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, Shape};
  14 use codemap::SpanUtils;
  15 use utils::{format_mutability, format_visibility, contains_skip, end_typaram, wrap_str,
  16             last_line_width, format_unsafety, trim_newlines, stmt_expr, semicolon_for_expr,
  17             trimmed_last_line_width};
  18 use lists::{write_list, itemize_list, ListItem, ListFormatting, SeparatorTactic, list_helper,
  19             DefinitiveListTactic, ListTactic, definitive_tactic, format_item_list};
  20 use expr::{is_empty_block, is_simple_block_stmt, rewrite_assign_rhs, type_annotation_separator};
  21 use comment::{FindUncommented, contains_comment};
  22 use visitor::FmtVisitor;
  23 use rewrite::{Rewrite, RewriteContext};
  24 use config::{Config, BlockIndentStyle, Density, ReturnIndent, BraceStyle, FnArgLayoutStyle, Style};
  25 use itertools::Itertools;
  26
  27 use syntax::{ast, abi, codemap, ptr, symbol};
  28 use syntax::codemap::{Span, BytePos, mk_sp};
  29 use syntax::ast::ImplItem;
  30
  31 // Statements of the form
  32 // let pat: ty = init;
  33 impl Rewrite for ast::Local {
  34     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
  35         debug!("Local::rewrite {:?} {} {:?}",
  36                self,
  37                shape.width,
  38                shape.indent);
  39         let mut result = "let ".to_owned();
  40         let pattern_offset = shape.indent + result.len();
  41         // 1 = ;
  42         let pattern_width = try_opt!(shape.width.checked_sub(pattern_offset.width() + 1));
  43
  44         let pat_str = try_opt!(self.pat.rewrite(&context,
  45                                                 Shape::legacy(pattern_width, pattern_offset)));
  46         result.push_str(&pat_str);
  47
  48         // String that is placed within the assignment pattern and expression.
  49         let infix = {
  50             let mut infix = String::new();
  51
  52             if let Some(ref ty) = self.ty {
  53                 let separator = type_annotation_separator(context.config);
  54                 let indent = shape.indent + last_line_width(&result) + separator.len();
  55                 // 1 = ;
  56                 let budget = try_opt!(shape.width.checked_sub(indent.width() + 1));
  57                 let rewrite = try_opt!(ty.rewrite(context, Shape::legacy(budget, indent)));
  58
  59                 infix.push_str(separator);
  60                 infix.push_str(&rewrite);
  61             }
  62
  63             if self.init.is_some() {
  64                 infix.push_str(" =");
  65             }
  66
  67             infix
  68         };
  69
  70         result.push_str(&infix);
  71
  72         if let Some(ref ex) = self.init {
  73             // 1 = trailing semicolon;
  74             let budget = try_opt!(shape.width.checked_sub(shape.indent.block_only().width() + 1));
  75
  76             result = try_opt!(rewrite_assign_rhs(&context,
  77                                                  result,
  78                                                  ex,
  79                                                  Shape::legacy(budget, shape.indent.block_only())));
  80         }
  81
  82         result.push(';');
  83         Some(result)
  84     }
  85 }
  86
  87 // TODO convert to using rewrite style rather than visitor
  88 // TODO format modules in this style
  89 #[allow(dead_code)]
  90 struct Item<'a> {
  91     keyword: &'static str,
  92     abi: String,
  93     vis: Option<&'a ast::Visibility>,
  94     body: Vec<BodyElement<'a>>,
  95     span: Span,
  96 }
  97
  98 impl<'a> Item<'a> {
  99     fn from_foreign_mod(fm: &'a ast::ForeignMod, span: Span, config: &Config) -> Item<'a> {
 100         let abi = if fm.abi == abi::Abi::C && !config.force_explicit_abi {
 101             "extern".into()
 102         } else {
 103             format!("extern {}", fm.abi)
 104         };
 105         Item {
 106             keyword: "",
 107             abi: abi,
 108             vis: None,
 109             body: fm.items
 110                 .iter()
 111                 .map(|i| BodyElement::ForeignItem(i))
 112                 .collect(),
 113             span: span,
 114         }
 115     }
 116 }
 117
 118 enum BodyElement<'a> {
 119     // Stmt(&'a ast::Stmt),
 120     // Field(&'a ast::Field),
 121     // Variant(&'a ast::Variant),
 122     // Item(&'a ast::Item),
 123     ForeignItem(&'a ast::ForeignItem),
 124 }
 125
 126 impl<'a> FmtVisitor<'a> {
 127     fn format_item(&mut self, item: Item) {
 128         self.buffer.push_str(&item.abi);
 129         self.buffer.push_str(" ");
 130
 131         let snippet = self.snippet(item.span);
 132         let brace_pos = snippet.find_uncommented("{").unwrap();
 133
 134         self.buffer.push_str("{");
 135         if !item.body.is_empty() || contains_comment(&snippet[brace_pos..]) {
 136             // FIXME: this skips comments between the extern keyword and the opening
 137             // brace.
 138             self.last_pos = item.span.lo + BytePos(brace_pos as u32 + 1);
 139             self.block_indent = self.block_indent.block_indent(self.config);
 140
 141             if item.body.is_empty() {
 142                 self.format_missing_no_indent(item.span.hi - BytePos(1));
 143                 self.block_indent = self.block_indent.block_unindent(self.config);
 144
 145                 self.buffer.push_str(&self.block_indent.to_string(self.config));
 146             } else {
 147                 for item in &item.body {
 148                     self.format_body_element(item);
 149                 }
 150
 151                 self.block_indent = self.block_indent.block_unindent(self.config);
 152                 self.format_missing_with_indent(item.span.hi - BytePos(1));
 153             }
 154         }
 155
 156         self.buffer.push_str("}");
 157         self.last_pos = item.span.hi;
 158     }
 159
 160     fn format_body_element(&mut self, element: &BodyElement) {
 161         match *element {
 162             BodyElement::ForeignItem(ref item) => self.format_foreign_item(item),
 163         }
 164     }
 165
 166     pub fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
 167         let item = Item::from_foreign_mod(fm, span, self.config);
 168         self.format_item(item);
 169     }
 170
 171     fn format_foreign_item(&mut self, item: &ast::ForeignItem) {
 172         self.format_missing_with_indent(item.span.lo);
 173         // Drop semicolon or it will be interpreted as comment.
 174         // FIXME: this may be a faulty span from libsyntax.
 175         let span = mk_sp(item.span.lo, item.span.hi - BytePos(1));
 176
 177         match item.node {
 178             ast::ForeignItemKind::Fn(ref fn_decl, ref generics) => {
 179                 let indent = self.block_indent;
 180                 let rewrite = rewrite_fn_base(&self.get_context(),
 181                                               indent,
 182                                               item.ident,
 183                                               fn_decl,
 184                                               generics,
 185                                               ast::Unsafety::Normal,
 186                                               ast::Constness::NotConst,
 187                                               ast::Defaultness::Final,
 188                                               // These are not actually rust functions,
 189                                               // but we format them as such.
 190                                               abi::Abi::Rust,
 191                                               &item.vis,
 192                                               span,
 193                                               false,
 194                                               false);
 195
 196                 match rewrite {
 197                     Some((new_fn, _)) => {
 198                         self.buffer.push_str(&new_fn);
 199                         self.buffer.push_str(";");
 200                     }
 201                     None => self.format_missing(item.span.hi),
 202                 }
 203             }
 204             ast::ForeignItemKind::Static(ref ty, is_mutable) => {
 205                 // FIXME(#21): we're dropping potential comments in between the
 206                 // function keywords here.
 207                 let vis = format_visibility(&item.vis);
 208                 let mut_str = if is_mutable { "mut " } else { "" };
 209                 let prefix = format!("{}static {}{}: ", vis, mut_str, item.ident);
 210                 let offset = self.block_indent + prefix.len();
 211                 // 1 = ;
 212                 let width = self.config.max_width - offset.width() - 1;
 213                 let rewrite = ty.rewrite(&self.get_context(), Shape::legacy(width, offset));
 214
 215                 match rewrite {
 216                     Some(result) => {
 217                         self.buffer.push_str(&prefix);
 218                         self.buffer.push_str(&result);
 219                         self.buffer.push_str(";");
 220                     }
 221                     None => self.format_missing(item.span.hi),
 222                 }
 223             }
 224         }
 225
 226         self.last_pos = item.span.hi;
 227     }
 228
 229     pub fn rewrite_fn(&mut self,
 230                       indent: Indent,
 231                       ident: ast::Ident,
 232                       fd: &ast::FnDecl,
 233                       generics: &ast::Generics,
 234                       unsafety: ast::Unsafety,
 235                       constness: ast::Constness,
 236                       defaultness: ast::Defaultness,
 237                       abi: abi::Abi,
 238                       vis: &ast::Visibility,
 239                       span: Span,
 240                       block: &ast::Block)
 241                       -> Option<String> {
 242         let mut newline_brace = newline_for_brace(self.config, &generics.where_clause);
 243         let context = self.get_context();
 244
 245         let block_snippet = self.snippet(codemap::mk_sp(block.span.lo, block.span.hi));
 246         let has_body = !block_snippet[1..block_snippet.len() - 1].trim().is_empty() ||
 247                        !context.config.fn_empty_single_line;
 248
 249         let (mut result, force_newline_brace) = try_opt!(rewrite_fn_base(&context,
 250                                                                          indent,
 251                                                                          ident,
 252                                                                          fd,
 253                                                                          generics,
 254                                                                          unsafety,
 255                                                                          constness,
 256                                                                          defaultness,
 257                                                                          abi,
 258                                                                          vis,
 259                                                                          span,
 260                                                                          newline_brace,
 261                                                                          has_body));
 262
 263         if self.config.fn_brace_style != BraceStyle::AlwaysNextLine && !result.contains('\n') {
 264             newline_brace = false;
 265         } else if force_newline_brace {
 266             newline_brace = true;
 267         }
 268
 269         // Prepare for the function body by possibly adding a newline and
 270         // indent.
 271         // FIXME we'll miss anything between the end of the signature and the
 272         // start of the body, but we need more spans from the compiler to solve
 273         // this.
