247     // Account for sugary self.
2248     // FIXME: the comment for the self argument is dropped. This is blocked
2249     // on rust issue #27522.
2250     let min_args = explicit_self
2251         .and_then(|explicit_self| rewrite_explicit_self(explicit_self, args, context))
2252         .map_or(1, |self_str| {
2253             arg_item_strs[0] = self_str;
2254             2
2255         });
2256
2257     // Comments between args.
2258     let mut arg_items = Vec::new();
2259     if min_args == 2 {
2260         arg_items.push(ListItem::from_str(""));
2261     }
2262
2263     // FIXME(#21): if there are no args, there might still be a comment, but
2264     // without spans for the comment or parens, there is no chance of
2265     // getting it right. You also don't get to put a comment on self, unless
2266     // it is explicit.
2267     if args.len() >= min_args || variadic {
2268         let comment_span_start = if min_args == 2 {
2269             let second_arg_start = if arg_has_pattern(&args[1]) {
2270                 args[1].pat.span.lo()
2271             } else {
2272                 args[1].ty.span.lo()
2273             };
2274             let reduced_span = mk_sp(span.lo(), second_arg_start);
2275
2276             context.snippet_provider.span_after_last(reduced_span, ",")
2277         } else {
2278             span.lo()
2279         };
2280
2281         enum ArgumentKind<'a> {
2282             Regular(&'a ast::Arg),
2283             Variadic(BytePos),
2284         }
2285
2286         let variadic_arg = if variadic {
2287             let variadic_span = mk_sp(args.last().unwrap().ty.span.hi(), span.hi());
2288             let variadic_start =
2289                 context.snippet_provider.span_after(variadic_span, "...") - BytePos(3);
2290             Some(ArgumentKind::Variadic(variadic_start))
2291         } else {
2292             None
2293         };
2294
2295         let more_items = itemize_list(
2296             context.snippet_provider,
2297             args[min_args - 1..]
2298                 .iter()
2299                 .map(ArgumentKind::Regular)
2300                 .chain(variadic_arg),
2301             ")",
2302             ",",
2303             |arg| match *arg {
2304                 ArgumentKind::Regular(arg) => span_lo_for_arg(arg),
2305                 ArgumentKind::Variadic(start) => start,
2306             },
2307             |arg| match *arg {
2308                 ArgumentKind::Regular(arg) => arg.ty.span.hi(),
2309                 ArgumentKind::Variadic(start) => start + BytePos(3),
2310             },
2311             |arg| match *arg {
2312                 ArgumentKind::Regular(..) => None,
2313                 ArgumentKind::Variadic(..) => Some("...".to_owned()),
2314             },
2315             comment_span_start,
2316             span.hi(),
2317             false,
2318         );
2319
2320         arg_items.extend(more_items);
2321     }
2322
2323     let fits_in_one_line = !generics_str_contains_newline
2324         && (arg_items.is_empty()
2325             || arg_items.len() == 1 && arg_item_strs[0].len() <= one_line_budget);
2326
2327     for (item, arg) in arg_items.iter_mut().zip(arg_item_strs) {
2328         item.item = Some(arg);
2329     }
2330
2331     let last_line_ends_with_comment = arg_items
2332         .iter()
2333         .last()
2334         .and_then(|item| item.post_comment.as_ref())
2335         .map_or(false, |s| s.trim().starts_with("//"));
2336
2337     let (indent, trailing_comma) = match context.config.indent_style() {
2338         IndentStyle::Block if fits_in_one_line => {
2339             (indent.block_indent(context.config), SeparatorTactic::Never)
2340         }
2341         IndentStyle::Block => (
2342             indent.block_indent(context.config),
2343             context.config.trailing_comma(),
2344         ),
2345         IndentStyle::Visual if last_line_ends_with_comment => {
2346             (arg_indent, context.config.trailing_comma())
2347         }
2348         IndentStyle::Visual => (arg_indent, SeparatorTactic::Never),
2349     };
2350
2351     let tactic = definitive_tactic(
2352         &arg_items,
2353         context.config.fn_args_density().to_list_tactic(),
2354         Separator::Comma,
2355         one_line_budget,
