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;
  15
  16 use syntax::{abi, ast, ptr, symbol};
  17 use syntax::ast::{CrateSugar, ImplItem};
  18 use syntax::codemap::{BytePos, Span};
  19 use syntax::visit;
  20
  21 use spanned::Spanned;
  22 use codemap::{LineRangeUtils, SpanUtils};
  23 use comment::{combine_strs_with_missing_comments, contains_comment, recover_comment_removed,
  24               recover_missing_comment_in_span, rewrite_missing_comment, FindUncommented};
  25 use config::{BraceStyle, Config, Density, IndentStyle, ReturnIndent, Style};
  26 use expr::{format_expr, is_empty_block, is_simple_block_stmt, rewrite_assign_rhs,
  27            rewrite_call_inner, ExprType};
  28 use lists::{definitive_tactic, itemize_list, write_list, DefinitiveListTactic, ListFormatting,
  29             ListItem, ListTactic, Separator, SeparatorPlace, SeparatorTactic};
  30 use rewrite::{Rewrite, RewriteContext};
  31 use shape::{Indent, Shape};
  32 use types::join_bounds;
  33 use utils::{colon_spaces, contains_skip, end_typaram, first_line_width, format_abi,
  34             format_constness, format_defaultness, format_mutability, format_unsafety,
  35             format_visibility, is_attributes_extendable, last_line_contains_single_line_comment,
  36             last_line_used_width, last_line_width, mk_sp, semicolon_for_expr, starts_with_newline,
  37             stmt_expr, trim_newlines, trimmed_last_line_width};
  38 use vertical::rewrite_with_alignment;
  39 use visitor::FmtVisitor;
  40
  41 fn type_annotation_separator(config: &Config) -> &str {
  42     colon_spaces(
  43         config.space_before_type_annotation(),
  44         config.space_after_type_annotation_colon(),
  45     )
  46 }
  47
  48 // Statements of the form
  49 // let pat: ty = init;
  50 impl Rewrite for ast::Local {
  51     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  52         debug!(
  53             "Local::rewrite {:?} {} {:?}",
  54             self,
  55             shape.width,
  56             shape.indent
  57         );
  58
  59         skip_out_of_file_lines_range!(context, self.span);
  60
  61         if contains_skip(&self.attrs) {
  62             return None;
  63         }
  64
  65         let attrs_str = self.attrs.rewrite(context, shape)?;
  66         let mut result = if attrs_str.is_empty() {
  67             "let ".to_owned()
  68         } else {
  69             combine_strs_with_missing_comments(
  70                 context,
  71                 &attrs_str,
  72                 "let ",
  73                 mk_sp(
  74                     self.attrs.last().map(|a| a.span.hi()).unwrap(),
  75                     self.span.lo(),
  76                 ),
  77                 shape,
  78                 false,
  79             )?
  80         };
  81
  82         // 4 = "let ".len()
  83         let pat_shape = shape.offset_left(4)?;
  84         // 1 = ;
  85         let pat_shape = pat_shape.sub_width(1)?;
  86         let pat_str = self.pat.rewrite(context, pat_shape)?;
  87         result.push_str(&pat_str);
  88
  89         // String that is placed within the assignment pattern and expression.
  90         let infix = {
  91             let mut infix = String::with_capacity(32);
  92
  93             if let Some(ref ty) = self.ty {
  94                 let separator = type_annotation_separator(context.config);
  95                 let indent = shape.indent + last_line_width(&result) + separator.len();
  96                 // 1 = ;
  97                 let budget = shape.width.checked_sub(indent.width() + 1)?;
  98                 let rewrite = ty.rewrite(context, Shape::legacy(budget, indent))?;
  99
 100                 infix.push_str(separator);
 101                 infix.push_str(&rewrite);
 102             }
 103
 104             if self.init.is_some() {
 105                 infix.push_str(" =");
 106             }
 107
 108             infix
 109         };
 110
 111         result.push_str(&infix);
 112
 113         if let Some(ref ex) = self.init {
 114             // 1 = trailing semicolon;
 115             let nested_shape = shape.sub_width(1)?;
 116
 117             result = rewrite_assign_rhs(context, result, ex, nested_shape)?;
 118         }
 119
 120         result.push(';');
 121         Some(result)
 122     }
 123 }
 124
 125 // TODO convert to using rewrite style rather than visitor
 126 // TODO format modules in this style
 127 #[allow(dead_code)]
 128 struct Item<'a> {
 129     keyword: &'static str,
 130     abi: Cow<'static, str>,
 131     vis: Option<&'a ast::Visibility>,
 132     body: Vec<BodyElement<'a>>,
 133     span: Span,
 134 }
 135
 136 impl<'a> Item<'a> {
 137     fn from_foreign_mod(fm: &'a ast::ForeignMod, span: Span, config: &Config) -> Item<'a> {
 138         Item {
 139             keyword: "",
 140             abi: format_abi(fm.abi, config.force_explicit_abi(), true),
 141             vis: None,
 142             body: fm.items
 143                 .iter()
 144                 .map(|i| BodyElement::ForeignItem(i))
 145                 .collect(),
 146             span: span,
 147         }
 148     }
 149 }
 150
 151 enum BodyElement<'a> {
 152     // Stmt(&'a ast::Stmt),
 153     // Field(&'a ast::Field),
 154     // Variant(&'a ast::Variant),
 155     // Item(&'a ast::Item),
 156     ForeignItem(&'a ast::ForeignItem),
 157 }
 158
 159 /// Represents a fn's signature.
 160 pub struct FnSig<'a> {
 161     decl: &'a ast::FnDecl,
 162     generics: &'a ast::Generics,
 163     abi: abi::Abi,
 164     constness: ast::Constness,
 165     defaultness: ast::Defaultness,
 166     unsafety: ast::Unsafety,
 167     visibility: ast::Visibility,
 168 }
 169
 170 impl<'a> FnSig<'a> {
 171     pub fn new(
 172         decl: &'a ast::FnDecl,
 173         generics: &'a ast::Generics,
 174         vis: ast::Visibility,
 175     ) -> FnSig<'a> {
 176         FnSig {
 177             decl: decl,
 178             generics: generics,
 179             abi: abi::Abi::Rust,
 180             constness: ast::Constness::NotConst,
 181             defaultness: ast::Defaultness::Final,
 182             unsafety: ast::Unsafety::Normal,
 183             visibility: vis,
 184         }
 185     }
 186
 187     pub fn from_method_sig(
 188         method_sig: &'a ast::MethodSig,
 189         generics: &'a ast::Generics,
 190     ) -> FnSig<'a> {
 191         FnSig {
 192             unsafety: method_sig.unsafety,
 193             constness: method_sig.constness.node,
 194             defaultness: ast::Defaultness::Final,
 195             abi: method_sig.abi,
 196             decl: &*method_sig.decl,
 197             generics: generics,
 198             visibility: ast::Visibility::Inherited,
 199         }
 200     }
 201
 202     pub fn from_fn_kind(
 203         fn_kind: &'a visit::FnKind,
 204         generics: &'a ast::Generics,
 205         decl: &'a ast::FnDecl,
 206         defualtness: ast::Defaultness,
 207     ) -> FnSig<'a> {
 208         match *fn_kind {
 209             visit::FnKind::ItemFn(_, unsafety, constness, abi, visibility, _) => FnSig {
 210                 decl: decl,
 211                 generics: generics,
 212                 abi: abi,
 213                 constness: constness.node,
 214                 defaultness: defualtness,
 215                 unsafety: unsafety,
 216                 visibility: visibility.clone(),
 217             },
 218             visit::FnKind::Method(_, method_sig, vis, _) => {
 219                 let mut fn_sig = FnSig::from_method_sig(method_sig, generics);
 220                 fn_sig.defaultness = defualtness;
 221                 if let Some(vis) = vis {
 222                     fn_sig.visibility = vis.clone();
 223                 }
 224                 fn_sig
 225             }
 226             _ => unreachable!(),
 227         }
 228     }
 229
 230     fn to_str(&self, context: &RewriteContext) -> String {
 231         let mut result = String::with_capacity(128);
 232         // Vis defaultness constness unsafety abi.
 233         result.push_str(&*format_visibility(&self.visibility));
 234         result.push_str(format_defaultness(self.defaultness));
 235         result.push_str(format_constness(self.constness));
 236         result.push_str(format_unsafety(self.unsafety));
 237         result.push_str(&format_abi(
 238             self.abi,
 239             context.config.force_explicit_abi(),
 240             false,
 241         ));
 242         result
 243     }
 244 }
 245
 246 impl<'a> FmtVisitor<'a> {
 247     fn format_item(&mut self, item: Item) {
 248         self.buffer.push_str(&item.abi);
 249
 250         let snippet = self.snippet(item.span);
 251         let brace_pos = snippet.find_uncommented("{").unwrap();
 252
 253         self.buffer.push_str("{");
 254         if !item.body.is_empty() || contains_comment(&snippet[brace_pos..]) {
 255             // FIXME: this skips comments between the extern keyword and the opening
 256             // brace.
 257             self.last_pos = item.span.lo() + BytePos(brace_pos as u32 + 1);
 258             self.block_indent = self.block_indent.block_indent(self.config);
 259
 260             if item.body.is_empty() {
 261                 self.format_missing_no_indent(item.span.hi() - BytePos(1));
 262                 self.block_indent = self.block_indent.block_unindent(self.config);
 263
 264                 self.buffer
 265                     .push_str(&self.block_indent.to_string(self.config));
 266             } else {
 267                 for item in &item.body {
 268                     self.format_body_element(item);
 269                 }
 270
 271                 self.block_indent = self.block_indent.block_unindent(self.config);
 272                 self.format_missing_with_indent(item.span.hi() - BytePos(1));
 273             }
 274         }
 275
 276         self.buffer.push_str("}");
 277         self.last_pos = item.span.hi();
 278     }
 279
 280     fn format_body_element(&mut self, element: &BodyElement) {
 281         match *element {
 282             BodyElement::ForeignItem(item) => self.format_foreign_item(item),
 283         }
 284     }
 285
 286     pub fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
 287         let item = Item::from_foreign_mod(fm, span, self.config);
 288         self.format_item(item);
 289     }
 290
 291
 292     fn format_foreign_item(&mut self, item: &ast::ForeignItem) {
 293         let rewrite = item.rewrite(&self.get_context(), self.shape());
 294         self.push_rewrite(item.span(), rewrite);
 295         self.last_pos = item.span.hi();
 296     }
 297
 298     pub fn rewrite_fn(
 299         &mut self,
 300         indent: Indent,
 301         ident: ast::Ident,
 302         fn_sig: &FnSig,
 303         span: Span,
 304         block: &ast::Block,
 305     ) -> Option<String> {
 306         let context = self.get_context();
 307
 308         let has_body =
 309             !is_empty_block(block, self.codemap) || !context.config.fn_empty_single_line();
 310         let mut newline_brace =
 311             newline_for_brace(self.config, &fn_sig.generics.where_clause, has_body);
 312
 313         let (mut result, force_newline_brace) =
 314             rewrite_fn_base(&context, indent, ident, fn_sig, span, newline_brace, true)?;
 315
 316         // 2 = ` {`
 317         if self.config.fn_brace_style() == BraceStyle::AlwaysNextLine || 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('\n');
 332             result.push_str(&indent.to_string(self.config));
 333         } else {
 334             result.push(' ');
 335         }
 336
 337         self.single_line_fn(&result, block).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(&self, fn_str: &str, block: &ast::Block) -> Option<String> {
 369         if fn_str.contains('\n') {
 370             return None;
 371         }
 372
 373         let codemap = self.get_context().codemap;
 374
 375         if self.config.fn_empty_single_line() && is_empty_block(block, codemap)
 376             && self.block_indent.width() + fn_str.len() + 2 <= self.config.max_width()
 377         {
 378             return Some(format!("{}{{}}", fn_str));
 379         }
 380
 381         if self.config.fn_single_line() && is_simple_block_stmt(block, codemap) {
 382             let rewrite = {
 383                 if let Some(stmt) = block.stmts.first() {
 384                     match stmt_expr(stmt) {
 385                         Some(e) => {
 386                             let suffix = if semicolon_for_expr(&self.get_context(), e) {
 387                                 ";"
 388                             } else {
 389                                 ""
 390                             };
 391
 392                             format_expr(e, ExprType::Statement, &self.get_context(), self.shape())
 393                                 .map(|s| s + suffix)
 394                                 .or_else(|| Some(self.snippet(e.span)))
 395                         }
 396                         None => stmt.rewrite(&self.get_context(), self.shape()),
 397                     }
 398                 } else {
 399                     None
 400                 }
 401             };
 402
 403             if let Some(res) = rewrite {
 404                 let width = self.block_indent.width() + fn_str.len() + res.len() + 4;
 405                 if !res.contains('\n') && width <= self.config.max_width() {
 406                     return Some(format!("{}{{ {} }}", fn_str, res));
 407                 }
 408             }
 409         }
 410
 411         None
 412     }
 413
 414     pub fn visit_static(&mut self, static_parts: &StaticParts) {
 415         let rewrite = rewrite_static(&self.get_context(), static_parts, self.block_indent);
 416         self.push_rewrite(static_parts.span, rewrite);
 417     }
 418
 419     pub fn visit_struct(&mut self, struct_parts: &StructParts) {
 420         let is_tuple = struct_parts.def.is_tuple();
 421         let rewrite = format_struct(&self.get_context(), struct_parts, self.block_indent, None)
 422             .map(|s| if is_tuple { s + ";" } else { s });
 423         self.push_rewrite(struct_parts.span, rewrite);
 424     }
 425
 426     pub fn visit_enum(
 427         &mut self,
 428         ident: ast::Ident,
 429         vis: &ast::Visibility,
 430         enum_def: &ast::EnumDef,
 431         generics: &ast::Generics,
 432         span: Span,
 433     ) {
 434         let enum_header = format_header("enum ", ident, vis);
 435         self.buffer.push_str(&enum_header);
 436
 437         let enum_snippet = self.snippet(span);
 438         let brace_pos = enum_snippet.find_uncommented("{").unwrap();
 439         let body_start = span.lo() + BytePos(brace_pos as u32 + 1);
 440         let generics_str = format_generics(
 441             &self.get_context(),
 442             generics,
 443             self.config.item_brace_style(),
 444             if enum_def.variants.is_empty() {
 445                 BracePos::ForceSameLine
 446             } else {
 447                 BracePos::Auto
 448             },
 449             self.block_indent,
 450             mk_sp(span.lo(), body_start),
 451             last_line_width(&enum_header),
 452         ).unwrap();
 453         self.buffer.push_str(&generics_str);
 454
 455         self.last_pos = body_start;
 456
 457         self.block_indent = self.block_indent.block_indent(self.config);
 458         let variant_list = self.format_variant_list(enum_def, body_start, span.hi() - BytePos(1));
 459         match variant_list {
 460             Some(ref body_str) => self.buffer.push_str(body_str),
 461             None => if contains_comment(&enum_snippet[brace_pos..]) {
 462                 self.format_missing_no_indent(span.hi() - BytePos(1))
 463             },
 464         }
 465         self.block_indent = self.block_indent.block_unindent(self.config);
 466
 467         if variant_list.is_some() || contains_comment(&enum_snippet[brace_pos..]) {
 468             self.buffer
 469                 .push_str(&self.block_indent.to_string(self.config));
 470         }
 471         self.buffer.push_str("}");
 472         self.last_pos = span.hi();
 473     }
 474
 475     // Format the body of an enum definition
 476     fn format_variant_list(
 477         &self,
 478         enum_def: &ast::EnumDef,
 479         body_lo: BytePos,
 480         body_hi: BytePos,
 481     ) -> Option<String> {
 482         if enum_def.variants.is_empty() {
 483             return None;
 484         }
 485         let mut result = String::with_capacity(1024);
 486         result.push('\n');
 487         let indentation = self.block_indent.to_string(self.config);
 488         result.push_str(&indentation);
 489
 490         let items = itemize_list(
 491             self.codemap,
 492             enum_def.variants.iter(),
 493             "}",
 494             |f| if !f.node.attrs.is_empty() {
 495                 f.node.attrs[0].span.lo()
 496             } else {
 497                 f.span.lo()
 498             },
 499             |f| f.span.hi(),
 500             |f| self.format_variant(f),
 501             body_lo,
 502             body_hi,
 503             false,
 504         );
 505
 506         let shape = self.shape().sub_width(2).unwrap();
 507         let fmt = ListFormatting {
 508             tactic: DefinitiveListTactic::Vertical,
 509             separator: ",",
 510             trailing_separator: self.config.trailing_comma(),
 511             separator_place: SeparatorPlace::Back,
 512             shape: shape,
 513             ends_with_newline: true,
 514             preserve_newline: true,
 515             config: self.config,
 516         };
 517
 518         let list = write_list(&items.collect::<Vec<_>>(), &fmt)?;
 519         result.push_str(&list);
 520         result.push('\n');
 521         Some(result)
 522     }
 523
 524     // Variant of an enum.
