src/items.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 // Formatting top-level items - functions, structs, enums, traits, impls.
  12
  13 use Indent;
  14 use utils::{CodeMapSpanUtils, format_mutability, format_visibility, contains_skip, end_typaram,
  15             wrap_str, last_line_width, semicolon_for_expr, format_unsafety, trim_newlines};
  16 use lists::{write_list, itemize_list, ListItem, ListFormatting, SeparatorTactic,
  17             DefinitiveListTactic, ListTactic, definitive_tactic, format_item_list};
  18 use expr::{is_empty_block, is_simple_block_stmt, rewrite_assign_rhs};
  19 use comment::{FindUncommented, contains_comment};
  20 use visitor::FmtVisitor;
  21 use rewrite::{Rewrite, RewriteContext};
  22 use config::{Config, BlockIndentStyle, Density, ReturnIndent, BraceStyle, FnArgLayoutStyle};
  23
  24 use syntax::{ast, abi, ptr, codemap};
  25 use syntax::codemap::{Span, BytePos, mk_sp};
  26 use syntax::parse::token;
  27 use syntax::ast::ImplItem;
  28
  29 // Statements of the form
  30 // let pat: ty = init;
  31 impl Rewrite for ast::Local {
  32     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
  33         let mut result = "let ".to_owned();
  34         let pattern_offset = offset + result.len();
  35         // 1 = ;
  36         let pattern_width = try_opt!(width.checked_sub(pattern_offset.width() + 1));
  37
  38         let pat_str = try_opt!(self.pat.rewrite(&context, pattern_width, pattern_offset));
  39         result.push_str(&pat_str);
  40
  41         // String that is placed within the assignment pattern and expression.
  42         let infix = {
  43             let mut infix = String::new();
  44
  45             if let Some(ref ty) = self.ty {
  46                 // 2 = ": ".len()
  47                 // 1 = ;
  48                 let indent = offset + last_line_width(&result) + 2;
  49                 let budget = try_opt!(width.checked_sub(indent.width() + 1));
  50                 let rewrite = try_opt!(ty.rewrite(context, budget, indent));
  51
  52                 infix.push_str(": ");
  53                 infix.push_str(&rewrite);
  54             }
  55
  56             if self.init.is_some() {
  57                 infix.push_str(" =");
  58             }
  59
  60             infix
  61         };
  62
  63         result.push_str(&infix);
  64
  65         if let Some(ref ex) = self.init {
  66             let budget = try_opt!(width.checked_sub(context.block_indent.width() + 1));
  67
  68             // 1 = trailing semicolon;
  69             result =
  70                 try_opt!(rewrite_assign_rhs(&context, result, ex, budget, context.block_indent));
  71         }
  72
  73         result.push(';');
  74         Some(result)
  75     }
  76 }
  77
  78 impl<'a> FmtVisitor<'a> {
  79     pub fn format_foreign_mod(&mut self, fm: &ast::ForeignMod, span: Span) {
  80         let abi_str = ::utils::format_abi(fm.abi, self.config.force_explicit_abi);
  81         self.buffer.push_str(&abi_str);
  82
  83         let snippet = self.snippet(span);
  84         let brace_pos = snippet.find_uncommented("{").unwrap();
  85
  86         if fm.items.is_empty() && !contains_comment(&snippet[brace_pos..]) {
  87             self.buffer.push_str("{");
  88         } else {
  89             // FIXME: this skips comments between the extern keyword and the opening
  90             // brace.
  91             self.last_pos = span.lo + BytePos(brace_pos as u32);
  92             self.block_indent = self.block_indent.block_indent(self.config);
  93
  94             for item in &fm.items {
  95                 self.format_foreign_item(&*item);
  96             }
  97
  98             self.block_indent = self.block_indent.block_unindent(self.config);
  99             self.format_missing_with_indent(span.hi - BytePos(1));
 100         }
 101
 102         self.buffer.push_str("}");
 103         self.last_pos = span.hi;
 104     }
 105
 106     fn format_foreign_item(&mut self, item: &ast::ForeignItem) {
 107         self.format_missing_with_indent(item.span.lo);
 108         // Drop semicolon or it will be interpreted as comment.
 109         // FIXME: this may be a faulty span from libsyntax.
 110         let span = mk_sp(item.span.lo, item.span.hi - BytePos(1));
 111
 112         match item.node {
 113             ast::ForeignItemKind::Fn(ref fn_decl, ref generics) => {
 114                 let indent = self.block_indent;
 115                 let rewrite = rewrite_fn_base(&self.get_context(),
 116                                               indent,
 117                                               item.ident,
 118                                               fn_decl,
 119                                               generics,
 120                                               ast::Unsafety::Normal,
 121                                               ast::Constness::NotConst,
 122                                               // These are not actually rust functions,
 123                                               // but we format them as such.
 124                                               abi::Abi::Rust,
 125                                               &item.vis,
 126                                               span,
 127                                               false,
 128                                               false);
 129
 130                 match rewrite {
 131                     Some((new_fn, _)) => {
 132                         self.buffer.push_str(&new_fn);
 133                         self.buffer.push_str(";");
 134                     }
 135                     None => self.format_missing(item.span.hi),
 136                 }
 137             }
 138             ast::ForeignItemKind::Static(ref ty, is_mutable) => {
 139                 // FIXME(#21): we're dropping potential comments in between the
 140                 // function keywords here.
 141                 let vis = format_visibility(&item.vis);
 142                 let mut_str = if is_mutable {
 143                     "mut "
 144                 } else {
 145                     ""
 146                 };
 147                 let prefix = format!("{}static {}{}: ", vis, mut_str, item.ident);
 148                 let offset = self.block_indent + prefix.len();
 149                 // 1 = ;
 150                 let width = self.config.max_width - offset.width() - 1;
 151                 let rewrite = ty.rewrite(&self.get_context(), width, offset);
 152
 153                 match rewrite {
 154                     Some(result) => {
 155                         self.buffer.push_str(&prefix);
 156                         self.buffer.push_str(&result);
 157                         self.buffer.push_str(";");
 158                     }
 159                     None => self.format_missing(item.span.hi),
 160                 }
 161             }
 162         }
 163
 164         self.last_pos = item.span.hi;
 165     }
 166
 167     pub fn rewrite_fn(&mut self,
 168                       indent: Indent,
 169                       ident: ast::Ident,
 170                       fd: &ast::FnDecl,
 171                       generics: &ast::Generics,
 172                       unsafety: ast::Unsafety,
 173                       constness: ast::Constness,
 174                       abi: abi::Abi,
 175                       vis: &ast::Visibility,
 176                       span: Span,
 177                       block: &ast::Block)
 178                       -> Option<String> {
 179         let mut newline_brace = newline_for_brace(self.config, &generics.where_clause);
 180         let context = self.get_context();
 181
 182         let block_snippet = self.snippet(codemap::mk_sp(block.span.lo, block.span.hi));
 183         let has_body = !block_snippet[1..block_snippet.len() - 1].trim().is_empty() ||
 184                        !context.config.fn_empty_single_line;
 185
 186         let (mut result, force_newline_brace) = try_opt!(rewrite_fn_base(&context,
 187                                                                          indent,
 188                                                                          ident,
 189                                                                          fd,
 190                                                                          generics,
 191                                                                          unsafety,
 192                                                                          constness,
 193                                                                          abi,
 194                                                                          vis,
 195                                                                          span,
 196                                                                          newline_brace,
 197                                                                          has_body));
 198
 199         if self.config.fn_brace_style != BraceStyle::AlwaysNextLine && !result.contains('\n') {
 200             newline_brace = false;
 201         } else if force_newline_brace {
 202             newline_brace = true;
 203         }
 204
 205         // Prepare for the function body by possibly adding a newline and
 206         // indent.