 274         if newline_brace {
 275             result.push('\n');
 276             result.push_str(&indent.to_string(self.config));
 277         } else {
 278             result.push(' ');
 279         }
 280
 281         self.single_line_fn(&result, block).or_else(|| Some(result))
 282     }
 283
 284     pub fn rewrite_required_fn(&mut self,
 285                                indent: Indent,
 286                                ident: ast::Ident,
 287                                sig: &ast::MethodSig,
 288                                span: Span)
 289                                -> Option<String> {
 290         // Drop semicolon or it will be interpreted as comment.
 291         let span = mk_sp(span.lo, span.hi - BytePos(1));
 292         let context = self.get_context();
 293
 294         let (mut result, _) = try_opt!(rewrite_fn_base(&context,
 295                                                        indent,
 296                                                        ident,
 297                                                        &sig.decl,
 298                                                        &sig.generics,
 299                                                        sig.unsafety,
 300                                                        sig.constness.node,
 301                                                        ast::Defaultness::Final,
 302                                                        sig.abi,
 303                                                        &ast::Visibility::Inherited,
 304                                                        span,
 305                                                        false,
 306                                                        false));
 307
 308         // Re-attach semicolon
 309         result.push(';');
 310
 311         Some(result)
 312     }
 313
 314     fn single_line_fn(&self, fn_str: &str, block: &ast::Block) -> Option<String> {
 315         if fn_str.contains('\n') {
 316             return None;
 317         }
 318
 319         let codemap = self.get_context().codemap;
 320
 321         if self.config.fn_empty_single_line && is_empty_block(block, codemap) &&
 322            self.block_indent.width() + fn_str.len() + 2 <= self.config.max_width {
 323             return Some(format!("{}{{}}", fn_str));
 324         }
 325
 326         if self.config.fn_single_line && is_simple_block_stmt(block, codemap) {
 327             let rewrite = {
 328                 if let Some(ref stmt) = block.stmts.first() {
 329                     match stmt_expr(stmt) {
 330                         Some(e) => {
 331                             let suffix = if semicolon_for_expr(e) { ";" } else { "" };
 332
 333                             e.rewrite(&self.get_context(),
 334                                          Shape::legacy(self.config.max_width -
 335                                                        self.block_indent.width(),
 336                                                        self.block_indent))
 337                                 .map(|s| s + suffix)
 338                                 .or_else(|| Some(self.snippet(e.span)))
 339                         }
 340                         None => {
 341                             stmt.rewrite(&self.get_context(),
 342                                          Shape::legacy(self.config.max_width -
 343                                                        self.block_indent.width(),
 344                                                        self.block_indent))
 345                         }
 346                     }
 347                 } else {
 348                     None
 349                 }
 350             };
 351
 352             if let Some(res) = rewrite {
 353                 let width = self.block_indent.width() + fn_str.len() + res.len() + 4;
 354                 if !res.contains('\n') && width <= self.config.max_width {
 355                     return Some(format!("{}{{ {} }}", fn_str, res));
 356                 }
 357             }
 358         }
 359
 360         None
 361     }
 362
 363     pub fn visit_enum(&mut self,
 364                       ident: ast::Ident,
 365                       vis: &ast::Visibility,
 366                       enum_def: &ast::EnumDef,
 367                       generics: &ast::Generics,
 368                       span: Span) {
 369         self.buffer.push_str(&format_header("enum ", ident, vis));
 370
 371         let enum_snippet = self.snippet(span);
 372         let brace_pos = enum_snippet.find_uncommented("{").unwrap();
 373         let body_start = span.lo + BytePos(brace_pos as u32 + 1);
 374         let generics_str = format_generics(&self.get_context(),
 375                                            generics,
 376                                            "{",
 377                                            "{",
 378                                            self.config.item_brace_style,
 379                                            enum_def.variants.is_empty(),
 380                                            self.block_indent,
 381                                            self.block_indent.block_indent(self.config),
 382                                            mk_sp(span.lo, body_start))
 383                 .unwrap();
 384         self.buffer.push_str(&generics_str);
 385
 386         self.last_pos = body_start;
 387
 388         self.block_indent = self.block_indent.block_indent(self.config);
 389         let variant_list = self.format_variant_list(enum_def, body_start, span.hi - BytePos(1));
 390         match variant_list {
 391             Some(ref body_str) => self.buffer.push_str(body_str),
 392             None => {
 393                 if contains_comment(&enum_snippet[brace_pos..]) {
 394                     self.format_missing_no_indent(span.hi - BytePos(1))
 395                 } else {
 396                     self.format_missing(span.hi - BytePos(1))
 397                 }
 398             }
 399         }
 400         self.block_indent = self.block_indent.block_unindent(self.config);
 401
 402         if variant_list.is_some() || contains_comment(&enum_snippet[brace_pos..]) {
 403             self.buffer.push_str(&self.block_indent.to_string(self.config));
 404         }
 405         self.buffer.push_str("}");
 406         self.last_pos = span.hi;
 407     }
 408
 409     // Format the body of an enum definition
 410     fn format_variant_list(&self,
 411                            enum_def: &ast::EnumDef,
 412                            body_lo: BytePos,
 413                            body_hi: BytePos)
 414                            -> Option<String> {
 415         if enum_def.variants.is_empty() {
 416             return None;
 417         }
 418         let mut result = String::with_capacity(1024);
 419         result.push('\n');
 420         let indentation = self.block_indent.to_string(self.config);
 421         result.push_str(&indentation);
 422
 423         let items = itemize_list(self.codemap,
 424                                  enum_def.variants.iter(),
 425                                  "}",
 426                                  |f| if !f.node.attrs.is_empty() {
 427                                      f.node.attrs[0].span.lo
 428                                  } else {
 429                                      f.span.lo
 430                                  },
 431                                  |f| f.span.hi,
 432                                  |f| self.format_variant(f),
 433                                  body_lo,
 434                                  body_hi);
 435
 436         let budget = self.config.max_width - self.block_indent.width() - 2;
 437         let fmt = ListFormatting {
 438             tactic: DefinitiveListTactic::Vertical,
 439             separator: ",",
 440             trailing_separator: self.config.trailing_comma,
 441             shape: Shape::legacy(budget, self.block_indent),
 442             ends_with_newline: true,
 443             config: self.config,
 444         };
 445
 446         let list = try_opt!(write_list(items, &fmt));
 447         result.push_str(&list);
 448         result.push('\n');
 449         Some(result)
 450     }
 451
 452     // Variant of an enum.
 453     fn format_variant(&self, field: &ast::Variant) -> Option<String> {
 454         if contains_skip(&field.node.attrs) {
 455             let lo = field.node.attrs[0].span.lo;
 456             let span = mk_sp(lo, field.span.hi);
 457             return Some(self.snippet(span));
 458         }
 459
 460         let indent = self.block_indent;
 461         let mut result = try_opt!(field.node.attrs.rewrite(&self.get_context(),
 462                                                            Shape::legacy(self.config.max_width -
 463                                                                          indent.width(),
 464                                                                          indent)));
 465         if !result.is_empty() {
 466             result.push('\n');
 467             result.push_str(&indent.to_string(self.config));
 468         }
 469
 470         let context = self.get_context();
 471         let variant_body = match field.node.data {
 472             ast::VariantData::Tuple(..) |
 473             ast::VariantData::Struct(..) => {
 474                 // FIXME: Should limit the width, as we have a trailing comma
 475                 format_struct(&context,
 476                               "",
 477                               field.node.name,
 478                               &ast::Visibility::Inherited,
 479                               &field.node.data,
 480                               None,
 481                               field.span,
 482                               indent,
 483                               Some(self.config.struct_variant_width))
 484             }
 485             ast::VariantData::Unit(..) => {
 486                 let tag = if let Some(ref expr) = field.node.disr_expr {
 487                     format!("{} = {}", field.node.name, self.snippet(expr.span))
 488                 } else {
 489                     field.node.name.to_string()
 490                 };
 491
 492                 wrap_str(tag,
 493                          self.config.max_width,
 494                          Shape::legacy(self.config.max_width - indent.width(), indent))
 495             }
 496         };
 497
 498         if let Some(variant_str) = variant_body {
 499             result.push_str(&variant_str);
 500             Some(result)
 501         } else {
 502             None
 503         }
 504     }
 505 }
 506
 507 pub fn format_impl(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 508     if let ast::ItemKind::Impl(_, _, ref generics, ref trait_ref, _, ref items) = item.node {
 509         let mut result = String::new();
 510         // First try to format the ref and type without a split at the 'for'.
 511         let mut ref_and_type = try_opt!(format_impl_ref_and_type(context, item, offset, false));
 512
 513         // If there is a line break present in the first result format it again
 514         // with a split at the 'for'. Skip this if there is no trait ref and
 515         // therefore no 'for'.
