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 {ReturnIndent, BraceStyle};
  14 use utils::{format_visibility, make_indent, FindUncommented};
  15 use lists::{write_list, ListFormatting, SeparatorTactic, ListTactic};
  16 use visitor::FmtVisitor;
  17 use syntax::{ast, abi};
  18 use syntax::codemap::{self, Span, BytePos};
  19 use syntax::print::pprust;
  20 use syntax::parse::token;
  21
  22 impl<'a> FmtVisitor<'a> {
  23     pub fn rewrite_fn(&mut self,
  24                       indent: usize,
  25                       ident: ast::Ident,
  26                       fd: &ast::FnDecl,
  27                       explicit_self: Option<&ast::ExplicitSelf>,
  28                       generics: &ast::Generics,
  29                       unsafety: &ast::Unsafety,
  30                       constness: &ast::Constness,
  31                       abi: &abi::Abi,
  32                       vis: ast::Visibility,
  33                       span_end: BytePos)
  34         -> String
  35     {
  36         let newline_brace = self.newline_for_brace(&generics.where_clause);
  37
  38         let mut result = self.rewrite_fn_base(indent,
  39                                               ident,
  40                                               fd,
  41                                               explicit_self,
  42                                               generics,
  43                                               unsafety,
  44                                               constness,
  45                                               abi,
  46                                               vis,
  47                                               span_end,
  48                                               newline_brace);
  49
  50         // Prepare for the function body by possibly adding a newline and indent.
  51         // FIXME we'll miss anything between the end of the signature and the start
  52         // of the body, but we need more spans from the compiler to solve this.
  53         if newline_brace {
  54             result.push('\n');
  55             result.push_str(&make_indent(indent));
  56         } else {
  57             result.push(' ');
  58         }
  59
  60         result
  61     }
  62
  63     pub fn rewrite_required_fn(&mut self,
  64                                indent: usize,
  65                                ident: ast::Ident,
  66                                sig: &ast::MethodSig,
  67                                span: Span)
  68         -> String
  69     {
  70         // Drop semicolon or it will be interpreted as comment
  71         let span_end = span.hi - BytePos(1);
  72
  73         let mut result = self.rewrite_fn_base(indent,
  74                                               ident,
  75                                               &sig.decl,
  76                                               Some(&sig.explicit_self),
  77                                               &sig.generics,
  78                                               &sig.unsafety,
  79                                               &sig.constness,
  80                                               &sig.abi,
  81                                               ast::Visibility::Inherited,
  82                                               span_end,
  83                                               false);
  84
  85         // Re-attach semicolon
  86         result.push(';');
  87
  88         result
  89     }
  90
  91     fn rewrite_fn_base(&mut self,
  92                        indent: usize,
  93                        ident: ast::Ident,
  94                        fd: &ast::FnDecl,
  95                        explicit_self: Option<&ast::ExplicitSelf>,
  96                        generics: &ast::Generics,
  97                        unsafety: &ast::Unsafety,
  98                        constness: &ast::Constness,
  99                        abi: &abi::Abi,
 100                        vis: ast::Visibility,
 101                        span_end: BytePos,
 102                        newline_brace: bool)
 103         -> String
 104     {
 105         // FIXME we'll lose any comments in between parts of the function decl, but anyone
 106         // who comments there probably deserves what they get.
 107
 108         let where_clause = &generics.where_clause;
 109
 110         let mut result = String::with_capacity(1024);
 111         // Vis unsafety abi.
 112         result.push_str(format_visibility(vis));
 113
 114         if let &ast::Unsafety::Unsafe = unsafety {
 115             result.push_str("unsafe ");
 116         }
 117         if let &ast::Constness::Const = constness {
 118             result.push_str("const ");
 119         }
 120         if *abi != abi::Rust {
 121             result.push_str("extern ");
 122             result.push_str(&abi.to_string());
 123             result.push(' ');
 124         }
 125
 126         // fn foo
 127         result.push_str("fn ");
 128         result.push_str(&token::get_ident(ident));
 129
 130         // Generics.
 131         let generics_indent = indent + result.len();
 132         result.push_str(&self.rewrite_generics(generics,
 133                                                generics_indent,
 134                                                span_for_return(&fd.output).lo));
 135
 136         let ret_str = self.rewrite_return(&fd.output);
 137
 138         // Args.
