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 Indent;
  14 use codemap::SpanUtils;
  15 use utils::{format_mutability, format_visibility, contains_skip, end_typaram, wrap_str,
  16             last_line_width, format_unsafety, trim_newlines, stmt_expr, semicolon_for_expr};
  17 use lists::{write_list, itemize_list, ListItem, ListFormatting, SeparatorTactic,
  18             DefinitiveListTactic, ListTactic, definitive_tactic, format_item_list};
  19 use expr::{is_empty_block, is_simple_block_stmt, rewrite_assign_rhs, type_annotation_separator};
  20 use comment::{FindUncommented, contains_comment};
  21 use visitor::FmtVisitor;
  22 use rewrite::{Rewrite, RewriteContext};
  23 use config::{Config, BlockIndentStyle, Density, ReturnIndent, BraceStyle, FnArgLayoutStyle};
  24 use itertools::Itertools;
  25
  26 use syntax::{ast, abi, ptr, codemap};
  27 use syntax::codemap::{Span, BytePos, mk_sp};
  28 use syntax::parse::token;
  29 use syntax::ast::ImplItem;
  30
  31 // Statements of the form
  32 // let pat: ty = init;
  33 impl Rewrite for ast::Local {
  34     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
  35         let mut result = "let ".to_owned();
  36         let pattern_offset = offset + result.len();
  37         // 1 = ;
  38         let pattern_width = try_opt!(width.checked_sub(pattern_offset.width() + 1));
  39
  40         let pat_str = try_opt!(self.pat.rewrite(&context, pattern_width, pattern_offset));
  41         result.push_str(&pat_str);
  42
  43         // String that is placed within the assignment pattern and expression.
  44         let infix = {
  45             let mut infix = String::new();
  46
  47             if let Some(ref ty) = self.ty {
  48                 let separator = type_annotation_separator(context.config);
  49                 let indent = offset + last_line_width(&result) + separator.len();
  50                 // 1 = ;
  51                 let budget = try_opt!(width.checked_sub(indent.width() + 1));
  52                 let rewrite = try_opt!(ty.rewrite(context, budget, indent));
  53
  54                 infix.push_str(separator);
  55                 infix.push_str(&rewrite);
  56             }
  57
  58             if self.init.is_some() {
  59                 infix.push_str(" =");
  60             }
  61
  62             infix
  63         };
  64
  65         result.push_str(&infix);
  66
  67         if let Some(ref ex) = self.init {
  68             let budget = try_opt!(width.checked_sub(context.block_indent.width() + 1));
  69
  70             // 1 = trailing semicolon;
  71             result =
  72                 try_opt!(rewrite_assign_rhs(&context, result, ex, budget, context.block_indent));
  73         }
  74
  75         result.push(';');
  76         Some(result)
  77     }
  78 }
  79
  80 impl<'a> FmtVisitor<'a> {
  81     pub fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
  82         let abi_str = ::utils::format_abi(fm.abi, self.config.force_explicit_abi);
  83         self.buffer.push_str(&abi_str);
  84
  85         let snippet = self.snippet(span);
  86         let brace_pos = snippet.find_uncommented("{").unwrap();
  87
  88         self.buffer.push_str("{");
  89         if !fm.items.is_empty() || contains_comment(&snippet[brace_pos..]) {
  90             // FIXME: this skips comments between the extern keyword and the opening
  91             // brace.
  92             self.last_pos = span.lo + BytePos(brace_pos as u32 + 1);
  93             self.block_indent = self.block_indent.block_indent(self.config);
  94
  95             if fm.items.is_empty() {
  96                 self.format_missing_no_indent(span.hi - BytePos(1));
  97                 self.block_indent = self.block_indent.block_unindent(self.config);
  98
  99                 self.buffer.push_str(&self.block_indent.to_string(self.config));
 100             } else {
 101                 for item in &fm.items {
 102                     self.format_foreign_item(&*item);
 103                 }
 104
 105                 self.block_indent = self.block_indent.block_unindent(self.config);
 106                 self.format_missing_with_indent(span.hi - BytePos(1));
 107             }
 108         }
 109
 110         self.buffer.push_str("}");
 111         self.last_pos = span.hi;
 112     }
 113
 114     fn format_foreign_item(&mut self, item: &ast::ForeignItem) {
 115         self.format_missing_with_indent(item.span.lo);
 116         // Drop semicolon or it will be interpreted as comment.
 117         // FIXME: this may be a faulty span from libsyntax.
 118         let span = mk_sp(item.span.lo, item.span.hi - BytePos(1));
 119
 120         match item.node {
 121             ast::ForeignItemKind::Fn(ref fn_decl, ref generics) => {
 122                 let indent = self.block_indent;
 123                 let rewrite = rewrite_fn_base(&self.get_context(),
 124                                               indent,
 125                                               item.ident,
 126                                               fn_decl,
 127                                               generics,
 128                                               ast::Unsafety::Normal,
 129                                               ast::Constness::NotConst,
 130                                               ast::Defaultness::Final,
 131                                               // These are not actually rust functions,
 132                                               // but we format them as such.
 133                                               abi::Abi::Rust,
 134                                               &item.vis,
 135                                               span,
 136                                               false,
 137                                               false);
 138
 139                 match rewrite {
 140                     Some((new_fn, _)) => {
 141                         self.buffer.push_str(&new_fn);
 142                         self.buffer.push_str(";");
 143                     }
 144                     None => self.format_missing(item.span.hi),
 145                 }
 146             }
 147             ast::ForeignItemKind::Static(ref ty, is_mutable) => {
 148                 // FIXME(#21): we're dropping potential comments in between the
 149                 // function keywords here.
 150                 let vis = format_visibility(&item.vis);
 151                 let mut_str = if is_mutable { "mut " } else { "" };
 152                 let prefix = format!("{}static {}{}: ", vis, mut_str, item.ident);
 153                 let offset = self.block_indent + prefix.len();
 154                 // 1 = ;
 155                 let width = self.config.max_width - offset.width() - 1;
 156                 let rewrite = ty.rewrite(&self.get_context(), width, offset);
 157
 158                 match rewrite {
 159                     Some(result) => {
 160                         self.buffer.push_str(&prefix);
 161                         self.buffer.push_str(&result);
 162                         self.buffer.push_str(";");
 163                     }
 164                     None => self.format_missing(item.span.hi),
 165                 }
 166             }
 167         }
 168
 169         self.last_pos = item.span.hi;
 170     }
 171
 172     pub fn rewrite_fn(&mut self,
 173                       indent: Indent,
 174                       ident: ast::Ident,
 175                       fd: &ast::FnDecl,
 176                       generics: &ast::Generics,
 177                       unsafety: ast::Unsafety,
 178                       constness: ast::Constness,
 179                       defaultness: ast::Defaultness,
 180                       abi: abi::Abi,
 181                       vis: &ast::Visibility,
 182                       span: Span,
 183                       block: &ast::Block)
 184                       -> Option<String> {
 185         let mut newline_brace = newline_for_brace(self.config, &generics.where_clause);
 186         let context = self.get_context();
 187
 188         let block_snippet = self.snippet(codemap::mk_sp(block.span.lo, block.span.hi));
 189         let has_body = !block_snippet[1..block_snippet.len() - 1].trim().is_empty() ||
 190                        !context.config.fn_empty_single_line;
 191
 192         let (mut result, force_newline_brace) = try_opt!(rewrite_fn_base(&context,
 193                                                                          indent,
 194                                                                          ident,
 195                                                                          fd,
 196                                                                          generics,
 197                                                                          unsafety,
 198                                                                          constness,
 199                                                                          defaultness,
 200                                                                          abi,
 201                                                                          vis,
 202                                                                          span,
 203                                                                          newline_brace,
 204                                                                          has_body));
 205
 206         if self.config.fn_brace_style != BraceStyle::AlwaysNextLine && !result.contains('\n') {
 207             newline_brace = false;
 208         } else if force_newline_brace {
 209             newline_brace = true;
 210         }
 211
 212         // Prepare for the function body by possibly adding a newline and
 213         // indent.
 214         // FIXME we'll miss anything between the end of the signature and the
 215         // start of the body, but we need more spans from the compiler to solve
 216         // this.
 217         if newline_brace {
 218             result.push('\n');
 219             result.push_str(&indent.to_string(self.config));
 220         } else {
 221             result.push(' ');
 222         }
 223
 224         self.single_line_fn(&result, block).or_else(|| Some(result))
 225     }
 226
 227     pub fn rewrite_required_fn(&mut self,
 228                                indent: Indent,
 229                                ident: ast::Ident,
 230                                sig: &ast::MethodSig,
 231                                span: Span)
 232                                -> Option<String> {
 233         // Drop semicolon or it will be interpreted as comment.