2356     );
2357     let budget = match tactic {
2358         DefinitiveListTactic::Horizontal => one_line_budget,
2359         _ => multi_line_budget,
2360     };
2361
2362     debug!("rewrite_args: budget: {}, tactic: {:?}", budget, tactic);
2363
2364     let fmt = ListFormatting {
2365         tactic,
2366         separator: ",",
2367         trailing_separator: if variadic {
2368             SeparatorTactic::Never
2369         } else {
2370             trailing_comma
2371         },
2372         separator_place: SeparatorPlace::Back,
2373         shape: Shape::legacy(budget, indent),
2374         ends_with_newline: tactic.ends_with_newline(context.config.indent_style()),
2375         preserve_newline: true,
2376         nested: false,
2377         config: context.config,
2378     };
2379
2380     write_list(&arg_items, &fmt)
2381 }
2382
2383 fn arg_has_pattern(arg: &ast::Arg) -> bool {
2384     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
2385         ident != symbol::keywords::Invalid.ident()
2386     } else {
2387         true
2388     }
2389 }
2390
2391 fn compute_budgets_for_args(
2392     context: &RewriteContext,
2393     result: &str,
2394     indent: Indent,
2395     ret_str_len: usize,
2396     newline_brace: bool,
2397     has_braces: bool,
2398     force_vertical_layout: bool,
2399 ) -> Option<((usize, usize, Indent))> {
2400     debug!(
2401         "compute_budgets_for_args {} {:?}, {}, {}",
2402         result.len(),
2403         indent,
2404         ret_str_len,
2405         newline_brace
2406     );
2407     // Try keeping everything on the same line.
2408     if !result.contains('\n') && !force_vertical_layout {
2409         // 2 = `()`, 3 = `() `, space is before ret_string.
2410         let overhead = if ret_str_len == 0 { 2 } else { 3 };
2411         let mut used_space = indent.width() + result.len() + ret_str_len + overhead;
2412         if has_braces {
2413             if !newline_brace {
2414                 // 2 = `{}`
2415                 used_space += 2;
2416             }
2417         } else {
2418             // 1 = `;`
2419             used_space += 1;
2420         }
2421         let one_line_budget = context.budget(used_space);
2422
2423         if one_line_budget > 0 {
2424             // 4 = "() {".len()
2425             let (indent, multi_line_budget) = match context.config.indent_style() {
2426                 IndentStyle::Block => {
2427                     let indent = indent.block_indent(context.config);
2428                     (indent, context.budget(indent.width() + 1))
2429                 }
2430                 IndentStyle::Visual => {
2431                     let indent = indent + result.len() + 1;
2432                     let multi_line_overhead = indent.width() + if newline_brace { 2 } else { 4 };
2433                     (indent, context.budget(multi_line_overhead))
2434                 }
2435             };
2436
2437             return Some((one_line_budget, multi_line_budget, indent));
2438         }
2439     }
2440
2441     // Didn't work. we must force vertical layout and put args on a newline.
2442     let new_indent = indent.block_indent(context.config);
2443     let used_space = match context.config.indent_style() {
2444         // 1 = `,`
2445         IndentStyle::Block => new_indent.width() + 1,
2446         // Account for `)` and possibly ` {`.
2447         IndentStyle::Visual => new_indent.width() + if ret_str_len == 0 { 1 } else { 3 },
2448     };
2449     Some((0, context.budget(used_space), new_indent))
2450 }
2451
2452 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> bool {
2453     let predicate_count = where_clause.predicates.len();
2454
2455     if config.where_single_line() && predicate_count == 1 {
2456         return false;
2457     }
2458     let brace_style = config.brace_style();
2459
2460     brace_style == BraceStyle::AlwaysNextLine
2461         || (brace_style == BraceStyle::SameLineWhere && predicate_count > 0)
2462 }
2463
2464 fn rewrite_generics(
2465     context: &RewriteContext,
2466     ident: &str,
2467     generics: &ast::Generics,
2468     shape: Shape,
2469     span: Span,
2470 ) -> Option<String> {
2471     // FIXME: convert bounds to where clauses where they get too big or if
2472     // there is a where clause at all.