 139         let (one_line_budget, multi_line_budget, mut arg_indent) =
 140             self.compute_budgets_for_args(&result, indent, ret_str.len(), newline_brace);
 141
 142         debug!("rewrite_fn: one_line_budget: {}, multi_line_budget: {}, arg_indent: {}",
 143                one_line_budget, multi_line_budget, arg_indent);
 144
 145         // Check if vertical layout was forced by compute_budget_for_args.
 146         if one_line_budget <= 0 {
 147             if self.config.fn_args_paren_newline {
 148                 result.push('\n');
 149                 result.push_str(&make_indent(arg_indent));
 150                 arg_indent = arg_indent + 1; // extra space for `(`
 151                 result.push('(');
 152             } else {
 153                 result.push_str("(\n");
 154                 result.push_str(&make_indent(arg_indent));
 155             }
 156         } else {
 157             result.push('(');
 158         }
 159
 160         result.push_str(&self.rewrite_args(&fd.inputs,
 161                                            explicit_self,
 162                                            one_line_budget,
 163                                            multi_line_budget,
 164                                            arg_indent,
 165                                            span_for_return(&fd.output)));
 166         result.push(')');
 167
 168         // Return type.
 169         if ret_str.len() > 0 {
 170             // If we've already gone multi-line, or the return type would push
 171             // over the max width, then put the return type on a new line.
 172             if result.contains("\n") ||
 173                result.len() + indent + ret_str.len() > self.config.max_width {
 174                 let indent = match self.config.fn_return_indent {
 175                     ReturnIndent::WithWhereClause => indent + 4,
 176                     // TODO we might want to check that using the arg indent doesn't
 177                     // blow our budget, and if it does, then fallback to the where
 178                     // clause indent.
 179                     _ => arg_indent,
 180                 };
 181
 182                 result.push('\n');
 183                 result.push_str(&make_indent(indent));
 184             } else {
 185                 result.push(' ');
 186             }
 187             result.push_str(&ret_str);
 188
 189             // Comment between return type and the end of the decl.
 190             let snippet_lo = fd.output.span().hi;
 191             if where_clause.predicates.len() == 0 {
 192                 let snippet_hi = span_end;
 193                 let snippet = self.snippet(codemap::mk_sp(snippet_lo, snippet_hi));
 194                 let snippet = snippet.trim();
 195                 if snippet.len() > 0 {
 196                     result.push(' ');
 197                     result.push_str(snippet);
 198                 }
 199             } else {
 200                 // FIXME it would be nice to catch comments between the return type
 201                 // and the where clause, but we don't have a span for the where
 202                 // clause.
 203             }
 204         }
 205
 206         // Where clause.
 207         result.push_str(&self.rewrite_where_clause(where_clause, indent, span_end));
 208
 209         result
 210     }
 211
 212     fn rewrite_args(&self,
 213                     args: &[ast::Arg],
 214                     explicit_self: Option<&ast::ExplicitSelf>,
 215                     one_line_budget: usize,
 216                     multi_line_budget: usize,
 217                     arg_indent: usize,
 218                     ret_span: Span)
 219         -> String
 220     {
 221         let mut arg_item_strs: Vec<_> = args.iter().map(|a| self.rewrite_fn_input(a)).collect();
 222         // Account for sugary self.
 223         let mut min_args = 1;
 224         if let Some(explicit_self) = explicit_self {
 225             match explicit_self.node {
 226                 ast::ExplicitSelf_::SelfRegion(ref lt, ref m, _) => {
 227                     let lt_str = match lt {
 228                         &Some(ref l) => format!("{} ", pprust::lifetime_to_string(l)),
 229                         &None => String::new(),
 230                     };
 231                     let mut_str = match m {
 232                         &ast::Mutability::MutMutable => "mut ".to_owned(),
 233                         &ast::Mutability::MutImmutable => String::new(),
 234                     };
 235                     arg_item_strs[0] = format!("&{}{}self", lt_str, mut_str);
 236                     min_args = 2;
 237                 }
 238                 ast::ExplicitSelf_::SelfExplicit(ref ty, _) => {
 239                     arg_item_strs[0] = format!("self: {}", pprust::ty_to_string(ty));
 240                 }
 241                 ast::ExplicitSelf_::SelfValue(_) => {
 242                     assert!(args.len() >= 1, "&[ast::Arg] shouldn't be empty.");
 243
 244                     // this hacky solution caused by absence of `Mutability` in `SelfValue`.