 234         let span = mk_sp(span.lo, span.hi - BytePos(1));
 235         let context = self.get_context();
 236
 237         let (mut result, _) = try_opt!(rewrite_fn_base(&context,
 238                                                        indent,
 239                                                        ident,
 240                                                        &sig.decl,
 241                                                        &sig.generics,
 242                                                        sig.unsafety,
 243                                                        sig.constness.node,
 244                                                        ast::Defaultness::Final,
 245                                                        sig.abi,
 246                                                        &ast::Visibility::Inherited,
 247                                                        span,
 248                                                        false,
 249                                                        false));
 250
 251         // Re-attach semicolon
 252         result.push(';');
 253
 254         Some(result)
 255     }
 256
 257     fn single_line_fn(&self, fn_str: &str, block: &ast::Block) -> Option<String> {
 258         if fn_str.contains('\n') {
 259             return None;
 260         }
 261
 262         let codemap = self.get_context().codemap;
 263
 264         if self.config.fn_empty_single_line && is_empty_block(block, codemap) &&
 265            self.block_indent.width() + fn_str.len() + 2 <= self.config.max_width {
 266             return Some(format!("{}{{}}", fn_str));
 267         }
 268
 269         if self.config.fn_single_line && is_simple_block_stmt(block, codemap) {
 270             let rewrite = {
 271                 if let Some(ref stmt) = block.stmts.first() {
 272                     match stmt_expr(stmt) {
 273                         Some(e) => {
 274                             let suffix = if semicolon_for_expr(e) { ";" } else { "" };
 275
 276                             e.rewrite(&self.get_context(),
 277                                          self.config.max_width - self.block_indent.width(),
 278                                          self.block_indent)
 279                                 .map(|s| s + suffix)
 280                                 .or_else(|| Some(self.snippet(e.span)))
 281                         }
 282                         None => {
 283                             stmt.rewrite(&self.get_context(),
 284                                          self.config.max_width - self.block_indent.width(),
 285                                          self.block_indent)
 286                         }
 287                     }
 288                 } else {
 289                     None
 290                 }
 291             };
 292
 293             if let Some(res) = rewrite {
 294                 let width = self.block_indent.width() + fn_str.len() + res.len() + 4;
 295                 if !res.contains('\n') && width <= self.config.max_width {
 296                     return Some(format!("{}{{ {} }}", fn_str, res));
 297                 }
 298             }
 299         }
 300
 301         None
 302     }
 303
 304     pub fn visit_enum(&mut self,
 305                       ident: ast::Ident,
 306                       vis: &ast::Visibility,
 307                       enum_def: &ast::EnumDef,
 308                       generics: &ast::Generics,
 309                       span: Span) {
 310         self.buffer.push_str(&format_header("enum ", ident, vis));
 311
 312         let enum_snippet = self.snippet(span);
 313         let brace_pos = enum_snippet.find_uncommented("{").unwrap();
 314         let body_start = span.lo + BytePos(brace_pos as u32 + 1);
 315         let generics_str = format_generics(&self.get_context(),
 316                                            generics,
 317                                            "{",
 318                                            "{",
 319                                            self.config.item_brace_style,
 320                                            enum_def.variants.is_empty(),
 321                                            self.block_indent,
 322                                            self.block_indent.block_indent(self.config),
 323                                            mk_sp(span.lo, body_start))
 324             .unwrap();
 325         self.buffer.push_str(&generics_str);
 326
 327         self.last_pos = body_start;
 328
 329         self.block_indent = self.block_indent.block_indent(self.config);
 330         let variant_list = self.format_variant_list(enum_def, body_start, span.hi - BytePos(1));
 331         match variant_list {
 332             Some(ref body_str) => self.buffer.push_str(body_str),
 333             None => {
 334                 if contains_comment(&enum_snippet[brace_pos..]) {
 335                     self.format_missing_no_indent(span.hi - BytePos(1))
 336                 } else {
 337                     self.format_missing(span.hi - BytePos(1))
 338                 }
 339             }
 340         }
 341         self.block_indent = self.block_indent.block_unindent(self.config);
 342
 343         if variant_list.is_some() || contains_comment(&enum_snippet[brace_pos..]) {
 344             self.buffer.push_str(&self.block_indent.to_string(self.config));
 345         }
 346         self.buffer.push_str("}");
 347         self.last_pos = span.hi;
 348     }
 349
 350     // Format the body of an enum definition
 351     fn format_variant_list(&self,
 352                            enum_def: &ast::EnumDef,
 353                            body_lo: BytePos,
 354                            body_hi: BytePos)
 355                            -> Option<String> {
 356         if enum_def.variants.is_empty() {
 357             return None;
 358         }
 359         let mut result = String::with_capacity(1024);
 360         result.push('\n');
 361         let indentation = self.block_indent.to_string(self.config);
 362         result.push_str(&indentation);
 363
 364         let items = itemize_list(self.codemap,
 365                                  enum_def.variants.iter(),
 366                                  "}",
 367                                  |f| {
 368             if !f.node.attrs.is_empty() {
 369                 f.node.attrs[0].span.lo
 370             } else {
 371                 f.span.lo
 372             }
 373         },
 374                                  |f| f.span.hi,
 375                                  |f| self.format_variant(f),
 376                                  body_lo,
 377                                  body_hi);
 378
 379         let budget = self.config.max_width - self.block_indent.width() - 2;
 380         let fmt = ListFormatting {
 381             tactic: DefinitiveListTactic::Vertical,
 382             separator: ",",
 383             trailing_separator: SeparatorTactic::from_bool(self.config.enum_trailing_comma),
 384             indent: self.block_indent,
 385             width: budget,
 386             ends_with_newline: true,
 387             config: self.config,
 388         };
 389
 390         let list = try_opt!(write_list(items, &fmt));
 391         result.push_str(&list);
 392         result.push('\n');
 393         Some(result)
 394     }
 395
 396     // Variant of an enum.
 397     fn format_variant(&self, field: &ast::Variant) -> Option<String> {
 398         if contains_skip(&field.node.attrs) {
 399             let lo = field.node.attrs[0].span.lo;
 400             let span = mk_sp(lo, field.span.hi);
 401             return Some(self.snippet(span));
 402         }
 403
 404         let indent = self.block_indent;
 405         let mut result = try_opt!(field.node
 406             .attrs
 407             .rewrite(&self.get_context(),
 408                      self.config.max_width - indent.width(),
 409                      indent));
 410         if !result.is_empty() {
 411             result.push('\n');
 412             result.push_str(&indent.to_string(self.config));
 413         }
 414
 415         let context = self.get_context();
 416         let variant_body = match field.node.data {
 417             ast::VariantData::Tuple(..) |
 418             ast::VariantData::Struct(..) => {
 419                 // FIXME: Should limit the width, as we have a trailing comma
 420                 format_struct(&context,
 421                               "",
 422                               field.node.name,
 423                               &ast::Visibility::Inherited,
 424                               &field.node.data,
 425                               None,
 426                               field.span,
 427                               indent,
 428                               Some(self.config.struct_variant_width))
 429             }
 430             ast::VariantData::Unit(..) => {
 431                 let tag = if let Some(ref expr) = field.node.disr_expr {
 432                     format!("{} = {}", field.node.name, self.snippet(expr.span))
 433                 } else {
 434                     field.node.name.to_string()
 435                 };
 436
 437                 wrap_str(tag,
 438                          self.config.max_width,
 439                          self.config.max_width - indent.width(),
 440                          indent)
 441             }
 442         };
 443
 444         if let Some(variant_str) = variant_body {
 445             result.push_str(&variant_str);
 446             Some(result)
 447         } else {
 448             None
 449         }
 450     }
 451 }
 452
 453 pub fn format_impl(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 454     if let ast::ItemKind::Impl(_, _, ref generics, ref trait_ref, _, ref items) = item.node {
 455         let mut result = String::new();
 456
 457         // First try to format the ref and type without a split at the 'for'.
 458         let mut ref_and_type = try_opt!(format_impl_ref_and_type(context, item, offset, false));
 459
 460         // If there is a line break present in the first result format it again
 461         // with a split at the 'for'. Skip this if there is no trait ref and
 462         // therefore no 'for'.