2473
2474     if generics.params.is_empty() {
2475         return Some(ident.to_owned());
2476     }
2477
2478     let params = &generics.params.iter().map(|e| &*e).collect::<Vec<_>>();
2479     overflow::rewrite_with_angle_brackets(context, ident, params, shape, span)
2480 }
2481
2482 pub fn generics_shape_from_config(config: &Config, shape: Shape, offset: usize) -> Option<Shape> {
2483     match config.indent_style() {
2484         IndentStyle::Visual => shape.visual_indent(1 + offset).sub_width(offset + 2),
2485         IndentStyle::Block => {
2486             // 1 = ","
2487             shape
2488                 .block()
2489                 .block_indent(config.tab_spaces())
2490                 .with_max_width(config)
2491                 .sub_width(1)
2492         }
2493     }
2494 }
2495
2496 fn rewrite_where_clause_rfc_style(
2497     context: &RewriteContext,
2498     where_clause: &ast::WhereClause,
2499     shape: Shape,
2500     terminator: &str,
2501     span_end: Option<BytePos>,
2502     span_end_before_where: BytePos,
2503     where_clause_option: WhereClauseOption,
2504     is_args_multi_line: bool,
2505 ) -> Option<String> {
2506     let block_shape = shape.block().with_max_width(context.config);
2507
2508     let (span_before, span_after) =
2509         missing_span_before_after_where(span_end_before_where, where_clause);
2510     let (comment_before, comment_after) =
2511         rewrite_comments_before_after_where(context, span_before, span_after, shape)?;
2512
2513     let starting_newline = if where_clause_option.snuggle && comment_before.is_empty() {
2514         Cow::from(" ")
2515     } else {
2516         block_shape.indent.to_string_with_newline(context.config)
2517     };
2518
2519     let clause_shape = block_shape.block_left(context.config.tab_spaces())?;
2520     // 1 = `,`
2521     let clause_shape = clause_shape.sub_width(1)?;
2522     // each clause on one line, trailing comma (except if suppress_comma)
2523     let span_start = where_clause.predicates[0].span().lo();
2524     // If we don't have the start of the next span, then use the end of the
2525     // predicates, but that means we miss comments.
2526     let len = where_clause.predicates.len();
2527     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2528     let span_end = span_end.unwrap_or(end_of_preds);
2529     let items = itemize_list(
2530         context.snippet_provider,
2531         where_clause.predicates.iter(),
2532         terminator,
2533         ",",
2534         |pred| pred.span().lo(),
2535         |pred| pred.span().hi(),
2536         |pred| pred.rewrite(context, clause_shape),
2537         span_start,
2538         span_end,
2539         false,
2540     );
2541     let where_single_line = context.config.where_single_line() && len == 1 && !is_args_multi_line;
2542     let comma_tactic = if where_clause_option.suppress_comma || where_single_line {
2543         SeparatorTactic::Never
2544     } else {
2545         context.config.trailing_comma()
2546     };
2547
2548     // shape should be vertical only and only if we have `where_single_line` option enabled
2549     // and the number of items of the where clause is equal to 1
2550     let shape_tactic = if where_single_line {
2551         DefinitiveListTactic::Horizontal
2552     } else {
2553         DefinitiveListTactic::Vertical
2554     };
2555
2556     let fmt = ListFormatting {
2557         tactic: shape_tactic,
2558         separator: ",",
2559         trailing_separator: comma_tactic,
2560         separator_place: SeparatorPlace::Back,
2561         shape: clause_shape,
2562         ends_with_newline: true,
2563         preserve_newline: true,
2564         nested: false,
2565         config: context.config,
2566     };
2567     let preds_str = write_list(&items.collect::<Vec<_>>(), &fmt)?;
2568
2569     let comment_separator = |comment: &str, shape: Shape| {
2570         if comment.is_empty() {
2571             Cow::from("")
2572         } else {
2573             shape.indent.to_string_with_newline(context.config)
2574         }
2575     };
2576     let newline_before_where = comment_separator(&comment_before, shape);
2577     let newline_after_where = comment_separator(&comment_after, clause_shape);
2578
2579     // 6 = `where `
2580     let clause_sep = if where_clause_option.compress_where
2581         && comment_before.is_empty()
2582         && comment_after.is_empty()
2583         && !preds_str.contains('\n')
2584         && 6 + preds_str.len() <= shape.width
2585         || where_single_line
2586     {
2587         Cow::from(" ")
2588     } else {
2589         clause_shape.indent.to_string_with_newline(context.config)