 207         // FIXME we'll miss anything between the end of the signature and the
 208         // start of the body, but we need more spans from the compiler to solve
 209         // this.
 210         if newline_brace {
 211             result.push('\n');
 212             result.push_str(&indent.to_string(self.config));
 213         } else {
 214             result.push(' ');
 215         }
 216
 217         self.single_line_fn(&result, block).or_else(|| Some(result))
 218     }
 219
 220     pub fn rewrite_required_fn(&mut self,
 221                                indent: Indent,
 222                                ident: ast::Ident,
 223                                sig: &ast::MethodSig,
 224                                span: Span)
 225                                -> Option<String> {
 226         // Drop semicolon or it will be interpreted as comment.
 227         let span = mk_sp(span.lo, span.hi - BytePos(1));
 228         let context = self.get_context();
 229
 230         let (mut result, _) = try_opt!(rewrite_fn_base(&context,
 231                                                        indent,
 232                                                        ident,
 233                                                        &sig.decl,
 234                                                        &sig.generics,
 235                                                        sig.unsafety,
 236                                                        sig.constness,
 237                                                        sig.abi,
 238                                                        &ast::Visibility::Inherited,
 239                                                        span,
 240                                                        false,
 241                                                        false));
 242
 243         // Re-attach semicolon
 244         result.push(';');
 245
 246         Some(result)
 247     }
 248
 249     fn single_line_fn(&self, fn_str: &str, block: &ast::Block) -> Option<String> {
 250         if fn_str.contains('\n') {
 251             return None;
 252         }
 253
 254         let codemap = self.get_context().codemap;
 255
 256         if self.config.fn_empty_single_line && is_empty_block(block, codemap) &&
 257            self.block_indent.width() + fn_str.len() + 2 <= self.config.max_width {
 258             return Some(format!("{}{{}}", fn_str));
 259         }
 260
 261         if self.config.fn_single_line && is_simple_block_stmt(block, codemap) {
 262             let rewrite = {
 263                 if let Some(ref e) = block.expr {
 264                     let suffix = if semicolon_for_expr(e) {
 265                         ";"
 266                     } else {
 267                         ""
 268                     };
 269
 270                     e.rewrite(&self.get_context(),
 271                                  self.config.max_width - self.block_indent.width(),
 272                                  self.block_indent)
 273                         .map(|s| s + suffix)
 274                         .or_else(|| Some(self.snippet(e.span)))
 275                 } else if let Some(ref stmt) = block.stmts.first() {
 276                     stmt.rewrite(&self.get_context(),
 277                                  self.config.max_width - self.block_indent.width(),
 278                                  self.block_indent)
 279                 } else {
 280                     None
 281                 }
 282             };
 283
 284             if let Some(res) = rewrite {
 285                 let width = self.block_indent.width() + fn_str.len() + res.len() + 4;
 286                 if !res.contains('\n') && width <= self.config.max_width {
 287                     return Some(format!("{}{{ {} }}", fn_str, res));
 288                 }
 289             }
 290         }
 291
 292         None
 293     }
 294
 295     pub fn visit_enum(&mut self,
 296                       ident: ast::Ident,
 297                       vis: &ast::Visibility,
 298                       enum_def: &ast::EnumDef,
 299                       generics: &ast::Generics,
 300                       span: Span) {
 301         self.buffer.push_str(&format_header("enum ", ident, vis));
 302
 303         let enum_snippet = self.snippet(span);
 304         let body_start = span.lo + BytePos(enum_snippet.find_uncommented("{").unwrap() as u32 + 1);
 305         let generics_str = format_generics(&self.get_context(),
 306                                            generics,
 307                                            "{",
 308                                            "{",
 309                                            self.config.item_brace_style,
 310                                            enum_def.variants.is_empty(),
 311                                            self.block_indent,
 312                                            self.block_indent.block_indent(self.config),
 313                                            mk_sp(span.lo, body_start))
 314             .unwrap();
 315         self.buffer.push_str(&generics_str);
 316
 317         self.last_pos = body_start;
 318
 319         self.block_indent = self.block_indent.block_indent(self.config);
 320         let variant_list = self.format_variant_list(enum_def, body_start, span.hi - BytePos(1));
 321         match variant_list {
 322             Some(ref body_str) => self.buffer.push_str(&body_str),
 323             None => self.format_missing(span.hi - BytePos(1)),
 324         }
 325         self.block_indent = self.block_indent.block_unindent(self.config);
 326
 327         if variant_list.is_some() {
 328             self.buffer.push_str(&self.block_indent.to_string(self.config));
 329         }
 330         self.buffer.push_str("}");
 331         self.last_pos = span.hi;
 332     }
 333
 334     // Format the body of an enum definition
 335     fn format_variant_list(&self,
 336                            enum_def: &ast::EnumDef,
 337                            body_lo: BytePos,
 338                            body_hi: BytePos)
 339                            -> Option<String> {
 340         if enum_def.variants.is_empty() {
 341             return None;
 342         }
 343         let mut result = String::with_capacity(1024);
 344         result.push('\n');
 345         let indentation = self.block_indent.to_string(self.config);
 346         result.push_str(&indentation);
 347
 348         let items = itemize_list(self.codemap,
 349                                  enum_def.variants.iter(),
 350                                  "}",
 351                                  |f| {
 352             if !f.node.attrs.is_empty() {
 353                 f.node.attrs[0].span.lo
 354             } else {
 355                 f.span.lo
 356             }
 357         },
 358                                  |f| f.span.hi,
 359                                  |f| self.format_variant(f),
 360                                  body_lo,
 361                                  body_hi);
 362
 363         let budget = self.config.max_width - self.block_indent.width() - 2;
 364         let fmt = ListFormatting {
 365             tactic: DefinitiveListTactic::Vertical,
 366             separator: ",",
 367             trailing_separator: SeparatorTactic::from_bool(self.config.enum_trailing_comma),
 368             indent: self.block_indent,
 369             width: budget,
 370             ends_with_newline: true,
 371             config: self.config,
 372         };
 373
 374         let list = try_opt!(write_list(items, &fmt));
 375         result.push_str(&list);
 376         result.push('\n');
 377         Some(result)
 378     }
 379
 380     // Variant of an enum.
 381     fn format_variant(&self, field: &ast::Variant) -> Option<String> {
 382         if contains_skip(&field.node.attrs) {
 383             let lo = field.node.attrs[0].span.lo;
 384             let span = mk_sp(lo, field.span.hi);
 385             return Some(self.snippet(span));
 386         }
 387
 388         let indent = self.block_indent;
 389         let mut result = try_opt!(field.node
 390             .attrs
 391             .rewrite(&self.get_context(),
 392                      self.config.max_width - indent.width(),
 393                      indent));
 394         if !result.is_empty() {
 395             result.push('\n');
 396             result.push_str(&indent.to_string(self.config));
 397         }
 398
 399         let context = self.get_context();
 400         let variant_body = match field.node.data {
 401             ast::VariantData::Tuple(..) |
 402             ast::VariantData::Struct(..) => {
 403                 // FIXME: Should limit the width, as we have a trailing comma
 404                 format_struct(&context,
 405                               "",
 406                               field.node.name,
 407                               &ast::Visibility::Inherited,
 408                               &field.node.data,
 409                               None,
 410                               field.span,
 411                               indent,
 412                               Some(self.config.struct_variant_width))
 413             }
 414             ast::VariantData::Unit(..) => {
 415                 let tag = if let Some(ref expr) = field.node.disr_expr {
 416                     format!("{} = {}", field.node.name, self.snippet(expr.span))
 417                 } else {
 418                     field.node.name.to_string()
 419                 };
 420
 421                 wrap_str(tag,
 422                          self.config.max_width,
 423                          self.config.max_width - indent.width(),
 424                          indent)
 425             }
 426         };
 427
 428         if let Some(variant_str) = variant_body {
 429             result.push_str(&variant_str);
 430             Some(result)
 431         } else {
 432             None
 433         }
 434     }
 435 }
 436
 437 pub fn format_impl(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 438     if let ast::ItemKind::Impl(unsafety,
 439                                polarity,
 440                                ref generics,
 441                                ref trait_ref,
 442                                ref self_ty,
 443                                ref items) = item.node {
 444         let mut result = String::new();
 445         result.push_str(&*format_visibility(&item.vis));
 446         result.push_str(format_unsafety(unsafety));
 447         result.push_str("impl");
 448
 449         let lo = context.codemap.span_after(item.span, "impl");
 450         let hi = match *trait_ref {
 451             Some(ref tr) => tr.path.span.lo,
 452             None => self_ty.span.lo,
 453         };
 454         let generics_str = try_opt!(rewrite_generics(context,
 455                                                      generics,
 456                                                      offset,
 457                                                      context.config.max_width,
 458                                                      offset + result.len(),
 459                                                      mk_sp(lo, hi)));
 460         result.push_str(&generics_str);
 461
 462         // FIXME might need to linebreak in the impl header, here would be a
 463         // good place.
