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