 516         if ref_and_type.contains('\n') && trait_ref.is_some() {
 517             ref_and_type = try_opt!(format_impl_ref_and_type(context, item, offset, true));
 518         }
 519         result.push_str(&ref_and_type);
 520
 521         let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
 522         let where_clause_str = try_opt!(rewrite_where_clause(context,
 523                                                              &generics.where_clause,
 524                                                              context.config.item_brace_style,
 525                                                              Shape::legacy(where_budget,
 526                                                                            offset.block_only()),
 527                                                              context.config.where_density,
 528                                                              "{",
 529                                                              false,
 530                                                              last_line_width(&ref_and_type) == 1,
 531                                                              None));
 532
 533         if try_opt!(is_impl_single_line(context, &items, &result, &where_clause_str, &item)) {
 534             result.push_str(&where_clause_str);
 535             if where_clause_str.contains('\n') {
 536                 let white_space = offset.to_string(context.config);
 537                 result.push_str(&format!("\n{}{{\n{}}}", &white_space, &white_space));
 538             } else {
 539                 result.push_str(" {}");
 540             }
 541             return Some(result);
 542         }
 543
 544         if !where_clause_str.is_empty() && !where_clause_str.contains('\n') {
 545             result.push('\n');
 546             let width = offset.block_indent + context.config.tab_spaces - 1;
 547             let where_indent = Indent::new(0, width);
 548             result.push_str(&where_indent.to_string(context.config));
 549         }
 550         result.push_str(&where_clause_str);
 551
 552         match context.config.item_brace_style {
 553             BraceStyle::AlwaysNextLine => {
 554                 result.push('\n');
 555                 result.push_str(&offset.to_string(context.config));
 556             }
 557             BraceStyle::PreferSameLine => result.push(' '),
 558             BraceStyle::SameLineWhere => {
 559                 if !where_clause_str.is_empty() {
 560                     result.push('\n');
 561                     result.push_str(&offset.to_string(context.config));
 562                 } else {
 563                     result.push(' ');
 564                 }
 565             }
 566         }
 567
 568         result.push('{');
 569
 570         let snippet = context.snippet(item.span);
 571         let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 572
 573         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 574             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 575             visitor.block_indent = offset.block_only().block_indent(context.config);
 576             visitor.last_pos = item.span.lo + BytePos(open_pos as u32);
 577
 578             for item in items {
 579                 visitor.visit_impl_item(item);
 580             }
 581
 582             visitor.format_missing(item.span.hi - BytePos(1));
 583
 584             let inner_indent_str = visitor.block_indent.to_string(context.config);
 585             let outer_indent_str = offset.block_only().to_string(context.config);
 586
 587             result.push('\n');
 588             result.push_str(&inner_indent_str);
 589             result.push_str(trim_newlines(visitor.buffer.to_string().trim()));
 590             result.push('\n');
 591             result.push_str(&outer_indent_str);
 592         }
 593
 594         if result.chars().last().unwrap() == '{' {
 595             result.push('\n');
 596             result.push_str(&offset.to_string(context.config));
 597         }
 598         result.push('}');
 599
 600         Some(result)
 601     } else {
 602         unreachable!();
 603     }
 604 }
 605
 606 fn is_impl_single_line(context: &RewriteContext,
 607                        items: &[ImplItem],
 608                        result: &str,
 609                        where_clause_str: &str,
 610                        item: &ast::Item)
 611                        -> Option<bool> {
 612     let snippet = context.snippet(item.span);
 613     let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 614
 615     Some(context.config.impl_empty_single_line && items.is_empty() &&
 616          result.len() + where_clause_str.len() <= context.config.max_width &&
 617          !contains_comment(&snippet[open_pos..]))
 618 }
 619
 620 fn format_impl_ref_and_type(context: &RewriteContext,
 621                             item: &ast::Item,
 622                             offset: Indent,
 623                             split_at_for: bool)
 624                             -> Option<String> {
 625     if let ast::ItemKind::Impl(unsafety, polarity, ref generics, ref trait_ref, ref self_ty, _) =
 626         item.node {
 627         let mut result = String::new();
 628
 629         result.push_str(&format_visibility(&item.vis));
 630         result.push_str(format_unsafety(unsafety));
 631         result.push_str("impl");
 632
 633         let lo = context.codemap.span_after(item.span, "impl");
 634         let hi = match *trait_ref {
 635             Some(ref tr) => tr.path.span.lo,
 636             None => self_ty.span.lo,
 637         };
 638         let generics_str = try_opt!(rewrite_generics(context,
 639                                                      generics,
 640                                                      Shape::legacy(context.config.max_width,
 641                                                                    offset),
 642                                                      offset + result.len(),
 643                                                      mk_sp(lo, hi)));
 644         result.push_str(&generics_str);
 645
 646         if polarity == ast::ImplPolarity::Negative {
 647             result.push_str(" !");
 648         }
 649         if let Some(ref trait_ref) = *trait_ref {
 650             if polarity != ast::ImplPolarity::Negative {
 651                 result.push_str(" ");
 652             }
 653             let used_space = last_line_width(&result);
 654             let budget = try_opt!(context.config.max_width.checked_sub(used_space));
 655             let indent = offset + used_space;
 656             result.push_str(&*try_opt!(trait_ref.rewrite(context, Shape::legacy(budget, indent))));
 657
 658             if split_at_for {
 659                 result.push('\n');
 660
 661                 // Add indentation of one additional tab.
 662                 let width = offset.block_indent + context.config.tab_spaces;
 663                 let for_indent = Indent::new(0, width);
 664                 result.push_str(&for_indent.to_string(context.config));
 665
 666                 result.push_str("for");
 667             } else {
 668                 result.push_str(" for");
 669             }
 670         }
 671
 672         let mut used_space = last_line_width(&result);
 673         if generics.where_clause.predicates.is_empty() {
 674             // If there is no where clause adapt budget for type formatting to take space and curly
 675             // brace into account.
 676             match context.config.item_brace_style {
 677                 BraceStyle::AlwaysNextLine => {}
 678                 BraceStyle::PreferSameLine => used_space += 2,
 679                 BraceStyle::SameLineWhere => used_space += 2,
 680             }
 681         }
 682
 683         // 1 = space before the type.
 684         let budget = try_opt!(context.config.max_width.checked_sub(used_space + 1));
 685         let indent = offset + result.len() + 1;
 686         let self_ty_str = self_ty.rewrite(context, Shape::legacy(budget, indent));
 687         if let Some(self_ty_str) = self_ty_str {
 688             result.push_str(" ");
 689             result.push_str(&self_ty_str);
 690             return Some(result);
 691         }
 692
 693         // Can't fit the self type on what's left of the line, so start a new one.
 694         let indent = offset.block_indent(context.config);
 695         result.push_str(&format!("\n{}", indent.to_string(context.config)));
 696         let budget = try_opt!(context.config.max_width.checked_sub(indent.width()));
 697         result.push_str(&*try_opt!(self_ty.rewrite(context, Shape::legacy(budget, indent))));
 698         Some(result)
 699     } else {
 700         unreachable!();
 701     }
 702 }
 703
 704 pub fn format_struct(context: &RewriteContext,
 705                      item_name: &str,
 706                      ident: ast::Ident,
 707                      vis: &ast::Visibility,
 708                      struct_def: &ast::VariantData,
 709                      generics: Option<&ast::Generics>,
 710                      span: Span,
 711                      offset: Indent,
 712                      one_line_width: Option<usize>)
 713                      -> Option<String> {
 714     match *struct_def {
 715         ast::VariantData::Unit(..) => Some(format_unit_struct(item_name, ident, vis)),
 716         ast::VariantData::Tuple(ref fields, _) => {
 717             format_tuple_struct(context,
 718                                 item_name,
 719                                 ident,
 720                                 vis,
 721                                 fields,
 722                                 generics,
 723                                 span,
 724                                 offset)
 725         }
 726         ast::VariantData::Struct(ref fields, _) => {
 727             format_struct_struct(context,
 728                                  item_name,
 729                                  ident,
 730                                  vis,
 731                                  fields,
 732                                  generics,
 733                                  span,
 734                                  offset,
 735                                  one_line_width)
 736         }
 737     }
 738 }
 739
 740 pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 741     if let ast::ItemKind::Trait(unsafety, ref generics, ref type_param_bounds, ref trait_items) =
 742         item.node {
 743         let mut result = String::new();
 744         let header = format!("{}{}trait {}",
 745                              format_visibility(&item.vis),
 746                              format_unsafety(unsafety),
 747                              item.ident);
 748
 749         result.push_str(&header);
 750
 751         let body_lo = context.codemap.span_after(item.span, "{");
 752
 753         let generics_str = try_opt!(rewrite_generics(context,
 754                                                      generics,
 755                                                      Shape::legacy(context.config.max_width,
 756                                                                    offset),
 757                                                      offset + result.len(),
 758                                                      mk_sp(item.span.lo, body_lo)));
 759         result.push_str(&generics_str);
 760
 761         let trait_bound_str =
 762             try_opt!(rewrite_trait_bounds(context,
 763                                           type_param_bounds,
 764                                           Shape::legacy(context.config.max_width, offset)));
 765         // If the trait, generics, and trait bound cannot fit on the same line,
 766         // put the trait bounds on an indented new line
 767         if offset.width() + last_line_width(&result) + trait_bound_str.len() >
 768            context.config.ideal_width {
 769             result.push('\n');
 770             let trait_indent = offset.block_only().block_indent(context.config);
 771             result.push_str(&trait_indent.to_string(context.config));
 772         }
 773         result.push_str(&trait_bound_str);
 774
 775         let has_body = !trait_items.is_empty();
 776
 777         let where_density =
 778             if (context.config.where_density == Density::Compressed &&
 779                 (!result.contains('\n') ||
 780                  context.config.fn_args_layout == FnArgLayoutStyle::Block)) ||
 781                (context.config.fn_args_layout == FnArgLayoutStyle::Block && result.is_empty()) ||
 782                (context.config.where_density == Density::CompressedIfEmpty && !has_body &&
 783                 !result.contains('\n')) {
 784                 Density::Compressed
 785             } else {
 786                 Density::Tall
 787             };
 788
 789         let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
 790         let where_clause_str = try_opt!(rewrite_where_clause(context,
 791                                                              &generics.where_clause,
 792                                                              context.config.item_brace_style,
 793                                                              Shape::legacy(where_budget,
 794                                                                            offset.block_only()),
 795                                                              where_density,
 796                                                              "{",
 797                                                              !has_body,
 798                                                              false,
 799                                                              None));
 800         // If the where clause cannot fit on the same line,
 801         // put the where clause on a new line
 802         if !where_clause_str.contains('\n') &&
 803            last_line_width(&result) + where_clause_str.len() + offset.width() >
 804            context.config.ideal_width {
 805             result.push('\n');
 806             let width = offset.block_indent + context.config.tab_spaces - 1;
 807             let where_indent = Indent::new(0, width);
 808             result.push_str(&where_indent.to_string(context.config));
 809         }
 810         result.push_str(&where_clause_str);
 811
 812         match context.config.item_brace_style {
 813             BraceStyle::AlwaysNextLine => {
 814                 result.push('\n');
 815                 result.push_str(&offset.to_string(context.config));
 816             }
 817             BraceStyle::PreferSameLine => result.push(' '),
 818             BraceStyle::SameLineWhere => {
 819                 if !where_clause_str.is_empty() &&
 820                    (!trait_items.is_empty() || result.contains('\n')) {
 821                     result.push('\n');
 822                     result.push_str(&offset.to_string(context.config));
 823                 } else {
 824                     result.push(' ');
 825                 }
 826             }
 827         }
 828         result.push('{');
 829
 830         let snippet = context.snippet(item.span);
 831         let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 832
 833         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
 834             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 835             visitor.block_indent = offset.block_only().block_indent(context.config);
 836             visitor.last_pos = item.span.lo + BytePos(open_pos as u32);
 837
 838             for item in trait_items {
 839                 visitor.visit_trait_item(item);
 840             }
 841
 842             visitor.format_missing(item.span.hi - BytePos(1));
 843
 844             let inner_indent_str = visitor.block_indent.to_string(context.config);
 845             let outer_indent_str = offset.block_only().to_string(context.config);
 846
 847             result.push('\n');
 848             result.push_str(&inner_indent_str);
 849             result.push_str(trim_newlines(visitor.buffer.to_string().trim()));
 850             result.push('\n');
 851             result.push_str(&outer_indent_str);
 852         } else if result.contains('\n') {
 853             result.push('\n');
 854         }
 855
 856         result.push('}');
 857         Some(result)
 858     } else {
 859         unreachable!();
 860     }
 861 }
 862
 863 fn format_unit_struct(item_name: &str, ident: ast::Ident, vis: &ast::Visibility) -> String {
 864     format!("{};", format_header(item_name, ident, vis))
 865 }
 866
 867 fn format_struct_struct(context: &RewriteContext,
 868                         item_name: &str,
 869                         ident: ast::Ident,
 870                         vis: &ast::Visibility,
 871                         fields: &[ast::StructField],
 872                         generics: Option<&ast::Generics>,
 873                         span: Span,
 874                         offset: Indent,
 875                         one_line_width: Option<usize>)
 876                         -> Option<String> {
 877     let mut result = String::with_capacity(1024);
 878
 879     let header_str = format_header(item_name, ident, vis);
 880     result.push_str(&header_str);
 881
 882     let body_lo = context.codemap.span_after(span, "{");
 883
 884     let generics_str = match generics {
 885         Some(g) => {
 886             try_opt!(format_generics(context,
 887                                      g,
 888                                      "{",
 889                                      "{",
 890                                      context.config.item_brace_style,
 891                                      fields.is_empty(),
 892                                      offset,
 893                                      offset + header_str.len(),
 894                                      mk_sp(span.lo, body_lo)))
 895         }
 896         None => {
 897             if context.config.item_brace_style == BraceStyle::AlwaysNextLine && !fields.is_empty() {
 898                 format!("\n{}{{", offset.block_only().to_string(context.config))
 899             } else {
 900                 " {".to_owned()
 901             }
 902         }
 903     };
 904     result.push_str(&generics_str);
 905
 906     // FIXME(#919): properly format empty structs and their comments.