 525     fn format_variant(&self, field: &ast::Variant) -> Option<String> {
 526         if contains_skip(&field.node.attrs) {
 527             let lo = field.node.attrs[0].span.lo();
 528             let span = mk_sp(lo, field.span.hi());
 529             return Some(self.snippet(span));
 530         }
 531
 532         let context = self.get_context();
 533         let indent = self.block_indent;
 534         let shape = self.shape();
 535         let attrs_str = field.node.attrs.rewrite(&context, shape)?;
 536         let lo = field
 537             .node
 538             .attrs
 539             .last()
 540             .map_or(field.span.lo(), |attr| attr.span.hi());
 541         let span = mk_sp(lo, field.span.lo());
 542
 543         let variant_body = match field.node.data {
 544             ast::VariantData::Tuple(..) | ast::VariantData::Struct(..) => {
 545                 // FIXME: Should limit the width, as we have a trailing comma
 546                 format_struct(
 547                     &context,
 548                     &StructParts::from_variant(field),
 549                     indent,
 550                     Some(self.config.struct_variant_width()),
 551                 )?
 552             }
 553             ast::VariantData::Unit(..) => if let Some(ref expr) = field.node.disr_expr {
 554                 let lhs = format!("{} =", field.node.name);
 555                 // 1 = ','
 556                 rewrite_assign_rhs(&context, lhs, expr, shape.sub_width(1)?)?
 557             } else {
 558                 field.node.name.to_string()
 559             },
 560         };
 561
 562         let attrs_extendable = attrs_str.is_empty()
 563             || (context.config.attributes_on_same_line_as_variant()
 564                 && is_attributes_extendable(&attrs_str));
 565         combine_strs_with_missing_comments(
 566             &context,
 567             &attrs_str,
 568             &variant_body,
 569             span,
 570             shape,
 571             attrs_extendable,
 572         )
 573     }
 574 }
 575
 576 pub fn format_impl(
 577     context: &RewriteContext,
 578     item: &ast::Item,
 579     offset: Indent,
 580     where_span_end: Option<BytePos>,
 581 ) -> Option<String> {
 582     if let ast::ItemKind::Impl(_, _, _, ref generics, _, ref self_ty, ref items) = item.node {
 583         let mut result = String::with_capacity(128);
 584         let ref_and_type = format_impl_ref_and_type(context, item, offset)?;
 585         let indent_str = offset.to_string(context.config);
 586         let sep = format!("\n{}", &indent_str);
 587         result.push_str(&ref_and_type);
 588
 589         let where_budget = if result.contains('\n') {
 590             context.config.max_width()
 591         } else {
 592             context.budget(last_line_width(&result))
 593         };
 594         let option = WhereClauseOption::snuggled(&ref_and_type);
 595         let where_clause_str = rewrite_where_clause(
 596             context,
 597             &generics.where_clause,
 598             context.config.item_brace_style(),
 599             Shape::legacy(where_budget, offset.block_only()),
 600             context.config.where_density(),
 601             "{",
 602             where_span_end,
 603             self_ty.span.hi(),
 604             option,
 605             false,
 606         )?;
 607
 608         // If there is no where clause, we may have missing comments between the trait name and
 609         // the opening brace.
 610         if generics.where_clause.predicates.is_empty() {
 611             if let Some(hi) = where_span_end {
 612                 match recover_missing_comment_in_span(
 613                     mk_sp(self_ty.span.hi(), hi),
 614                     Shape::indented(offset, context.config),
 615                     context,
 616                     last_line_width(&result),
 617                 ) {
 618                     Some(ref missing_comment) if !missing_comment.is_empty() => {
 619                         result.push_str(missing_comment);
 620                     }
 621                     _ => (),
 622                 }
 623             }
 624         }
 625
 626         if is_impl_single_line(context, items, &result, &where_clause_str, item)? {
 627             result.push_str(&where_clause_str);
 628             if where_clause_str.contains('\n') || last_line_contains_single_line_comment(&result) {
 629                 result.push_str(&format!("{}{{{}}}", &sep, &sep));
 630             } else {
 631                 result.push_str(" {}");
 632             }
 633             return Some(result);
 634         }
 635
 636         if !where_clause_str.is_empty() && !where_clause_str.contains('\n') {
 637             result.push('\n');
 638             let width = offset.block_indent + context.config.tab_spaces() - 1;
 639             let where_indent = Indent::new(0, width);
 640             result.push_str(&where_indent.to_string(context.config));
 641         }
 642         result.push_str(&where_clause_str);
 643
 644         match context.config.item_brace_style() {
 645             _ if last_line_contains_single_line_comment(&result) => result.push_str(&sep),
 646             BraceStyle::AlwaysNextLine => result.push_str(&sep),
 647             BraceStyle::PreferSameLine => result.push(' '),
 648             BraceStyle::SameLineWhere => if !where_clause_str.is_empty() {
 649                 result.push_str(&sep);
 650             } else {
 651                 result.push(' ');
 652             },
 653         }
 654
 655         result.push('{');
 656
 657         let snippet = context.snippet(item.span);
 658         let open_pos = snippet.find_uncommented("{")? + 1;
 659
 660         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 661             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 662             visitor.block_indent = offset.block_only().block_indent(context.config);
 663             visitor.last_pos = item.span.lo() + BytePos(open_pos as u32);
 664
 665             visitor.visit_attrs(&item.attrs, ast::AttrStyle::Inner);
 666             for item in items {
 667                 visitor.visit_impl_item(item);
 668             }
 669
 670             visitor.format_missing(item.span.hi() - BytePos(1));
 671
 672             let inner_indent_str = visitor.block_indent.to_string(context.config);
 673             let outer_indent_str = offset.block_only().to_string(context.config);
 674
 675             result.push('\n');
 676             result.push_str(&inner_indent_str);
 677             result.push_str(trim_newlines(visitor.buffer.to_string().trim()));
 678             result.push('\n');
 679             result.push_str(&outer_indent_str);
 680         }
 681
 682         if result.ends_with('{') {
 683             result.push_str(&sep);
 684         }
 685         result.push('}');
 686
 687         Some(result)
 688     } else {
 689         unreachable!();
 690     }
 691 }
 692
 693 fn is_impl_single_line(
 694     context: &RewriteContext,
 695     items: &[ImplItem],
 696     result: &str,
 697     where_clause_str: &str,
 698     item: &ast::Item,
 699 ) -> Option<bool> {
 700     let snippet = context.snippet(item.span);
 701     let open_pos = snippet.find_uncommented("{")? + 1;
 702
 703     Some(
 704         context.config.impl_empty_single_line() && items.is_empty() && !result.contains('\n')
 705             && result.len() + where_clause_str.len() <= context.config.max_width()
 706             && !contains_comment(&snippet[open_pos..]),
 707     )
 708 }
 709
 710 fn format_impl_ref_and_type(
 711     context: &RewriteContext,
 712     item: &ast::Item,
 713     offset: Indent,
 714 ) -> Option<String> {
 715     if let ast::ItemKind::Impl(
 716         unsafety,
 717         polarity,
 718         defaultness,
 719         ref generics,
 720         ref trait_ref,
 721         ref self_ty,
 722         _,
 723     ) = item.node
 724     {
 725         let mut result = String::with_capacity(128);
 726
 727         result.push_str(&format_visibility(&item.vis));
 728         result.push_str(format_defaultness(defaultness));
 729         result.push_str(format_unsafety(unsafety));
 730         result.push_str("impl");
 731
 732         let lo = context.codemap.span_after(item.span, "impl");
 733         let hi = match *trait_ref {
 734             Some(ref tr) => tr.path.span.lo(),
 735             None => self_ty.span.lo(),
 736         };
 737         let shape = generics_shape_from_config(
 738             context.config,
 739             Shape::indented(offset + last_line_width(&result), context.config),
 740             0,
 741         )?;
 742         let one_line_budget = shape.width.checked_sub(last_line_width(&result) + 2)?;
 743         let generics_str =
 744             rewrite_generics_inner(context, generics, shape, one_line_budget, mk_sp(lo, hi))?;
 745
 746         let polarity_str = if polarity == ast::ImplPolarity::Negative {
 747             "!"
 748         } else {
 749             ""
 750         };
 751
 752         if let Some(ref trait_ref) = *trait_ref {
 753             let result_len = result.len();
 754             if let Some(trait_ref_str) = rewrite_trait_ref(
 755                 context,
 756                 trait_ref,
 757                 offset,
 758                 &generics_str,
 759                 true,
 760                 polarity_str,
 761                 result_len,
 762             ) {
 763                 result.push_str(&trait_ref_str);
 764             } else {
 765                 let generics_str =
 766                     rewrite_generics_inner(context, generics, shape, 0, mk_sp(lo, hi))?;
 767                 result.push_str(&rewrite_trait_ref(
 768                     context,
 769                     trait_ref,
 770                     offset,
 771                     &generics_str,
 772                     false,
 773                     polarity_str,
 774                     result_len,
 775                 )?);
 776             }
 777         } else {
 778             result.push_str(&generics_str);
 779         }
 780
 781         // Try to put the self type in a single line.
 782         // ` for`
 783         let trait_ref_overhead = if trait_ref.is_some() { 4 } else { 0 };
 784         let curly_brace_overhead = if generics.where_clause.predicates.is_empty() {
 785             // If there is no where clause adapt budget for type formatting to take space and curly
 786             // brace into account.