 464         result.push(' ');
 465         if polarity == ast::ImplPolarity::Negative {
 466             result.push_str("!");
 467         }
 468         if let Some(ref trait_ref) = *trait_ref {
 469             let budget = try_opt!(context.config.max_width.checked_sub(result.len()));
 470             let indent = offset + result.len();
 471             result.push_str(&*try_opt!(trait_ref.rewrite(context, budget, indent)));
 472             result.push_str(" for ");
 473         }
 474
 475         let budget = try_opt!(context.config.max_width.checked_sub(result.len()));
 476         let indent = offset + result.len();
 477         result.push_str(&*try_opt!(self_ty.rewrite(context, budget, indent)));
 478
 479         let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
 480         let where_clause_str = try_opt!(rewrite_where_clause(context,
 481                                                              &generics.where_clause,
 482                                                              context.config,
 483                                                              context.config.item_brace_style,
 484                                                              context.block_indent,
 485                                                              where_budget,
 486                                                              context.config.where_density,
 487                                                              "{",
 488                                                              true,
 489                                                              None));
 490
 491         if try_opt!(is_impl_single_line(context, &items, &result, &where_clause_str, &item)) {
 492             result.push_str(&where_clause_str);
 493             if where_clause_str.contains('\n') {
 494                 let white_space = offset.to_string(context.config);
 495                 result.push_str(&format!("\n{}{{\n{}}}", &white_space, &white_space));
 496             } else {
 497                 result.push_str(" {}");
 498             }
 499             return Some(result);
 500         }
 501
 502         if !where_clause_str.is_empty() && !where_clause_str.contains('\n') {
 503             result.push('\n');
 504             let width = context.block_indent.width() + context.config.tab_spaces - 1;
 505             let where_indent = Indent::new(0, width);
 506             result.push_str(&where_indent.to_string(context.config));
 507         }
 508         result.push_str(&where_clause_str);
 509
 510         match context.config.item_brace_style {
 511             BraceStyle::AlwaysNextLine => result.push('\n'),
 512             BraceStyle::PreferSameLine => result.push(' '),
 513             BraceStyle::SameLineWhere => {
 514                 if !where_clause_str.is_empty() {
 515                     result.push('\n');
 516                     result.push_str(&offset.to_string(context.config));
 517                 } else {
 518                     result.push(' ');
 519                 }
 520             }
 521         }
 522
 523         result.push('{');
 524
 525         let snippet = context.snippet(item.span);
 526         let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 527
 528         if !items.is_empty() || contains_comment(&snippet[open_pos..]) {
 529             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 530             visitor.block_indent = context.block_indent.block_indent(context.config);
 531             visitor.last_pos = item.span.lo + BytePos(open_pos as u32);
 532
 533             for item in items {
 534                 visitor.visit_impl_item(&item);
 535             }
 536
 537             visitor.format_missing(item.span.hi - BytePos(1));
 538
 539             let inner_indent_str = visitor.block_indent.to_string(context.config);
 540             let outer_indent_str = context.block_indent.to_string(context.config);
 541
 542             result.push('\n');
 543             result.push_str(&inner_indent_str);
 544             result.push_str(&trim_newlines(&visitor.buffer.to_string().trim()));
 545             result.push('\n');
 546             result.push_str(&outer_indent_str);
 547         }
 548
 549         if result.chars().last().unwrap() == '{' {
 550             result.push('\n');
 551         }
 552         result.push('}');
 553
 554         Some(result)
 555     } else {
 556         unreachable!();
 557     }
 558 }
 559
 560 fn is_impl_single_line(context: &RewriteContext,
 561                        items: &Vec<ImplItem>,
 562                        result: &str,
 563                        where_clause_str: &str,
 564                        item: &ast::Item)
 565                        -> Option<bool> {
 566     let snippet = context.snippet(item.span);
 567     let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 568
 569     Some(context.config.impl_empty_single_line && items.is_empty() &&
 570          result.len() + where_clause_str.len() <= context.config.max_width &&
 571          !contains_comment(&snippet[open_pos..]))
 572 }
 573
 574 pub fn format_struct(context: &RewriteContext,
 575                      item_name: &str,
 576                      ident: ast::Ident,
 577                      vis: &ast::Visibility,
 578                      struct_def: &ast::VariantData,
 579                      generics: Option<&ast::Generics>,
 580                      span: Span,
 581                      offset: Indent,
 582                      one_line_width: Option<usize>)
 583                      -> Option<String> {
 584     match *struct_def {
 585         ast::VariantData::Unit(..) => Some(format_unit_struct(item_name, ident, vis)),
 586         ast::VariantData::Tuple(ref fields, _) => {
 587             format_tuple_struct(context,
 588                                 item_name,
 589                                 ident,
 590                                 vis,
 591                                 fields,
 592                                 generics,
 593                                 span,
 594                                 offset)
 595         }
 596         ast::VariantData::Struct(ref fields, _) => {
 597             format_struct_struct(context,
 598                                  item_name,
 599                                  ident,
 600                                  vis,
 601                                  fields,
 602                                  generics,
 603                                  span,
 604                                  offset,
 605                                  one_line_width)
 606         }
 607     }
 608 }
 609
 610 pub fn format_trait(context: &RewriteContext, item: &ast::Item, offset: Indent) -> Option<String> {
 611     if let ast::ItemKind::Trait(unsafety, ref generics, ref type_param_bounds, ref trait_items) =
 612            item.node {
 613         let mut result = String::new();
 614         let header = format!("{}{}trait {}",
 615                              format_visibility(&item.vis),
 616                              format_unsafety(unsafety),
 617                              item.ident);
 618
 619         result.push_str(&header);
 620
 621         let body_lo = context.codemap.span_after(item.span, "{");
 622
 623         let generics_str = try_opt!(rewrite_generics(context,
 624                                                      generics,
 625                                                      offset,
 626                                                      context.config.max_width,
 627                                                      offset + result.len(),
 628                                                      mk_sp(item.span.lo, body_lo)));
 629         result.push_str(&generics_str);
 630
 631         let trait_bound_str = try_opt!(rewrite_trait_bounds(context,
 632                                                             type_param_bounds,
 633                                                             offset,
 634                                                             context.config.max_width));
 635         // If the trait, generics, and trait bound cannot fit on the same line,
 636         // put the trait bounds on an indented new line
 637         if offset.width() + last_line_width(&result) + trait_bound_str.len() >
 638            context.config.ideal_width {
 639             result.push('\n');
 640             let width = context.block_indent.width() + context.config.tab_spaces;
 641             let trait_indent = Indent::new(0, width);
 642             result.push_str(&trait_indent.to_string(context.config));
 643         }
 644         result.push_str(&trait_bound_str);
 645
 646         let has_body = !trait_items.is_empty();
 647
 648         let where_density =
 649             if (context.config.where_density == Density::Compressed &&
 650                 (!result.contains('\n') ||