 907     if fields.is_empty() {
 908         let snippet = context.snippet(mk_sp(body_lo, span.hi - BytePos(1)));
 909         if snippet.trim().is_empty() {
 910             // `struct S {}`
 911         } else if snippet.trim_right_matches(&[' ', '\t'][..]).ends_with('\n') {
 912             // fix indent
 913             result.push_str(&snippet.trim_right());
 914             result.push('\n');
 915             result.push_str(&offset.to_string(context.config));
 916         } else {
 917             result.push_str(&snippet);
 918         }
 919         result.push('}');
 920         return Some(result);
 921     }
 922
 923     let item_indent = offset.block_indent(context.config);
 924     // 1 = ","
 925     let item_budget = try_opt!(context.config.max_width.checked_sub(item_indent.width() + 1));
 926
 927     let items =
 928         itemize_list(context.codemap,
 929                      fields.iter(),
 930                      "}",
 931                      |field| {
 932             // Include attributes and doc comments, if present
 933             if !field.attrs.is_empty() {
 934                 field.attrs[0].span.lo
 935             } else {
 936                 field.span.lo
 937             }
 938         },
 939                      |field| field.ty.span.hi,
 940                      |field| field.rewrite(context, Shape::legacy(item_budget, item_indent)),
 941                      context.codemap.span_after(span, "{"),
 942                      span.hi)
 943                 .collect::<Vec<_>>();
 944     // 1 = ,
 945     let budget = context.config.max_width - offset.width() + context.config.tab_spaces - 1;
 946
 947     let tactic = match one_line_width {
 948         Some(w) => definitive_tactic(&items, ListTactic::LimitedHorizontalVertical(w), budget),
 949         None => DefinitiveListTactic::Vertical,
 950     };
 951
 952     let fmt = ListFormatting {
 953         tactic: tactic,
 954         separator: ",",
 955         trailing_separator: context.config.trailing_comma,
 956         shape: Shape::legacy(budget, item_indent),
 957         ends_with_newline: true,
 958         config: context.config,
 959     };
 960     let items_str = try_opt!(write_list(&items, &fmt));
 961     if one_line_width.is_some() && !items_str.contains('\n') {
 962         Some(format!("{} {} }}", result, items_str))
 963     } else {
 964         Some(format!("{}\n{}{}\n{}}}",
 965                      result,
 966                      offset.block_indent(context.config).to_string(context.config),
 967                      items_str,
 968                      offset.to_string(context.config)))
 969     }
 970 }
 971
 972 fn format_tuple_struct(context: &RewriteContext,
 973                        item_name: &str,
 974                        ident: ast::Ident,
 975                        vis: &ast::Visibility,
 976                        fields: &[ast::StructField],
 977                        generics: Option<&ast::Generics>,
 978                        span: Span,
 979                        offset: Indent)
 980                        -> Option<String> {
 981     let mut result = String::with_capacity(1024);
 982
 983     let header_str = format_header(item_name, ident, vis);
 984     result.push_str(&header_str);
 985
 986     // FIXME(#919): don't lose comments on empty tuple structs.
 987     let body_lo = if fields.is_empty() {
 988         span.hi
 989     } else {
 990         fields[0].span.lo
 991     };
 992
 993     let where_clause_str = match generics {
 994         Some(generics) => {
 995             let generics_str = try_opt!(rewrite_generics(context,
 996                                                          generics,
 997                                                          Shape::legacy(context.config.max_width,
 998                                                                        offset),
 999                                                          offset + header_str.len(),
1000                                                          mk_sp(span.lo, body_lo)));
1001             result.push_str(&generics_str);
1002
1003             let where_budget =
1004                 try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
1005             try_opt!(rewrite_where_clause(context,
1006                                           &generics.where_clause,
1007                                           context.config.item_brace_style,
1008                                           Shape::legacy(where_budget, offset.block_only()),
1009                                           Density::Compressed,
1010                                           ";",
1011                                           true,
1012                                           false,
1013                                           None))
1014         }
1015         None => "".to_owned(),
1016     };
1017
1018     let (tactic, item_indent) = match context.config.fn_args_layout {
1019         FnArgLayoutStyle::Visual => {
1020             result.push('(');
1021             (ListTactic::HorizontalVertical, offset.block_only() + result.len())
1022         }
1023         FnArgLayoutStyle::Block | FnArgLayoutStyle::BlockAlways => {
1024             let indent = offset.block_only().block_indent(&context.config);
1025             result.push_str("(\n");
1026             result.push_str(&indent.to_string(&context.config));
1027             (ListTactic::Vertical, indent)
1028         }
1029     };
1030     // 2 = ");"
1031     let item_budget = try_opt!(context.config.max_width.checked_sub(item_indent.width() + 2));
1032
1033     let items =
1034         itemize_list(context.codemap,
1035                      fields.iter(),
1036                      ")",
1037                      |field| {
1038             // Include attributes and doc comments, if present
1039             if !field.attrs.is_empty() {
1040                 field.attrs[0].span.lo
1041             } else {
1042                 field.span.lo
1043             }
1044         },
1045                      |field| field.ty.span.hi,
1046                      |field| field.rewrite(context, Shape::legacy(item_budget, item_indent)),
1047                      context.codemap.span_after(span, "("),
1048                      span.hi);
1049     let body = try_opt!(list_helper(items,
1050                                     Shape::legacy(item_budget, item_indent),
1051                                     context.config,
1052                                     tactic));
1053
1054     if context.config.spaces_within_parens && body.len() > 0 {
1055         result.push(' ');
1056     }
1057
1058     result.push_str(&body);
1059
1060     if context.config.spaces_within_parens && body.len() > 0 {
1061         result.push(' ');
1062     }
1063
1064     match context.config.fn_args_layout {
1065         FnArgLayoutStyle::Visual => {
1066             result.push(')');
1067         }
1068         FnArgLayoutStyle::Block | FnArgLayoutStyle::BlockAlways => {
1069             result.push('\n');
1070             result.push_str(&offset.block_only().to_string(&context.config));
1071             result.push(')');
1072         }
1073     }
1074
1075     if !where_clause_str.is_empty() && !where_clause_str.contains('\n') &&
1076        (result.contains('\n') ||
1077         offset.block_indent + result.len() + where_clause_str.len() + 1 >
1078         context.config.max_width) {
1079         // We need to put the where clause on a new line, but we didn't
1080         // know that earlier, so the where clause will not be indented properly.