 463         if let Some(_) = *trait_ref {
 464             if ref_and_type.contains('\n') {
 465                 ref_and_type = try_opt!(format_impl_ref_and_type(context, item, offset, true));
 466             }
 467         }
 468         result.push_str(&ref_and_type);
 469
 470         let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
 471         let where_clause_str = try_opt!(rewrite_where_clause(context,
 472                                                              &generics.where_clause,
 473                                                              context.config,
 474                                                              context.config.item_brace_style,
 475                                                              context.block_indent,
 476                                                              where_budget,
 477                                                              context.config.where_density,
 478                                                              "{",
 479                                                              true,
 480                                                              None));
 481
 482         if try_opt!(is_impl_single_line(context, &items, &result, &where_clause_str, &item)) {
 483             result.push_str(&where_clause_str);
 484             if where_clause_str.contains('\n') {
 485                 let white_space = offset.to_string(context.config);
 486                 result.push_str(&format!("\n{}{{\n{}}}", &white_space, &white_space));
 487             } else {
 488                 result.push_str(" {}");
 489             }
 490             return Some(result);
 491         }
 492
 493         if !where_clause_str.is_empty() && !where_clause_str.contains('\n') {
 494             result.push('\n');
 495             let width = context.block_indent.width() + context.config.tab_spaces - 1;
 496             let where_indent = Indent::new(0, width);
 497             result.push_str(&where_indent.to_string(context.config));
 498         }
 499         result.push_str(&where_clause_str);
 500
 501         match context.config.item_brace_style {
 502             BraceStyle::AlwaysNextLine => result.push('\n'),
 503             BraceStyle::PreferSameLine => result.push(' '),
 504             BraceStyle::SameLineWhere => {
 505                 if !where_clause_str.is_empty() {
 506                     result.push('\n');
 507                     result.push_str(&offset.to_string(context.config));
 508                 } else {
 509                     result.push(' ');
 510                 }
 511             }
 512         }
 513
 514         result.push('{');
 515
 516         let snippet = context.snippet(item.span);
 517         let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 518
 519         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 520             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 521             visitor.block_indent = context.block_indent.block_indent(context.config);
 522             visitor.last_pos = item.span.lo + BytePos(open_pos as u32);
 523
 524             for item in items {
 525                 visitor.visit_impl_item(item);
 526             }
 527
 528             visitor.format_missing(item.span.hi - BytePos(1));
 529
 530             let inner_indent_str = visitor.block_indent.to_string(context.config);
 531             let outer_indent_str = context.block_indent.to_string(context.config);
 532
 533             result.push('\n');
 534             result.push_str(&inner_indent_str);
 535             result.push_str(trim_newlines(visitor.buffer.to_string().trim()));
 536             result.push('\n');
 537             result.push_str(&outer_indent_str);
 538         }
 539
 540         if result.chars().last().unwrap() == '{' {
 541             result.push('\n');
 542         }
 543         result.push('}');
 544
 545         Some(result)
 546     } else {
 547         unreachable!();
 548     }
 549 }
 550
 551 fn is_impl_single_line(context: &RewriteContext,
 552                        items: &[ImplItem],
 553                        result: &str,
 554                        where_clause_str: &str,
 555                        item: &ast::Item)
 556                        -> Option<bool> {
 557     let snippet = context.snippet(item.span);
 558     let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 559
 560     Some(context.config.impl_empty_single_line && items.is_empty() &&
 561          result.len() + where_clause_str.len() <= context.config.max_width &&
 562          !contains_comment(&snippet[open_pos..]))
 563 }
 564
 565 fn format_impl_ref_and_type(context: &RewriteContext,
 566                             item: &ast::Item,
 567                             offset: Indent,
 568                             split_at_for: bool)
 569                             -> Option<String> {
 570     if let ast::ItemKind::Impl(unsafety, polarity, ref generics, ref trait_ref, ref self_ty, _) =
 571         item.node {
 572         let mut result = String::new();
 573
 574         result.push_str(&*format_visibility(&item.vis));
 575         result.push_str(format_unsafety(unsafety));
 576         result.push_str("impl");
 577
 578         let lo = context.codemap.span_after(item.span, "impl");
 579         let hi = match *trait_ref {
 580             Some(ref tr) => tr.path.span.lo,
 581             None => self_ty.span.lo,
 582         };
 583         let generics_str = try_opt!(rewrite_generics(context,
 584                                                      generics,
 585                                                      offset,
 586                                                      context.config.max_width,
 587                                                      offset + result.len(),
 588                                                      mk_sp(lo, hi)));
 589         result.push_str(&generics_str);
 590
 591         result.push(' ');
 592         if polarity == ast::ImplPolarity::Negative {
 593             result.push('!');
 594         }
 595         if let Some(ref trait_ref) = *trait_ref {
 596             let budget = try_opt!(context.config.max_width.checked_sub(result.len()));
 597             let indent = offset + result.len();
 598             result.push_str(&*try_opt!(trait_ref.rewrite(context, budget, indent)));
 599
 600             if split_at_for {
 601                 result.push('\n');
 602
 603                 // Add indentation of one additional tab.
 604                 let width = context.block_indent.width() + context.config.tab_spaces;
 605                 let for_indent = Indent::new(0, width);
 606                 result.push_str(&for_indent.to_string(context.config));
 607
 608                 result.push_str("for ");
 609             } else {
 610                 result.push_str(" for ");
 611             }
 612         }
 613
 614         let mut used_space = last_line_width(&result);
 615         if generics.where_clause.predicates.is_empty() {
 616             // If there is no where clause adapt budget for type formatting to take space and curly
 617             // brace into account.
 618             match context.config.item_brace_style {
 619                 BraceStyle::AlwaysNextLine => {}
 620                 BraceStyle::PreferSameLine => used_space += 2,
 621                 BraceStyle::SameLineWhere => used_space += 2,
 622             }
 623         }
 624
 625         let budget = try_opt!(context.config.max_width.checked_sub(used_space));
 626         let indent = offset + result.len();
 627         result.push_str(&*try_opt!(self_ty.rewrite(context, budget, indent)));
 628
 629         Some(result)
 630     } else {
 631         unreachable!();
 632     }
 633 }
 634
 635 pub fn format_struct(context: &RewriteContext,
 636                      item_name: &str,
 637                      ident: ast::Ident,
 638                      vis: &ast::Visibility,
 639                      struct_def: &ast::VariantData,
 640                      generics: Option<&ast::Generics>,
 641                      span: Span,
 642                      offset: Indent,
 643                      one_line_width: Option<usize>)
 644                      -> Option<String> {
 645     match *struct_def {
 646         ast::VariantData::Unit(..) => Some(format_unit_struct(item_name, ident, vis)),
 647         ast::VariantData::Tuple(ref fields, _) => {
 648             format_tuple_struct(context,
 649                                 item_name,
 650                                 ident,
 651                                 vis,
 652                                 fields,
 653                                 generics,
 654                                 span,
 655                                 offset)
 656         }
 657         ast::VariantData::Struct(ref fields, _) => {
 658             format_struct_struct(context,
 659                                  item_name,
 660                                  ident,
 661                                  vis,
 662                                  fields,
 663                                  generics,
 664                                  span,
 665                                  offset,
 666                                  one_line_width)
 667         }
 668     }
 669 }
 670
 671 pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 672     if let ast::ItemKind::Trait(unsafety, ref generics, ref type_param_bounds, ref trait_items) =
 673         item.node {
 674         let mut result = String::new();
 675         let header = format!("{}{}trait {}",
 676                              format_visibility(&item.vis),
 677                              format_unsafety(unsafety),
 678                              item.ident);
 679
 680         result.push_str(&header);
 681
 682         let body_lo = context.codemap.span_after(item.span, "{");
 683
 684         let generics_str = try_opt!(rewrite_generics(context,
 685                                                      generics,
 686                                                      offset,
 687                                                      context.config.max_width,
 688                                                      offset + result.len(),
 689                                                      mk_sp(item.span.lo, body_lo)));
 690         result.push_str(&generics_str);
 691
 692         let trait_bound_str = try_opt!(rewrite_trait_bounds(context,
 693                                                             type_param_bounds,
 694                                                             offset,
 695                                                             context.config.max_width));
 696         // If the trait, generics, and trait bound cannot fit on the same line,
 697         // put the trait bounds on an indented new line
 698         if offset.width() + last_line_width(&result) + trait_bound_str.len() >
 699            context.config.ideal_width {
 700             result.push('\n');
 701             let width = context.block_indent.width() + context.config.tab_spaces;
 702             let trait_indent = Indent::new(0, width);
 703             result.push_str(&trait_indent.to_string(context.config));
 704         }
 705         result.push_str(&trait_bound_str);
 706
 707         let has_body = !trait_items.is_empty();
 708
 709         let where_density =
 710             if (context.config.where_density == Density::Compressed &&
 711                 (!result.contains('\n') ||
 712                  context.config.fn_args_layout == FnArgLayoutStyle::Block)) ||
 713                (context.config.fn_args_layout == FnArgLayoutStyle::Block && result.is_empty()) ||
 714                (context.config.where_density == Density::CompressedIfEmpty && !has_body &&
 715                 !result.contains('\n')) {