 787             match context.config.item_brace_style() {
 788                 BraceStyle::AlwaysNextLine => 0,
 789                 _ => 2,
 790             }
 791         } else {
 792             0
 793         };
 794         let used_space = last_line_width(&result) + trait_ref_overhead + curly_brace_overhead;
 795         // 1 = space before the type.
 796         let budget = context.budget(used_space + 1);
 797         if let Some(self_ty_str) = self_ty.rewrite(context, Shape::legacy(budget, offset)) {
 798             if !self_ty_str.contains('\n') {
 799                 if trait_ref.is_some() {
 800                     result.push_str(" for ");
 801                 } else {
 802                     result.push(' ');
 803                 }
 804                 result.push_str(&self_ty_str);
 805                 return Some(result);
 806             }
 807         }
 808
 809         // Couldn't fit the self type on a single line, put it on a new line.
 810         result.push('\n');
 811         // Add indentation of one additional tab.
 812         let new_line_offset = offset.block_indent(context.config);
 813         result.push_str(&new_line_offset.to_string(context.config));
 814         if trait_ref.is_some() {
 815             result.push_str("for ");
 816         }
 817         let budget = context.budget(last_line_width(&result));
 818         let type_offset = match context.config.where_style() {
 819             Style::Legacy => new_line_offset + trait_ref_overhead,
 820             Style::Rfc => new_line_offset,
 821         };
 822         result.push_str(&*self_ty
 823             .rewrite(context, Shape::legacy(budget, type_offset))?);
 824         Some(result)
 825     } else {
 826         unreachable!();
 827     }
 828 }
 829
 830 fn rewrite_trait_ref(
 831     context: &RewriteContext,
 832     trait_ref: &ast::TraitRef,
 833     offset: Indent,
 834     generics_str: &str,
 835     retry: bool,
 836     polarity_str: &str,
 837     result_len: usize,
 838 ) -> Option<String> {
 839     // 1 = space between generics and trait_ref
 840     let used_space = 1 + polarity_str.len() + last_line_used_width(generics_str, result_len);
 841     let shape = Shape::indented(offset + used_space, context.config);
 842     if let Some(trait_ref_str) = trait_ref.rewrite(context, shape) {
 843         if !(retry && trait_ref_str.contains('\n')) {
 844             return Some(format!(
 845                 "{} {}{}",
 846                 generics_str,
 847                 polarity_str,
 848                 &trait_ref_str
 849             ));
 850         }
 851     }
 852     // We could not make enough space for trait_ref, so put it on new line.
 853     if !retry {
 854         let offset = offset.block_indent(context.config);
 855         let shape = Shape::indented(offset, context.config);
 856         let trait_ref_str = trait_ref.rewrite(context, shape)?;
 857         Some(format!(
 858             "{}\n{}{}{}",
 859             generics_str,
 860             &offset.to_string(context.config),
 861             polarity_str,
 862             &trait_ref_str
 863         ))
 864     } else {
 865         None
 866     }
 867 }
 868
 869 pub struct StructParts<'a> {
 870     prefix: &'a str,
 871     ident: ast::Ident,
 872     vis: &'a ast::Visibility,
 873     def: &'a ast::VariantData,
 874     generics: Option<&'a ast::Generics>,
 875     span: Span,
 876 }
 877
 878 impl<'a> StructParts<'a> {
 879     fn format_header(&self) -> String {
 880         format_header(self.prefix, self.ident, self.vis)
 881     }
 882
 883     fn from_variant(variant: &'a ast::Variant) -> Self {
 884         StructParts {
 885             prefix: "",
 886             ident: variant.node.name,
 887             vis: &ast::Visibility::Inherited,
 888             def: &variant.node.data,
 889             generics: None,
 890             span: variant.span,
 891         }
 892     }
 893
 894     pub fn from_item(item: &'a ast::Item) -> Self {
 895         let (prefix, def, generics) = match item.node {
 896             ast::ItemKind::Struct(ref def, ref generics) => ("struct ", def, generics),
 897             ast::ItemKind::Union(ref def, ref generics) => ("union ", def, generics),
 898             _ => unreachable!(),
 899         };
 900         StructParts {
 901             prefix: prefix,
 902             ident: item.ident,
 903             vis: &item.vis,
 904             def: def,
 905             generics: Some(generics),
 906             span: item.span,
 907         }
 908     }
 909 }
 910
 911 fn format_struct(
 912     context: &RewriteContext,
 913     struct_parts: &StructParts,
 914     offset: Indent,
 915     one_line_width: Option<usize>,
 916 ) -> Option<String> {
 917     match *struct_parts.def {
 918         ast::VariantData::Unit(..) => format_unit_struct(context, struct_parts, offset),
 919         ast::VariantData::Tuple(ref fields, _) => {
 920             format_tuple_struct(context, struct_parts, fields, offset)
 921         }
 922         ast::VariantData::Struct(ref fields, _) => {
 923             format_struct_struct(context, struct_parts, fields, offset, one_line_width)
 924         }
 925     }
 926 }
 927
 928 pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 929     if let ast::ItemKind::Trait(_, unsafety, ref generics, ref type_param_bounds, ref trait_items) =
 930         item.node
 931     {
 932         let mut result = String::with_capacity(128);
 933         let header = format!(
 934             "{}{}trait {}",
 935             format_visibility(&item.vis),
 936             format_unsafety(unsafety),
 937             item.ident
 938         );
 939
 940         result.push_str(&header);
 941
 942         let body_lo = context.codemap.span_after(item.span, "{");
 943
 944         let shape = Shape::indented(offset, context.config);
 945         let generics_str =
 946             rewrite_generics(context, generics, shape, mk_sp(item.span.lo(), body_lo))?;
 947         result.push_str(&generics_str);
 948
 949         // FIXME(#2055): rustfmt fails to format when there are comments between trait bounds.
 950         if !type_param_bounds.is_empty() {
 951             let ident_hi = context.codemap.span_after(item.span, &format!("{}", item.ident));
 952             let bound_hi = type_param_bounds.last().unwrap().span().hi();
 953             let snippet = context.snippet(mk_sp(ident_hi, bound_hi));
 954             if contains_comment(&snippet) {
 955                 return None;
 956             }
 957         }
 958         let trait_bound_str = rewrite_trait_bounds(
 959             context,
 960             type_param_bounds,
 961             Shape::indented(offset, context.config),
 962         )?;
 963         // If the trait, generics, and trait bound cannot fit on the same line,
 964         // put the trait bounds on an indented new line
 965         if offset.width() + last_line_width(&result) + trait_bound_str.len()
 966             > context.config.comment_width()
 967         {
 968             result.push('\n');
 969             let trait_indent = offset.block_only().block_indent(context.config);
 970             result.push_str(&trait_indent.to_string(context.config));
 971         }
 972         result.push_str(&trait_bound_str);
 973
 974         let has_body = !trait_items.is_empty();
 975
 976         let where_density = if (context.config.where_density() == Density::Compressed
 977             && (!result.contains('\n') || context.config.fn_args_indent() == IndentStyle::Block))
 978             || (context.config.fn_args_indent() == IndentStyle::Block && result.is_empty())
 979             || (context.config.where_density() == Density::CompressedIfEmpty && !has_body
 980                 && !result.contains('\n'))
 981         {
 982             Density::Compressed
 983         } else {
 984             Density::Tall
 985         };
 986
 987         let where_budget = context.budget(last_line_width(&result));
 988         let pos_before_where = if type_param_bounds.is_empty() {
 989             generics.where_clause.span.lo()
 990         } else {
 991             type_param_bounds[type_param_bounds.len() - 1].span().hi()
 992         };
 993         let option = WhereClauseOption::snuggled(&generics_str);
 994         let where_clause_str = rewrite_where_clause(
 995             context,
 996             &generics.where_clause,
 997             context.config.item_brace_style(),
 998             Shape::legacy(where_budget, offset.block_only()),
 999             where_density,
1000             "{",
1001             None,
1002             pos_before_where,
1003             option,
1004             false,
1005         )?;
1006         // If the where clause cannot fit on the same line,
1007         // put the where clause on a new line
1008         if !where_clause_str.contains('\n')
1009             && last_line_width(&result) + where_clause_str.len() + offset.width()
1010                 > context.config.comment_width()
1011         {
1012             result.push('\n');
1013             let width = offset.block_indent + context.config.tab_spaces() - 1;
1014             let where_indent = Indent::new(0, width);
1015             result.push_str(&where_indent.to_string(context.config));
1016         }
1017         result.push_str(&where_clause_str);
1018
1019         if generics.where_clause.predicates.is_empty() {
1020             let item_snippet = context.snippet(item.span);
1021             if let Some(lo) = item_snippet.chars().position(|c| c == '/') {
1022                 // 1 = `{`
1023                 let comment_hi = body_lo - BytePos(1);
1024                 let comment_lo = item.span.lo() + BytePos(lo as u32);
1025                 if comment_lo < comment_hi {
1026                     match recover_missing_comment_in_span(
1027                         mk_sp(comment_lo, comment_hi),
1028                         Shape::indented(offset, context.config),
1029                         context,
1030                         last_line_width(&result),
1031                     ) {
1032                         Some(ref missing_comment) if !missing_comment.is_empty() => {
1033                             result.push_str(missing_comment);
1034                         }
1035                         _ => (),
1036                     }
1037                 }
1038             }
1039         }
1040
1041         match context.config.item_brace_style() {
1042             _ if last_line_contains_single_line_comment(&result) => {
1043                 result.push('\n');
1044                 result.push_str(&offset.to_string(context.config));
1045             }
1046             BraceStyle::AlwaysNextLine => {
1047                 result.push('\n');
1048                 result.push_str(&offset.to_string(context.config));
1049             }
1050             BraceStyle::PreferSameLine => result.push(' '),
1051             BraceStyle::SameLineWhere => if !where_clause_str.is_empty()
1052                 && (!trait_items.is_empty() || result.contains('\n'))
1053             {
1054                 result.push('\n');
1055                 result.push_str(&offset.to_string(context.config));
1056             } else {
1057                 result.push(' ');
1058             },
1059         }
1060         result.push('{');
1061
1062         let snippet = context.snippet(item.span);
1063         let open_pos = snippet.find_uncommented("{")? + 1;
1064
1065         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
1066             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
1067             visitor.block_indent = offset.block_only().block_indent(context.config);
1068             visitor.last_pos = item.span.lo() + BytePos(open_pos as u32);
1069
1070             for item in trait_items {
1071                 visitor.visit_trait_item(item);
1072             }
1073
1074             visitor.format_missing(item.span.hi() - BytePos(1));
1075
1076             let inner_indent_str = visitor.block_indent.to_string(context.config);
1077             let outer_indent_str = offset.block_only().to_string(context.config);
1078
1079             result.push('\n');
1080             result.push_str(&inner_indent_str);
1081             result.push_str(trim_newlines(visitor.buffer.to_string().trim()));
1082             result.push('\n');
1083             result.push_str(&outer_indent_str);
1084         } else if result.contains('\n') {
1085             result.push('\n');
1086         }
1087
1088         result.push('}');
1089         Some(result)
1090     } else {
1091         unreachable!();
1092     }
1093 }
1094
1095 fn format_unit_struct(context: &RewriteContext, p: &StructParts, offset: Indent) -> Option<String> {
1096     let header_str = format_header(p.prefix, p.ident, p.vis);
1097     let generics_str = if let Some(generics) = p.generics {
1098         let hi = if generics.where_clause.predicates.is_empty() {
1099             generics.span.hi()
1100         } else {
1101             generics.where_clause.span.hi()
1102         };
1103         format_generics(
1104             context,
1105             generics,
1106             context.config.item_brace_style(),
1107             BracePos::None,
1108             offset,
1109             mk_sp(generics.span.lo(), hi),
1110             last_line_width(&header_str),
1111         )?
1112     } else {
1113         String::new()
1114     };
1115     Some(format!("{}{};", header_str, generics_str))
1116 }
1117
1118 pub fn format_struct_struct(
1119     context: &RewriteContext,
1120     struct_parts: &StructParts,
1121     fields: &[ast::StructField],
1122     offset: Indent,
1123     one_line_width: Option<usize>,
1124 ) -> Option<String> {
1125     let mut result = String::with_capacity(1024);
1126     let span = struct_parts.span;
1127
1128     let header_str = struct_parts.format_header();
1129     result.push_str(&header_str);
1130
1131     let header_hi = span.lo() + BytePos(header_str.len() as u32);
1132     let body_lo = context.codemap.span_after(span, "{");
1133
1134     let generics_str = match struct_parts.generics {
1135         Some(g) => format_generics(
1136             context,
1137             g,
1138             context.config.item_brace_style(),
1139             if fields.is_empty() {
1140                 BracePos::ForceSameLine
1141             } else {
1142                 BracePos::Auto
1143             },
1144             offset,
1145             mk_sp(header_hi, body_lo),
1146             last_line_width(&result),
1147         )?,
1148         None => {
1149             // 3 = ` {}`, 2 = ` {`.