2590     };
2591     Some(format!(
2592         "{}{}{}where{}{}{}{}",
2593         starting_newline,
2594         comment_before,
2595         newline_before_where,
2596         newline_after_where,
2597         comment_after,
2598         clause_sep,
2599         preds_str
2600     ))
2601 }
2602
2603 fn rewrite_where_clause(
2604     context: &RewriteContext,
2605     where_clause: &ast::WhereClause,
2606     brace_style: BraceStyle,
2607     shape: Shape,
2608     density: Density,
2609     terminator: &str,
2610     span_end: Option<BytePos>,
2611     span_end_before_where: BytePos,
2612     where_clause_option: WhereClauseOption,
2613     is_args_multi_line: bool,
2614 ) -> Option<String> {
2615     if where_clause.predicates.is_empty() {
2616         return Some(String::new());
2617     }
2618
2619     if context.config.indent_style() == IndentStyle::Block {
2620         return rewrite_where_clause_rfc_style(
2621             context,
2622             where_clause,
2623             shape,
2624             terminator,
2625             span_end,
2626             span_end_before_where,
2627             where_clause_option,
2628             is_args_multi_line,
2629         );
2630     }
2631
2632     let extra_indent = Indent::new(context.config.tab_spaces(), 0);
2633
2634     let offset = match context.config.indent_style() {
2635         IndentStyle::Block => shape.indent + extra_indent.block_indent(context.config),
2636         // 6 = "where ".len()
2637         IndentStyle::Visual => shape.indent + extra_indent + 6,
2638     };
2639     // FIXME: if indent_style != Visual, then the budgets below might
2640     // be out by a char or two.
2641
2642     let budget = context.config.max_width() - offset.width();
2643     let span_start = where_clause.predicates[0].span().lo();
2644     // If we don't have the start of the next span, then use the end of the
2645     // predicates, but that means we miss comments.
2646     let len = where_clause.predicates.len();
2647     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2648     let span_end = span_end.unwrap_or(end_of_preds);
2649     let items = itemize_list(
2650         context.snippet_provider,
2651         where_clause.predicates.iter(),
2652         terminator,
2653         ",",
2654         |pred| pred.span().lo(),
2655         |pred| pred.span().hi(),
2656         |pred| pred.rewrite(context, Shape::legacy(budget, offset)),
2657         span_start,
2658         span_end,
2659         false,
2660     );
2661     let item_vec = items.collect::<Vec<_>>();
2662     // FIXME: we don't need to collect here
2663     let tactic = definitive_tactic(&item_vec, ListTactic::Vertical, Separator::Comma, budget);
2664
2665     let mut comma_tactic = context.config.trailing_comma();
2666     // Kind of a hack because we don't usually have trailing commas in where clauses.
2667     if comma_tactic == SeparatorTactic::Vertical || where_clause_option.suppress_comma {
2668         comma_tactic = SeparatorTactic::Never;
2669     }
2670
2671     let fmt = ListFormatting {
2672         tactic,
2673         separator: ",",
2674         trailing_separator: comma_tactic,
2675         separator_place: SeparatorPlace::Back,
2676         shape: Shape::legacy(budget, offset),
2677         ends_with_newline: tactic.ends_with_newline(context.config.indent_style()),
2678         preserve_newline: true,
2679         nested: false,
2680         config: context.config,
2681     };
2682     let preds_str = write_list(&item_vec, &fmt)?;
2683
2684     let end_length = if terminator == "{" {
2685         // If the brace is on the next line we don't need to count it otherwise it needs two
2686         // characters " {"
2687         match brace_style {
2688             BraceStyle::AlwaysNextLine | BraceStyle::SameLineWhere => 0,
2689             BraceStyle::PreferSameLine => 2,
2690         }
2691     } else if terminator == "=" {
2692         2
2693     } else {
2694         terminator.len()
2695     };
2696     if density == Density::Tall
2697         || preds_str.contains('\n')
2698         || shape.indent.width() + " where ".len() + preds_str.len() + end_length > shape.width
2699     {
2700         Some(format!(
2701             "\n{}where {}",
2702             (shape.indent + extra_indent).to_string(context.config),
2703             preds_str
2704         ))
2705     } else {
2706         Some(format!(" where {}", preds_str))
2707     }
2708 }
2709
2710 fn missing_span_before_after_where(
2711     before_item_span_end: BytePos,
2712     where_clause: &ast::WhereClause,
2713 ) -> (Span, Span) {