 716                 Density::Compressed
 717             } else {
 718                 Density::Tall
 719             };
 720
 721         let where_budget = try_opt!(context.config
 722             .max_width
 723             .checked_sub(last_line_width(&result)));
 724         let where_clause_str = try_opt!(rewrite_where_clause(context,
 725                                                              &generics.where_clause,
 726                                                              context.config,
 727                                                              context.config.item_brace_style,
 728                                                              context.block_indent,
 729                                                              where_budget,
 730                                                              where_density,
 731                                                              "{",
 732                                                              has_body,
 733                                                              None));
 734         // If the where clause cannot fit on the same line,
 735         // put the where clause on a new line
 736         if !where_clause_str.contains('\n') &&
 737            last_line_width(&result) + where_clause_str.len() + offset.width() >
 738            context.config.ideal_width {
 739             result.push('\n');
 740             let width = context.block_indent.width() + context.config.tab_spaces - 1;
 741             let where_indent = Indent::new(0, width);
 742             result.push_str(&where_indent.to_string(context.config));
 743         }
 744         result.push_str(&where_clause_str);
 745
 746         match context.config.item_brace_style {
 747             BraceStyle::AlwaysNextLine => {
 748                 result.push('\n');
 749                 result.push_str(&offset.to_string(context.config));
 750             }
 751             BraceStyle::PreferSameLine => result.push(' '),
 752             BraceStyle::SameLineWhere => {
 753                 if !where_clause_str.is_empty() &&
 754                    (!trait_items.is_empty() || result.contains('\n')) {
 755                     result.push('\n');
 756                     result.push_str(&offset.to_string(context.config));
 757                 } else {
 758                     result.push(' ');
 759                 }
 760             }
 761         }
 762         result.push('{');
 763
 764         let snippet = context.snippet(item.span);
 765         let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 766
 767         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
 768             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 769             visitor.block_indent = context.block_indent.block_indent(context.config);
 770             visitor.last_pos = item.span.lo + BytePos(open_pos as u32);
 771
 772             for item in trait_items {
 773                 visitor.visit_trait_item(item);
 774             }
 775
 776             visitor.format_missing(item.span.hi - BytePos(1));
 777
 778             let inner_indent_str = visitor.block_indent.to_string(context.config);
 779             let outer_indent_str = context.block_indent.to_string(context.config);
 780
 781             result.push('\n');
 782             result.push_str(&inner_indent_str);
 783             result.push_str(trim_newlines(visitor.buffer.to_string().trim()));
 784             result.push('\n');
 785             result.push_str(&outer_indent_str);
 786         } else if result.contains('\n') {
 787             result.push('\n');
 788         }
 789
 790         result.push('}');
 791         Some(result)
 792     } else {
 793         unreachable!();
 794     }
 795 }
 796
 797 fn format_unit_struct(item_name: &str, ident: ast::Ident, vis: &ast::Visibility) -> String {
 798     format!("{};", format_header(item_name, ident, vis))
 799 }
 800
 801 fn format_struct_struct(context: &RewriteContext,
 802                         item_name: &str,
 803                         ident: ast::Ident,
 804                         vis: &ast::Visibility,
 805                         fields: &[ast::StructField],
 806                         generics: Option<&ast::Generics>,
 807                         span: Span,
 808                         offset: Indent,
 809                         one_line_width: Option<usize>)
 810                         -> Option<String> {
 811     let mut result = String::with_capacity(1024);
 812
 813     let header_str = format_header(item_name, ident, vis);
 814     result.push_str(&header_str);
 815
 816     let body_lo = context.codemap.span_after(span, "{");
 817
 818     let generics_str = match generics {
 819         Some(g) => {
 820             try_opt!(format_generics(context,
 821                                      g,
 822                                      "{",
 823                                      "{",
 824                                      context.config.item_brace_style,
 825                                      fields.is_empty(),
 826                                      offset,
 827                                      offset + header_str.len(),
 828                                      mk_sp(span.lo, body_lo)))
 829         }
 830         None => {
 831             if context.config.item_brace_style == BraceStyle::AlwaysNextLine && !fields.is_empty() {
 832                 format!("\n{}{{", context.block_indent.to_string(context.config))
 833             } else {
 834                 " {".to_owned()
 835             }
 836         }
 837     };
 838     result.push_str(&generics_str);
 839
 840     // FIXME(#919): properly format empty structs and their comments.
 841     if fields.is_empty() {
 842         result.push_str(&context.snippet(mk_sp(body_lo, span.hi)));
 843         return Some(result);
 844     }
 845
 846     let item_indent = offset.block_indent(context.config);
 847     // 1 = ","
 848     let item_budget = try_opt!(context.config.max_width.checked_sub(item_indent.width() + 1));
 849
 850     let items = itemize_list(context.codemap,
 851                              fields.iter(),
 852                              "}",
 853                              |field| {
 854         // Include attributes and doc comments, if present
 855         if !field.attrs.is_empty() {
 856             field.attrs[0].span.lo
 857         } else {
 858             field.span.lo
 859         }
 860     },
 861                              |field| field.ty.span.hi,
 862                              |field| field.rewrite(context, item_budget, item_indent),
 863                              context.codemap.span_after(span, "{"),
 864                              span.hi)
 865         .collect::<Vec<_>>();
 866     // 1 = ,
 867     let budget = context.config.max_width - offset.width() + context.config.tab_spaces - 1;
 868
 869     let tactic = match one_line_width {
 870         Some(w) => definitive_tactic(&items, ListTactic::LimitedHorizontalVertical(w), budget),
 871         None => DefinitiveListTactic::Vertical,
 872     };
 873
 874     let fmt = ListFormatting {
 875         tactic: tactic,
 876         separator: ",",
 877         trailing_separator: context.config.struct_trailing_comma,
 878         indent: item_indent,
 879         width: budget,
 880         ends_with_newline: true,
 881         config: context.config,
 882     };
 883     let items_str = try_opt!(write_list(&items, &fmt));
 884     if one_line_width.is_some() && !items_str.contains('\n') {
 885         Some(format!("{} {} }}", result, items_str))
 886     } else {
 887         Some(format!("{}\n{}{}\n{}}}",
 888                      result,
 889                      offset.block_indent(context.config).to_string(context.config),
 890                      items_str,
 891                      offset.to_string(context.config)))
 892     }
 893 }
 894
 895 fn format_tuple_struct(context: &RewriteContext,
 896                        item_name: &str,
 897                        ident: ast::Ident,
 898                        vis: &ast::Visibility,
 899                        fields: &[ast::StructField],
 900                        generics: Option<&ast::Generics>,
 901                        span: Span,
 902                        offset: Indent)
 903                        -> Option<String> {
 904     let mut result = String::with_capacity(1024);
 905
 906     let header_str = format_header(item_name, ident, vis);
 907     result.push_str(&header_str);
 908
 909     // FIXME(#919): don't lose comments on empty tuple structs.
 910     let body_lo = if fields.is_empty() {
 911         span.hi
 912     } else {
 913         fields[0].span.lo
 914     };
 915
 916     let where_clause_str = match generics {
 917         Some(generics) => {
 918             let generics_str = try_opt!(rewrite_generics(context,
 919                                                          generics,
 920                                                          offset,
 921                                                          context.config.max_width,
 922                                                          offset + header_str.len(),
 923                                                          mk_sp(span.lo, body_lo)));
 924             result.push_str(&generics_str);
 925
 926             let where_budget = try_opt!(context.config
 927                 .max_width
 928                 .checked_sub(last_line_width(&result)));
 929             try_opt!(rewrite_where_clause(context,
 930                                           &generics.where_clause,
 931                                           context.config,
 932                                           context.config.item_brace_style,
 933                                           context.block_indent,
 934                                           where_budget,
 935                                           Density::Compressed,
 936                                           ";",
 937                                           false,
 938                                           None))
 939         }
 940         None => "".to_owned(),
 941     };
 942     result.push('(');
 943
 944     let item_indent = context.block_indent + result.len();
 945     // 2 = ");"
 946     let item_budget = try_opt!(context.config.max_width.checked_sub(item_indent.width() + 2));
 947
 948     let items = itemize_list(context.codemap,
 949                              fields.iter(),
 950                              ")",
 951                              |field| {
 952         // Include attributes and doc comments, if present
 953         if !field.attrs.is_empty() {
 954             field.attrs[0].span.lo
 955         } else {
 956             field.span.lo
 957         }
 958     },
 959                              |field| field.ty.span.hi,
 960                              |field| field.rewrite(context, item_budget, item_indent),
 961                              context.codemap.span_after(span, "("),
 962                              span.hi);
 963     let body = try_opt!(format_item_list(items, item_budget, item_indent, context.config));
 964
 965     if context.config.spaces_within_parens && body.len() > 0 {
 966         result.push(' ');
 967     }
 968
 969     result.push_str(&body);
 970
 971     if context.config.spaces_within_parens && body.len() > 0 {
 972         result.push(' ');
 973     }
 974
 975     result.push(')');
 976
 977     if !where_clause_str.is_empty() && !where_clause_str.contains('\n') &&
 978        (result.contains('\n') ||
 979         context.block_indent.width() + result.len() + where_clause_str.len() + 1 >
 980         context.config.max_width) {
 981         // We need to put the where clause on a new line, but we didn'to_string
 982         // know that earlier, so the where clause will not be indented properly.