 651                  context.config.fn_args_layout == FnArgLayoutStyle::Block)) ||
 652                (context.config.fn_args_layout == FnArgLayoutStyle::Block && result.is_empty()) ||
 653                (context.config.where_density == Density::CompressedIfEmpty && !has_body &&
 654                 !result.contains('\n')) {
 655                 Density::Compressed
 656             } else {
 657                 Density::Tall
 658             };
 659
 660         let where_budget = try_opt!(context.config
 661             .max_width
 662             .checked_sub(last_line_width(&result)));
 663         let where_clause_str = try_opt!(rewrite_where_clause(context,
 664                                                              &generics.where_clause,
 665                                                              context.config,
 666                                                              context.config.item_brace_style,
 667                                                              context.block_indent,
 668                                                              where_budget,
 669                                                              where_density,
 670                                                              "{",
 671                                                              has_body,
 672                                                              None));
 673         // If the where clause cannot fit on the same line,
 674         // put the where clause on a new line
 675         if !where_clause_str.contains('\n') &&
 676            last_line_width(&result) + where_clause_str.len() + offset.width() >
 677            context.config.ideal_width {
 678             result.push('\n');
 679             let width = context.block_indent.width() + context.config.tab_spaces - 1;
 680             let where_indent = Indent::new(0, width);
 681             result.push_str(&where_indent.to_string(context.config));
 682         }
 683         result.push_str(&where_clause_str);
 684
 685         match context.config.item_brace_style {
 686             BraceStyle::AlwaysNextLine => {
 687                 result.push('\n');
 688                 result.push_str(&offset.to_string(context.config));
 689             }
 690             BraceStyle::PreferSameLine => result.push(' '),
 691             BraceStyle::SameLineWhere => {
 692                 if !where_clause_str.is_empty() &&
 693                    (trait_items.len() > 0 || result.contains('\n')) {
 694                     result.push('\n');
 695                     result.push_str(&offset.to_string(context.config));
 696                 } else {
 697                     result.push(' ');
 698                 }
 699             }
 700         }
 701         result.push('{');
 702
 703         let snippet = context.snippet(item.span);
 704         let open_pos = try_opt!(snippet.find_uncommented("{")) + 1;
 705
 706         if !trait_items.is_empty() || contains_comment(&snippet[open_pos..]) {
 707             let mut visitor = FmtVisitor::from_codemap(context.parse_session, context.config);
 708             visitor.block_indent = context.block_indent.block_indent(context.config);
 709             visitor.last_pos = item.span.lo + BytePos(open_pos as u32);
 710
 711             for item in trait_items {
 712                 visitor.visit_trait_item(&item);
 713             }
 714
 715             visitor.format_missing(item.span.hi - BytePos(1));
 716
 717             let inner_indent_str = visitor.block_indent.to_string(context.config);
 718             let outer_indent_str = context.block_indent.to_string(context.config);
 719
 720             result.push('\n');
 721             result.push_str(&inner_indent_str);
 722             result.push_str(&trim_newlines(&visitor.buffer.to_string().trim()));
 723             result.push('\n');
 724             result.push_str(&outer_indent_str);
 725         } else if result.contains('\n') {
 726             result.push('\n');
 727         }
 728
 729         result.push('}');
 730         Some(result)
 731     } else {
 732         unreachable!();
 733     }
 734 }
 735
 736 fn format_unit_struct(item_name: &str, ident: ast::Ident, vis: &ast::Visibility) -> String {
 737     format!("{};", format_header(item_name, ident, vis))
 738 }
 739
 740 fn format_struct_struct(context: &RewriteContext,
 741                         item_name: &str,
 742                         ident: ast::Ident,
 743                         vis: &ast::Visibility,
 744                         fields: &[ast::StructField],
 745                         generics: Option<&ast::Generics>,
 746                         span: Span,
 747                         offset: Indent,
 748                         one_line_width: Option<usize>)
 749                         -> Option<String> {
 750     let mut result = String::with_capacity(1024);
 751
 752     let header_str = format_header(item_name, ident, vis);
 753     result.push_str(&header_str);
 754
 755     let body_lo = context.codemap.span_after(span, "{");
 756
 757     let generics_str = match generics {
 758         Some(g) => {
 759             try_opt!(format_generics(context,
 760                                      g,
 761                                      "{",
 762                                      "{",
 763                                      context.config.item_brace_style,
 764                                      fields.is_empty(),
 765                                      offset,
 766                                      offset + header_str.len(),
 767                                      mk_sp(span.lo, body_lo)))
 768         }
 769         None => {
 770             if context.config.item_brace_style == BraceStyle::AlwaysNextLine && !fields.is_empty() {
 771                 format!("\n{}{{", context.block_indent.to_string(context.config))
 772             } else {
 773                 " {".to_owned()
 774             }
 775         }
 776     };
 777     result.push_str(&generics_str);
 778
 779     // FIXME(#919): properly format empty structs and their comments.
 780     if fields.is_empty() {
 781         result.push_str(&context.snippet(mk_sp(body_lo, span.hi)));
 782         return Some(result);
 783     }
 784
 785     let item_indent = offset.block_indent(context.config);
 786     // 1 = ","
 787     let item_budget = try_opt!(context.config.max_width.checked_sub(item_indent.width() + 1));
 788
 789     let items = itemize_list(context.codemap,
 790                              fields.iter(),
 791                              "}",
 792                              |field| {
 793         // Include attributes and doc comments, if present
 794         if !field.attrs.is_empty() {
 795             field.attrs[0].span.lo
 796         } else {
 797             field.span.lo
 798         }
 799     },
 800                              |field| field.ty.span.hi,
 801                              |field| field.rewrite(context, item_budget, item_indent),
 802                              context.codemap.span_after(span, "{"),
 803                              span.hi)
 804         .collect::<Vec<_>>();
 805     // 1 = ,
 806     let budget = context.config.max_width - offset.width() + context.config.tab_spaces - 1;
 807
 808     let tactic = match one_line_width {
 809         Some(w) => definitive_tactic(&items, ListTactic::LimitedHorizontalVertical(w), budget),
 810         None => DefinitiveListTactic::Vertical,
 811     };
 812
 813     let fmt = ListFormatting {
 814         tactic: tactic,
 815         separator: ",",
 816         trailing_separator: context.config.struct_trailing_comma,
 817         indent: item_indent,
 818         width: budget,
 819         ends_with_newline: true,
 820         config: context.config,
 821     };
 822     let items_str = try_opt!(write_list(&items, &fmt));
 823     if one_line_width.is_some() && !items_str.contains('\n') {
 824         Some(format!("{} {} }}", result, items_str))
 825     } else {
 826         Some(format!("{}\n{}{}\n{}}}",
 827                      result,
 828                      offset.block_indent(context.config).to_string(context.config),
 829                      items_str,
 830                      offset.to_string(context.config)))
 831     }
 832 }
 833
 834 fn format_tuple_struct(context: &RewriteContext,
 835                        item_name: &str,
 836                        ident: ast::Ident,
 837                        vis: &ast::Visibility,
 838                        fields: &[ast::StructField],
 839                        generics: Option<&ast::Generics>,
 840                        span: Span,
 841                        offset: Indent)
 842                        -> Option<String> {
 843     let mut result = String::with_capacity(1024);
 844
 845     let header_str = format_header(item_name, ident, vis);
 846     result.push_str(&header_str);
 847
 848     // FIXME(#919): don't lose comments on empty tuple structs.