2714     let missing_span_before = mk_sp(before_item_span_end, where_clause.span.lo());
2715     // 5 = `where`
2716     let pos_after_where = where_clause.span.lo() + BytePos(5);
2717     let missing_span_after = mk_sp(pos_after_where, where_clause.predicates[0].span().lo());
2718     (missing_span_before, missing_span_after)
2719 }
2720
2721 fn rewrite_comments_before_after_where(
2722     context: &RewriteContext,
2723     span_before_where: Span,
2724     span_after_where: Span,
2725     shape: Shape,
2726 ) -> Option<(String, String)> {
2727     let before_comment = rewrite_missing_comment(span_before_where, shape, context)?;
2728     let after_comment = rewrite_missing_comment(
2729         span_after_where,
2730         shape.block_indent(context.config.tab_spaces()),
2731         context,
2732     )?;
2733     Some((before_comment, after_comment))
2734 }
2735
2736 fn format_header(
2737     context: &RewriteContext,
2738     item_name: &str,
2739     ident: ast::Ident,
2740     vis: &ast::Visibility,
2741 ) -> String {
2742     format!(
2743         "{}{}{}",
2744         format_visibility(context, vis),
2745         item_name,
2746         rewrite_ident(context, ident)
2747     )
2748 }
2749
2750 #[derive(PartialEq, Eq, Clone, Copy)]
2751 enum BracePos {
2752     None,
2753     Auto,
2754     ForceSameLine,
2755 }
2756
2757 fn format_generics(
2758     context: &RewriteContext,
2759     generics: &ast::Generics,
2760     brace_style: BraceStyle,
2761     brace_pos: BracePos,
2762     offset: Indent,
2763     span: Span,
2764     used_width: usize,
2765 ) -> Option<String> {
2766     let shape = Shape::legacy(context.budget(used_width + offset.width()), offset);
2767     let mut result = rewrite_generics(context, "", generics, shape, span)?;
2768
2769     let same_line_brace = if !generics.where_clause.predicates.is_empty() || result.contains('\n') {
2770         let budget = context.budget(last_line_used_width(&result, offset.width()));
2771         let mut option = WhereClauseOption::snuggled(&result);
2772         if brace_pos == BracePos::None {
2773             option.suppress_comma = true;
2774         }
2775         // If the generics are not parameterized then generics.span.hi() == 0,
2776         // so we use span.lo(), which is the position after `struct Foo`.
2777         let span_end_before_where = if !generics.params.is_empty() {
2778             generics.span.hi()
2779         } else {
2780             span.lo()
2781         };
2782         let where_clause_str = rewrite_where_clause(
2783             context,
2784             &generics.where_clause,
2785             brace_style,
2786             Shape::legacy(budget, offset.block_only()),
2787             Density::Tall,
2788             "{",
2789             Some(span.hi()),
2790             span_end_before_where,
2791             option,
2792             false,
2793         )?;
2794         result.push_str(&where_clause_str);
2795         brace_pos == BracePos::ForceSameLine
2796             || brace_style == BraceStyle::PreferSameLine
2797             || (generics.where_clause.predicates.is_empty()
2798                 && trimmed_last_line_width(&result) == 1)
2799     } else {
2800         brace_pos == BracePos::ForceSameLine
2801             || trimmed_last_line_width(&result) == 1
2802             || brace_style != BraceStyle::AlwaysNextLine
2803     };
2804     if brace_pos == BracePos::None {
2805         return Some(result);
2806     }
2807     let total_used_width = last_line_used_width(&result, used_width);
2808     let remaining_budget = context.budget(total_used_width);
2809     // If the same line brace if forced, it indicates that we are rewriting an item with empty body,
2810     // and hence we take the closer into account as well for one line budget.
2811     // We assume that the closer has the same length as the opener.
2812     let overhead = if brace_pos == BracePos::ForceSameLine {
2813         // 3 = ` {}`
2814         3
2815     } else {
2816         // 2 = ` {`
2817         2
2818     };
2819     let forbid_same_line_brace = overhead > remaining_budget;
2820     if !forbid_same_line_brace && same_line_brace {
2821         result.push(' ');
2822     } else {
2823         result.push('\n');
2824         result.push_str(&offset.block_only().to_string(context.config));
2825     }
2826     result.push('{');
2827
2828     Some(result)
2829 }
2830
2831 impl Rewrite for ast::ForeignItem {
2832     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
2833         let attrs_str = self.attrs.rewrite(context, shape)?;
2834         // Drop semicolon or it will be interpreted as comment.