 983         result.push('\n');
 984         result.push_str(&(context.block_indent + (context.config.tab_spaces - 1))
 985             .to_string(context.config));
 986     }
 987     result.push_str(&where_clause_str);
 988
 989     Some(result)
 990 }
 991
 992 pub fn rewrite_type_alias(context: &RewriteContext,
 993                           indent: Indent,
 994                           ident: ast::Ident,
 995                           ty: &ast::Ty,
 996                           generics: &ast::Generics,
 997                           vis: &ast::Visibility,
 998                           span: Span)
 999                           -> Option<String> {
1000     let mut result = String::new();
1001
1002     result.push_str(&format_visibility(vis));
1003     result.push_str("type ");
1004     result.push_str(&ident.to_string());
1005
1006     let generics_indent = indent + result.len();
1007     let generics_span = mk_sp(context.codemap.span_after(span, "type"), ty.span.lo);
1008     let generics_width = context.config.max_width - " =".len();
1009     let generics_str = try_opt!(rewrite_generics(context,
1010                                                  generics,
1011                                                  indent,
1012                                                  generics_width,
1013                                                  generics_indent,
1014                                                  generics_span));
1015
1016     result.push_str(&generics_str);
1017
1018     let where_budget = try_opt!(context.config
1019         .max_width
1020         .checked_sub(last_line_width(&result)));
1021     let where_clause_str = try_opt!(rewrite_where_clause(context,
1022                                                          &generics.where_clause,
1023                                                          context.config,
1024                                                          context.config.item_brace_style,
1025                                                          indent,
1026                                                          where_budget,
1027                                                          context.config.where_density,
1028                                                          "=",
1029                                                          false,
1030                                                          Some(span.hi)));
1031     result.push_str(&where_clause_str);
1032     result.push_str(" = ");
1033
1034     let line_width = last_line_width(&result);
1035     // This checked_sub may fail as the extra space after '=' is not taken into account
1036     // In that case the budget is set to 0 which will make ty.rewrite retry on a new line
1037     let budget = context.config
1038         .max_width
1039         .checked_sub(indent.width() + line_width + ";".len())
1040         .unwrap_or(0);
1041     let type_indent = indent + line_width;
1042     // Try to fit the type on the same line
1043     let ty_str = try_opt!(ty.rewrite(context, budget, type_indent)
1044         .or_else(|| {
1045             // The line was too short, try to put the type on the next line
1046
1047             // Remove the space after '='
1048             result.pop();
1049             let type_indent = indent.block_indent(context.config);
1050             result.push('\n');
1051             result.push_str(&type_indent.to_string(context.config));
1052             let budget = try_opt!(context.config
1053                 .max_width
1054                 .checked_sub(type_indent.width() + ";".len()));
1055             ty.rewrite(context, budget, type_indent)
1056         }));
1057     result.push_str(&ty_str);
1058     result.push_str(";");
1059     Some(result)
1060 }
1061
1062 fn type_annotation_spacing(config: &Config) -> (&str, &str) {
1063     (if config.space_before_type_annotation {
1064          " "
1065      } else {
1066          ""
1067      },
1068      if config.space_after_type_annotation_colon {
1069          " "
1070      } else {
1071          ""
1072      })
1073 }
1074
1075 impl Rewrite for ast::StructField {
1076     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
1077         if contains_skip(&self.attrs) {
1078             let span = context.snippet(mk_sp(self.attrs[0].span.lo, self.span.hi));
1079             return wrap_str(span, context.config.max_width, width, offset);
1080         }
1081
1082         let name = self.ident;
1083         let vis = format_visibility(&self.vis);
1084         let mut attr_str = try_opt!(self.attrs
1085             .rewrite(context, context.config.max_width - offset.width(), offset));
1086         if !attr_str.is_empty() {
1087             attr_str.push('\n');
1088             attr_str.push_str(&offset.to_string(context.config));
1089         }
1090
1091         let type_annotation_spacing = type_annotation_spacing(context.config);
1092         let result = match name {
1093             Some(name) => {
1094                 format!("{}{}{}{}:{}",
1095                         attr_str,
1096                         vis,
1097                         name,
1098                         type_annotation_spacing.0,
1099                         type_annotation_spacing.1)
1100             }
1101             None => format!("{}{}", attr_str, vis),
1102         };
1103
1104         let last_line_width = last_line_width(&result);
1105         let budget = try_opt!(width.checked_sub(last_line_width));
1106         let rewrite = try_opt!(self.ty.rewrite(context, budget, offset + last_line_width));
1107         Some(result + &rewrite)
1108     }
1109 }
1110
1111 pub fn rewrite_static(prefix: &str,
1112                       vis: &ast::Visibility,
1113                       ident: ast::Ident,
1114                       ty: &ast::Ty,
1115                       mutability: ast::Mutability,
1116                       expr_opt: Option<&ptr::P<ast::Expr>>,
1117                       context: &RewriteContext)
1118                       -> Option<String> {
1119     let type_annotation_spacing = type_annotation_spacing(context.config);
1120     let prefix = format!("{}{} {}{}{}:{}",
1121                          format_visibility(vis),
1122                          prefix,
1123                          format_mutability(mutability),
1124                          ident,
1125                          type_annotation_spacing.0,
1126                          type_annotation_spacing.1);
1127     // 2 = " =".len()
1128     let ty_str = try_opt!(ty.rewrite(context,
1129                                      context.config.max_width - context.block_indent.width() -
1130                                      prefix.len() - 2,
1131                                      context.block_indent));
1132
1133     if let Some(expr) = expr_opt {
1134         let lhs = format!("{}{} =", prefix, ty_str);
1135         // 1 = ;
1136         let remaining_width = context.config.max_width - context.block_indent.width() - 1;
1137         rewrite_assign_rhs(context, lhs, expr, remaining_width, context.block_indent)
1138             .map(|s| s + ";")
1139     } else {
1140         let lhs = format!("{}{};", prefix, ty_str);
1141         Some(lhs)
1142     }
1143 }
1144
1145 pub fn rewrite_associated_type(ident: ast::Ident,
1146                                ty_opt: Option<&ptr::P<ast::Ty>>,
1147                                ty_param_bounds_opt: Option<&ast::TyParamBounds>,
1148                                context: &RewriteContext,
1149                                indent: Indent)
1150                                -> Option<String> {
1151     let prefix = format!("type {}", ident);
1152
1153     let type_bounds_str = if let Some(ty_param_bounds) = ty_param_bounds_opt {
1154         let bounds: &[_] = ty_param_bounds;
1155         let bound_str = try_opt!(bounds.iter()
1156             .map(|ty_bound| ty_bound.rewrite(context, context.config.max_width, indent))
1157             .intersperse(Some(" + ".to_string()))
1158             .collect::<Option<String>>());
1159         if bounds.len() > 0 {
1160             format!(": {}", bound_str)
1161         } else {
1162             String::new()
1163         }
1164     } else {
1165         String::new()
1166     };
1167
1168     if let Some(ty) = ty_opt {
1169         let ty_str = try_opt!(ty.rewrite(context,
1170                                          context.config.max_width - context.block_indent.width() -
1171                                          prefix.len() -
1172                                          2,
1173                                          context.block_indent));
1174         Some(format!("{} = {};", prefix, ty_str))
1175     } else {
1176         Some(format!("{}{};", prefix, type_bounds_str))
1177     }
1178 }
1179
1180 impl Rewrite for ast::FunctionRetTy {
1181     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
1182         match *self {
1183             ast::FunctionRetTy::Default(_) => Some(String::new()),
1184             ast::FunctionRetTy::Ty(ref ty) => {
1185                 let inner_width = try_opt!(width.checked_sub(3));
1186                 ty.rewrite(context, inner_width, offset + 3).map(|r| format!("-> {}", r))
1187             }
1188         }
1189     }
1190 }
1191
1192 impl Rewrite for ast::Arg {
1193     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
1194         if is_named_arg(self) {
1195             let mut result = try_opt!(self.pat.rewrite(context, width, offset));
1196
1197             if self.ty.node != ast::TyKind::Infer {
1198                 if context.config.space_before_type_annotation {
1199                     result.push_str(" ");
1200                 }
1201                 result.push_str(":");
1202                 if context.config.space_after_type_annotation_colon {
1203                     result.push_str(" ");
1204                 }
1205                 let max_width = try_opt!(width.checked_sub(result.len()));
1206                 let ty_str = try_opt!(self.ty.rewrite(context, max_width, offset + result.len()));
1207                 result.push_str(&ty_str);
1208             }
1209
1210             Some(result)
1211         } else {
1212             self.ty.rewrite(context, width, offset)
1213         }
1214     }
1215 }
1216
1217 fn rewrite_explicit_self(explicit_self: &ast::ExplicitSelf,
1218                          args: &[ast::Arg],
1219                          context: &RewriteContext)
1220                          -> Option<String> {
1221     match explicit_self.node {
1222         ast::SelfKind::Region(lt, m) => {
1223             let mut_str = format_mutability(m);
1224             match lt {
1225                 Some(ref l) => {
1226                     let lifetime_str =
1227                         try_opt!(l.rewrite(context, usize::max_value(), Indent::empty()));
1228                     Some(format!("&{} {}self", lifetime_str, mut_str))
1229                 }
1230                 None => Some(format!("&{}self", mut_str)),
1231             }
1232         }
1233         ast::SelfKind::Explicit(ref ty, _) => {
1234             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1235
1236             let mutability = explicit_self_mutability(&args[0]);
1237             let type_str = try_opt!(ty.rewrite(context, usize::max_value(), Indent::empty()));
1238
1239             Some(format!("{}self: {}", format_mutability(mutability), type_str))
1240         }
1241         ast::SelfKind::Value(_) => {
1242             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1243
1244             let mutability = explicit_self_mutability(&args[0]);
1245
1246             Some(format!("{}self", format_mutability(mutability)))
1247         }
1248     }
1249 }
1250
1251 // Hacky solution caused by absence of `Mutability` in `SelfValue` and
1252 // `SelfExplicit` variants of `ast::ExplicitSelf_`.