 849     let body_lo = if fields.is_empty() {
 850         span.hi
 851     } else {
 852         fields[0].span.lo
 853     };
 854
 855     let where_clause_str = match generics {
 856         Some(ref generics) => {
 857             let generics_str = try_opt!(rewrite_generics(context,
 858                                                          generics,
 859                                                          offset,
 860                                                          context.config.max_width,
 861                                                          offset + header_str.len(),
 862                                                          mk_sp(span.lo, body_lo)));
 863             result.push_str(&generics_str);
 864
 865             let where_budget = try_opt!(context.config
 866                 .max_width
 867                 .checked_sub(last_line_width(&result)));
 868             try_opt!(rewrite_where_clause(context,
 869                                           &generics.where_clause,
 870                                           context.config,
 871                                           context.config.item_brace_style,
 872                                           context.block_indent,
 873                                           where_budget,
 874                                           Density::Compressed,
 875                                           ";",
 876                                           false,
 877                                           None))
 878         }
 879         None => "".to_owned(),
 880     };
 881     result.push('(');
 882
 883     let item_indent = context.block_indent + result.len();
 884     // 2 = ");"
 885     let item_budget = try_opt!(context.config.max_width.checked_sub(item_indent.width() + 2));
 886
 887     let items = itemize_list(context.codemap,
 888                              fields.iter(),
 889                              ")",
 890                              |field| {
 891         // Include attributes and doc comments, if present
 892         if !field.attrs.is_empty() {
 893             field.attrs[0].span.lo
 894         } else {
 895             field.span.lo
 896         }
 897     },
 898                              |field| field.ty.span.hi,
 899                              |field| field.rewrite(context, item_budget, item_indent),
 900                              context.codemap.span_after(span, "("),
 901                              span.hi);
 902     let body = try_opt!(format_item_list(items, item_budget, item_indent, context.config));
 903     result.push_str(&body);
 904     result.push(')');
 905
 906     if !where_clause_str.is_empty() && !where_clause_str.contains('\n') &&
 907        (result.contains('\n') ||
 908         context.block_indent.width() + result.len() + where_clause_str.len() + 1 >
 909         context.config.max_width) {
 910         // We need to put the where clause on a new line, but we didn'to_string
 911         // know that earlier, so the where clause will not be indented properly.
 912         result.push('\n');
 913         result.push_str(&(context.block_indent + (context.config.tab_spaces - 1))
 914             .to_string(context.config));
 915     }
 916     result.push_str(&where_clause_str);
 917
 918     Some(result)
 919 }
 920
 921 pub fn rewrite_type_alias(context: &RewriteContext,
 922                           indent: Indent,
 923                           ident: ast::Ident,
 924                           ty: &ast::Ty,
 925                           generics: &ast::Generics,
 926                           vis: &ast::Visibility,
 927                           span: Span)
 928                           -> Option<String> {
 929     let mut result = String::new();
 930
 931     result.push_str(&format_visibility(&vis));
 932     result.push_str("type ");
 933     result.push_str(&ident.to_string());
 934
 935     let generics_indent = indent + result.len();
 936     let generics_span = mk_sp(context.codemap.span_after(span, "type"), ty.span.lo);
 937     let generics_width = context.config.max_width - " =".len();
 938     let generics_str = try_opt!(rewrite_generics(context,
 939                                                  generics,
 940                                                  indent,
 941                                                  generics_width,
 942                                                  generics_indent,
 943                                                  generics_span));
 944
 945     result.push_str(&generics_str);
 946
 947     let where_budget = try_opt!(context.config
 948         .max_width
 949         .checked_sub(last_line_width(&result)));
 950     let where_clause_str = try_opt!(rewrite_where_clause(context,
 951                                                          &generics.where_clause,
 952                                                          context.config,
 953                                                          context.config.item_brace_style,
 954                                                          indent,
 955                                                          where_budget,
 956                                                          context.config.where_density,
 957                                                          "=",
 958                                                          false,
 959                                                          Some(span.hi)));
 960     result.push_str(&where_clause_str);
 961     result.push_str(" = ");
 962
 963     let line_width = last_line_width(&result);
 964     // This checked_sub may fail as the extra space after '=' is not taken into account
 965     // In that case the budget is set to 0 which will make ty.rewrite retry on a new line
 966     let budget = context.config
 967         .max_width
 968         .checked_sub(indent.width() + line_width + ";".len())
 969         .unwrap_or(0);
 970     let type_indent = indent + line_width;
 971     // Try to fit the type on the same line
 972     let ty_str = try_opt!(ty.rewrite(context, budget, type_indent)
 973         .or_else(|| {
 974             // The line was too short, try to put the type on the next line
 975
 976             // Remove the space after '='
 977             result.pop();
 978             let type_indent = indent.block_indent(context.config);
 979             result.push('\n');
 980             result.push_str(&type_indent.to_string(context.config));
 981             let budget = try_opt!(context.config
 982                 .max_width
 983                 .checked_sub(type_indent.width() + ";".len()));
 984             ty.rewrite(context, budget, type_indent)
 985         }));
 986     result.push_str(&ty_str);
 987     result.push_str(";");
 988     Some(result)
 989 }
 990
 991 impl Rewrite for ast::StructField {
 992     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
 993         if contains_skip(&self.attrs) {
 994             let span = context.snippet(mk_sp(self.attrs[0].span.lo, self.span.hi));
 995             return wrap_str(span, context.config.max_width, width, offset);
 996         }
 997
 998         let name = self.ident;
 999         let vis = format_visibility(&self.vis);
1000         let mut attr_str = try_opt!(self.attrs
1001             .rewrite(context, context.config.max_width - offset.width(), offset));
1002         if !attr_str.is_empty() {
1003             attr_str.push('\n');
1004             attr_str.push_str(&offset.to_string(context.config));
1005         }
1006
1007         let result = match name {
1008             Some(name) => format!("{}{}{}: ", attr_str, vis, name),
1009             None => format!("{}{}", attr_str, vis),
1010         };
1011
1012         let last_line_width = last_line_width(&result);
1013         let budget = try_opt!(width.checked_sub(last_line_width));
1014         let rewrite = try_opt!(self.ty.rewrite(context, budget, offset + last_line_width));
1015         Some(result + &rewrite)
1016     }
1017 }
1018
1019 pub fn rewrite_static(prefix: &str,
1020                       vis: &ast::Visibility,
1021                       ident: ast::Ident,
1022                       ty: &ast::Ty,
1023                       mutability: ast::Mutability,
1024                       expr_opt: Option<&ptr::P<ast::Expr>>,
1025                       context: &RewriteContext)
1026                       -> Option<String> {
1027     let prefix = format!("{}{} {}{}: ",
1028                          format_visibility(vis),
1029                          prefix,