2835         // FIXME: this may be a faulty span from libsyntax.
2836         let span = mk_sp(self.span.lo(), self.span.hi() - BytePos(1));
2837
2838         let item_str = match self.node {
2839             ast::ForeignItemKind::Fn(ref fn_decl, ref generics) => rewrite_fn_base(
2840                 context,
2841                 shape.indent,
2842                 self.ident,
2843                 &FnSig::new(fn_decl, generics, self.vis.clone()),
2844                 span,
2845                 false,
2846                 false,
2847             ).map(|(s, _)| format!("{};", s)),
2848             ast::ForeignItemKind::Static(ref ty, is_mutable) => {
2849                 // FIXME(#21): we're dropping potential comments in between the
2850                 // function keywords here.
2851                 let vis = format_visibility(context, &self.vis);
2852                 let mut_str = if is_mutable { "mut " } else { "" };
2853                 let prefix = format!(
2854                     "{}static {}{}:",
2855                     vis,
2856                     mut_str,
2857                     rewrite_ident(context, self.ident)
2858                 );
2859                 // 1 = ;
2860                 rewrite_assign_rhs(context, prefix, &**ty, shape.sub_width(1)?).map(|s| s + ";")
2861             }
2862             ast::ForeignItemKind::Ty => {
2863                 let vis = format_visibility(context, &self.vis);
2864                 Some(format!(
2865                     "{}type {};",
2866                     vis,
2867                     rewrite_ident(context, self.ident)
2868                 ))
2869             }
2870             ast::ForeignItemKind::Macro(ref mac) => {
2871                 rewrite_macro(mac, None, context, shape, MacroPosition::Item)
2872             }
2873         }?;
2874
2875         let missing_span = if self.attrs.is_empty() {
2876             mk_sp(self.span.lo(), self.span.lo())
2877         } else {
2878             mk_sp(self.attrs[self.attrs.len() - 1].span.hi(), self.span.lo())
2879         };
2880         combine_strs_with_missing_comments(
2881             context,
2882             &attrs_str,
2883             &item_str,
2884             missing_span,
2885             shape,
2886             false,
2887         )
2888     }
2889 }
2890
2891 /// Rewrite an inline mod.
2892 pub fn rewrite_mod(context: &RewriteContext, item: &ast::Item) -> String {
2893     let mut result = String::with_capacity(32);
2894     result.push_str(&*format_visibility(context, &item.vis));
2895     result.push_str("mod ");
2896     result.push_str(rewrite_ident(context, item.ident));
2897     result.push(';');
2898     result
2899 }
2900
2901 /// Rewrite `extern crate foo;` WITHOUT attributes.
2902 pub fn rewrite_extern_crate(context: &RewriteContext, item: &ast::Item) -> Option<String> {
2903     assert!(is_extern_crate(item));
2904     let new_str = context.snippet(item.span);
2905     Some(if contains_comment(new_str) {
2906         new_str.to_owned()
2907     } else {
2908         let no_whitespace = &new_str.split_whitespace().collect::<Vec<&str>>().join(" ");
2909         String::from(&*Regex::new(r"\s;").unwrap().replace(no_whitespace, ";"))
2910     })
2911 }
2912
2913 /// Returns true for `mod foo;`, false for `mod foo { .. }`.
2914 pub fn is_mod_decl(item: &ast::Item) -> bool {
2915     match item.node {
2916         ast::ItemKind::Mod(ref m) => m.inner.hi() != item.span.hi(),
2917         _ => false,
2918     }
2919 }
2920
2921 pub fn is_use_item(item: &ast::Item) -> bool {
2922     match item.node {
2923         ast::ItemKind::Use(_) => true,
2924         _ => false,
2925     }
2926 }
2927
2928 pub fn is_extern_crate(item: &ast::Item) -> bool {
2929     match item.node {
2930         ast::ItemKind::ExternCrate(..) => true,
2931         _ => false,
2932     }
2933 }