1253 fn explicit_self_mutability(arg: &ast::Arg) -> ast::Mutability {
1254     if let ast::PatKind::Ident(ast::BindingMode::ByValue(mutability), _, _) = arg.pat.node {
1255         mutability
1256     } else {
1257         unreachable!()
1258     }
1259 }
1260
1261 pub fn span_lo_for_arg(arg: &ast::Arg) -> BytePos {
1262     if is_named_arg(arg) {
1263         arg.pat.span.lo
1264     } else {
1265         arg.ty.span.lo
1266     }
1267 }
1268
1269 pub fn span_hi_for_arg(arg: &ast::Arg) -> BytePos {
1270     match arg.ty.node {
1271         ast::TyKind::Infer if is_named_arg(arg) => arg.pat.span.hi,
1272         _ => arg.ty.span.hi,
1273     }
1274 }
1275
1276 pub fn is_named_arg(arg: &ast::Arg) -> bool {
1277     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
1278         ident.node != token::keywords::Invalid.ident()
1279     } else {
1280         true
1281     }
1282 }
1283
1284 fn span_for_return(ret: &ast::FunctionRetTy) -> Span {
1285     match *ret {
1286         ast::FunctionRetTy::Default(ref span) => span.clone(),
1287         ast::FunctionRetTy::Ty(ref ty) => ty.span,
1288     }
1289 }
1290
1291 fn span_for_ty_param(ty: &ast::TyParam) -> Span {
1292     // Note that ty.span is the span for ty.ident, not the whole item.
1293     let lo = ty.span.lo;
1294     if let Some(ref def) = ty.default {
1295         return mk_sp(lo, def.span.hi);
1296     }
1297     if ty.bounds.is_empty() {
1298         return ty.span;
1299     }
1300     let hi = match ty.bounds[ty.bounds.len() - 1] {
1301         ast::TyParamBound::TraitTyParamBound(ref ptr, _) => ptr.span.hi,
1302         ast::TyParamBound::RegionTyParamBound(ref l) => l.span.hi,
1303     };
1304     mk_sp(lo, hi)
1305 }
1306
1307 fn span_for_where_pred(pred: &ast::WherePredicate) -> Span {
1308     match *pred {
1309         ast::WherePredicate::BoundPredicate(ref p) => p.span,
1310         ast::WherePredicate::RegionPredicate(ref p) => p.span,
1311         ast::WherePredicate::EqPredicate(ref p) => p.span,
1312     }
1313 }
1314
1315 // Return type is (result, force_new_line_for_brace)
1316 fn rewrite_fn_base(context: &RewriteContext,
1317                    indent: Indent,
1318                    ident: ast::Ident,
1319                    fd: &ast::FnDecl,
1320                    generics: &ast::Generics,
1321                    unsafety: ast::Unsafety,
1322                    constness: ast::Constness,
1323                    defaultness: ast::Defaultness,
1324                    abi: abi::Abi,
1325                    vis: &ast::Visibility,
1326                    span: Span,
1327                    newline_brace: bool,
1328                    has_body: bool)
1329                    -> Option<(String, bool)> {
1330     let mut force_new_line_for_brace = false;
1331     // FIXME we'll lose any comments in between parts of the function decl, but
1332     // anyone who comments there probably deserves what they get.
1333
1334     let where_clause = &generics.where_clause;
1335
1336     let mut result = String::with_capacity(1024);
1337     // Vis unsafety abi.
1338     result.push_str(&*format_visibility(vis));
1339
1340     if let ast::Defaultness::Default = defaultness {
1341         result.push_str("default ");
1342     }
1343
1344     if let ast::Constness::Const = constness {
1345         result.push_str("const ");
1346     }
1347
1348     result.push_str(::utils::format_unsafety(unsafety));
1349
1350     if abi != abi::Abi::Rust {
1351         result.push_str(&::utils::format_abi(abi, context.config.force_explicit_abi));
1352     }
1353
1354     // fn foo
1355     result.push_str("fn ");
1356     result.push_str(&ident.to_string());
1357
1358     // Generics.
1359     let generics_indent = indent + result.len();
1360     let generics_span = mk_sp(span.lo, span_for_return(&fd.output).lo);
1361     let generics_str = try_opt!(rewrite_generics(context,
1362                                                  generics,
1363                                                  indent,
1364                                                  context.config.max_width,
1365                                                  generics_indent,
1366                                                  generics_span));
1367     result.push_str(&generics_str);
1368
1369     // Note that if the width and indent really matter, we'll re-layout the
1370     // return type later anyway.
1371     let ret_str = try_opt!(fd.output
1372         .rewrite(&context, context.config.max_width - indent.width(), indent));
1373
1374     let multi_line_ret_str = ret_str.contains('\n');
1375     let ret_str_len = if multi_line_ret_str { 0 } else { ret_str.len() };
1376
1377     // Args.
1378     let (mut one_line_budget, mut multi_line_budget, mut arg_indent) =
1379         try_opt!(compute_budgets_for_args(context, &result, indent, ret_str_len, newline_brace));
1380
1381     if context.config.fn_args_layout == FnArgLayoutStyle::Block ||
1382        context.config.fn_args_layout == FnArgLayoutStyle::BlockAlways {
1383         arg_indent = indent.block_indent(context.config);
1384         multi_line_budget = context.config.max_width - arg_indent.width();
1385     }
1386
1387     debug!("rewrite_fn: one_line_budget: {}, multi_line_budget: {}, arg_indent: {:?}",
1388            one_line_budget,
1389            multi_line_budget,
1390            arg_indent);
1391
1392     // Check if vertical layout was forced by compute_budget_for_args.
1393     if one_line_budget == 0 {
1394         if context.config.fn_args_paren_newline {
1395             result.push('\n');
1396             result.push_str(&arg_indent.to_string(context.config));
1397             arg_indent = arg_indent + 1; // extra space for `(`
1398             result.push('(');
1399             if context.config.spaces_within_parens && fd.inputs.len() > 0 {
1400                 result.push(' ')
1401             }
1402         } else {
1403             result.push_str("(\n");
1404             result.push_str(&arg_indent.to_string(context.config));
1405         }
1406     } else {
1407         result.push('(');
1408         if context.config.spaces_within_parens && fd.inputs.len() > 0 {
1409             result.push(' ')
1410         }
1411     }
1412
1413     if multi_line_ret_str {
1414         one_line_budget = 0;
1415     }
1416
1417     // A conservative estimation, to goal is to be over all parens in generics
1418     let args_start = generics.ty_params
1419         .last()
1420         .map_or(span.lo, |tp| end_typaram(tp));
1421     let args_span = mk_sp(context.codemap.span_after(mk_sp(args_start, span.hi), "("),
1422                           span_for_return(&fd.output).lo);
1423     let arg_str = try_opt!(rewrite_args(context,
1424                                         &fd.inputs,
1425                                         fd.get_self().as_ref(),
1426                                         one_line_budget,
1427                                         multi_line_budget,
1428                                         indent,
1429                                         arg_indent,
1430                                         args_span,
1431                                         fd.variadic));
1432
1433     let multi_line_arg_str = arg_str.contains('\n');
1434
1435     let put_args_in_block = match context.config.fn_args_layout {
1436         FnArgLayoutStyle::Block => multi_line_arg_str,
1437         FnArgLayoutStyle::BlockAlways => true,
1438         _ => false,
1439     } && !fd.inputs.is_empty();
1440
1441     if put_args_in_block {
1442         arg_indent = indent.block_indent(context.config);
1443         result.push('\n');
1444         result.push_str(&arg_indent.to_string(context.config));
1445         result.push_str(&arg_str);
1446         result.push('\n');
1447         result.push_str(&indent.to_string(context.config));
1448         result.push(')');
1449     } else {
1450         result.push_str(&arg_str);
1451         if context.config.spaces_within_parens && fd.inputs.len() > 0 {
1452             result.push(' ')
1453         }
1454         result.push(')');
1455     }
1456
1457     // Return type.
1458     if !ret_str.is_empty() {
1459         let ret_should_indent = match context.config.fn_args_layout {
1460             // If our args are block layout then we surely must have space.
1461             FnArgLayoutStyle::Block if put_args_in_block => false,
1462             FnArgLayoutStyle::BlockAlways => false,
1463             _ => {
1464                 // If we've already gone multi-line, or the return type would push over the max
1465                 // width, then put the return type on a new line. With the +1 for the signature
1466                 // length an additional space between the closing parenthesis of the argument and
1467                 // the arrow '->' is considered.
1468                 let mut sig_length = result.len() + indent.width() + ret_str_len + 1;
1469
1470                 // If there is no where clause, take into account the space after the return type
1471                 // and the brace.
1472                 if where_clause.predicates.is_empty() {
1473                     sig_length += 2;
1474                 }
1475
1476                 let overlong_sig = sig_length > context.config.max_width;
1477
1478                 result.contains('\n') || multi_line_ret_str || overlong_sig
1479             }
1480         };
1481         let ret_indent = if ret_should_indent {
1482             let indent = match context.config.fn_return_indent {
1483                 ReturnIndent::WithWhereClause => indent + 4,
1484                 // Aligning with non-existent args looks silly.