1030                          format_mutability(mutability),
1031                          ident);
1032     // 2 = " =".len()
1033     let ty_str = try_opt!(ty.rewrite(context,
1034                                      context.config.max_width - context.block_indent.width() -
1035                                      prefix.len() - 2,
1036                                      context.block_indent));
1037
1038     if let Some(ref expr) = expr_opt {
1039         let lhs = format!("{}{} =", prefix, ty_str);
1040         // 1 = ;
1041         let remaining_width = context.config.max_width - context.block_indent.width() - 1;
1042         rewrite_assign_rhs(context, lhs, expr, remaining_width, context.block_indent)
1043             .map(|s| s + ";")
1044     } else {
1045         let lhs = format!("{}{};", prefix, ty_str);
1046         Some(lhs)
1047     }
1048 }
1049
1050 pub fn rewrite_associated_type(ident: ast::Ident,
1051                                ty_opt: Option<&ptr::P<ast::Ty>>,
1052                                ty_param_bounds_opt: Option<&ast::TyParamBounds>,
1053                                context: &RewriteContext,
1054                                indent: Indent)
1055                                -> Option<String> {
1056     let prefix = format!("type {}", ident);
1057
1058     let type_bounds_str = if let Some(ty_param_bounds) = ty_param_bounds_opt {
1059         let bounds: &[_] = &ty_param_bounds;
1060         let bound_str = bounds.iter()
1061             .filter_map(|ty_bound| ty_bound.rewrite(context, context.config.max_width, indent))
1062             .collect::<Vec<String>>()
1063             .join(" + ");
1064         if bounds.len() > 0 {
1065             format!(": {}", bound_str)
1066         } else {
1067             String::new()
1068         }
1069     } else {
1070         String::new()
1071     };
1072
1073     if let Some(ty) = ty_opt {
1074         let ty_str = try_opt!(ty.rewrite(context,
1075                                          context.config.max_width - context.block_indent.width() -
1076                                          prefix.len() -
1077                                          2,
1078                                          context.block_indent));
1079         Some(format!("{} = {};", prefix, ty_str))
1080     } else {
1081         Some(format!("{}{};", prefix, type_bounds_str))
1082     }
1083 }
1084
1085 impl Rewrite for ast::FunctionRetTy {
1086     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
1087         match *self {
1088             ast::FunctionRetTy::Default(_) => Some(String::new()),
1089             ast::FunctionRetTy::None(_) => {
1090                 if width >= 4 {
1091                     Some("-> !".to_owned())
1092                 } else {
1093                     None
1094                 }
1095             }
1096             ast::FunctionRetTy::Ty(ref ty) => {
1097                 let inner_width = try_opt!(width.checked_sub(3));
1098                 ty.rewrite(context, inner_width, offset + 3).map(|r| format!("-> {}", r))
1099             }
1100         }
1101     }
1102 }
1103
1104 impl Rewrite for ast::Arg {
1105     fn rewrite(&self, context: &RewriteContext, width: usize, offset: Indent) -> Option<String> {
1106         if is_named_arg(self) {
1107             let mut result = try_opt!(self.pat.rewrite(context, width, offset));
1108
1109             if self.ty.node != ast::TyKind::Infer {
1110                 result.push_str(": ");
1111                 let max_width = try_opt!(width.checked_sub(result.len()));
1112                 let ty_str = try_opt!(self.ty.rewrite(context, max_width, offset + result.len()));
1113                 result.push_str(&ty_str);
1114             }
1115
1116             Some(result)
1117         } else {
1118             self.ty.rewrite(context, width, offset)
1119         }
1120     }
1121 }
1122
1123 fn rewrite_explicit_self(explicit_self: &ast::ExplicitSelf,
1124                          args: &[ast::Arg],
1125                          context: &RewriteContext)
1126                          -> Option<String> {
1127     match explicit_self.node {
1128         ast::SelfKind::Region(lt, m) => {
1129             let mut_str = format_mutability(m);
1130             match lt {
1131                 Some(ref l) => {
1132                     let lifetime_str =
1133                         try_opt!(l.rewrite(context, usize::max_value(), Indent::empty()));
1134                     Some(format!("&{} {}self", lifetime_str, mut_str))
1135                 }
1136                 None => Some(format!("&{}self", mut_str)),
1137             }
1138         }
1139         ast::SelfKind::Explicit(ref ty, _) => {
1140             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1141
1142             let mutability = explicit_self_mutability(&args[0]);
1143             let type_str = try_opt!(ty.rewrite(context, usize::max_value(), Indent::empty()));
1144
1145             Some(format!("{}self: {}", format_mutability(mutability), type_str))
1146         }
1147         ast::SelfKind::Value(_) => {
1148             assert!(!args.is_empty(), "&[ast::Arg] shouldn't be empty.");
1149
1150             let mutability = explicit_self_mutability(&args[0]);
1151
1152             Some(format!("{}self", format_mutability(mutability)))
1153         }
1154     }
1155 }
1156
1157 // Hacky solution caused by absence of `Mutability` in `SelfValue` and
1158 // `SelfExplicit` variants of `ast::ExplicitSelf_`.
1159 fn explicit_self_mutability(arg: &ast::Arg) -> ast::Mutability {
1160     if let ast::PatKind::Ident(ast::BindingMode::ByValue(mutability), _, _) = arg.pat.node {
1161         mutability
1162     } else {
1163         unreachable!()
1164     }
1165 }
1166
1167 pub fn span_lo_for_arg(arg: &ast::Arg) -> BytePos {
1168     if is_named_arg(arg) {
1169         arg.pat.span.lo
1170     } else {
1171         arg.ty.span.lo
1172     }
1173 }
1174
1175 pub fn span_hi_for_arg(arg: &ast::Arg) -> BytePos {
1176     match arg.ty.node {
1177         ast::TyKind::Infer if is_named_arg(arg) => arg.pat.span.hi,
1178         _ => arg.ty.span.hi,
1179     }
1180 }
1181
1182 pub fn is_named_arg(arg: &ast::Arg) -> bool {
1183     if let ast::PatKind::Ident(_, ident, _) = arg.pat.node {
1184         ident.node != token::keywords::Invalid.ident()
1185     } else {
1186         true
1187     }
1188 }
1189
1190 fn span_for_return(ret: &ast::FunctionRetTy) -> Span {
1191     match *ret {
1192         ast::FunctionRetTy::None(ref span) |
1193         ast::FunctionRetTy::Default(ref span) => span.clone(),
1194         ast::FunctionRetTy::Ty(ref ty) => ty.span,
1195     }
1196 }
1197
1198 fn span_for_ty_param(ty: &ast::TyParam) -> Span {
1199     // Note that ty.span is the span for ty.ident, not the whole item.
1200     let lo = ty.span.lo;
1201     if let Some(ref def) = ty.default {
1202         return mk_sp(lo, def.span.hi);
1203     }
1204     if ty.bounds.is_empty() {
1205         return ty.span;
1206     }
1207     let hi = match ty.bounds[ty.bounds.len() - 1] {
1208         ast::TyParamBound::TraitTyParamBound(ref ptr, _) => ptr.span.hi,
1209         ast::TyParamBound::RegionTyParamBound(ref l) => l.span.hi,
1210     };
1211     mk_sp(lo, hi)
1212 }
1213
1214 fn span_for_where_pred(pred: &ast::WherePredicate) -> Span {
1215     match *pred {
1216         ast::WherePredicate::BoundPredicate(ref p) => p.span,
1217         ast::WherePredicate::RegionPredicate(ref p) => p.span,
1218         ast::WherePredicate::EqPredicate(ref p) => p.span,
1219     }
1220 }
1221
1222 // Return type is (result, force_new_line_for_brace)
1223 fn rewrite_fn_base(context: &RewriteContext,
1224                    indent: Indent,
1225                    ident: ast::Ident,
1226                    fd: &ast::FnDecl,
1227                    generics: &ast::Generics,
1228                    unsafety: ast::Unsafety,
1229                    constness: ast::Constness,
1230                    abi: abi::Abi,
1231                    vis: &ast::Visibility,
1232                    span: Span,
1233                    newline_brace: bool,
1234                    has_body: bool)
1235                    -> Option<(String, bool)> {
1236     let mut force_new_line_for_brace = false;
1237     // FIXME we'll lose any comments in between parts of the function decl, but
1238     // anyone who comments there probably deserves what they get.
1239
1240     let where_clause = &generics.where_clause;
1241
1242     let mut result = String::with_capacity(1024);
1243     // Vis unsafety abi.