 245                     let mut_str = {
 246                         if let ast::Pat_::PatIdent(ast::BindingMode::BindByValue(mutability), _, _)
 247                                 = args[0].pat.node {
 248                             match mutability {
 249                                 ast::Mutability::MutMutable => "mut ",
 250                                 ast::Mutability::MutImmutable => "",
 251                             }
 252                         } else {
 253                             panic!("there is a bug or change in structure of AST, aborting.");
 254                         }
 255                     };
 256
 257                     arg_item_strs[0] = format!("{}self", mut_str);
 258                     min_args = 2;
 259                 }
 260                 _ => {}
 261             }
 262         }
 263
 264         // Comments between args
 265         let mut arg_comments = Vec::new();
 266         if min_args == 2 {
 267             arg_comments.push("".to_owned());
 268         }
 269         // TODO if there are no args, there might still be a comment, but without
 270         // spans for the comment or parens, there is no chance of getting it right.
 271         // You also don't get to put a comment on self, unless it is explicit.
 272         if args.len() >= min_args {
 273             arg_comments = self.make_comments_for_list(arg_comments,
 274                                                        args[min_args-1..].iter(),
 275                                                        ",",
 276                                                        ")",
 277                                                        |arg| arg.pat.span.lo,
 278                                                        |arg| arg.ty.span.hi,
 279                                                        ret_span.lo);
 280         }
 281
 282         debug!("comments: {:?}", arg_comments);
 283
 284         // If there are // comments, keep them multi-line.
 285         let mut list_tactic = ListTactic::HorizontalVertical;
 286         if arg_comments.iter().any(|c| c.contains("//")) {
 287             list_tactic = ListTactic::Vertical;
 288         }
 289
 290         assert_eq!(arg_item_strs.len(), arg_comments.len());
 291         let arg_strs: Vec<_> = arg_item_strs.into_iter().zip(arg_comments.into_iter()).collect();
 292
 293         let fmt = ListFormatting {
 294             tactic: list_tactic,
 295             separator: ",",
 296             trailing_separator: SeparatorTactic::Never,
 297             indent: arg_indent,
 298             h_width: one_line_budget,
 299             v_width: multi_line_budget,
 300         };
 301
 302         write_list(&arg_strs, &fmt)
 303     }
 304
 305     // Gets comments in between items of a list.
 306     fn make_comments_for_list<T, I, F1, F2>(&self,
 307                                             prefix: Vec<String>,
 308                                             mut it: I,
 309                                             separator: &str,
 310                                             terminator: &str,
 311                                             get_lo: F1,
 312                                             get_hi: F2,
 313                                             next_span_start: BytePos)
 314         -> Vec<String>
 315         where I: Iterator<Item=T>,
 316               F1: Fn(&T) -> BytePos,
 317               F2: Fn(&T) -> BytePos
 318     {
 319         let mut result = prefix;
 320
 321         let mut prev_end = get_hi(&it.next().unwrap());
 322         for item in it {
 323             let cur_start = get_lo(&item);
 324             let snippet = self.snippet(codemap::mk_sp(prev_end, cur_start));
 325             let mut snippet = snippet.trim();
 326             let white_space: &[_] = &[' ', '\t'];
 327             if snippet.starts_with(separator) {
 328                 snippet = snippet[separator.len()..].trim_matches(white_space);
 329             } else if snippet.ends_with(separator) {
 330                 snippet = snippet[..snippet.len()-separator.len()].trim_matches(white_space);
 331             }
 332             result.push(snippet.to_owned());
 333             prev_end = get_hi(&item);
 334         }
 335         // Get the last commment.
 336         // FIXME If you thought the crap with the commas was ugly, just wait.
 337         // This is awful. We're going to look from the last item span to the
 338         // start of the return type span, then we drop everything after the
 339         // first closing paren.
 340         // The fix is comments in the AST or a span for the closing paren.