1485                 _ if arg_str.is_empty() => {
1486                     force_new_line_for_brace = true;
1487                     indent + 4
1488                 }
1489                 // FIXME: we might want to check that using the arg indent
1490                 // doesn't blow our budget, and if it does, then fallback to
1491                 // the where clause indent.
1492                 _ => arg_indent,
1493             };
1494
1495             result.push('\n');
1496             result.push_str(&indent.to_string(context.config));
1497             indent
1498         } else {
1499             result.push(' ');
1500             Indent::new(indent.width(), result.len())
1501         };
1502
1503         if multi_line_ret_str {
1504             // Now that we know the proper indent and width, we need to
1505             // re-layout the return type.
1506             let budget = try_opt!(context.config.max_width.checked_sub(ret_indent.width()));
1507             let ret_str = try_opt!(fd.output.rewrite(context, budget, ret_indent));
1508             result.push_str(&ret_str);
1509         } else {
1510             result.push_str(&ret_str);
1511         }
1512
1513         // Comment between return type and the end of the decl.
1514         let snippet_lo = fd.output.span().hi;
1515         if where_clause.predicates.is_empty() {
1516             let snippet_hi = span.hi;
1517             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
1518             let snippet = snippet.trim();
1519             if !snippet.is_empty() {
1520                 result.push(' ');
1521                 result.push_str(snippet);
1522             }
1523         } else {
1524             // FIXME it would be nice to catch comments between the return type
1525             // and the where clause, but we don't have a span for the where
1526             // clause.
1527         }
1528     }
1529
1530     let should_compress_where = match context.config.where_density {
1531         Density::Compressed => !result.contains('\n') || put_args_in_block,
1532         Density::CompressedIfEmpty => !has_body && !result.contains('\n'),
1533         _ => false,
1534     } || (put_args_in_block && ret_str.is_empty());
1535
1536     let where_density = if should_compress_where {
1537         Density::Compressed
1538     } else {
1539         Density::Tall
1540     };
1541
1542     // Where clause.
1543     let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
1544     let where_clause_str = try_opt!(rewrite_where_clause(context,
1545                                                          where_clause,
1546                                                          context.config,
1547                                                          context.config.fn_brace_style,
1548                                                          indent,
1549                                                          where_budget,
1550                                                          where_density,
1551                                                          "{",
1552                                                          has_body,
1553                                                          Some(span.hi)));
1554
1555     if last_line_width(&result) + where_clause_str.len() > context.config.max_width &&
1556        !where_clause_str.contains('\n') {
1557         result.push('\n');
1558     }
1559
1560     result.push_str(&where_clause_str);
1561
1562     Some((result, force_new_line_for_brace))
1563 }
1564
1565 fn rewrite_args(context: &RewriteContext,
1566                 args: &[ast::Arg],
1567                 explicit_self: Option<&ast::ExplicitSelf>,
1568                 one_line_budget: usize,
1569                 multi_line_budget: usize,
1570                 indent: Indent,
1571                 arg_indent: Indent,
1572                 span: Span,
1573                 variadic: bool)
1574                 -> Option<String> {
1575     let mut arg_item_strs = try_opt!(args.iter()
1576         .map(|arg| arg.rewrite(&context, multi_line_budget, arg_indent))
1577         .collect::<Option<Vec<_>>>());
1578
1579     // Account for sugary self.
1580     // FIXME: the comment for the self argument is dropped. This is blocked
1581     // on rust issue #27522.
1582     let min_args =
1583         explicit_self.and_then(|explicit_self| rewrite_explicit_self(explicit_self, args, context))
1584             .map_or(1, |self_str| {
1585                 arg_item_strs[0] = self_str;
1586                 2
1587             });
1588
1589     // Comments between args.
1590     let mut arg_items = Vec::new();
1591     if min_args == 2 {
1592         arg_items.push(ListItem::from_str(""));
1593     }
1594
1595     // FIXME(#21): if there are no args, there might still be a comment, but
1596     // without spans for the comment or parens, there is no chance of
1597     // getting it right. You also don't get to put a comment on self, unless
1598     // it is explicit.
1599     if args.len() >= min_args || variadic {
1600         let comment_span_start = if min_args == 2 {
1601             let second_arg_start = if arg_has_pattern(&args[1]) {
1602                 args[1].pat.span.lo
1603             } else {
1604                 args[1].ty.span.lo
1605             };
1606             let reduced_span = mk_sp(span.lo, second_arg_start);
1607
1608             context.codemap.span_after_last(reduced_span, ",")
1609         } else {
1610             span.lo
1611         };
1612
1613         enum ArgumentKind<'a> {
1614             Regular(&'a ast::Arg),
1615             Variadic(BytePos),
1616         }
1617
1618         let variadic_arg = if variadic {
1619             let variadic_span = mk_sp(args.last().unwrap().ty.span.hi, span.hi);
1620             let variadic_start = context.codemap.span_after(variadic_span, "...") - BytePos(3);
1621             Some(ArgumentKind::Variadic(variadic_start))
1622         } else {
1623             None
1624         };
1625
1626         let more_items = itemize_list(context.codemap,
1627                                       args[min_args - 1..]
1628                                           .iter()
1629                                           .map(ArgumentKind::Regular)
1630                                           .chain(variadic_arg),
1631                                       ")",
1632                                       |arg| {
1633                                           match *arg {
1634                                               ArgumentKind::Regular(arg) => span_lo_for_arg(arg),
1635                                               ArgumentKind::Variadic(start) => start,
1636                                           }
1637                                       },
1638                                       |arg| {
1639                                           match *arg {
1640                                               ArgumentKind::Regular(arg) => arg.ty.span.hi,
1641                                               ArgumentKind::Variadic(start) => start + BytePos(3),
1642                                           }
1643                                       },
1644                                       |arg| {
1645                                           match *arg {
1646                                               ArgumentKind::Regular(..) => None,
1647                                               ArgumentKind::Variadic(..) => Some("...".to_owned()),
1648                                           }
1649                                       },
1650                                       comment_span_start,
1651                                       span.hi);
1652
1653         arg_items.extend(more_items);
1654     }
1655
1656     for (item, arg) in arg_items.iter_mut().zip(arg_item_strs) {
1657         item.item = Some(arg);
1658     }
1659
1660     let indent = match context.config.fn_arg_indent {
1661         BlockIndentStyle::Inherit => indent,
1662         BlockIndentStyle::Tabbed => indent.block_indent(context.config),
1663         BlockIndentStyle::Visual => arg_indent,
1664     };
1665
1666     let tactic = definitive_tactic(&arg_items,
1667                                    context.config.fn_args_density.to_list_tactic(),
1668                                    one_line_budget);
1669     let budget = match tactic {
1670         DefinitiveListTactic::Horizontal => one_line_budget,
1671         _ => multi_line_budget,
1672     };
1673
1674     debug!("rewrite_args: budget: {}, tactic: {:?}", budget, tactic);
1675
1676     let end_with_newline = match context.config.fn_args_layout {
1677         FnArgLayoutStyle::Block |
1678         FnArgLayoutStyle::BlockAlways => true,
1679         _ => false,
1680     };
1681
1682     let fmt = ListFormatting {
1683         tactic: tactic,
1684         separator: ",",
1685         trailing_separator: SeparatorTactic::Never,
1686         indent: indent,
1687         width: budget,
1688         ends_with_newline: end_with_newline,
1689         config: context.config,
1690     };
1691
1692     write_list(&arg_items, &fmt)
1693 }
1694
1695 fn arg_has_pattern(arg: &ast::Arg) -> bool {
1696     if let ast::PatKind::Ident(_,
1697                                codemap::Spanned {
1698                                    node: ast::Ident { name: ast::Name(0u32), .. },
1699                                    ..
1700                                },
1701                                _) = arg.pat.node {
1702         false
1703     } else {
1704         true
1705     }
1706 }
1707
1708 fn compute_budgets_for_args(context: &RewriteContext,
1709                             result: &str,
1710                             indent: Indent,
1711                             ret_str_len: usize,
1712                             newline_brace: bool)
1713                             -> Option<((usize, usize, Indent))> {
1714     // Try keeping everything on the same line.
1715     if !result.contains('\n') {
1716         // 3 = `() `, space is before ret_string.
1717         let mut used_space = indent.width() + result.len() + ret_str_len + 3;
1718         if !newline_brace {
1719             used_space += 2;
1720         }
1721         let one_line_budget = context.config.max_width.checked_sub(used_space).unwrap_or(0);
1722
1723         if one_line_budget > 0 {
1724             // 4 = "() {".len()
1725             let multi_line_budget =
1726                 try_opt!(context.config.max_width.checked_sub(indent.width() + result.len() + 4));
1727
1728             return Some((one_line_budget, multi_line_budget, indent + result.len() + 1));
1729         }
1730     }
1731
1732     // Didn't work. we must force vertical layout and put args on a newline.
1733     let new_indent = indent.block_indent(context.config);
1734     let used_space = new_indent.width() + 4; // Account for `(` and `)` and possibly ` {`.