1081         result.push('\n');
1082         result.push_str(&(offset.block_only() + (context.config.tab_spaces - 1))
1083                              .to_string(context.config));
1084     }
1085     result.push_str(&where_clause_str);
1086
1087     Some(result)
1088 }
1089
1090 pub fn rewrite_type_alias(context: &RewriteContext,
1091                           indent: Indent,
1092                           ident: ast::Ident,
1093                           ty: &ast::Ty,
1094                           generics: &ast::Generics,
1095                           vis: &ast::Visibility,
1096                           span: Span)
1097                           -> Option<String> {
1098     let mut result = String::new();
1099
1100     result.push_str(&format_visibility(vis));
1101     result.push_str("type ");
1102     result.push_str(&ident.to_string());
1103
1104     let generics_indent = indent + result.len();
1105     let generics_span = mk_sp(context.codemap.span_after(span, "type"), ty.span.lo);
1106     let generics_width = context.config.max_width - " =".len();
1107     let generics_str = try_opt!(rewrite_generics(context,
1108                                                  generics,
1109                                                  Shape::legacy(generics_width, indent),
1110                                                  generics_indent,
1111                                                  generics_span));
1112
1113     result.push_str(&generics_str);
1114
1115     let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
1116     let where_clause_str = try_opt!(rewrite_where_clause(context,
1117                                                          &generics.where_clause,
1118                                                          context.config.item_brace_style,
1119                                                          Shape::legacy(where_budget, indent),
1120                                                          context.config.where_density,
1121                                                          "=",
1122                                                          true,
1123                                                          true,
1124                                                          Some(span.hi)));
1125     result.push_str(&where_clause_str);
1126     result.push_str(" = ");
1127
1128     let line_width = last_line_width(&result);
1129     // This checked_sub may fail as the extra space after '=' is not taken into account
1130     // In that case the budget is set to 0 which will make ty.rewrite retry on a new line
1131     let budget = context.config
1132         .max_width
1133         .checked_sub(indent.width() + line_width + ";".len())
1134         .unwrap_or(0);
1135     let type_indent = indent + line_width;
1136     // Try to fit the type on the same line
1137     let ty_str = try_opt!(ty.rewrite(context, Shape::legacy(budget, type_indent)).or_else(|| {
1138         // The line was too short, try to put the type on the next line
1139
1140         // Remove the space after '='
1141         result.pop();
1142         let type_indent = indent.block_indent(context.config);
1143         result.push('\n');
1144         result.push_str(&type_indent.to_string(context.config));
1145         let budget = try_opt!(context.config.max_width.checked_sub(type_indent.width() +
1146                                                                    ";".len()));
1147         ty.rewrite(context, Shape::legacy(budget, type_indent))
1148     }));
1149     result.push_str(&ty_str);
1150     result.push_str(";");
1151     Some(result)
1152 }
1153
1154 fn type_annotation_spacing(config: &Config) -> (&str, &str) {
1155     (if config.space_before_type_annotation {
1156          " "
1157      } else {
1158          ""
1159      },
1160      if config.space_after_type_annotation_colon {
1161          " "
1162      } else {
1163          ""
1164      })
1165 }
1166
1167 impl Rewrite for ast::StructField {
1168     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1169         if contains_skip(&self.attrs) {
1170             let span = context.snippet(mk_sp(self.attrs[0].span.lo, self.span.hi));
1171             return wrap_str(span, context.config.max_width, shape);
1172         }
1173
1174         let name = self.ident;
1175         let vis = format_visibility(&self.vis);
1176         let mut attr_str = try_opt!(self.attrs.rewrite(context,
1177                                                        Shape::legacy(context.config.max_width -
1178                                                                      shape.indent.width(),
1179                                                                      shape.indent)));
1180         if !attr_str.is_empty() {
1181             attr_str.push('\n');
1182             attr_str.push_str(&shape.indent.to_string(context.config));
1183         }
1184
1185         let type_annotation_spacing = type_annotation_spacing(context.config);
1186         let result = match name {
1187             Some(name) => {
1188                 format!("{}{}{}{}:{}",
1189                         attr_str,
1190                         vis,
1191                         name,
1192                         type_annotation_spacing.0,
1193                         type_annotation_spacing.1)
1194             }
1195             None => format!("{}{}", attr_str, vis),
1196         };
1197
1198         let last_line_width = last_line_width(&result);
1199         let budget = try_opt!(shape.width.checked_sub(last_line_width));
1200         let rewrite = try_opt!(self.ty.rewrite(context,
1201                                                Shape::legacy(budget,
1202                                                              shape.indent + last_line_width)));
1203         Some(result + &rewrite)
1204     }
1205 }
1206
1207 pub fn rewrite_static(prefix: &str,
1208                       vis: &ast::Visibility,
1209                       ident: ast::Ident,
1210                       ty: &ast::Ty,
1211                       mutability: ast::Mutability,
1212                       expr_opt: Option<&ptr::P<ast::Expr>>,
1213                       offset: Indent,
1214                       context: &RewriteContext)
1215                       -> Option<String> {
1216     let type_annotation_spacing = type_annotation_spacing(context.config);
1217     let prefix = format!("{}{} {}{}{}:{}",
1218                          format_visibility(vis),
1219                          prefix,
1220                          format_mutability(mutability),
1221                          ident,
1222                          type_annotation_spacing.0,
1223                          type_annotation_spacing.1);
1224     // 2 = " =".len()
1225     let ty_str = try_opt!(ty.rewrite(context,
1226                                      Shape::legacy(context.config.max_width - offset.block_indent -
1227                                                    prefix.len() -
1228                                                    2,
1229                                                    offset.block_only())));
1230
1231     if let Some(expr) = expr_opt {
1232         let lhs = format!("{}{} =", prefix, ty_str);
1233         // 1 = ;
1234         let remaining_width = context.config.max_width - offset.block_indent - 1;
1235         rewrite_assign_rhs(context,
1236                            lhs,
1237                            expr,
1238                            Shape::legacy(remaining_width, offset.block_only()))
1239                 .map(|s| s + ";")
1240     } else {
1241         let lhs = format!("{}{};", prefix, ty_str);
1242         Some(lhs)
1243     }
1244 }
1245
1246 pub fn rewrite_associated_type(ident: ast::Ident,
1247                                ty_opt: Option<&ptr::P<ast::Ty>>,
1248                                ty_param_bounds_opt: Option<&ast::TyParamBounds>,
1249                                context: &RewriteContext,
1250                                indent: Indent)
1251                                -> Option<String> {
1252     let prefix = format!("type {}", ident);
1253
1254     let type_bounds_str = if let Some(ty_param_bounds) = ty_param_bounds_opt {
1255         let bounds: &[_] = ty_param_bounds;
1256         let bound_str = try_opt!(bounds.iter()
1257             .map(|ty_bound| {
1258                 ty_bound.rewrite(context, Shape::legacy(context.config.max_width, indent))
1259             })
1260             .intersperse(Some(" + ".to_string()))
1261             .collect::<Option<String>>());
1262         if bounds.len() > 0 {
1263             format!(": {}", bound_str)
1264         } else {
1265             String::new()
1266         }
1267     } else {
1268         String::new()
1269     };
1270
1271     if let Some(ty) = ty_opt {
1272         let ty_str = try_opt!(ty.rewrite(context,
1273                                          Shape::legacy(context.config.max_width -
1274                                                        indent.block_indent -
1275                                                        prefix.len() -
1276                                                        2,
1277                                                        indent.block_only())));
1278         Some(format!("{} = {};", prefix, ty_str))
1279     } else {
1280         Some(format!("{}{};", prefix, type_bounds_str))
1281     }
1282 }
1283
1284 pub fn rewrite_associated_impl_type(ident: ast::Ident,
1285                                     defaultness: ast::Defaultness,
1286                                     ty_opt: Option<&ptr::P<ast::Ty>>,
1287                                     ty_param_bounds_opt: Option<&ast::TyParamBounds>,
1288                                     context: &RewriteContext,
1289                                     indent: Indent)
1290                                     -> Option<String> {
1291     let result =
1292         try_opt!(rewrite_associated_type(ident, ty_opt, ty_param_bounds_opt, context, indent));
1293
1294     match defaultness {
1295         ast::Defaultness::Default => Some(format!("default {}", result)),
1296         _ => Some(result),
1297     }
1298 }
1299
1300 impl Rewrite for ast::FunctionRetTy {
1301     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1302         match *self {
1303             ast::FunctionRetTy::Default(_) => Some(String::new()),
1304             ast::FunctionRetTy::Ty(ref ty) => {
1305                 let inner_width = try_opt!(shape.width.checked_sub(3));
1306                 ty.rewrite(context, Shape::legacy(inner_width, shape.indent + 3)).map(|r| {
1307                     format!("-> {}", r)
1308                 })
1309             }
1310         }
1311     }
1312 }
1313
1314 impl Rewrite for ast::Arg {
1315     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
1316         if is_named_arg(self) {
1317             let mut result = try_opt!(self.pat.rewrite(context,
1318                                                        Shape::legacy(shape.width, shape.indent)));
1319
1320             if self.ty.node != ast::TyKind::Infer {
1321                 if context.config.space_before_type_annotation {
1322                     result.push_str(" ");
1323                 }
1324                 result.push_str(":");
1325                 if context.config.space_after_type_annotation_colon {
1326                     result.push_str(" ");
1327                 }
1328                 let max_width = try_opt!(shape.width.checked_sub(result.len()));
1329                 let ty_str = try_opt!(self.ty.rewrite(context,
1330                                                       Shape::legacy(max_width,
1331                                                                     shape.indent + result.len())));
1332                 result.push_str(&ty_str);
1333             }
1334
1335             Some(result)
1336         } else {
1337             self.ty.rewrite(context, shape)
1338         }
1339     }
1340 }
1341
1342 fn rewrite_explicit_self(explicit_self: &ast::ExplicitSelf,
1343                          args: &[ast::Arg],
1344                          context: &RewriteContext)
1345                          -> Option<String> {
1346     match explicit_self.node {
1347         ast::SelfKind::Region(lt, m) => {
1348             let mut_str = format_mutability(m);
1349             match lt {
1350                 Some(ref l) => {
1351                     let lifetime_str = try_opt!(l.rewrite(context,
1352                                                           Shape::legacy(usize::max_value(),
1353                                                                         Indent::empty())));
1354                     Some(format!("&{} {}self", lifetime_str, mut_str))
1355                 }
1356                 None => Some(format!("&{}self", mut_str)),
1357             }
1358         }
1359         ast::SelfKind::Explicit(ref ty, _) => {
1360             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1361
1362             let mutability = explicit_self_mutability(&args[0]);
1363             let type_str = try_opt!(ty.rewrite(context,
1364                                                Shape::legacy(usize::max_value(), Indent::empty())));
1365
1366             Some(format!("{}self: {}", format_mutability(mutability), type_str))
1367         }
1368         ast::SelfKind::Value(_) => {
1369             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1370
1371             let mutability = explicit_self_mutability(&args[0]);
1372
1373             Some(format!("{}self", format_mutability(mutability)))
1374         }
1375     }
1376 }
1377
1378 // Hacky solution caused by absence of `Mutability` in `SelfValue` and
1379 // `SelfExplicit` variants of `ast::ExplicitSelf_`.
1380 fn explicit_self_mutability(arg: &ast::Arg) -> ast::Mutability {
1381     if let ast::PatKind::Ident(ast::BindingMode::ByValue(mutability), _, _) = arg.pat.node {
1382         mutability
1383     } else {
1384         unreachable!()
1385     }
1386 }
1387
1388 pub fn span_lo_for_arg(arg: &ast::Arg) -> BytePos {
1389     if is_named_arg(arg) {
1390         arg.pat.span.lo
1391     } else {
1392         arg.ty.span.lo
1393     }
1394 }
1395
1396 pub fn span_hi_for_arg(arg: &ast::Arg) -> BytePos {
1397     match arg.ty.node {
1398         ast::TyKind::Infer if is_named_arg(arg) => arg.pat.span.hi,
1399         _ => arg.ty.span.hi,
1400     }
1401 }
1402
1403 pub fn is_named_arg(arg: &ast::Arg) -> bool {
1404     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
1405         ident.node != symbol::keywords::Invalid.ident()
1406     } else {
1407         true
1408     }
1409 }
1410
1411 fn span_for_return(ret: &ast::FunctionRetTy) -> Span {
1412     match *ret {
1413         ast::FunctionRetTy::Default(ref span) => span.clone(),
1414         ast::FunctionRetTy::Ty(ref ty) => ty.span,
1415     }
1416 }
1417
1418 fn span_for_ty_param(ty: &ast::TyParam) -> Span {
1419     // Note that ty.span is the span for ty.ident, not the whole item.