1150             let overhead = if fields.is_empty() { 3 } else { 2 };
1151             if (context.config.item_brace_style() == BraceStyle::AlwaysNextLine
1152                 && !fields.is_empty())
1153                 || context.config.max_width() < overhead + result.len()
1154             {
1155                 format!("\n{}{{", offset.block_only().to_string(context.config))
1156             } else {
1157                 " {".to_owned()
1158             }
1159         }
1160     };
1161     // 1 = `}`
1162     let overhead = if fields.is_empty() { 1 } else { 0 };
1163     let total_width = result.len() + generics_str.len() + overhead;
1164     if !generics_str.is_empty() && !generics_str.contains('\n')
1165         && total_width > context.config.max_width()
1166     {
1167         result.push('\n');
1168         result.push_str(&offset.to_string(context.config));
1169         result.push_str(generics_str.trim_left());
1170     } else {
1171         result.push_str(&generics_str);
1172     }
1173
1174     if fields.is_empty() {
1175         let snippet = context.snippet(mk_sp(body_lo, span.hi() - BytePos(1)));
1176         if snippet.trim().is_empty() {
1177             // `struct S {}`
1178         } else if snippet.trim_right_matches(&[' ', '\t'][..]).ends_with('\n') {
1179             // fix indent
1180             result.push_str(snippet.trim_right());
1181             result.push('\n');
1182             result.push_str(&offset.to_string(context.config));
1183         } else {
1184             result.push_str(&snippet);
1185         }
1186         result.push('}');
1187         return Some(result);
1188     }
1189
1190     // 3 = ` ` and ` }`
1191     let one_line_budget = context.budget(result.len() + 3 + offset.width());
1192     let one_line_budget =
1193         one_line_width.map_or(0, |one_line_width| min(one_line_width, one_line_budget));
1194
1195     let items_str = rewrite_with_alignment(
1196         fields,
1197         context,
1198         Shape::indented(offset, context.config),
1199         mk_sp(body_lo, span.hi()),
1200         one_line_budget,
1201     )?;
1202
1203     if !items_str.contains('\n') && !result.contains('\n') && items_str.len() <= one_line_budget {
1204         Some(format!("{} {} }}", result, items_str))
1205     } else {
1206         Some(format!(
1207             "{}\n{}{}\n{}}}",
1208             result,
1209             offset
1210                 .block_indent(context.config)
1211                 .to_string(context.config),
1212             items_str,
1213             offset.to_string(context.config)
1214         ))
1215     }
1216 }
1217
1218 /// Returns a bytepos that is after that of `(` in `pub(..)`. If the given visibility does not
1219 /// contain `pub(..)`, then return the `lo` of the `defualt_span`. Yeah, but for what? Well, we need
1220 /// to bypass the `(` in the visibility when creating a span of tuple's body or fn's args.
1221 fn get_bytepos_after_visibility(
1222     context: &RewriteContext,
1223     vis: &ast::Visibility,
1224     default_span: Span,
1225     terminator: &str,
1226 ) -> BytePos {
1227     match *vis {
1228         ast::Visibility::Crate(s, CrateSugar::PubCrate) => context
1229             .codemap
1230             .span_after(mk_sp(s.hi(), default_span.hi()), terminator),
1231         ast::Visibility::Crate(s, CrateSugar::JustCrate) => s.hi(),
1232         ast::Visibility::Restricted { ref path, .. } => path.span.hi(),
1233         _ => default_span.lo(),
1234     }
1235 }
1236
1237 fn format_tuple_struct(
1238     context: &RewriteContext,
1239     struct_parts: &StructParts,
1240     fields: &[ast::StructField],
1241     offset: Indent,
1242 ) -> Option<String> {
1243     let mut result = String::with_capacity(1024);
1244     let span = struct_parts.span;
1245
1246     let header_str = struct_parts.format_header();
1247     result.push_str(&header_str);
1248
1249     let body_lo = if fields.is_empty() {
1250         let lo = get_bytepos_after_visibility(context, struct_parts.vis, span, ")");
1251         context.codemap.span_after(mk_sp(lo, span.hi()), "(")
1252     } else {
1253         fields[0].span.lo()
1254     };
1255     let body_hi = if fields.is_empty() {
1256         context.codemap.span_after(mk_sp(body_lo, span.hi()), ")")
1257     } else {
1258         // This is a dirty hack to work around a missing `)` from the span of the last field.
1259         let last_arg_span = fields[fields.len() - 1].span;
1260         if context.snippet(last_arg_span).ends_with(')') {
1261             last_arg_span.hi()
1262         } else {
1263             context
1264                 .codemap
1265                 .span_after(mk_sp(last_arg_span.hi(), span.hi()), ")")
1266         }
1267     };
1268
1269     let where_clause_str = match struct_parts.generics {
1270         Some(generics) => {
1271             let budget = context.budget(last_line_width(&header_str));
1272             let shape = Shape::legacy(budget, offset);
1273             let g_span = mk_sp(span.lo(), body_lo);
1274             let generics_str = rewrite_generics(context, generics, shape, g_span)?;
1275             result.push_str(&generics_str);
1276
1277             let where_budget = context.budget(last_line_width(&result));
1278             let option = WhereClauseOption::new(true, false);
1279             rewrite_where_clause(
1280                 context,
1281                 &generics.where_clause,
1282                 context.config.item_brace_style(),
1283                 Shape::legacy(where_budget, offset.block_only()),
1284                 Density::Compressed,
1285                 ";",
1286                 None,
1287                 body_hi,
1288                 option,
1289                 false,
1290             )?
1291         }
1292         None => "".to_owned(),
1293     };
1294
1295     if fields.is_empty() {
1296         // 3 = `();`
1297         let used_width = last_line_used_width(&result, offset.width()) + 3;
1298         if used_width > context.config.max_width() {
1299             result.push('\n');
1300             result.push_str(&offset
1301                 .block_indent(context.config)
1302                 .to_string(context.config))
1303         }
1304         result.push('(');
1305         let snippet = context.snippet(mk_sp(
1306             body_lo,
1307             context.codemap.span_before(mk_sp(body_lo, span.hi()), ")"),
1308         ));
1309         if snippet.is_empty() {
1310             // `struct S ()`
1311         } else if snippet.trim_right_matches(&[' ', '\t'][..]).ends_with('\n') {
1312             result.push_str(snippet.trim_right());
1313             result.push('\n');
1314             result.push_str(&offset.to_string(context.config));
1315         } else {
1316             result.push_str(&snippet);
1317         }
1318         result.push(')');
1319     } else {
1320         let shape = Shape::indented(offset, context.config);
1321         let fields = &fields.iter().map(|field| field).collect::<Vec<_>>()[..];
1322         let one_line_width = context.config.fn_call_width();
1323         result = rewrite_call_inner(context, &result, fields, span, shape, one_line_width, false)?;
1324     }
1325
1326     if !where_clause_str.is_empty() && !where_clause_str.contains('\n')
1327         && (result.contains('\n')
1328             || offset.block_indent + result.len() + where_clause_str.len() + 1
1329                 > context.config.max_width())
1330     {
1331         // We need to put the where clause on a new line, but we didn't
1332         // know that earlier, so the where clause will not be indented properly.
1333         result.push('\n');
1334         result.push_str(&(offset.block_only() + (context.config.tab_spaces() - 1))
1335             .to_string(context.config));
1336     }
1337     result.push_str(&where_clause_str);
1338
1339     Some(result)
1340 }
1341
1342 pub fn rewrite_type_alias(
1343     context: &RewriteContext,
1344     indent: Indent,
1345     ident: ast::Ident,
1346     ty: &ast::Ty,
1347     generics: &ast::Generics,
1348     vis: &ast::Visibility,
1349     span: Span,
1350 ) -> Option<String> {
1351     let mut result = String::with_capacity(128);
1352
1353     result.push_str(&format_visibility(vis));
1354     result.push_str("type ");
1355     result.push_str(&ident.to_string());
1356
1357     // 2 = `= `
1358     let shape = Shape::indented(indent + result.len(), context.config).sub_width(2)?;
1359     let g_span = mk_sp(context.codemap.span_after(span, "type"), ty.span.lo());
1360     let generics_str = rewrite_generics(context, generics, shape, g_span)?;
1361     result.push_str(&generics_str);
1362
1363     let where_budget = context.budget(last_line_width(&result));
1364     let option = WhereClauseOption::snuggled(&result);
1365     let where_clause_str = rewrite_where_clause(
1366         context,
1367         &generics.where_clause,
1368         context.config.item_brace_style(),
1369         Shape::legacy(where_budget, indent),
1370         context.config.where_density(),
1371         "=",
1372         Some(span.hi()),
1373         generics.span.hi(),
1374         option,
1375         false,
1376     )?;
1377     result.push_str(&where_clause_str);
1378     if where_clause_str.is_empty() {
1379         result.push_str(" = ");
1380     } else {
1381         result.push_str(&format!("\n{}= ", indent.to_string(context.config)));
1382     }
1383
1384     let line_width = last_line_width(&result);
1385     // This checked_sub may fail as the extra space after '=' is not taken into account
1386     // In that case the budget is set to 0 which will make ty.rewrite retry on a new line
1387     let budget = context.budget(indent.width() + line_width + ";".len());
1388     let type_indent = indent + line_width;
1389     // Try to fit the type on the same line
1390     let ty_str = ty.rewrite(context, Shape::legacy(budget, type_indent))
1391         .or_else(|| {
1392             // The line was too short, try to put the type on the next line
1393
1394             // Remove the space after '='
1395             result.pop();
1396             let type_indent = indent.block_indent(context.config);
1397             result.push('\n');
1398             result.push_str(&type_indent.to_string(context.config));
1399             let budget = context.budget(type_indent.width() + ";".len());
1400             ty.rewrite(context, Shape::legacy(budget, type_indent))
1401         })?;
1402     result.push_str(&ty_str);
1403     result.push_str(";");
1404     Some(result)
1405 }
1406
1407 fn type_annotation_spacing(config: &Config) -> (&str, &str) {
1408     (
1409         if config.space_before_type_annotation() {
1410             " "
1411         } else {
1412             ""
1413         },
1414         if config.space_after_type_annotation_colon() {
1415             " "
1416         } else {
1417             ""
1418         },
1419     )
1420 }
1421
1422 pub fn rewrite_struct_field_prefix(
1423     context: &RewriteContext,
1424     field: &ast::StructField,
1425 ) -> Option<String> {
1426     let vis = format_visibility(&field.vis);
1427     let type_annotation_spacing = type_annotation_spacing(context.config);
1428     Some(match field.ident {
1429         Some(name) => format!("{}{}{}:", vis, name, type_annotation_spacing.0),
1430         None => format!("{}", vis),
1431     })
1432 }
1433
1434 impl Rewrite for ast::StructField {
1435     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1436         rewrite_struct_field(context, self, shape, 0)
1437     }
1438 }
1439
1440 pub fn rewrite_struct_field(
1441     context: &RewriteContext,
1442     field: &ast::StructField,
1443     shape: Shape,
1444     lhs_max_width: usize,
1445 ) -> Option<String> {
1446     if contains_skip(&field.attrs) {
1447         return Some(context.snippet(mk_sp(field.attrs[0].span.lo(), field.span.hi())));
1448     }
1449
1450     let type_annotation_spacing = type_annotation_spacing(context.config);
1451     let prefix = rewrite_struct_field_prefix(context, field)?;
1452
1453     let attrs_str = field.attrs.rewrite(context, shape)?;
1454     let attrs_extendable = attrs_str.is_empty()
1455         || (context.config.attributes_on_same_line_as_field()
1456             && is_attributes_extendable(&attrs_str));
1457     let missing_span = if field.attrs.is_empty() {
1458         mk_sp(field.span.lo(), field.span.lo())
1459     } else {
1460         mk_sp(field.attrs.last().unwrap().span.hi(), field.span.lo())
1461     };
1462     let mut spacing = String::from(if field.ident.is_some() {
1463         type_annotation_spacing.1
1464     } else {
1465         ""
1466     });
1467     // Try to put everything on a single line.
1468     let attr_prefix = combine_strs_with_missing_comments(
1469         context,
1470         &attrs_str,
1471         &prefix,
1472         missing_span,
1473         shape,
1474         attrs_extendable,
1475     )?;
1476     let overhead = last_line_width(&attr_prefix);
1477     let lhs_offset = lhs_max_width.checked_sub(overhead).unwrap_or(0);
1478     for _ in 0..lhs_offset {
1479         spacing.push(' ');
1480     }
1481     // In this extreme case we will be missing a space betweeen an attribute and a field.
1482     if prefix.is_empty() && !attrs_str.is_empty() && attrs_extendable && spacing.is_empty() {
1483         spacing.push(' ');
1484     }
1485     let ty_shape = shape.offset_left(overhead + spacing.len())?;
1486     if let Some(ref ty) = field.ty.rewrite(context, ty_shape) {
1487         if !ty.contains('\n') {
1488             return Some(attr_prefix + &spacing + ty);
1489         }
1490     }
1491
1492     // We must use multiline.