1735     let max_space = context.config.max_width;
1736     if used_space <= max_space {
1737         Some((0, max_space - used_space, new_indent))
1738     } else {
1739         // Whoops! bankrupt.
1740         None
1741     }
1742 }
1743
1744 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> bool {
1745     match config.fn_brace_style {
1746         BraceStyle::AlwaysNextLine => true,
1747         BraceStyle::SameLineWhere if !where_clause.predicates.is_empty() => true,
1748         _ => false,
1749     }
1750 }
1751
1752 fn rewrite_generics(context: &RewriteContext,
1753                     generics: &ast::Generics,
1754                     offset: Indent,
1755                     width: usize,
1756                     generics_offset: Indent,
1757                     span: Span)
1758                     -> Option<String> {
1759     // FIXME: convert bounds to where clauses where they get too big or if
1760     // there is a where clause at all.
1761     let lifetimes: &[_] = &generics.lifetimes;
1762     let tys: &[_] = &generics.ty_params;
1763     if lifetimes.is_empty() && tys.is_empty() {
1764         return Some(String::new());
1765     }
1766
1767     let offset = match context.config.generics_indent {
1768         BlockIndentStyle::Inherit => offset,
1769         BlockIndentStyle::Tabbed => offset.block_indent(context.config),
1770         // 1 = <
1771         BlockIndentStyle::Visual => generics_offset + 1,
1772     };
1773
1774     let h_budget = try_opt!(width.checked_sub(generics_offset.width() + 2));
1775     // FIXME: might need to insert a newline if the generics are really long.
1776
1777     // Strings for the generics.
1778     let lt_strs = lifetimes.iter().map(|lt| lt.rewrite(context, h_budget, offset));
1779     let ty_strs = tys.iter().map(|ty_param| ty_param.rewrite(context, h_budget, offset));
1780
1781     // Extract comments between generics.
1782     let lt_spans = lifetimes.iter().map(|l| {
1783         let hi = if l.bounds.is_empty() {
1784             l.lifetime.span.hi
1785         } else {
1786             l.bounds[l.bounds.len() - 1].span.hi
1787         };
1788         mk_sp(l.lifetime.span.lo, hi)
1789     });
1790     let ty_spans = tys.iter().map(span_for_ty_param);
1791
1792     let items = itemize_list(context.codemap,
1793                              lt_spans.chain(ty_spans).zip(lt_strs.chain(ty_strs)),
1794                              ">",
1795                              |&(sp, _)| sp.lo,
1796                              |&(sp, _)| sp.hi,
1797                              // FIXME: don't clone
1798                              |&(_, ref str)| str.clone(),
1799                              context.codemap.span_after(span, "<"),
1800                              span.hi);
1801     let list_str = try_opt!(format_item_list(items, h_budget, offset, context.config));
1802
1803     Some(if context.config.spaces_within_angle_brackets {
1804         format!("< {} >", list_str)
1805     } else {
1806         format!("<{}>", list_str)
1807     })
1808 }
1809
1810 fn rewrite_trait_bounds(context: &RewriteContext,
1811                         type_param_bounds: &ast::TyParamBounds,
1812                         indent: Indent,
1813                         width: usize)
1814                         -> Option<String> {
1815     let bounds: &[_] = type_param_bounds;
1816
1817     if bounds.is_empty() {
1818         return Some(String::new());
1819     }
1820
1821     let bound_str = try_opt!(bounds.iter()
1822         .map(|ty_bound| ty_bound.rewrite(&context, width, indent))
1823         .intersperse(Some(" + ".to_string()))
1824         .collect::<Option<String>>());
1825
1826     let mut result = String::new();
1827     result.push_str(": ");
1828     result.push_str(&bound_str);
1829     Some(result)
1830 }
1831
1832 fn rewrite_where_clause(context: &RewriteContext,
1833                         where_clause: &ast::WhereClause,
1834                         config: &Config,
1835                         brace_style: BraceStyle,
1836                         indent: Indent,
1837                         width: usize,
1838                         density: Density,
1839                         terminator: &str,
1840                         allow_trailing_comma: bool,
1841                         span_end: Option<BytePos>)
1842                         -> Option<String> {
1843     if where_clause.predicates.is_empty() {
1844         return Some(String::new());
1845     }
1846
1847     let extra_indent = match context.config.where_indent {
1848         BlockIndentStyle::Inherit => Indent::empty(),
1849         BlockIndentStyle::Tabbed | BlockIndentStyle::Visual => Indent::new(config.tab_spaces, 0),
1850     };
1851
1852     let offset = match context.config.where_pred_indent {
1853         BlockIndentStyle::Inherit => indent + extra_indent,
1854         BlockIndentStyle::Tabbed => indent + extra_indent.block_indent(config),
1855         // 6 = "where ".len()
1856         BlockIndentStyle::Visual => indent + extra_indent + 6,
1857     };
1858     // FIXME: if where_pred_indent != Visual, then the budgets below might
1859     // be out by a char or two.
1860
1861     let budget = context.config.max_width - offset.width();
1862     let span_start = span_for_where_pred(&where_clause.predicates[0]).lo;
1863     // If we don't have the start of the next span, then use the end of the
1864     // predicates, but that means we miss comments.
1865     let len = where_clause.predicates.len();
1866     let end_of_preds = span_for_where_pred(&where_clause.predicates[len - 1]).hi;
1867     let span_end = span_end.unwrap_or(end_of_preds);
1868     let items = itemize_list(context.codemap,
1869                              where_clause.predicates.iter(),
1870                              terminator,
1871                              |pred| span_for_where_pred(pred).lo,
1872                              |pred| span_for_where_pred(pred).hi,
1873                              |pred| pred.rewrite(context, budget, offset),
1874                              span_start,
1875                              span_end);
1876     let item_vec = items.collect::<Vec<_>>();
1877     // FIXME: we don't need to collect here if the where_layout isn't
1878     // HorizontalVertical.
1879     let tactic = definitive_tactic(&item_vec, context.config.where_layout, budget);
1880     let use_trailing_comma = allow_trailing_comma && context.config.where_trailing_comma;
1881
1882     let fmt = ListFormatting {
1883         tactic: tactic,
1884         separator: ",",
1885         trailing_separator: SeparatorTactic::from_bool(use_trailing_comma),
1886         indent: offset,
1887         width: budget,
1888         ends_with_newline: true,
1889         config: context.config,
1890     };
1891     let preds_str = try_opt!(write_list(&item_vec, &fmt));
1892
1893     let end_length = if terminator == "{" {
1894         // If the brace is on the next line we don't need to count it otherwise it needs two
1895         // characters " {"
1896         match brace_style {
1897             BraceStyle::AlwaysNextLine |
1898             BraceStyle::SameLineWhere => 0,
1899             BraceStyle::PreferSameLine => 2,
1900         }
1901     } else if terminator == "=" {
1902         2
1903     } else {
1904         terminator.len()
1905     };
1906     if density == Density::Tall || preds_str.contains('\n') ||
1907        indent.width() + " where ".len() + preds_str.len() + end_length > width {
1908         Some(format!("\n{}where {}",
1909                      (indent + extra_indent).to_string(context.config),
1910                      preds_str))
1911     } else {
1912         Some(format!(" where {}", preds_str))
1913     }
1914 }
1915
1916 fn format_header(item_name: &str, ident: ast::Ident, vis: &ast::Visibility) -> String {
1917     format!("{}{}{}", format_visibility(vis), item_name, ident)
1918 }
1919
1920 fn format_generics(context: &RewriteContext,
1921                    generics: &ast::Generics,
1922                    opener: &str,
1923                    terminator: &str,
1924                    brace_style: BraceStyle,
1925                    force_same_line_brace: bool,
1926                    offset: Indent,
1927                    generics_offset: Indent,
1928                    span: Span)
1929                    -> Option<String> {
1930     let mut result = try_opt!(rewrite_generics(context,
1931                                                generics,
1932                                                offset,
1933                                                context.config.max_width,
1934                                                generics_offset,
1935                                                span));
1936
1937     if !generics.where_clause.predicates.is_empty() || result.contains('\n') {
1938         let budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
1939         let where_clause_str = try_opt!(rewrite_where_clause(context,
1940                                                              &generics.where_clause,
1941                                                              context.config,
1942                                                              brace_style,
1943                                                              context.block_indent,
1944                                                              budget,
1945                                                              Density::Tall,
1946                                                              terminator,
1947                                                              true,
1948                                                              Some(span.hi)));
1949         result.push_str(&where_clause_str);
1950         if !force_same_line_brace &&
1951            (brace_style == BraceStyle::SameLineWhere || brace_style == BraceStyle::AlwaysNextLine) {
1952             result.push('\n');
1953             result.push_str(&context.block_indent.to_string(context.config));
1954         } else {
1955             result.push(' ');
1956         }
1957         result.push_str(opener);
1958     } else {
1959         if !force_same_line_brace && brace_style == BraceStyle::AlwaysNextLine {
1960             result.push('\n');
1961             result.push_str(&context.block_indent.to_string(context.config));
1962         } else {
1963             result.push(' ');
1964         }
1965         result.push_str(opener);
1966     }
1967
1968     Some(result)
1969 }