1420     let lo = ty.span.lo;
1421     if let Some(ref def) = ty.default {
1422         return mk_sp(lo, def.span.hi);
1423     }
1424     if ty.bounds.is_empty() {
1425         return ty.span;
1426     }
1427     let hi = match ty.bounds[ty.bounds.len() - 1] {
1428         ast::TyParamBound::TraitTyParamBound(ref ptr, _) => ptr.span.hi,
1429         ast::TyParamBound::RegionTyParamBound(ref l) => l.span.hi,
1430     };
1431     mk_sp(lo, hi)
1432 }
1433
1434 fn span_for_where_pred(pred: &ast::WherePredicate) -> Span {
1435     match *pred {
1436         ast::WherePredicate::BoundPredicate(ref p) => p.span,
1437         ast::WherePredicate::RegionPredicate(ref p) => p.span,
1438         ast::WherePredicate::EqPredicate(ref p) => p.span,
1439     }
1440 }
1441
1442 // Return type is (result, force_new_line_for_brace)
1443 fn rewrite_fn_base(context: &RewriteContext,
1444                    indent: Indent,
1445                    ident: ast::Ident,
1446                    fd: &ast::FnDecl,
1447                    generics: &ast::Generics,
1448                    unsafety: ast::Unsafety,
1449                    constness: ast::Constness,
1450                    defaultness: ast::Defaultness,
1451                    abi: abi::Abi,
1452                    vis: &ast::Visibility,
1453                    span: Span,
1454                    newline_brace: bool,
1455                    has_body: bool)
1456                    -> Option<(String, bool)> {
1457     let mut force_new_line_for_brace = false;
1458
1459     let where_clause = &generics.where_clause;
1460
1461     let mut result = String::with_capacity(1024);
1462     // Vis unsafety abi.
1463     result.push_str(&*format_visibility(vis));
1464
1465     if let ast::Defaultness::Default = defaultness {
1466         result.push_str("default ");
1467     }
1468
1469     if let ast::Constness::Const = constness {
1470         result.push_str("const ");
1471     }
1472
1473     result.push_str(::utils::format_unsafety(unsafety));
1474
1475     if abi != abi::Abi::Rust {
1476         result.push_str(&::utils::format_abi(abi, context.config.force_explicit_abi));
1477     }
1478
1479     // fn foo
1480     result.push_str("fn ");
1481     result.push_str(&ident.to_string());
1482
1483     // Generics.
1484     let generics_indent = indent + result.len();
1485     let generics_span = mk_sp(span.lo, span_for_return(&fd.output).lo);
1486     let generics_str = try_opt!(rewrite_generics(context,
1487                                                  generics,
1488                                                  Shape::legacy(context.config.max_width, indent),
1489                                                  generics_indent,
1490                                                  generics_span));
1491     result.push_str(&generics_str);
1492
1493     let snuggle_angle_bracket = last_line_width(&generics_str) == 1;
1494
1495     // Note that the width and indent don't really matter, we'll re-layout the
1496     // return type later anyway.
1497     let ret_str = try_opt!(fd.output.rewrite(&context,
1498                                              Shape::legacy(context.config.max_width -
1499                                                            indent.width(),
1500                                                            indent)));
1501
1502     let multi_line_ret_str = ret_str.contains('\n');
1503     let ret_str_len = if multi_line_ret_str { 0 } else { ret_str.len() };
1504
1505     // Args.
1506     let (mut one_line_budget, mut multi_line_budget, mut arg_indent) =
1507         try_opt!(compute_budgets_for_args(context, &result, indent, ret_str_len, newline_brace));
1508
1509     if context.config.fn_args_layout == FnArgLayoutStyle::Block ||
1510        context.config.fn_args_layout == FnArgLayoutStyle::BlockAlways {
1511         arg_indent = indent.block_indent(context.config);
1512         multi_line_budget = context.config.max_width - arg_indent.width();
1513     }
1514
1515     debug!("rewrite_fn_base: one_line_budget: {}, multi_line_budget: {}, arg_indent: {:?}",
1516            one_line_budget,
1517            multi_line_budget,
1518            arg_indent);
1519
1520     // Check if vertical layout was forced.
1521     if one_line_budget == 0 {
1522         if snuggle_angle_bracket {
1523             result.push_str("(");
1524         } else if context.config.fn_args_paren_newline {
1525             result.push('\n');
1526             result.push_str(&arg_indent.to_string(context.config));
1527             arg_indent = arg_indent + 1; // extra space for `(`
1528             result.push('(');
1529             if context.config.spaces_within_parens && fd.inputs.len() > 0 {
1530                 result.push(' ')
1531             }
1532         } else {
1533             result.push_str("(\n");
1534             result.push_str(&arg_indent.to_string(context.config));
1535         }
1536     } else {
1537         result.push('(');
1538         if context.config.spaces_within_parens && fd.inputs.len() > 0 {
1539             result.push(' ')
1540         }
1541     }
1542
1543     if multi_line_ret_str {
1544         one_line_budget = 0;
1545     }
1546
1547     // A conservative estimation, to goal is to be over all parens in generics
1548     let args_start = generics.ty_params.last().map_or(span.lo, |tp| end_typaram(tp));
1549     let args_span = mk_sp(context.codemap.span_after(mk_sp(args_start, span.hi), "("),
1550                           span_for_return(&fd.output).lo);
1551     let arg_str = try_opt!(rewrite_args(context,
1552                                         &fd.inputs,
1553                                         fd.get_self().as_ref(),
1554                                         one_line_budget,
1555                                         multi_line_budget,
1556                                         indent,
1557                                         arg_indent,
1558                                         args_span,
1559                                         fd.variadic));
1560
1561     let multi_line_arg_str = arg_str.contains('\n');
1562
1563     let put_args_in_block = (match context.config.fn_args_layout {
1564         FnArgLayoutStyle::Block => multi_line_arg_str,
1565         FnArgLayoutStyle::BlockAlways => true,
1566         _ => false,
1567     } || generics_str.contains('\n') )&& !fd.inputs.is_empty();
1568
1569     if put_args_in_block {
1570         arg_indent = indent.block_indent(context.config);
1571         result.push('\n');
1572         result.push_str(&arg_indent.to_string(context.config));
1573         result.push_str(&arg_str);
1574         result.push('\n');
1575         result.push_str(&indent.to_string(context.config));
1576         result.push(')');
1577     } else {
1578         result.push_str(&arg_str);
1579         if context.config.spaces_within_parens && fd.inputs.len() > 0 {
1580             result.push(' ')
1581         }
1582         result.push(')');
1583     }
1584
1585     // Return type.
1586     if !ret_str.is_empty() {
1587         let ret_should_indent = match context.config.fn_args_layout {
1588             // If our args are block layout then we surely must have space.
1589             FnArgLayoutStyle::Block if put_args_in_block => false,
1590             FnArgLayoutStyle::BlockAlways => false,
1591             _ => {
1592                 // If we've already gone multi-line, or the return type would push over the max
1593                 // width, then put the return type on a new line. With the +1 for the signature
1594                 // length an additional space between the closing parenthesis of the argument and
1595                 // the arrow '->' is considered.
1596                 let mut sig_length = result.len() + indent.width() + ret_str_len + 1;
1597
1598                 // If there is no where clause, take into account the space after the return type
1599                 // and the brace.
1600                 if where_clause.predicates.is_empty() {
1601                     sig_length += 2;
1602                 }
1603
1604                 let overlong_sig = sig_length > context.config.max_width;
1605
1606                 result.contains('\n') || multi_line_ret_str || overlong_sig
1607             }
1608         };
1609         let ret_indent = if ret_should_indent {
1610             let indent = match context.config.fn_return_indent {
1611                 ReturnIndent::WithWhereClause => indent + 4,
1612                 // Aligning with non-existent args looks silly.
1613                 _ if arg_str.is_empty() => {
1614                     force_new_line_for_brace = true;
1615                     indent + 4
1616                 }
1617                 // FIXME: we might want to check that using the arg indent
1618                 // doesn't blow our budget, and if it does, then fallback to
1619                 // the where clause indent.
1620                 _ => arg_indent,
1621             };
1622
1623             result.push('\n');
1624             result.push_str(&indent.to_string(context.config));
1625             indent
1626         } else {
1627             result.push(' ');
1628             Indent::new(indent.width(), result.len())
1629         };
1630
1631         if multi_line_ret_str || ret_should_indent {
1632             // Now that we know the proper indent and width, we need to
1633             // re-layout the return type.
1634             let budget = try_opt!(context.config.max_width.checked_sub(ret_indent.width()));
1635             let ret_str = try_opt!(fd.output.rewrite(context, Shape::legacy(budget, ret_indent)));
1636             result.push_str(&ret_str);
1637         } else {
1638             result.push_str(&ret_str);
1639         }
1640
1641         // Comment between return type and the end of the decl.
1642         let snippet_lo = fd.output.span().hi;
1643         if where_clause.predicates.is_empty() {
1644             let snippet_hi = span.hi;
1645             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
1646             let snippet = snippet.trim();
1647             if !snippet.is_empty() {
1648                 result.push(' ');
1649                 result.push_str(snippet);
1650             }
1651         } else {
1652             // FIXME it would be nice to catch comments between the return type
1653             // and the where clause, but we don't have a span for the where
1654             // clause.