1493     let new_shape = shape.with_max_width(context.config);
1494     let ty_rewritten = field.ty.rewrite(context, new_shape)?;
1495
1496     let field_str = if prefix.is_empty() {
1497         ty_rewritten
1498     } else if prefix.len() + first_line_width(&ty_rewritten) + 1 <= shape.width {
1499         prefix + " " + &ty_rewritten
1500     } else {
1501         let type_offset = shape.indent.block_indent(context.config);
1502         let nested_shape = Shape::indented(type_offset, context.config);
1503         let nested_ty = field.ty.rewrite(context, nested_shape)?;
1504         prefix + "\n" + &type_offset.to_string(context.config) + &nested_ty
1505     };
1506     combine_strs_with_missing_comments(
1507         context,
1508         &attrs_str,
1509         &field_str,
1510         missing_span,
1511         shape,
1512         attrs_extendable,
1513     )
1514 }
1515
1516 pub struct StaticParts<'a> {
1517     prefix: &'a str,
1518     vis: &'a ast::Visibility,
1519     ident: ast::Ident,
1520     ty: &'a ast::Ty,
1521     mutability: ast::Mutability,
1522     expr_opt: Option<&'a ptr::P<ast::Expr>>,
1523     span: Span,
1524 }
1525
1526 impl<'a> StaticParts<'a> {
1527     pub fn from_item(item: &'a ast::Item) -> Self {
1528         let (prefix, ty, mutability, expr) = match item.node {
1529             ast::ItemKind::Static(ref ty, mutability, ref expr) => ("static", ty, mutability, expr),
1530             ast::ItemKind::Const(ref ty, ref expr) => {
1531                 ("const", ty, ast::Mutability::Immutable, expr)
1532             }
1533             _ => unreachable!(),
1534         };
1535         StaticParts {
1536             prefix: prefix,
1537             vis: &item.vis,
1538             ident: item.ident,
1539             ty: ty,
1540             mutability: mutability,
1541             expr_opt: Some(expr),
1542             span: item.span,
1543         }
1544     }
1545
1546     pub fn from_trait_item(ti: &'a ast::TraitItem) -> Self {
1547         let (ty, expr_opt) = match ti.node {
1548             ast::TraitItemKind::Const(ref ty, ref expr_opt) => (ty, expr_opt),
1549             _ => unreachable!(),
1550         };
1551         StaticParts {
1552             prefix: "const",
1553             vis: &ast::Visibility::Inherited,
1554             ident: ti.ident,
1555             ty: ty,
1556             mutability: ast::Mutability::Immutable,
1557             expr_opt: expr_opt.as_ref(),
1558             span: ti.span,
1559         }
1560     }
1561
1562     pub fn from_impl_item(ii: &'a ast::ImplItem) -> Self {
1563         let (ty, expr) = match ii.node {
1564             ast::ImplItemKind::Const(ref ty, ref expr) => (ty, expr),
1565             _ => unreachable!(),
1566         };
1567         StaticParts {
1568             prefix: "const",
1569             vis: &ii.vis,
1570             ident: ii.ident,
1571             ty: ty,
1572             mutability: ast::Mutability::Immutable,
1573             expr_opt: Some(expr),
1574             span: ii.span,
1575         }
1576     }
1577 }
1578
1579 fn rewrite_static(
1580     context: &RewriteContext,
1581     static_parts: &StaticParts,
1582     offset: Indent,
1583 ) -> Option<String> {
1584     let colon = colon_spaces(
1585         context.config.space_before_type_annotation(),
1586         context.config.space_after_type_annotation_colon(),
1587     );
1588     let prefix = format!(
1589         "{}{} {}{}{}",
1590         format_visibility(static_parts.vis),
1591         static_parts.prefix,
1592         format_mutability(static_parts.mutability),
1593         static_parts.ident,
1594         colon,
1595     );
1596     // 2 = " =".len()
1597     let ty_shape =
1598         Shape::indented(offset.block_only(), context.config).offset_left(prefix.len() + 2)?;
1599     let ty_str = static_parts.ty.rewrite(context, ty_shape)?;
1600
1601     if let Some(expr) = static_parts.expr_opt {
1602         let lhs = format!("{}{} =", prefix, ty_str);
1603         // 1 = ;
1604         let remaining_width = context.budget(offset.block_indent + 1);
1605         rewrite_assign_rhs(
1606             context,
1607             lhs,
1608             expr,
1609             Shape::legacy(remaining_width, offset.block_only()),
1610         ).and_then(|res| {
1611             recover_comment_removed(res, static_parts.span, context)
1612         })
1613             .map(|s| if s.ends_with(';') { s } else { s + ";" })
1614     } else {
1615         Some(format!("{}{};", prefix, ty_str))
1616     }
1617 }
1618
1619 pub fn rewrite_associated_type(
1620     ident: ast::Ident,
1621     ty_opt: Option<&ptr::P<ast::Ty>>,
1622     ty_param_bounds_opt: Option<&ast::TyParamBounds>,
1623     context: &RewriteContext,
1624     indent: Indent,
1625 ) -> Option<String> {
1626     let prefix = format!("type {}", ident);
1627
1628     let type_bounds_str = if let Some(ty_param_bounds) = ty_param_bounds_opt {
1629         // 2 = ": ".len()
1630         let shape = Shape::indented(indent, context.config).offset_left(prefix.len() + 2)?;
1631         let bounds: &[_] = ty_param_bounds;
1632         let bound_str = bounds
1633             .iter()
1634             .map(|ty_bound| ty_bound.rewrite(context, shape))
1635             .collect::<Option<Vec<_>>>()?;
1636         if !bounds.is_empty() {
1637             format!(": {}", join_bounds(context, shape, &bound_str))
1638         } else {
1639             String::new()
1640         }
1641     } else {
1642         String::new()
1643     };
1644
1645     if let Some(ty) = ty_opt {
1646         let ty_str = ty.rewrite(
1647             context,
1648             Shape::legacy(
1649                 context.budget(indent.block_indent + prefix.len() + 2),
1650                 indent.block_only(),
1651             ),
1652         )?;
1653         Some(format!("{}{} = {};", prefix, type_bounds_str, ty_str))
1654     } else {
1655         Some(format!("{}{};", prefix, type_bounds_str))
1656     }
1657 }
1658
1659 pub fn rewrite_associated_impl_type(
1660     ident: ast::Ident,
1661     defaultness: ast::Defaultness,
1662     ty_opt: Option<&ptr::P<ast::Ty>>,
1663     ty_param_bounds_opt: Option<&ast::TyParamBounds>,
1664     context: &RewriteContext,
1665     indent: Indent,
1666 ) -> Option<String> {
1667     let result = rewrite_associated_type(ident, ty_opt, ty_param_bounds_opt, context, indent)?;
1668
1669     match defaultness {
1670         ast::Defaultness::Default => Some(format!("default {}", result)),
1671         _ => Some(result),
1672     }
1673 }
1674
1675 impl Rewrite for ast::FunctionRetTy {
1676     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1677         match *self {
1678             ast::FunctionRetTy::Default(_) => Some(String::new()),
1679             ast::FunctionRetTy::Ty(ref ty) => {
1680                 let inner_width = shape.width.checked_sub(3)?;
1681                 ty.rewrite(context, Shape::legacy(inner_width, shape.indent + 3))
1682                     .map(|r| format!("-> {}", r))
1683             }
1684         }
1685     }
1686 }
1687
1688 fn is_empty_infer(context: &RewriteContext, ty: &ast::Ty) -> bool {
1689     match ty.node {
1690         ast::TyKind::Infer => {
1691             let original = context.snippet(ty.span);
1692             original != "_"
1693         }
1694         _ => false,
1695     }
1696 }
1697
1698 impl Rewrite for ast::Arg {
1699     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1700         if is_named_arg(self) {
1701             let mut result = self.pat
1702                 .rewrite(context, Shape::legacy(shape.width, shape.indent))?;
1703
1704             if !is_empty_infer(context, &*self.ty) {
1705                 if context.config.space_before_type_annotation() {
1706                     result.push_str(" ");
1707                 }
1708                 result.push_str(":");
1709                 if context.config.space_after_type_annotation_colon() {
1710                     result.push_str(" ");
1711                 }
1712                 let overhead = last_line_width(&result);
1713                 let max_width = shape.width.checked_sub(overhead)?;
1714                 let ty_str = self.ty
1715                     .rewrite(context, Shape::legacy(max_width, shape.indent))?;
1716                 result.push_str(&ty_str);
1717             }
1718
1719             Some(result)
1720         } else {
1721             self.ty.rewrite(context, shape)
1722         }
1723     }
1724 }
1725
1726 fn rewrite_explicit_self(
1727     explicit_self: &ast::ExplicitSelf,
1728     args: &[ast::Arg],
1729     context: &RewriteContext,
1730 ) -> Option<String> {
1731     match explicit_self.node {
1732         ast::SelfKind::Region(lt, m) => {
1733             let mut_str = format_mutability(m);
1734             match lt {
1735                 Some(ref l) => {
1736                     let lifetime_str = l.rewrite(
1737                         context,
1738                         Shape::legacy(context.config.max_width(), Indent::empty()),
1739                     )?;
1740                     Some(format!("&{} {}self", lifetime_str, mut_str))
1741                 }
1742                 None => Some(format!("&{}self", mut_str)),
1743             }
1744         }
1745         ast::SelfKind::Explicit(ref ty, _) => {
1746             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1747
1748             let mutability = explicit_self_mutability(&args[0]);
1749             let type_str = ty.rewrite(
1750                 context,
1751                 Shape::legacy(context.config.max_width(), Indent::empty()),
1752             )?;
1753
1754             Some(format!(
1755                 "{}self: {}",
1756                 format_mutability(mutability),
1757                 type_str
1758             ))
1759         }
1760         ast::SelfKind::Value(_) => {
1761             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1762
1763             let mutability = explicit_self_mutability(&args[0]);
1764
1765             Some(format!("{}self", format_mutability(mutability)))
1766         }
1767     }
1768 }
1769
1770 // Hacky solution caused by absence of `Mutability` in `SelfValue` and
1771 // `SelfExplicit` variants of `ast::ExplicitSelf_`.
1772 fn explicit_self_mutability(arg: &ast::Arg) -> ast::Mutability {
1773     if let ast::PatKind::Ident(ast::BindingMode::ByValue(mutability), _, _) = arg.pat.node {
1774         mutability
1775     } else {
1776         unreachable!()
1777     }
1778 }
1779
1780 pub fn span_lo_for_arg(arg: &ast::Arg) -> BytePos {
1781     if is_named_arg(arg) {
1782         arg.pat.span.lo()
1783     } else {
1784         arg.ty.span.lo()
1785     }
1786 }
1787
1788 pub fn span_hi_for_arg(context: &RewriteContext, arg: &ast::Arg) -> BytePos {
1789     match arg.ty.node {
1790         ast::TyKind::Infer if context.snippet(arg.ty.span) == "_" => arg.ty.span.hi(),
1791         ast::TyKind::Infer if is_named_arg(arg) => arg.pat.span.hi(),
1792         _ => arg.ty.span.hi(),
1793     }
1794 }
1795
1796 pub fn is_named_arg(arg: &ast::Arg) -> bool {
1797     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
1798         ident.node != symbol::keywords::Invalid.ident()
1799     } else {
1800         true
1801     }
1802 }
1803
1804 // Return type is (result, force_new_line_for_brace)
1805 fn rewrite_fn_base(
1806     context: &RewriteContext,
1807     indent: Indent,
1808     ident: ast::Ident,
1809     fn_sig: &FnSig,
1810     span: Span,
1811     newline_brace: bool,
1812     has_body: bool,
1813 ) -> Option<(String, bool)> {
1814     let mut force_new_line_for_brace = false;
1815
1816     let where_clause = &fn_sig.generics.where_clause;
1817
1818     let mut result = String::with_capacity(1024);
1819     result.push_str(&fn_sig.to_str(context));
1820
1821     // fn foo
1822     result.push_str("fn ");
1823     result.push_str(&ident.to_string());
1824
1825     // Generics.
1826     let overhead = if has_body && !newline_brace {
1827         // 4 = `() {`
1828         4
1829     } else {
1830         // 2 = `()`
1831         2
1832     };
1833     let used_width = last_line_used_width(&result, indent.width());
1834     let one_line_budget = context.budget(used_width + overhead);
1835     let shape = Shape {
1836         width: one_line_budget,
1837         indent: indent,
1838         offset: used_width,
1839     };
1840     let fd = fn_sig.decl;
1841     let g_span = mk_sp(span.lo(), fd.output.span().lo());
1842     let generics_str = rewrite_generics(context, fn_sig.generics, shape, g_span)?;
1843     result.push_str(&generics_str);
1844
1845     let snuggle_angle_bracket = generics_str
1846         .lines()
1847         .last()
1848         .map_or(false, |l| l.trim_left().len() == 1);
1849
1850     // Note that the width and indent don't really matter, we'll re-layout the
1851     // return type later anyway.
1852     let ret_str = fd.output
1853         .rewrite(context, Shape::indented(indent, context.config))?;
1854
1855     let multi_line_ret_str = ret_str.contains('\n');
1856     let ret_str_len = if multi_line_ret_str { 0 } else { ret_str.len() };
1857
1858     // Args.