 341         let snippet = self.snippet(codemap::mk_sp(prev_end, next_span_start));
 342         let snippet = snippet.trim();
 343         let snippet = &snippet[..snippet.find_uncommented(terminator).unwrap_or(snippet.len())];
 344         let snippet = snippet.trim();
 345         result.push(snippet.to_owned());
 346
 347         result
 348     }
 349
 350     fn compute_budgets_for_args(&self,
 351                                 result: &str,
 352                                 indent: usize,
 353                                 ret_str_len: usize,
 354                                 newline_brace: bool)
 355         -> (usize, usize, usize)
 356     {
 357         let mut budgets = None;
 358
 359         // Try keeping everything on the same line
 360         if !result.contains("\n") {
 361             // 3 = `() `, space is before ret_string
 362             let mut used_space = indent + result.len() + ret_str_len + 3;
 363             if !newline_brace {
 364                 used_space += 2;
 365             }
 366             let one_line_budget = if used_space > self.config.max_width {
 367                 0
 368             } else {
 369                 self.config.max_width - used_space
 370             };
 371
 372             // 2 = `()`
 373             let used_space = indent + result.len() + 2;
 374             let max_space = self.config.ideal_width + self.config.leeway;
 375             debug!("compute_budgets_for_args: used_space: {}, max_space: {}",
 376                    used_space, max_space);
 377             if used_space < max_space {
 378                 budgets = Some((one_line_budget,
 379                                 max_space - used_space,
 380                                 indent + result.len() + 1));
 381             }
 382         }
 383
 384         // Didn't work. we must force vertical layout and put args on a newline.
 385         if let None = budgets {
 386             let new_indent = indent + self.config.tab_spaces;
 387             let used_space = new_indent + 2; // account for `(` and `)`
 388             let max_space = self.config.ideal_width + self.config.leeway;
 389             if used_space > max_space {
 390                 // Whoops! bankrupt.
 391                 // TODO take evasive action, perhaps kill the indent or something.
 392             } else {
 393                 budgets = Some((0, max_space - used_space, new_indent));
 394             }
 395         }
 396
 397         budgets.unwrap()
 398     }
 399
 400     fn newline_for_brace(&self, where_clause: &ast::WhereClause) -> bool {
 401         match self.config.fn_brace_style {
 402             BraceStyle::AlwaysNextLine => true,
 403             BraceStyle::SameLineWhere if where_clause.predicates.len() > 0 => true,
 404             _ => false,
 405         }
 406     }
 407
 408     pub fn visit_enum(&mut self,
 409                       ident: ast::Ident,
 410                       vis: ast::Visibility,
 411                       enum_def: &ast::EnumDef,
 412                       generics: &ast::Generics,
 413                       span: Span)
 414     {
 415         let header_str = self.format_header("enum", ident, vis);
 416         self.changes.push_str_span(span, &header_str);
 417
 418         let enum_snippet = self.snippet(span);
 419         let body_start = span.lo + BytePos(enum_snippet.find_uncommented("{").unwrap() as u32 + 1);
 420         let generics_str = self.format_generics(generics, body_start);
 421         self.changes.push_str_span(span, &generics_str);
 422
 423         self.last_pos = body_start;
 424         self.block_indent += self.config.tab_spaces;
 425         for (i, f) in enum_def.variants.iter().enumerate() {
 426             let next_span_start: BytePos = if i == enum_def.variants.len() - 1 {
 427                 span.hi
 428             } else {
 429                 enum_def.variants[i + 1].span.lo
 430             };
 431
 432             self.visit_variant(f, i == enum_def.variants.len() - 1, next_span_start);
 433         }
 434         self.block_indent -= self.config.tab_spaces;
 435
 436         self.format_missing_with_indent(span.lo + BytePos(enum_snippet.rfind('}').unwrap() as u32));
 437         self.changes.push_str_span(span, "}");
 438     }
 439
 440     // Variant of an enum
 441     fn visit_variant(&mut self,
 442                      field: &ast::Variant,
 443                      last_field: bool,
 444                      next_span_start: BytePos)
 445     {
 446         if self.visit_attrs(&field.node.attrs) {
 447             return;
 448         }
 449
 450         if let ast::VariantKind::TupleVariantKind(ref types) = field.node.kind {
 451             self.format_missing_with_indent(field.span.lo);
 452
 453             let vis = format_visibility(field.node.vis);
 454             self.changes.push_str_span(field.span, vis);
 455             let name = field.node.name.to_string();
 456             self.changes.push_str_span(field.span, &name);
 457
 458             let mut result = String::new();
 459
 460             if types.len() > 0 {
 461                 let comments = self.make_comments_for_list(Vec::new(),
 462                                                            types.iter().map(|arg| arg.ty.span),
 463                                                            ",",
 464                                                            ")",
 465                                                            |span| span.lo,