1655         }
1656     }
1657
1658     let should_compress_where = match context.config.where_density {
1659         Density::Compressed => !result.contains('\n') || put_args_in_block,
1660         Density::CompressedIfEmpty => !has_body && !result.contains('\n'),
1661         _ => false,
1662     } || (put_args_in_block && ret_str.is_empty());
1663
1664     if where_clause.predicates.len() == 1 && should_compress_where {
1665         // TODO hitting this path, but using a newline
1666         let budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
1667         if let Some(where_clause_str) =
1668             rewrite_where_clause(context,
1669                                  where_clause,
1670                                  context.config.fn_brace_style,
1671                                  Shape::legacy(budget, indent),
1672                                  Density::Compressed,
1673                                  "{",
1674                                  !has_body,
1675                                  put_args_in_block && ret_str.is_empty(),
1676                                  Some(span.hi)) {
1677             if !where_clause_str.contains('\n') {
1678                 if last_line_width(&result) + where_clause_str.len() > context.config.max_width {
1679                     result.push('\n');
1680                 }
1681
1682                 result.push_str(&where_clause_str);
1683
1684                 return Some((result, force_new_line_for_brace));
1685             }
1686         }
1687     }
1688
1689     let budget = try_opt!(context.config.max_width.checked_sub(indent.block_indent));
1690     let where_clause_str = try_opt!(rewrite_where_clause(context,
1691                                                          where_clause,
1692                                                          context.config.fn_brace_style,
1693                                                          Shape::legacy(budget, indent),
1694                                                          Density::Tall,
1695                                                          "{",
1696                                                          !has_body,
1697                                                          put_args_in_block && ret_str.is_empty(),
1698                                                          Some(span.hi)));
1699
1700     result.push_str(&where_clause_str);
1701
1702     Some((result, force_new_line_for_brace))
1703 }
1704
1705 fn rewrite_args(context: &RewriteContext,
1706                 args: &[ast::Arg],
1707                 explicit_self: Option<&ast::ExplicitSelf>,
1708                 one_line_budget: usize,
1709                 multi_line_budget: usize,
1710                 indent: Indent,
1711                 arg_indent: Indent,
1712                 span: Span,
1713                 variadic: bool)
1714                 -> Option<String> {
1715     let mut arg_item_strs =
1716         try_opt!(args.iter()
1717                      .map(|arg| {
1718                               arg.rewrite(&context, Shape::legacy(multi_line_budget, arg_indent))
1719                           })
1720                      .collect::<Option<Vec<_>>>());
1721
1722     // Account for sugary self.
1723     // FIXME: the comment for the self argument is dropped. This is blocked
1724     // on rust issue #27522.
1725     let min_args =
1726         explicit_self.and_then(|explicit_self| rewrite_explicit_self(explicit_self, args, context))
1727             .map_or(1, |self_str| {
1728                 arg_item_strs[0] = self_str;
1729                 2
1730             });
1731
1732     // Comments between args.
1733     let mut arg_items = Vec::new();
1734     if min_args == 2 {
1735         arg_items.push(ListItem::from_str(""));
1736     }
1737
1738     // FIXME(#21): if there are no args, there might still be a comment, but
1739     // without spans for the comment or parens, there is no chance of
1740     // getting it right. You also don't get to put a comment on self, unless
1741     // it is explicit.
1742     if args.len() >= min_args || variadic {
1743         let comment_span_start = if min_args == 2 {
1744             let second_arg_start = if arg_has_pattern(&args[1]) {
1745                 args[1].pat.span.lo
1746             } else {
1747                 args[1].ty.span.lo
1748             };
1749             let reduced_span = mk_sp(span.lo, second_arg_start);
1750
1751             context.codemap.span_after_last(reduced_span, ",")
1752         } else {
1753             span.lo
1754         };
1755
1756         enum ArgumentKind<'a> {
1757             Regular(&'a ast::Arg),
1758             Variadic(BytePos),
1759         }
1760
1761         let variadic_arg = if variadic {
1762             let variadic_span = mk_sp(args.last()
1763                                           .unwrap()
1764                                           .ty
1765                                           .span
1766                                           .hi,
1767                                       span.hi);
1768             let variadic_start = context.codemap.span_after(variadic_span, "...") - BytePos(3);
1769             Some(ArgumentKind::Variadic(variadic_start))
1770         } else {
1771             None
1772         };
1773
1774         let more_items = itemize_list(context.codemap,
1775                                       args[min_args - 1..]
1776                                           .iter()
1777                                           .map(ArgumentKind::Regular)
1778                                           .chain(variadic_arg),
1779                                       ")",
1780                                       |arg| match *arg {
1781                                           ArgumentKind::Regular(arg) => span_lo_for_arg(arg),
1782                                           ArgumentKind::Variadic(start) => start,
1783                                       },
1784                                       |arg| match *arg {
1785                                           ArgumentKind::Regular(arg) => arg.ty.span.hi,
1786                                           ArgumentKind::Variadic(start) => start + BytePos(3),
1787                                       },
1788                                       |arg| match *arg {
1789                                           ArgumentKind::Regular(..) => None,
1790                                           ArgumentKind::Variadic(..) => Some("...".to_owned()),
1791                                       },
1792                                       comment_span_start,
1793                                       span.hi);
1794
1795         arg_items.extend(more_items);
1796     }
1797
1798     for (item, arg) in arg_items.iter_mut().zip(arg_item_strs) {
1799         item.item = Some(arg);
1800     }
1801
1802     let indent = match context.config.fn_arg_indent {
1803         BlockIndentStyle::Inherit => indent,
1804         BlockIndentStyle::Tabbed => indent.block_indent(context.config),
1805         BlockIndentStyle::Visual => arg_indent,
1806     };
1807
1808     let tactic = definitive_tactic(&arg_items,
1809                                    context.config.fn_args_density.to_list_tactic(),
1810                                    one_line_budget);
1811     let budget = match tactic {
1812         DefinitiveListTactic::Horizontal => one_line_budget,
1813         _ => multi_line_budget,
1814     };
1815
1816     debug!("rewrite_args: budget: {}, tactic: {:?}", budget, tactic);
1817
1818     let (trailing_comma, end_with_newline) = match context.config.fn_args_layout {
1819         FnArgLayoutStyle::Block => (SeparatorTactic::Vertical, true),
1820         FnArgLayoutStyle::BlockAlways => (SeparatorTactic::Always, true),
1821         _ => (SeparatorTactic::Never, false),
1822     };
1823
1824     let fmt = ListFormatting {
1825         tactic: tactic,
1826         separator: ",",
1827         trailing_separator: trailing_comma,
1828         shape: Shape::legacy(budget, indent),
1829         ends_with_newline: end_with_newline,
1830         config: context.config,
1831     };
1832
1833     write_list(&arg_items, &fmt)
1834 }
1835
1836 fn arg_has_pattern(arg: &ast::Arg) -> bool {
1837     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
1838         ident.node != symbol::keywords::Invalid.ident()
1839     } else {
1840         true
1841     }
1842 }
1843
1844 fn compute_budgets_for_args(context: &RewriteContext,
1845                             result: &str,
1846                             indent: Indent,
1847                             ret_str_len: usize,
1848                             newline_brace: bool)
1849                             -> Option<((usize, usize, Indent))> {
1850     debug!("compute_budgets_for_args {} {:?}, {}, {}",
1851            result.len(),
1852            indent,
1853            ret_str_len,
1854            newline_brace);
1855     // Try keeping everything on the same line.
1856     if !result.contains('\n') {
1857         // 3 = `() `, space is before ret_string.
1858         let mut used_space = indent.width() + result.len() + ret_str_len + 3;
1859         if !newline_brace {
1860             used_space += 2;
1861         }
1862         let one_line_budget = context.config
1863             .max_width
1864             .checked_sub(used_space)
1865             .unwrap_or(0);
1866
1867         if one_line_budget > 0 {
1868             // 4 = "() {".len()
1869             let multi_line_budget =
1870                 try_opt!(context.config.max_width.checked_sub(indent.width() + result.len() + 4));
1871
1872             return Some((one_line_budget, multi_line_budget, indent + result.len() + 1));
1873         }
1874     }
1875
1876     // Didn't work. we must force vertical layout and put args on a newline.
1877     let new_indent = indent.block_indent(context.config);
1878     let used_space = new_indent.width() + 4; // Account for `(` and `)` and possibly ` {`.
1879     let max_space = context.config.max_width;
1880     if used_space <= max_space {
1881         Some((0, max_space - used_space, new_indent))
1882     } else {
1883         // Whoops! bankrupt.
1884         None
1885     }
1886 }
1887
1888 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> bool {
1889     match config.fn_brace_style {
1890         BraceStyle::AlwaysNextLine => true,
1891         BraceStyle::SameLineWhere if !where_clause.predicates.is_empty() => true,
1892         _ => false,
1893     }
1894 }
1895
1896 fn rewrite_generics(context: &RewriteContext,
1897                     generics: &ast::Generics,
1898                     shape: Shape,
1899                     // TODO shouldn't need this
1900                     generics_offset: Indent,
1901                     span: Span)
1902                     -> Option<String> {
1903     // FIXME: convert bounds to where clauses where they get too big or if
1904     // there is a where clause at all.
1905     let lifetimes: &[_] = &generics.lifetimes;
1906     let tys: &[_] = &generics.ty_params;
1907     if lifetimes.is_empty() && tys.is_empty() {
1908         return Some(String::new());
1909     }
1910
1911     let offset = match context.config.generics_indent {
1912         BlockIndentStyle::Inherit => shape.indent,
1913         BlockIndentStyle::Tabbed => shape.indent.block_indent(context.config),
1914         // 1 = <
1915         BlockIndentStyle::Visual => generics_offset + 1,
1916     };
1917
1918     let h_budget = try_opt!(shape.width.checked_sub(generics_offset.width() + 2));
1919     // FIXME: might need to insert a newline if the generics are really long.
1920
1921     // Strings for the generics.
1922     let lt_strs = lifetimes.iter().map(|lt| lt.rewrite(context, Shape::legacy(h_budget, offset)));
1923     let ty_strs =
1924         tys.iter().map(|ty_param| ty_param.rewrite(context, Shape::legacy(h_budget, offset)));
1925
1926     // Extract comments between generics.