1859     let (one_line_budget, multi_line_budget, mut arg_indent) = compute_budgets_for_args(
1860         context,
1861         &result,
1862         indent,
1863         ret_str_len,
1864         newline_brace,
1865         has_body,
1866         multi_line_ret_str,
1867     )?;
1868
1869     debug!(
1870         "rewrite_fn_base: one_line_budget: {}, multi_line_budget: {}, arg_indent: {:?}",
1871         one_line_budget,
1872         multi_line_budget,
1873         arg_indent
1874     );
1875
1876     // Check if vertical layout was forced.
1877     if one_line_budget == 0 {
1878         if snuggle_angle_bracket {
1879             result.push('(');
1880         } else if context.config.fn_args_paren_newline() {
1881             result.push('\n');
1882             result.push_str(&arg_indent.to_string(context.config));
1883             if context.config.fn_args_indent() == IndentStyle::Visual {
1884                 arg_indent = arg_indent + 1; // extra space for `(`
1885             }
1886             result.push('(');
1887         } else {
1888             result.push_str("(");
1889             if context.config.fn_args_indent() == IndentStyle::Visual {
1890                 result.push('\n');
1891                 result.push_str(&arg_indent.to_string(context.config));
1892             }
1893         }
1894     } else {
1895         result.push('(');
1896     }
1897     if context.config.spaces_within_parens() && !fd.inputs.is_empty() && result.ends_with('(') {
1898         result.push(' ')
1899     }
1900
1901     // Skip `pub(crate)`.
1902     let lo_after_visibility = get_bytepos_after_visibility(context, &fn_sig.visibility, span, ")");
1903     // A conservative estimation, to goal is to be over all parens in generics
1904     let args_start = fn_sig
1905         .generics
1906         .ty_params
1907         .last()
1908         .map_or(lo_after_visibility, |tp| end_typaram(tp));
1909     let args_end = if fd.inputs.is_empty() {
1910         context
1911             .codemap
1912             .span_after(mk_sp(args_start, span.hi()), ")")
1913     } else {
1914         let last_span = mk_sp(fd.inputs[fd.inputs.len() - 1].span().hi(), span.hi());
1915         context.codemap.span_after(last_span, ")")
1916     };
1917     let args_span = mk_sp(
1918         context
1919             .codemap
1920             .span_after(mk_sp(args_start, span.hi()), "("),
1921         args_end,
1922     );
1923     let arg_str = rewrite_args(
1924         context,
1925         &fd.inputs,
1926         fd.get_self().as_ref(),
1927         one_line_budget,
1928         multi_line_budget,
1929         indent,
1930         arg_indent,
1931         args_span,
1932         fd.variadic,
1933         generics_str.contains('\n'),
1934     )?;
1935
1936     let put_args_in_block = match context.config.fn_args_indent() {
1937         IndentStyle::Block => arg_str.contains('\n') || arg_str.len() > one_line_budget,
1938         _ => false,
1939     } && !fd.inputs.is_empty();
1940
1941     let mut args_last_line_contains_comment = false;
1942     if put_args_in_block {
1943         arg_indent = indent.block_indent(context.config);
1944         result.push('\n');
1945         result.push_str(&arg_indent.to_string(context.config));
1946         result.push_str(&arg_str);
1947         result.push('\n');
1948         result.push_str(&indent.to_string(context.config));
1949         result.push(')');
1950     } else {
1951         result.push_str(&arg_str);
1952         let used_width = last_line_used_width(&result, indent.width()) + first_line_width(&ret_str);
1953         // Put the closing brace on the next line if it overflows the max width.
1954         // 1 = `)`
1955         if fd.inputs.is_empty() && used_width + 1 > context.config.max_width() {
1956             result.push('\n');
1957         }
1958         if context.config.spaces_within_parens() && !fd.inputs.is_empty() {
1959             result.push(' ')
1960         }
1961         // If the last line of args contains comment, we cannot put the closing paren
1962         // on the same line.
1963         if arg_str
1964             .lines()
1965             .last()
1966             .map_or(false, |last_line| last_line.contains("//"))
1967         {
1968             args_last_line_contains_comment = true;
1969             result.push('\n');
1970             result.push_str(&arg_indent.to_string(context.config));
1971         }
1972         result.push(')');
1973     }
1974
1975     // Return type.
1976     if let ast::FunctionRetTy::Ty(..) = fd.output {
1977         let ret_should_indent = match context.config.fn_args_indent() {
1978             // If our args are block layout then we surely must have space.
1979             IndentStyle::Block if put_args_in_block || fd.inputs.is_empty() => false,
1980             _ if args_last_line_contains_comment => false,
1981             _ if result.contains('\n') || multi_line_ret_str => true,
1982             _ => {
1983                 // If the return type would push over the max width, then put the return type on
1984                 // a new line. With the +1 for the signature length an additional space between
1985                 // the closing parenthesis of the argument and the arrow '->' is considered.
1986                 let mut sig_length = result.len() + indent.width() + ret_str_len + 1;
1987
1988                 // If there is no where clause, take into account the space after the return type
1989                 // and the brace.
1990                 if where_clause.predicates.is_empty() {
1991                     sig_length += 2;
1992                 }
1993
1994                 sig_length > context.config.max_width()
1995             }
1996         };
1997         let ret_indent = if ret_should_indent {
1998             let indent = match context.config.fn_return_indent() {
1999                 ReturnIndent::WithWhereClause => indent + 4,
2000                 // Aligning with non-existent args looks silly.
2001                 _ if arg_str.is_empty() => {
2002                     force_new_line_for_brace = true;
2003                     indent + 4
2004                 }
2005                 // FIXME: we might want to check that using the arg indent
2006                 // doesn't blow our budget, and if it does, then fallback to
2007                 // the where clause indent.
2008                 _ => arg_indent,
2009             };
2010
2011             result.push('\n');
2012             result.push_str(&indent.to_string(context.config));
2013             indent
2014         } else {
2015             result.push(' ');
2016             Indent::new(indent.block_indent, last_line_width(&result))
2017         };
2018
2019         if multi_line_ret_str || ret_should_indent {
2020             // Now that we know the proper indent and width, we need to
2021             // re-layout the return type.
2022             let ret_str = fd.output
2023                 .rewrite(context, Shape::indented(ret_indent, context.config))?;
2024             result.push_str(&ret_str);
2025         } else {
2026             result.push_str(&ret_str);
2027         }
2028
2029         // Comment between return type and the end of the decl.
2030         let snippet_lo = fd.output.span().hi();
2031         if where_clause.predicates.is_empty() {
2032             let snippet_hi = span.hi();
2033             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
2034             // Try to preserve the layout of the original snippet.
2035             let original_starts_with_newline = snippet
2036                 .find(|c| c != ' ')
2037                 .map_or(false, |i| starts_with_newline(&snippet[i..]));
2038             let original_ends_with_newline = snippet
2039                 .rfind(|c| c != ' ')
2040                 .map_or(false, |i| snippet[i..].ends_with('\n'));
2041             let snippet = snippet.trim();
2042             if !snippet.is_empty() {
2043                 result.push(if original_starts_with_newline {
2044                     '\n'
2045                 } else {
2046                     ' '
2047                 });
2048                 result.push_str(snippet);
2049                 if original_ends_with_newline {
2050                     force_new_line_for_brace = true;
2051                 }
2052             }
2053         }
2054     }
2055
2056     let should_compress_where = match context.config.where_density() {
2057         Density::Compressed => !result.contains('\n'),
2058         Density::CompressedIfEmpty => !has_body && !result.contains('\n'),
2059         _ => false,
2060     };
2061
2062     let pos_before_where = match fd.output {
2063         ast::FunctionRetTy::Default(..) => args_span.hi(),
2064         ast::FunctionRetTy::Ty(ref ty) => ty.span.hi(),
2065     };
2066
2067     let is_args_multi_lined = arg_str.contains('\n');
2068
2069     if where_clause.predicates.len() == 1 && should_compress_where {
2070         let budget = context.budget(last_line_used_width(&result, indent.width()));
2071         if let Some(where_clause_str) = rewrite_where_clause(
2072             context,
2073             where_clause,
2074             context.config.fn_brace_style(),
2075             Shape::legacy(budget, indent),
2076             Density::Compressed,
2077             "{",
2078             Some(span.hi()),
2079             pos_before_where,
2080             WhereClauseOption::compressed(),
2081             is_args_multi_lined,
2082         ) {
2083             result.push_str(&where_clause_str);
2084             force_new_line_for_brace |= last_line_contains_single_line_comment(&result);
2085             return Some((result, force_new_line_for_brace));
2086         }
2087     }
2088
2089     let option = WhereClauseOption::new(!has_body, put_args_in_block && ret_str.is_empty());
2090     let where_clause_str = rewrite_where_clause(
2091         context,
2092         where_clause,
2093         context.config.fn_brace_style(),
2094         Shape::indented(indent, context.config),
2095         Density::Tall,
2096         "{",
2097         Some(span.hi()),
2098         pos_before_where,
2099         option,
2100         is_args_multi_lined,
2101     )?;
2102     // If there are neither where clause nor return type, we may be missing comments between
2103     // args and `{`.
2104     if where_clause_str.is_empty() {
2105         if let ast::FunctionRetTy::Default(ret_span) = fd.output {
2106             match recover_missing_comment_in_span(
2107                 mk_sp(args_span.hi(), ret_span.hi()),
2108                 shape,
2109                 context,
2110                 last_line_width(&result),
2111             ) {
2112                 Some(ref missing_comment) if !missing_comment.is_empty() => {
2113                     result.push_str(missing_comment);
2114                     force_new_line_for_brace = true;
2115                 }
2116                 _ => (),
2117             }
2118         }
2119     }
2120
2121     result.push_str(&where_clause_str);
2122
2123     force_new_line_for_brace |= last_line_contains_single_line_comment(&result);
2124     force_new_line_for_brace |= is_args_multi_lined && context.config.where_single_line();
2125     Some((result, force_new_line_for_brace))
2126 }
2127
2128 #[derive(Copy, Clone)]
2129 struct WhereClauseOption {
2130     suppress_comma: bool, // Force no trailing comma
2131     snuggle: bool,        // Do not insert newline before `where`
2132     compress_where: bool, // Try single line where clause instead of vertical layout
2133 }
2134
2135 impl WhereClauseOption {
2136     pub fn new(suppress_comma: bool, snuggle: bool) -> WhereClauseOption {
2137         WhereClauseOption {
2138             suppress_comma: suppress_comma,
2139             snuggle: snuggle,
2140             compress_where: false,
2141         }
2142     }
2143
2144     pub fn compressed() -> WhereClauseOption {
2145         WhereClauseOption {
2146             suppress_comma: true,
2147             snuggle: false,
2148             compress_where: true,
2149         }
2150     }
2151
2152     pub fn snuggled(current: &str) -> WhereClauseOption {
2153         WhereClauseOption {
2154             suppress_comma: false,
2155             snuggle: trimmed_last_line_width(current) == 1,
2156             compress_where: false,
2157         }
2158     }
2159 }
2160
2161 fn rewrite_args(
2162     context: &RewriteContext,
2163     args: &[ast::Arg],
2164     explicit_self: Option<&ast::ExplicitSelf>,
2165     one_line_budget: usize,
2166     multi_line_budget: usize,
2167     indent: Indent,
2168     arg_indent: Indent,
2169     span: Span,
2170     variadic: bool,
2171     generics_str_contains_newline: bool,
2172 ) -> Option<String> {
2173     let mut arg_item_strs = args.iter()
2174         .map(|arg| {
2175             arg.rewrite(context, Shape::legacy(multi_line_budget, arg_indent))
2176         })
2177         .collect::<Option<Vec<_>>>()?;
2178
2179     // Account for sugary self.
2180     // FIXME: the comment for the self argument is dropped. This is blocked
2181     // on rust issue #27522.
2182     let min_args = explicit_self
2183         .and_then(|explicit_self| {
2184             rewrite_explicit_self(explicit_self, args, context)
2185         })
2186         .map_or(1, |self_str| {
2187             arg_item_strs[0] = self_str;
2188             2
2189         });
2190
2191     // Comments between args.
2192     let mut arg_items = Vec::new();
2193     if min_args == 2 {
2194         arg_items.push(ListItem::from_str(""));
2195     }
2196
2197     // FIXME(#21): if there are no args, there might still be a comment, but
2198     // without spans for the comment or parens, there is no chance of
2199     // getting it right. You also don't get to put a comment on self, unless
2200     // it is explicit.
2201     if args.len() >= min_args || variadic {
2202         let comment_span_start = if min_args == 2 {
2203             let second_arg_start = if arg_has_pattern(&args[1]) {
2204                 args[1].pat.span.lo()
2205             } else {
2206                 args[1].ty.span.lo()
2207             };
2208             let reduced_span = mk_sp(span.lo(), second_arg_start);
2209
2210             context.codemap.span_after_last(reduced_span, ",")
2211         } else {
2212             span.lo()
2213         };
2214
2215         enum ArgumentKind<'a> {
2216             Regular(&'a ast::Arg),
2217             Variadic(BytePos),
2218         }
2219
2220         let variadic_arg = if variadic {
2221             let variadic_span = mk_sp(args.last().unwrap().ty.span.hi(), span.hi());
2222             let variadic_start = context.codemap.span_after(variadic_span, "...") - BytePos(3);
2223             Some(ArgumentKind::Variadic(variadic_start))
2224         } else {
2225             None
2226         };
2227
2228         let more_items = itemize_list(
2229             context.codemap,
2230             args[min_args - 1..]