 466                                                            |span| span.hi,
 467                                                            next_span_start);
 468
 469                 let type_strings: Vec<_> = types.iter()
 470                                                 .map(|arg| pprust::ty_to_string(&arg.ty))
 471                                                 .zip(comments.into_iter())
 472                                                 .collect();
 473
 474                 result.push('(');
 475
 476                 let indent = self.block_indent
 477                              + vis.len()
 478                              + field.node.name.to_string().len()
 479                              + 1; // 1 = (
 480
 481                 let comma_cost = if self.config.enum_trailing_comma { 1 } else { 0 };
 482                 let budget = self.config.ideal_width - indent - comma_cost - 1; // 1 = )
 483
 484                 let fmt = ListFormatting {
 485                     tactic: ListTactic::HorizontalVertical,
 486                     separator: ",",
 487                     trailing_separator: SeparatorTactic::Never,
 488                     indent: indent,
 489                     h_width: budget,
 490                     v_width: budget,
 491                 };
 492                 result.push_str(&write_list(&type_strings, &fmt));
 493                 result.push(')');
 494             }
 495
 496             if let Some(ref expr) = field.node.disr_expr {
 497                 result.push_str(" = ");
 498                 let expr_snippet = self.snippet(expr.span);
 499                 result.push_str(&expr_snippet);
 500
 501                 // Make sure we do not exceed column limit
 502                 // 4 = " = ,"
 503                 assert!(self.config.max_width >= vis.len() + name.len() + expr_snippet.len() + 4,
 504                         "Enum variant exceeded column limit");
 505             }
 506
 507             self.changes.push_str_span(field.span, &result);
 508
 509             if !last_field || self.config.enum_trailing_comma {
 510                 self.changes.push_str_span(field.span, ",");
 511             }
 512         }
 513
 514         // TODO: deal with struct-like variants
 515
 516         self.last_pos = field.span.hi + BytePos(1);
 517     }
 518
 519     pub fn visit_struct(&mut self,
 520                         ident: ast::Ident,
 521                         vis: ast::Visibility,
 522                         struct_def: &ast::StructDef,
 523                         generics: &ast::Generics,
 524                         span: Span)
 525     {
 526         let header_str = self.format_header("struct", ident, vis);
 527         self.changes.push_str_span(span, &header_str);
 528
 529         if struct_def.fields.len() == 0 {
 530             assert!(generics.where_clause.predicates.len() == 0,
 531                     "No-field struct with where clause?");
 532             assert!(generics.lifetimes.len() == 0, "No-field struct with generics?");
 533             assert!(generics.ty_params.len() == 0, "No-field struct with generics?");
 534
 535             self.changes.push_str_span(span, ";");
 536             return;
 537         }
 538
 539         let generics_str = self.format_generics(generics, struct_def.fields[0].span.lo);
 540         self.changes.push_str_span(span, &generics_str);
 541
 542         let struct_snippet = self.snippet(span);
 543         // This will drop the comment in between the header and body.
 544         self.last_pos = span.lo + BytePos(struct_snippet.find_uncommented("{").unwrap() as u32 + 1);
 545
 546         self.block_indent += self.config.tab_spaces;
 547         for (i, f) in struct_def.fields.iter().enumerate() {
 548             self.visit_field(f, i == struct_def.fields.len() - 1, span.lo, &struct_snippet);
 549         }
 550         self.block_indent -= self.config.tab_spaces;
 551
 552         self.format_missing_with_indent(span.lo + BytePos(struct_snippet.rfind('}').unwrap() as u32));
 553         self.changes.push_str_span(span, "}");
 554     }
 555
 556     fn format_header(&self,
 557                      item_name: &str,
 558                      ident: ast::Ident,
 559                      vis: ast::Visibility)
 560         -> String
 561     {
 562         format!("{}{} {}", format_visibility(vis), item_name, &token::get_ident(ident))
 563     }
 564
 565     fn format_generics(&self,
 566                        generics: &ast::Generics,
 567                        span_end: BytePos)
 568         -> String
 569     {
 570         let mut result = self.rewrite_generics(generics, self.block_indent, span_end);
 571
 572         if generics.where_clause.predicates.len() > 0 {
 573             result.push_str(&self.rewrite_where_clause(&generics.where_clause,
 574                                                              self.block_indent,
 575                                                              span_end));
 576             result.push_str(&make_indent(self.block_indent));
 577             result.push_str("\n{");
 578
 579         } else {
 580             result.push_str(" {");
 581         }
 582
 583         result
 584     }
 585
 586     // Field of a struct
 587     fn visit_field(&mut self,
 588                    field: &ast::StructField,
 589                    last_field: bool,
 590                    // These two args are for missing spans hacks.