1927     let lt_spans = lifetimes.iter().map(|l| {
1928         let hi = if l.bounds.is_empty() {
1929             l.lifetime.span.hi
1930         } else {
1931             l.bounds[l.bounds.len() - 1].span.hi
1932         };
1933         mk_sp(l.lifetime.span.lo, hi)
1934     });
1935     let ty_spans = tys.iter().map(span_for_ty_param);
1936
1937     let items = itemize_list(context.codemap,
1938                              lt_spans.chain(ty_spans).zip(lt_strs.chain(ty_strs)),
1939                              ">",
1940                              |&(sp, _)| sp.lo,
1941                              |&(sp, _)| sp.hi,
1942                              // FIXME: don't clone
1943                              |&(_, ref str)| str.clone(),
1944                              context.codemap.span_after(span, "<"),
1945                              span.hi);
1946     let list_str =
1947         try_opt!(format_item_list(items, Shape::legacy(h_budget, offset), context.config));
1948
1949     let result = if context.config.generics_indent != BlockIndentStyle::Visual && list_str.contains('\n') {
1950         format!("<\n{}{}\n{}>", offset.to_string(context.config), list_str, shape.indent.to_string(context.config))
1951     } else if context.config.spaces_within_angle_brackets {
1952         format!("< {} >", list_str)
1953     } else {
1954         format!("<{}>", list_str)
1955     };
1956     Some(result)
1957 }
1958
1959 fn rewrite_trait_bounds(context: &RewriteContext,
1960                         type_param_bounds: &ast::TyParamBounds,
1961                         shape: Shape)
1962                         -> Option<String> {
1963     let bounds: &[_] = type_param_bounds;
1964
1965     if bounds.is_empty() {
1966         return Some(String::new());
1967     }
1968
1969     let bound_str = try_opt!(bounds.iter()
1970                                  .map(|ty_bound| ty_bound.rewrite(&context, shape))
1971                                  .intersperse(Some(" + ".to_string()))
1972                                  .collect::<Option<String>>());
1973
1974     let mut result = String::new();
1975     result.push_str(": ");
1976     result.push_str(&bound_str);
1977     Some(result)
1978 }
1979
1980 //   fn reflow_list_node_with_rule(
1981 //        &self,
1982 //        node: &CompoundNode,
1983 //        rule: &Rule,
1984 //        args: &[Arg],
1985 //        shape: &Shape
1986 //    ) -> Result<String, ()>
1987 //    where
1988 //        T: Foo,
1989 //    {
1990
1991
1992 fn rewrite_where_clause_rfc_style(context: &RewriteContext,
1993                                   where_clause: &ast::WhereClause,
1994                                   shape: Shape,
1995                                   terminator: &str,
1996                                   suppress_comma: bool,
1997                                   // where clause can be kept on the current line.
1998                                   snuggle: bool,
1999                                   span_end: Option<BytePos>)
2000                                   -> Option<String> {
2001     let block_shape = shape.block();
2002
2003     let starting_newline = if snuggle {
2004         " ".to_owned()
2005     } else {
2006         "\n".to_owned() + &block_shape.indent.to_string(context.config)
2007     };
2008
2009     let clause_shape = block_shape.block_indent(context.config.tab_spaces);
2010     // each clause on one line, trailing comma (except if suppress_comma)
2011     let span_start = span_for_where_pred(&where_clause.predicates[0]).lo;
2012     // If we don't have the start of the next span, then use the end of the
2013     // predicates, but that means we miss comments.
2014     let len = where_clause.predicates.len();
2015     let end_of_preds = span_for_where_pred(&where_clause.predicates[len - 1]).hi;
2016     let span_end = span_end.unwrap_or(end_of_preds);
2017     let items = itemize_list(context.codemap,
2018                              where_clause.predicates.iter(),
2019                              terminator,
2020                              |pred| span_for_where_pred(pred).lo,
2021                              |pred| span_for_where_pred(pred).hi,
2022                              |pred| pred.rewrite(context, clause_shape),
2023                              span_start,
2024                              span_end);
2025     let comma_tactic = if suppress_comma {
2026         SeparatorTactic::Never
2027     } else {
2028         SeparatorTactic::Always
2029     };
2030
2031     let fmt = ListFormatting {
2032         tactic: DefinitiveListTactic::Vertical,
2033         separator: ",",
2034         trailing_separator: comma_tactic,
2035         shape: clause_shape,
2036         ends_with_newline: true,
2037         config: context.config,
2038     };
2039     let preds_str = try_opt!(write_list(items, &fmt));
2040
2041     Some(format!("{}where\n{}{}",
2042                  starting_newline,
2043                  clause_shape.indent.to_string(context.config),
2044                  preds_str))
2045 }
2046
2047 fn rewrite_where_clause(context: &RewriteContext,
2048                         where_clause: &ast::WhereClause,
2049                         brace_style: BraceStyle,
2050                         shape: Shape,
2051                         density: Density,
2052                         terminator: &str,
2053                         suppress_comma: bool,
2054                         snuggle: bool,
2055                         span_end: Option<BytePos>)
2056                         -> Option<String> {
2057     if where_clause.predicates.is_empty() {
2058         return Some(String::new());
2059     }
2060
2061     if context.config.where_style == Style::Rfc {
2062         return rewrite_where_clause_rfc_style(context,
2063                                               where_clause,
2064                                               shape,
2065                                               terminator,
2066                                               suppress_comma,
2067                                               snuggle,
2068                                               span_end);
2069     }
2070
2071     let extra_indent = match context.config.where_indent {
2072         BlockIndentStyle::Inherit => Indent::empty(),
2073         BlockIndentStyle::Tabbed | BlockIndentStyle::Visual => {
2074             Indent::new(context.config.tab_spaces, 0)
2075         }
2076     };
2077
2078     let offset = match context.config.where_pred_indent {
2079         BlockIndentStyle::Inherit => shape.indent + extra_indent,
2080         BlockIndentStyle::Tabbed => shape.indent + extra_indent.block_indent(context.config),
2081         // 6 = "where ".len()
2082         BlockIndentStyle::Visual => shape.indent + extra_indent + 6,
2083     };
2084     // FIXME: if where_pred_indent != Visual, then the budgets below might
2085     // be out by a char or two.
2086
2087     let budget = context.config.max_width - offset.width();
2088     let span_start = span_for_where_pred(&where_clause.predicates[0]).lo;
2089     // If we don't have the start of the next span, then use the end of the
2090     // predicates, but that means we miss comments.
2091     let len = where_clause.predicates.len();
2092     let end_of_preds = span_for_where_pred(&where_clause.predicates[len - 1]).hi;
2093     let span_end = span_end.unwrap_or(end_of_preds);
2094     let items = itemize_list(context.codemap,
2095                              where_clause.predicates.iter(),
2096                              terminator,
2097                              |pred| span_for_where_pred(pred).lo,
2098                              |pred| span_for_where_pred(pred).hi,
2099                              |pred| pred.rewrite(context, Shape::legacy(budget, offset)),
2100                              span_start,
2101                              span_end);
2102     let item_vec = items.collect::<Vec<_>>();
2103     // FIXME: we don't need to collect here if the where_layout isn't
2104     // HorizontalVertical.
2105     let tactic = definitive_tactic(&item_vec, context.config.where_layout, budget);
2106
2107     let mut comma_tactic = context.config.trailing_comma;
2108     // Kind of a hack because we don't usually have trailing commas in where clauses.
2109     if comma_tactic == SeparatorTactic::Vertical || suppress_comma {
2110         comma_tactic = SeparatorTactic::Never;
2111     }
2112
2113     let fmt = ListFormatting {
2114         tactic: tactic,
2115         separator: ",",
2116         trailing_separator: comma_tactic,
2117         shape: Shape::legacy(budget, offset),
2118         ends_with_newline: true,
2119         config: context.config,
2120     };
2121     let preds_str = try_opt!(write_list(&item_vec, &fmt));
2122
2123     let end_length = if terminator == "{" {
2124         // If the brace is on the next line we don't need to count it otherwise it needs two
2125         // characters " {"
2126         match brace_style {
2127             BraceStyle::AlwaysNextLine |
2128             BraceStyle::SameLineWhere => 0,
2129             BraceStyle::PreferSameLine => 2,
2130         }
2131     } else if terminator == "=" {
2132         2
2133     } else {
2134         terminator.len()
2135     };
2136     if density == Density::Tall || preds_str.contains('\n') ||
2137        shape.indent.width() + " where ".len() + preds_str.len() + end_length > shape.width {
2138         Some(format!("\n{}where {}",
2139                      (shape.indent + extra_indent).to_string(context.config),
2140                      preds_str))
2141     } else {
2142         Some(format!(" where {}", preds_str))
2143     }
2144 }
2145
2146 fn format_header(item_name: &str, ident: ast::Ident, vis: &ast::Visibility) -> String {
2147     format!("{}{}{}", format_visibility(vis), item_name, ident)
2148 }
2149
2150 fn format_generics(context: &RewriteContext,
2151                    generics: &ast::Generics,
2152                    opener: &str,
2153                    terminator: &str,
2154                    brace_style: BraceStyle,
2155                    force_same_line_brace: bool,
2156                    offset: Indent,
2157                    generics_offset: Indent,
2158                    span: Span)
2159                    -> Option<String> {
2160     let mut result = try_opt!(rewrite_generics(context,
2161                                                generics,
2162                                                Shape::legacy(context.config.max_width, offset),
2163                                                generics_offset,
2164                                                span));
2165
2166     if !generics.where_clause.predicates.is_empty() || result.contains('\n') {
2167         let budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
2168         let where_clause_str = try_opt!(rewrite_where_clause(context,
2169                                                              &generics.where_clause,
2170                                                              brace_style,
2171                                                              Shape::legacy(budget,
2172                                                                            offset.block_only()),
2173                                                              Density::Tall,
2174                                                              terminator,
2175                                                              false,
2176                                                              trimmed_last_line_width(&result) == 1,
2177                                                              Some(span.hi)));
2178         result.push_str(&where_clause_str);
2179         let same_line_brace = force_same_line_brace || (generics.where_clause.predicates.is_empty() && trimmed_last_line_width(&result) == 1);
2180         if !same_line_brace &&
2181            (brace_style == BraceStyle::SameLineWhere || brace_style == BraceStyle::AlwaysNextLine) {
2182             result.push('\n');
2183             result.push_str(&offset.block_only().to_string(context.config));
2184         } else {
2185             result.push(' ');
2186         }
2187         result.push_str(opener);
2188     } else {
2189         if force_same_line_brace || trimmed_last_line_width(&result) == 1 || brace_style != BraceStyle::AlwaysNextLine {
2190             result.push(' ');
2191         } else {
2192             result.push('\n');
2193             result.push_str(&offset.block_only().to_string(context.config));
2194         }
2195         result.push_str(opener);
2196     }
2197
2198     Some(result)
2199 }