2231                 .iter()
2232                 .map(ArgumentKind::Regular)
2233                 .chain(variadic_arg),
2234             ")",
2235             |arg| match *arg {
2236                 ArgumentKind::Regular(arg) => span_lo_for_arg(arg),
2237                 ArgumentKind::Variadic(start) => start,
2238             },
2239             |arg| match *arg {
2240                 ArgumentKind::Regular(arg) => arg.ty.span.hi(),
2241                 ArgumentKind::Variadic(start) => start + BytePos(3),
2242             },
2243             |arg| match *arg {
2244                 ArgumentKind::Regular(..) => None,
2245                 ArgumentKind::Variadic(..) => Some("...".to_owned()),
2246             },
2247             comment_span_start,
2248             span.hi(),
2249             false,
2250         );
2251
2252         arg_items.extend(more_items);
2253     }
2254
2255     let fits_in_one_line = !generics_str_contains_newline
2256         && (arg_items.is_empty()
2257             || arg_items.len() == 1 && arg_item_strs[0].len() <= one_line_budget);
2258
2259     for (item, arg) in arg_items.iter_mut().zip(arg_item_strs) {
2260         item.item = Some(arg);
2261     }
2262
2263     let last_line_ends_with_comment = arg_items
2264         .iter()
2265         .last()
2266         .and_then(|item| item.post_comment.as_ref())
2267         .map_or(false, |s| s.trim().starts_with("//"));
2268
2269     let (indent, trailing_comma) = match context.config.fn_args_indent() {
2270         IndentStyle::Block if fits_in_one_line => {
2271             (indent.block_indent(context.config), SeparatorTactic::Never)
2272         }
2273         IndentStyle::Block => (
2274             indent.block_indent(context.config),
2275             context.config.trailing_comma(),
2276         ),
2277         IndentStyle::Visual if last_line_ends_with_comment => {
2278             (arg_indent, context.config.trailing_comma())
2279         }
2280         IndentStyle::Visual => (arg_indent, SeparatorTactic::Never),
2281     };
2282
2283     let tactic = definitive_tactic(
2284         &arg_items,
2285         context.config.fn_args_density().to_list_tactic(),
2286         Separator::Comma,
2287         one_line_budget,
2288     );
2289     let budget = match tactic {
2290         DefinitiveListTactic::Horizontal => one_line_budget,
2291         _ => multi_line_budget,
2292     };
2293
2294     debug!("rewrite_args: budget: {}, tactic: {:?}", budget, tactic);
2295
2296     let fmt = ListFormatting {
2297         tactic: tactic,
2298         separator: ",",
2299         trailing_separator: if variadic {
2300             SeparatorTactic::Never
2301         } else {
2302             trailing_comma
2303         },
2304         separator_place: SeparatorPlace::Back,
2305         shape: Shape::legacy(budget, indent),
2306         ends_with_newline: tactic.ends_with_newline(context.config.fn_args_indent()),
2307         preserve_newline: true,
2308         config: context.config,
2309     };
2310
2311     write_list(&arg_items, &fmt)
2312 }
2313
2314 fn arg_has_pattern(arg: &ast::Arg) -> bool {
2315     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
2316         ident.node != symbol::keywords::Invalid.ident()
2317     } else {
2318         true
2319     }
2320 }
2321
2322 fn compute_budgets_for_args(
2323     context: &RewriteContext,
2324     result: &str,
2325     indent: Indent,
2326     ret_str_len: usize,
2327     newline_brace: bool,
2328     has_braces: bool,
2329     force_vertical_layout: bool,
2330 ) -> Option<((usize, usize, Indent))> {
2331     debug!(
2332         "compute_budgets_for_args {} {:?}, {}, {}",
2333         result.len(),
2334         indent,
2335         ret_str_len,
2336         newline_brace
2337     );
2338     // Try keeping everything on the same line.
2339     if !result.contains('\n') && !force_vertical_layout {
2340         // 2 = `()`, 3 = `() `, space is before ret_string.
2341         let overhead = if ret_str_len == 0 { 2 } else { 3 };
2342         let mut used_space = indent.width() + result.len() + ret_str_len + overhead;
2343         if has_braces {
2344             if !newline_brace {
2345                 // 2 = `{}`
2346                 used_space += 2;
2347             }
2348         } else {
2349             // 1 = `;`
2350             used_space += 1;
2351         }
2352         let one_line_budget = context.budget(used_space);
2353
2354         if one_line_budget > 0 {
2355             // 4 = "() {".len()
2356             let (indent, multi_line_budget) = match context.config.fn_args_indent() {
2357                 IndentStyle::Block => {
2358                     let indent = indent.block_indent(context.config);
2359                     (indent, context.budget(indent.width() + 1))
2360                 }
2361                 IndentStyle::Visual => {
2362                     let indent = indent + result.len() + 1;
2363                     let multi_line_overhead = indent.width() + if newline_brace { 2 } else { 4 };
2364                     (indent, context.budget(multi_line_overhead))
2365                 }
2366             };
2367
2368             return Some((one_line_budget, multi_line_budget, indent));
2369         }
2370     }
2371
2372     // Didn't work. we must force vertical layout and put args on a newline.
2373     let new_indent = indent.block_indent(context.config);
2374     let used_space = match context.config.fn_args_indent() {
2375         // 1 = `,`
2376         IndentStyle::Block => new_indent.width() + 1,
2377         // Account for `)` and possibly ` {`.
2378         IndentStyle::Visual => new_indent.width() + if ret_str_len == 0 { 1 } else { 3 },
2379     };
2380     Some((0, context.budget(used_space), new_indent))
2381 }
2382
2383 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause, has_body: bool) -> bool {
2384     let predicate_count = where_clause.predicates.len();
2385
2386     if config.where_single_line() && predicate_count == 1 {
2387         return false;
2388     }
2389     match (config.fn_brace_style(), config.where_density()) {
2390         (BraceStyle::AlwaysNextLine, _) => true,
2391         (_, Density::Compressed) if predicate_count == 1 => false,
2392         (_, Density::CompressedIfEmpty) if predicate_count == 1 && !has_body => false,
2393         (BraceStyle::SameLineWhere, _) if predicate_count > 0 => true,
2394         _ => false,
2395     }
2396 }
2397
2398 fn rewrite_generics(
2399     context: &RewriteContext,
2400     generics: &ast::Generics,
2401     shape: Shape,
2402     span: Span,
2403 ) -> Option<String> {
2404     let g_shape = generics_shape_from_config(context.config, shape, 0)?;
2405     let one_line_width = shape.width.checked_sub(2).unwrap_or(0);
2406     rewrite_generics_inner(context, generics, g_shape, one_line_width, span).or_else(|| {
2407         rewrite_generics_inner(context, generics, g_shape, 0, span)
2408     })
2409 }
2410
2411 fn rewrite_generics_inner(
2412     context: &RewriteContext,
2413     generics: &ast::Generics,
2414     shape: Shape,
2415     one_line_width: usize,
2416     span: Span,
2417 ) -> Option<String> {
2418     // FIXME: convert bounds to where clauses where they get too big or if
2419     // there is a where clause at all.
2420
2421     // Wrapper type
2422     enum GenericsArg<'a> {
2423         Lifetime(&'a ast::LifetimeDef),
2424         TyParam(&'a ast::TyParam),
2425     }
2426     impl<'a> Rewrite for GenericsArg<'a> {
2427         fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
2428             match *self {
2429                 GenericsArg::Lifetime(lifetime) => lifetime.rewrite(context, shape),
2430                 GenericsArg::TyParam(ty) => ty.rewrite(context, shape),
2431             }
2432         }
2433     }
2434     impl<'a> Spanned for GenericsArg<'a> {
2435         fn span(&self) -> Span {
2436             match *self {
2437                 GenericsArg::Lifetime(lifetime) => lifetime.span(),
2438                 GenericsArg::TyParam(ty) => ty.span(),
2439             }
2440         }
2441     }
2442
2443     if generics.lifetimes.is_empty() && generics.ty_params.is_empty() {
2444         return Some(String::new());
2445     }
2446
2447     let generics_args = generics
2448         .lifetimes
2449         .iter()
2450         .map(|lt| GenericsArg::Lifetime(lt))
2451         .chain(generics.ty_params.iter().map(|ty| GenericsArg::TyParam(ty)));
2452     let items = itemize_list(
2453         context.codemap,
2454         generics_args,
2455         ">",
2456         |arg| arg.span().lo(),
2457         |arg| arg.span().hi(),
2458         |arg| arg.rewrite(context, shape),
2459         context.codemap.span_after(span, "<"),
2460         span.hi(),
2461         false,
2462     );
2463     format_generics_item_list(context, items, shape, one_line_width)
2464 }
2465
2466 pub fn generics_shape_from_config(config: &Config, shape: Shape, offset: usize) -> Option<Shape> {
2467     match config.generics_indent() {
2468         IndentStyle::Visual => shape.visual_indent(1 + offset).sub_width(offset + 2),
2469         IndentStyle::Block => {
2470             // 1 = ","
2471             shape
2472                 .block()
2473                 .block_indent(config.tab_spaces())
2474                 .with_max_width(config)
2475                 .sub_width(1)
2476         }
2477     }
2478 }
2479
2480 pub fn format_generics_item_list<I>(
2481     context: &RewriteContext,
2482     items: I,
2483     shape: Shape,
2484     one_line_budget: usize,
2485 ) -> Option<String>
2486 where
2487     I: Iterator<Item = ListItem>,
2488 {
2489     let item_vec = items.collect::<Vec<_>>();
2490
2491     let tactic = definitive_tactic(
2492         &item_vec,
2493         ListTactic::HorizontalVertical,
2494         Separator::Comma,
2495         one_line_budget,
2496     );
2497     let fmt = ListFormatting {
2498         tactic: tactic,
2499         separator: ",",
2500         trailing_separator: if context.config.generics_indent() == IndentStyle::Visual {
2501             SeparatorTactic::Never
2502         } else {
2503             context.config.trailing_comma()
2504         },
2505         separator_place: SeparatorPlace::Back,
2506         shape: shape,
2507         ends_with_newline: tactic.ends_with_newline(context.config.generics_indent()),
2508         preserve_newline: true,
2509         config: context.config,
2510     };
2511
2512     let list_str = write_list(&item_vec, &fmt)?;
2513
2514     Some(wrap_generics_with_angle_brackets(
2515         context,
2516         &list_str,
2517         shape.indent,
2518     ))
2519 }
2520
2521 pub fn wrap_generics_with_angle_brackets(
2522     context: &RewriteContext,
2523     list_str: &str,
2524     list_offset: Indent,
2525 ) -> String {
2526     if context.config.generics_indent() == IndentStyle::Block
2527         && (list_str.contains('\n') || list_str.ends_with(','))
2528     {
2529         format!(
2530             "<\n{}{}\n{}>",
2531             list_offset.to_string(context.config),
2532             list_str,
2533             list_offset
2534                 .block_unindent(context.config)
2535                 .to_string(context.config)
2536         )
2537     } else if context.config.spaces_within_angle_brackets() {
2538         format!("< {} >", list_str)
2539     } else {
2540         format!("<{}>", list_str)
2541     }
2542 }
2543
2544 fn rewrite_trait_bounds(
2545     context: &RewriteContext,
2546     type_param_bounds: &ast::TyParamBounds,
2547     shape: Shape,
2548 ) -> Option<String> {
2549     let bounds: &[_] = type_param_bounds;
2550
2551     if bounds.is_empty() {
2552         return Some(String::new());
2553     }
2554     let bound_str = bounds
2555         .iter()
2556         .map(|ty_bound| ty_bound.rewrite(context, shape))
2557         .collect::<Option<Vec<_>>>()?;
2558     Some(format!(": {}", join_bounds(context, shape, &bound_str)))
2559 }
2560
2561 fn rewrite_where_clause_rfc_style(
2562     context: &RewriteContext,
2563     where_clause: &ast::WhereClause,
2564     shape: Shape,
2565     terminator: &str,
2566     span_end: Option<BytePos>,
2567     span_end_before_where: BytePos,
2568     where_clause_option: WhereClauseOption,
2569     is_args_multi_line: bool,
2570 ) -> Option<String> {
2571     let block_shape = shape.block().with_max_width(context.config);
2572
2573     let (span_before, span_after) =
2574         missing_span_before_after_where(span_end_before_where, where_clause);
2575     let (comment_before, comment_after) =
2576         rewrite_comments_before_after_where(context, span_before, span_after, shape)?;
2577
2578     let starting_newline = if where_clause_option.snuggle && comment_before.is_empty() {
2579         " ".to_owned()
2580     } else {
2581         "\n".to_owned() + &block_shape.indent.to_string(context.config)
2582     };
2583
2584     let clause_shape = block_shape.block_left(context.config.tab_spaces())?;
2585     // 1 = `,`
2586     let clause_shape = clause_shape.sub_width(1)?;
2587     // each clause on one line, trailing comma (except if suppress_comma)
2588     let span_start = where_clause.predicates[0].span().lo();
2589     // If we don't have the start of the next span, then use the end of the
2590     // predicates, but that means we miss comments.