 591                    struct_start: BytePos,
 592                    struct_snippet: &str)
 593     {
 594         if self.visit_attrs(&field.node.attrs) {
 595             return;
 596         }
 597         self.format_missing_with_indent(field.span.lo);
 598
 599         let name = match field.node.kind {
 600             ast::StructFieldKind::NamedField(ident, _) => Some(token::get_ident(ident)),
 601             ast::StructFieldKind::UnnamedField(_) => None,
 602         };
 603         let vis = match field.node.kind {
 604             ast::StructFieldKind::NamedField(_, vis) |
 605             ast::StructFieldKind::UnnamedField(vis) => format_visibility(vis)
 606         };
 607         let typ = pprust::ty_to_string(&field.node.ty);
 608
 609         let mut field_str = match name {
 610             Some(name) => {
 611                 let budget = self.config.ideal_width - self.block_indent;
 612                 // 3 is being conservative and assuming that there will be a trailing comma.
 613                 if self.block_indent + vis.len() + name.len() + typ.len() + 3 > budget {
 614                     format!("{}{}:\n{}{}",
 615                             vis,
 616                             name,
 617                             &make_indent(self.block_indent + self.config.tab_spaces),
 618                             typ)
 619                 } else {
 620                     format!("{}{}: {}", vis, name, typ)
 621                 }
 622             }
 623             None => format!("{}{}", vis, typ),
 624         };
 625         if !last_field || self.config.struct_trailing_comma {
 626             field_str.push(',');
 627         }
 628         self.changes.push_str_span(field.span, &field_str);
 629
 630         // This hack makes sure we only add comments etc. after the comma, and
 631         // makes sure we don't repeat any commas.
 632         let hi = field.span.hi;
 633         let comma_pos = match struct_snippet[(hi.0 - struct_start.0) as usize..].find_uncommented(",") {
 634             Some(i) => i,
 635             None => 0,
 636         };
 637         self.last_pos = hi + BytePos(comma_pos as u32 + 1);
 638     }
 639
 640     fn rewrite_generics(&self, generics: &ast::Generics, indent: usize, span_end: BytePos) -> String {
 641         // FIXME convert bounds to where clauses where they get too big or if
 642         // there is a where clause at all.
 643         let mut result = String::new();
 644         let lifetimes: &[_] = &generics.lifetimes;
 645         let tys: &[_] = &generics.ty_params;
 646         if lifetimes.len() + tys.len() == 0 {
 647             return result;
 648         }
 649
 650         let budget = self.config.max_width - indent - 2;
 651         // TODO might need to insert a newline if the generics are really long
 652         result.push('<');
 653
 654         // Strings for the generics.
 655         let lt_strs = lifetimes.iter().map(|l| self.rewrite_lifetime_def(l));
 656         let ty_strs = tys.iter().map(|ty| self.rewrite_ty_param(ty));
 657
 658         // Extract comments between generics.
 659         let lt_spans = lifetimes.iter().map(|l| {
 660             let hi = if l.bounds.len() == 0 {
 661                 l.lifetime.span.hi
 662             } else {
 663                 l.bounds[l.bounds.len() - 1].span.hi
 664             };
 665             codemap::mk_sp(l.lifetime.span.lo, hi)
 666         });
 667         let ty_spans = tys.iter().map(span_for_ty_param);
 668         let comments = self.make_comments_for_list(Vec::new(),
 669                                                    lt_spans.chain(ty_spans),
 670                                                    ",",
 671                                                    ">",
 672                                                    |sp| sp.lo,
 673                                                    |sp| sp.hi,
 674                                                    span_end);
 675
 676         // If there are // comments, keep them multi-line.