1244     result.push_str(&*format_visibility(vis));
1245
1246     if let ast::Constness::Const = constness {
1247         result.push_str("const ");
1248     }
1249
1250     result.push_str(::utils::format_unsafety(unsafety));
1251
1252     if abi != abi::Abi::Rust {
1253         result.push_str(&::utils::format_abi(abi, context.config.force_explicit_abi));
1254     }
1255
1256     // fn foo
1257     result.push_str("fn ");
1258     result.push_str(&ident.to_string());
1259
1260     // Generics.
1261     let generics_indent = indent + result.len();
1262     let generics_span = mk_sp(span.lo, span_for_return(&fd.output).lo);
1263     let generics_str = try_opt!(rewrite_generics(context,
1264                                                  generics,
1265                                                  indent,
1266                                                  context.config.max_width,
1267                                                  generics_indent,
1268                                                  generics_span));
1269     result.push_str(&generics_str);
1270
1271     // Note that if the width and indent really matter, we'll re-layout the
1272     // return type later anyway.
1273     let ret_str = try_opt!(fd.output
1274         .rewrite(&context, context.config.max_width - indent.width(), indent));
1275
1276     let multi_line_ret_str = ret_str.contains('\n');
1277     let ret_str_len = if multi_line_ret_str {
1278         0
1279     } else {
1280         ret_str.len()
1281     };
1282
1283     // Args.
1284     let (mut one_line_budget, mut multi_line_budget, mut arg_indent) =
1285         try_opt!(compute_budgets_for_args(context, &result, indent, ret_str_len, newline_brace));
1286
1287     if context.config.fn_args_layout == FnArgLayoutStyle::Block ||
1288        context.config.fn_args_layout == FnArgLayoutStyle::BlockAlways {
1289         arg_indent = indent.block_indent(context.config);
1290         multi_line_budget = context.config.max_width - arg_indent.width();
1291     }
1292
1293     debug!("rewrite_fn: one_line_budget: {}, multi_line_budget: {}, arg_indent: {:?}",
1294            one_line_budget,
1295            multi_line_budget,
1296            arg_indent);
1297
1298     // Check if vertical layout was forced by compute_budget_for_args.
1299     if one_line_budget == 0 {
1300         if context.config.fn_args_paren_newline {
1301             result.push('\n');
1302             result.push_str(&arg_indent.to_string(context.config));
1303             arg_indent = arg_indent + 1; // extra space for `(`
1304             result.push('(');
1305         } else {
1306             result.push_str("(\n");
1307             result.push_str(&arg_indent.to_string(context.config));
1308         }
1309     } else {
1310         result.push('(');
1311     }
1312
1313     if multi_line_ret_str {
1314         one_line_budget = 0;
1315     }
1316
1317     // A conservative estimation, to goal is to be over all parens in generics
1318     let args_start = generics.ty_params
1319         .last()
1320         .map_or(span.lo, |tp| end_typaram(tp));
1321     let args_span = mk_sp(context.codemap.span_after(mk_sp(args_start, span.hi), "("),
1322                           span_for_return(&fd.output).lo);
1323     let arg_str = try_opt!(rewrite_args(context,
1324                                         &fd.inputs,
1325                                         fd.get_self().as_ref(),
1326                                         one_line_budget,
1327                                         multi_line_budget,
1328                                         indent,
1329                                         arg_indent,
1330                                         args_span,
1331                                         fd.variadic));
1332
1333     let multi_line_arg_str = arg_str.contains('\n');
1334
1335     let put_args_in_block = match context.config.fn_args_layout {
1336         FnArgLayoutStyle::Block => multi_line_arg_str,
1337         FnArgLayoutStyle::BlockAlways => true,
1338         _ => false,
1339     } && fd.inputs.len() > 0;
1340
1341     if put_args_in_block {
1342         arg_indent = indent.block_indent(context.config);
1343         result.push('\n');
1344         result.push_str(&arg_indent.to_string(context.config));
1345         result.push_str(&arg_str);
1346         result.push('\n');
1347         result.push_str(&indent.to_string(context.config));
1348         result.push(')');
1349     } else {
1350         result.push_str(&arg_str);
1351         result.push(')');
1352     }
1353
1354     // Return type.
1355     if !ret_str.is_empty() {
1356         let ret_should_indent = match context.config.fn_args_layout {
1357             // If our args are block layout then we surely must have space.
1358             FnArgLayoutStyle::Block if put_args_in_block => false,
1359             FnArgLayoutStyle::BlockAlways => false,
1360             _ => {
1361                 // If we've already gone multi-line, or the return type would push
1362                 // over the max width, then put the return type on a new line.
1363                 result.contains("\n") || multi_line_ret_str ||
1364                 result.len() + indent.width() + ret_str_len > context.config.max_width
1365             }
1366         };
1367         let ret_indent = if ret_should_indent {
1368             let indent = match context.config.fn_return_indent {
1369                 ReturnIndent::WithWhereClause => indent + 4,
1370                 // Aligning with non-existent args looks silly.
1371                 _ if arg_str.is_empty() => {
1372                     force_new_line_for_brace = true;
1373                     indent + 4
1374                 }
1375                 // FIXME: we might want to check that using the arg indent
1376                 // doesn't blow our budget, and if it does, then fallback to
1377                 // the where clause indent.
1378                 _ => arg_indent,
1379             };
1380
1381             result.push('\n');
1382             result.push_str(&indent.to_string(context.config));
1383             indent
1384         } else {
1385             result.push(' ');
1386             Indent::new(indent.width(), result.len())
1387         };
1388
1389         if multi_line_ret_str {
1390             // Now that we know the proper indent and width, we need to
1391             // re-layout the return type.
1392
1393             let budget = try_opt!(context.config.max_width.checked_sub(ret_indent.width()));
1394             let ret_str = try_opt!(fd.output
1395                 .rewrite(context, budget, ret_indent));
1396             result.push_str(&ret_str);
1397         } else {
1398             result.push_str(&ret_str);
1399         }
1400
1401         // Comment between return type and the end of the decl.
1402         let snippet_lo = fd.output.span().hi;
1403         if where_clause.predicates.is_empty() {
1404             let snippet_hi = span.hi;
1405             let snippet = context.snippet(mk_sp(snippet_lo, snippet_hi));
1406             let snippet = snippet.trim();
1407             if !snippet.is_empty() {
1408                 result.push(' ');
1409                 result.push_str(snippet);
1410             }
1411         } else {
1412             // FIXME it would be nice to catch comments between the return type
1413             // and the where clause, but we don't have a span for the where
1414             // clause.
1415         }
1416     }
1417
1418     let should_compress_where = match context.config.where_density {
1419         Density::Compressed => !result.contains('\n') || put_args_in_block,
1420         Density::CompressedIfEmpty => !has_body && !result.contains('\n'),
1421         _ => false,
1422     } || (put_args_in_block && ret_str.is_empty());
1423
1424     let where_density = if should_compress_where {
1425         Density::Compressed
1426     } else {
1427         Density::Tall
1428     };
1429
1430     // Where clause.