2591     let len = where_clause.predicates.len();
2592     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2593     let span_end = span_end.unwrap_or(end_of_preds);
2594     let items = itemize_list(
2595         context.codemap,
2596         where_clause.predicates.iter(),
2597         terminator,
2598         |pred| pred.span().lo(),
2599         |pred| pred.span().hi(),
2600         |pred| pred.rewrite(context, clause_shape),
2601         span_start,
2602         span_end,
2603         false,
2604     );
2605     let where_single_line = context.config.where_single_line() && len == 1 && !is_args_multi_line;
2606     let comma_tactic = if where_clause_option.suppress_comma || where_single_line {
2607         SeparatorTactic::Never
2608     } else {
2609         context.config.trailing_comma()
2610     };
2611
2612     // shape should be vertical only and only if we have `where_single_line` option enabled
2613     // and the number of items of the where clause is equal to 1
2614     let shape_tactic = if where_single_line {
2615         DefinitiveListTactic::Horizontal
2616     } else {
2617         DefinitiveListTactic::Vertical
2618     };
2619
2620     let fmt = ListFormatting {
2621         tactic: shape_tactic,
2622         separator: ",",
2623         trailing_separator: comma_tactic,
2624         separator_place: SeparatorPlace::Back,
2625         shape: clause_shape,
2626         ends_with_newline: true,
2627         preserve_newline: true,
2628         config: context.config,
2629     };
2630     let preds_str = write_list(&items.collect::<Vec<_>>(), &fmt)?;
2631
2632     let comment_separator = |comment: &str, shape: Shape| if comment.is_empty() {
2633         String::new()
2634     } else {
2635         format!("\n{}", shape.indent.to_string(context.config))
2636     };
2637     let newline_before_where = comment_separator(&comment_before, shape);
2638     let newline_after_where = comment_separator(&comment_after, clause_shape);
2639
2640     // 6 = `where `
2641     let clause_sep = if where_clause_option.compress_where && comment_before.is_empty()
2642         && comment_after.is_empty() && !preds_str.contains('\n')
2643         && 6 + preds_str.len() <= shape.width || where_single_line
2644     {
2645         String::from(" ")
2646     } else {
2647         format!("\n{}", clause_shape.indent.to_string(context.config))
2648     };
2649     Some(format!(
2650         "{}{}{}where{}{}{}{}",
2651         starting_newline,
2652         comment_before,
2653         newline_before_where,
2654         newline_after_where,
2655         comment_after,
2656         clause_sep,
2657         preds_str
2658     ))
2659 }
2660
2661 fn rewrite_where_clause(
2662     context: &RewriteContext,
2663     where_clause: &ast::WhereClause,
2664     brace_style: BraceStyle,
2665     shape: Shape,
2666     density: Density,
2667     terminator: &str,
2668     span_end: Option<BytePos>,
2669     span_end_before_where: BytePos,
2670     where_clause_option: WhereClauseOption,
2671     is_args_multi_line: bool,
2672 ) -> Option<String> {
2673     if where_clause.predicates.is_empty() {
2674         return Some(String::new());
2675     }
2676
2677     if context.config.where_style() == Style::Rfc {
2678         return rewrite_where_clause_rfc_style(
2679             context,
2680             where_clause,
2681             shape,
2682             terminator,
2683             span_end,
2684             span_end_before_where,
2685             where_clause_option,
2686             is_args_multi_line,
2687         );
2688     }
2689
2690     let extra_indent = Indent::new(context.config.tab_spaces(), 0);
2691
2692     let offset = match context.config.where_pred_indent() {
2693         IndentStyle::Block => shape.indent + extra_indent.block_indent(context.config),
2694         // 6 = "where ".len()
2695         IndentStyle::Visual => shape.indent + extra_indent + 6,
2696     };
2697     // FIXME: if where_pred_indent != Visual, then the budgets below might
2698     // be out by a char or two.
2699
2700     let budget = context.config.max_width() - offset.width();
2701     let span_start = where_clause.predicates[0].span().lo();
2702     // If we don't have the start of the next span, then use the end of the
2703     // predicates, but that means we miss comments.
2704     let len = where_clause.predicates.len();
2705     let end_of_preds = where_clause.predicates[len - 1].span().hi();
2706     let span_end = span_end.unwrap_or(end_of_preds);
2707     let items = itemize_list(
2708         context.codemap,
2709         where_clause.predicates.iter(),
2710         terminator,
2711         |pred| pred.span().lo(),
2712         |pred| pred.span().hi(),
2713         |pred| pred.rewrite(context, Shape::legacy(budget, offset)),
2714         span_start,
2715         span_end,
2716         false,
2717     );
2718     let item_vec = items.collect::<Vec<_>>();
2719     // FIXME: we don't need to collect here if the where_layout isn't
2720     // HorizontalVertical.
2721     let tactic = definitive_tactic(
2722         &item_vec,
2723         context.config.where_layout(),
2724         Separator::Comma,
2725         budget,
2726     );
2727
2728     let mut comma_tactic = context.config.trailing_comma();
2729     // Kind of a hack because we don't usually have trailing commas in where clauses.
2730     if comma_tactic == SeparatorTactic::Vertical || where_clause_option.suppress_comma {
2731         comma_tactic = SeparatorTactic::Never;
2732     }
2733
2734     let fmt = ListFormatting {
2735         tactic: tactic,
2736         separator: ",",
2737         trailing_separator: comma_tactic,
2738         separator_place: SeparatorPlace::Back,
2739         shape: Shape::legacy(budget, offset),
2740         ends_with_newline: tactic.ends_with_newline(context.config.where_pred_indent()),
2741         preserve_newline: true,
2742         config: context.config,
2743     };
2744     let preds_str = write_list(&item_vec, &fmt)?;
2745
2746     let end_length = if terminator == "{" {
2747         // If the brace is on the next line we don't need to count it otherwise it needs two
2748         // characters " {"
2749         match brace_style {
2750             BraceStyle::AlwaysNextLine | BraceStyle::SameLineWhere => 0,
2751             BraceStyle::PreferSameLine => 2,
2752         }
2753     } else if terminator == "=" {
2754         2
2755     } else {
2756         terminator.len()
2757     };
2758     if density == Density::Tall || preds_str.contains('\n')
2759         || shape.indent.width() + " where ".len() + preds_str.len() + end_length > shape.width
2760     {
2761         Some(format!(
2762             "\n{}where {}",
2763             (shape.indent + extra_indent).to_string(context.config),
2764             preds_str
2765         ))
2766     } else {
2767         Some(format!(" where {}", preds_str))
2768     }
2769 }
2770
2771 fn missing_span_before_after_where(
2772     before_item_span_end: BytePos,
2773     where_clause: &ast::WhereClause,
2774 ) -> (Span, Span) {
2775     let missing_span_before = mk_sp(before_item_span_end, where_clause.span.lo());
2776     // 5 = `where`
2777     let pos_after_where = where_clause.span.lo() + BytePos(5);
2778     let missing_span_after = mk_sp(pos_after_where, where_clause.predicates[0].span().lo());
2779     (missing_span_before, missing_span_after)
2780 }
2781
2782 fn rewrite_comments_before_after_where(
2783     context: &RewriteContext,
2784     span_before_where: Span,
2785     span_after_where: Span,
2786     shape: Shape,
2787 ) -> Option<(String, String)> {
2788     let before_comment = rewrite_missing_comment(span_before_where, shape, context)?;
2789     let after_comment = rewrite_missing_comment(
2790         span_after_where,
2791         shape.block_indent(context.config.tab_spaces()),
2792         context,
2793     )?;
2794     Some((before_comment, after_comment))
2795 }
2796
2797 fn format_header(item_name: &str, ident: ast::Ident, vis: &ast::Visibility) -> String {
2798     format!("{}{}{}", format_visibility(vis), item_name, ident)
2799 }
2800
2801 #[derive(PartialEq, Eq)]
2802 enum BracePos {
2803     None,
2804     Auto,
2805     ForceSameLine,
2806 }
2807
2808 fn format_generics(
2809     context: &RewriteContext,
2810     generics: &ast::Generics,
2811     brace_style: BraceStyle,
2812     brace_pos: BracePos,
2813     offset: Indent,
2814     span: Span,
2815     used_width: usize,
2816 ) -> Option<String> {
2817     let shape = Shape::legacy(context.budget(used_width + offset.width()), offset);
2818     let mut result = rewrite_generics(context, generics, shape, span)?;
2819
2820     let same_line_brace = if !generics.where_clause.predicates.is_empty() || result.contains('\n') {
2821         let budget = context.budget(last_line_used_width(&result, offset.width()));
2822         let mut option = WhereClauseOption::snuggled(&result);
2823         if brace_pos == BracePos::None {
2824             option.suppress_comma = true;
2825         }
2826         // If the generics are not parameterized then generics.span.hi() == 0,
2827         // so we use span.lo(), which is the position after `struct Foo`.
2828         let span_end_before_where = if generics.is_parameterized() {
2829             generics.span.hi()
2830         } else {
2831             span.lo()
2832         };
2833         let where_clause_str = rewrite_where_clause(
2834             context,
2835             &generics.where_clause,
2836             brace_style,
2837             Shape::legacy(budget, offset.block_only()),
2838             Density::Tall,
2839             "{",
2840             Some(span.hi()),
2841             span_end_before_where,
2842             option,
2843             false,
2844         )?;
2845         result.push_str(&where_clause_str);
2846         brace_pos == BracePos::ForceSameLine || brace_style == BraceStyle::PreferSameLine
2847             || (generics.where_clause.predicates.is_empty()
2848                 && trimmed_last_line_width(&result) == 1)
2849     } else {
2850         brace_pos == BracePos::ForceSameLine || trimmed_last_line_width(&result) == 1
2851             || brace_style != BraceStyle::AlwaysNextLine
2852     };
2853     if brace_pos == BracePos::None {
2854         return Some(result);
2855     }
2856     let total_used_width = last_line_used_width(&result, used_width);
2857     let remaining_budget = context.budget(total_used_width);
2858     // If the same line brace if forced, it indicates that we are rewriting an item with empty body,
2859     // and hence we take the closer into account as well for one line budget.
2860     // We assume that the closer has the same length as the opener.
2861     let overhead = if brace_pos == BracePos::ForceSameLine {
2862         // 3 = ` {}`
2863         3
2864     } else {
2865         // 2 = ` {`
2866         2
2867     };
2868     let forbid_same_line_brace = overhead > remaining_budget;
2869     if !forbid_same_line_brace && same_line_brace {
2870         result.push(' ');
2871     } else {
2872         result.push('\n');
2873         result.push_str(&offset.block_only().to_string(context.config));
2874     }
2875     result.push('{');
2876
2877     Some(result)
2878 }
2879
2880 impl Rewrite for ast::ForeignItem {
2881     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
2882         let attrs_str = self.attrs.rewrite(context, shape)?;
2883         // Drop semicolon or it will be interpreted as comment.
2884         // FIXME: this may be a faulty span from libsyntax.
2885         let span = mk_sp(self.span.lo(), self.span.hi() - BytePos(1));
2886
2887         let item_str = match self.node {
2888             ast::ForeignItemKind::Fn(ref fn_decl, ref generics) => {
2889                 rewrite_fn_base(
2890                     context,
2891                     shape.indent,
2892                     self.ident,
2893                     &FnSig::new(fn_decl, generics, self.vis.clone()),
2894                     span,
2895                     false,
2896                     false,
2897                 ).map(|(s, _)| format!("{};", s))
2898             }
2899             ast::ForeignItemKind::Static(ref ty, is_mutable) => {
2900                 // FIXME(#21): we're dropping potential comments in between the
2901                 // function keywords here.
2902                 let vis = format_visibility(&self.vis);
2903                 let mut_str = if is_mutable { "mut " } else { "" };
2904                 let prefix = format!("{}static {}{}:", vis, mut_str, self.ident);
2905                 // 1 = ;
2906                 let shape = shape.sub_width(1)?;
2907                 ty.rewrite(context, shape).map(|ty_str| {
2908                     // 1 = space between prefix and type.
2909                     let sep = if prefix.len() + ty_str.len() + 1 <= shape.width {
2910                         String::from(" ")
2911                     } else {
2912                         let nested_indent = shape.indent.block_indent(context.config);
2913                         format!("\n{}", nested_indent.to_string(context.config))
2914                     };
2915                     format!("{}{}{};", prefix, sep, ty_str)
2916                 })
2917             }
2918             ast::ForeignItemKind::Ty => {
2919                 let vis = format_visibility(&self.vis);
2920                 Some(format!("{}type {};", vis, self.ident))
2921             }
2922         }?;
2923
2924         let missing_span = if self.attrs.is_empty() {
2925             mk_sp(self.span.lo(), self.span.lo())
2926         } else {
2927             mk_sp(self.attrs[self.attrs.len() - 1].span.hi(), self.span.lo())
2928         };
2929         combine_strs_with_missing_comments(
2930             context,
2931             &attrs_str,
2932             &item_str,
2933             missing_span,
2934             shape,
2935             false,
2936         )
2937     }
2938 }