 677         let mut list_tactic = ListTactic::HorizontalVertical;
 678         if comments.iter().any(|c| c.contains("//")) {
 679             list_tactic = ListTactic::Vertical;
 680         }
 681
 682         let generics_strs: Vec<_> = lt_strs.chain(ty_strs).zip(comments.into_iter()).collect();
 683         let fmt = ListFormatting {
 684             tactic: list_tactic,
 685             separator: ",",
 686             trailing_separator: SeparatorTactic::Never,
 687             indent: indent + 1,
 688             h_width: budget,
 689             v_width: budget,
 690         };
 691         result.push_str(&write_list(&generics_strs, &fmt));
 692
 693         result.push('>');
 694
 695         result
 696     }
 697
 698     fn rewrite_where_clause(&self,
 699                             where_clause: &ast::WhereClause,
 700                             indent: usize,
 701                             span_end: BytePos)
 702         -> String
 703     {
 704         let mut result = String::new();
 705         if where_clause.predicates.len() == 0 {
 706             return result;
 707         }
 708
 709         result.push('\n');
 710         result.push_str(&make_indent(indent + 4));
 711         result.push_str("where ");
 712
 713         let comments = self.make_comments_for_list(Vec::new(),
 714                                                    where_clause.predicates.iter(),
 715                                                    ",",
 716                                                    "{",
 717                                                    |pred| span_for_where_pred(pred).lo,
 718                                                    |pred| span_for_where_pred(pred).hi,
 719                                                    span_end);
 720
 721         let where_strs: Vec<_> = where_clause.predicates.iter()
 722                                                         .map(|p| (self.rewrite_pred(p)))
 723                                                         .zip(comments.into_iter())
 724                                                         .collect();
 725
 726         let budget = self.config.ideal_width + self.config.leeway - indent - 10;
 727         let fmt = ListFormatting {
 728             tactic: ListTactic::Vertical,
 729             separator: ",",
 730             trailing_separator: SeparatorTactic::Never,
 731             indent: indent + 10,
 732             h_width: budget,
 733             v_width: budget,
 734         };
 735         result.push_str(&write_list(&where_strs, &fmt));
 736
 737         result
 738     }
 739
 740     fn rewrite_return(&self, ret: &ast::FunctionRetTy) -> String {
 741         match *ret {
 742             ast::FunctionRetTy::DefaultReturn(_) => String::new(),
 743             ast::FunctionRetTy::NoReturn(_) => "-> !".to_owned(),
 744             ast::FunctionRetTy::Return(ref ty) => "-> ".to_owned() + &pprust::ty_to_string(ty),
 745         }
 746     }
 747
 748     // TODO we farm this out, but this could spill over the column limit, so we ought to handle it properly
 749     fn rewrite_fn_input(&self, arg: &ast::Arg) -> String {
 750         format!("{}: {}",
 751                 pprust::pat_to_string(&arg.pat),
 752                 pprust::ty_to_string(&arg.ty))
 753     }
 754 }
 755
 756 fn span_for_return(ret: &ast::FunctionRetTy) -> Span {
 757     match *ret {
 758         ast::FunctionRetTy::NoReturn(ref span) |
 759         ast::FunctionRetTy::DefaultReturn(ref span) => span.clone(),
 760         ast::FunctionRetTy::Return(ref ty) => ty.span,
 761     }
 762 }
 763
 764 fn span_for_ty_param(ty: &ast::TyParam) -> Span {
 765     // Note that ty.span is the span for ty.ident, not the whole item.
 766     let lo = ty.span.lo;
 767     if let Some(ref def) = ty.default {
 768         return codemap::mk_sp(lo, def.span.hi);
 769     }
 770     if ty.bounds.len() == 0 {
 771         return ty.span;
 772     }
 773     let hi = match ty.bounds[ty.bounds.len() - 1] {
 774         ast::TyParamBound::TraitTyParamBound(ref ptr, _) => ptr.span.hi,
 775         ast::TyParamBound::RegionTyParamBound(ref l) => l.span.hi,
 776     };
 777     codemap::mk_sp(lo, hi)
 778 }
 779
 780 fn span_for_where_pred(pred: &ast::WherePredicate) -> Span {
 781     match *pred {
 782         ast::WherePredicate::BoundPredicate(ref p) => p.span,
 783         ast::WherePredicate::RegionPredicate(ref p) => p.span,
 784         ast::WherePredicate::EqPredicate(ref p) => p.span,
 785     }
 786 }