1431     let where_budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
1432     let where_clause_str = try_opt!(rewrite_where_clause(context,
1433                                                          where_clause,
1434                                                          context.config,
1435                                                          context.config.fn_brace_style,
1436                                                          indent,
1437                                                          where_budget,
1438                                                          where_density,
1439                                                          "{",
1440                                                          has_body,
1441                                                          Some(span.hi)));
1442
1443     if last_line_width(&result) + where_clause_str.len() > context.config.max_width &&
1444        !where_clause_str.contains('\n') {
1445         result.push('\n');
1446     }
1447
1448     result.push_str(&where_clause_str);
1449
1450     Some((result, force_new_line_for_brace))
1451 }
1452
1453 fn rewrite_args(context: &RewriteContext,
1454                 args: &[ast::Arg],
1455                 explicit_self: Option<&ast::ExplicitSelf>,
1456                 one_line_budget: usize,
1457                 multi_line_budget: usize,
1458                 indent: Indent,
1459                 arg_indent: Indent,
1460                 span: Span,
1461                 variadic: bool)
1462                 -> Option<String> {
1463     let mut arg_item_strs = try_opt!(args.iter()
1464         .map(|arg| arg.rewrite(&context, multi_line_budget, arg_indent))
1465         .collect::<Option<Vec<_>>>());
1466
1467     // Account for sugary self.
1468     // FIXME: the comment for the self argument is dropped. This is blocked
1469     // on rust issue #27522.
1470     let min_args =
1471         explicit_self.and_then(|explicit_self| rewrite_explicit_self(explicit_self, args, context))
1472             .map_or(1, |self_str| {
1473                 arg_item_strs[0] = self_str;
1474                 2
1475             });
1476
1477     // Comments between args.
1478     let mut arg_items = Vec::new();
1479     if min_args == 2 {
1480         arg_items.push(ListItem::from_str(""));
1481     }
1482
1483     // FIXME(#21): if there are no args, there might still be a comment, but
1484     // without spans for the comment or parens, there is no chance of
1485     // getting it right. You also don't get to put a comment on self, unless
1486     // it is explicit.
1487     if args.len() >= min_args || variadic {
1488         let comment_span_start = if min_args == 2 {
1489             let second_arg_start = if arg_has_pattern(&args[1]) {
1490                 args[1].pat.span.lo
1491             } else {
1492                 args[1].ty.span.lo
1493             };
1494             let reduced_span = mk_sp(span.lo, second_arg_start);
1495
1496             context.codemap.span_after_last(reduced_span, ",")
1497         } else {
1498             span.lo
1499         };
1500
1501         enum ArgumentKind<'a> {
1502             Regular(&'a ast::Arg),
1503             Variadic(BytePos),
1504         }
1505
1506         let variadic_arg = if variadic {
1507             let variadic_span = mk_sp(args.last().unwrap().ty.span.hi, span.hi);
1508             let variadic_start = context.codemap.span_after(variadic_span, "...") - BytePos(3);
1509             Some(ArgumentKind::Variadic(variadic_start))
1510         } else {
1511             None
1512         };
1513
1514         let more_items = itemize_list(context.codemap,
1515                                       args[min_args - 1..]
1516                                           .iter()
1517                                           .map(ArgumentKind::Regular)
1518                                           .chain(variadic_arg),
1519                                       ")",
1520                                       |arg| {
1521                                           match *arg {
1522                                               ArgumentKind::Regular(arg) => span_lo_for_arg(arg),
1523                                               ArgumentKind::Variadic(start) => start,
1524                                           }
1525                                       },
1526                                       |arg| {
1527                                           match *arg {
1528                                               ArgumentKind::Regular(arg) => arg.ty.span.hi,
1529                                               ArgumentKind::Variadic(start) => start + BytePos(3),
1530                                           }
1531                                       },
1532                                       |arg| {
1533                                           match *arg {
1534                                               ArgumentKind::Regular(..) => None,
1535                                               ArgumentKind::Variadic(..) => Some("...".to_owned()),
1536                                           }
1537                                       },
1538                                       comment_span_start,
1539                                       span.hi);
1540
1541         arg_items.extend(more_items);
1542     }
1543
1544     for (item, arg) in arg_items.iter_mut().zip(arg_item_strs) {
1545         item.item = Some(arg);
1546     }
1547
1548     let indent = match context.config.fn_arg_indent {
1549         BlockIndentStyle::Inherit => indent,
1550         BlockIndentStyle::Tabbed => indent.block_indent(context.config),
1551         BlockIndentStyle::Visual => arg_indent,
1552     };
1553
1554     let tactic = definitive_tactic(&arg_items,
1555                                    context.config.fn_args_density.to_list_tactic(),
1556                                    one_line_budget);
1557     let budget = match tactic {
1558         DefinitiveListTactic::Horizontal => one_line_budget,
1559         _ => multi_line_budget,
1560     };
1561
1562     debug!("rewrite_args: budget: {}, tactic: {:?}", budget, tactic);
1563
1564     let end_with_newline = match context.config.fn_args_layout {
1565         FnArgLayoutStyle::Block |
1566         FnArgLayoutStyle::BlockAlways => true,
1567         _ => false,
1568     };
1569
1570     let fmt = ListFormatting {
1571         tactic: tactic,
1572         separator: ",",
1573         trailing_separator: SeparatorTactic::Never,
1574         indent: indent,
1575         width: budget,
1576         ends_with_newline: end_with_newline,
1577         config: context.config,
1578     };
1579
1580     write_list(&arg_items, &fmt)
1581 }
1582
1583 fn arg_has_pattern(arg: &ast::Arg) -> bool {
1584     if let ast::PatKind::Ident(_,
1585                                codemap::Spanned {
1586                                    node: ast::Ident { name: ast::Name(0u32), .. },
1587                                    ..
1588                                },
1589                                _) = arg.pat.node {
1590         false
1591     } else {
1592         true
1593     }
1594 }
1595
1596 fn compute_budgets_for_args(context: &RewriteContext,
1597                             result: &str,
1598                             indent: Indent,
1599                             ret_str_len: usize,
1600                             newline_brace: bool)
1601                             -> Option<((usize, usize, Indent))> {
1602     // Try keeping everything on the same line.
1603     if !result.contains("\n") {
1604         // 3 = `() `, space is before ret_string.
1605         let mut used_space = indent.width() + result.len() + ret_str_len + 3;
1606         if !newline_brace {
1607             used_space += 2;
1608         }
1609         let one_line_budget = context.config.max_width.checked_sub(used_space).unwrap_or(0);
1610
1611         if one_line_budget > 0 {
1612             // 4 = "() {".len()
1613             let multi_line_budget =
1614                 try_opt!(context.config.max_width.checked_sub(indent.width() + result.len() + 4));
1615
1616             return Some((one_line_budget, multi_line_budget, indent + result.len() + 1));
1617         }
1618     }
1619
1620     // Didn't work. we must force vertical layout and put args on a newline.
1621     let new_indent = indent.block_indent(context.config);
1622     let used_space = new_indent.width() + 4; // Account for `(` and `)` and possibly ` {`.
1623     let max_space = context.config.max_width;
1624     if used_space <= max_space {
1625         Some((0, max_space - used_space, new_indent))
1626     } else {
1627         // Whoops! bankrupt.
1628         None
1629     }
1630 }
1631
1632 fn newline_for_brace(config: &Config, where_clause: &ast::WhereClause) -> bool {
1633     match config.fn_brace_style {
1634         BraceStyle::AlwaysNextLine => true,
1635         BraceStyle::SameLineWhere if !where_clause.predicates.is_empty() => true,
1636         _ => false,
1637     }
1638 }
1639
1640 fn rewrite_generics(context: &RewriteContext,
1641                     generics: &ast::Generics,
1642                     offset: Indent,
1643                     width: usize,
1644                     generics_offset: Indent,
1645                     span: Span)
1646                     -> Option<String> {
1647     // FIXME: convert bounds to where clauses where they get too big or if
1648     // there is a where clause at all.
1649     let lifetimes: &[_] = &generics.lifetimes;
1650     let tys: &[_] = &generics.ty_params;
1651     if lifetimes.is_empty() && tys.is_empty() {
1652         return Some(String::new());
1653     }
1654
1655     let offset = match context.config.generics_indent {
1656         BlockIndentStyle::Inherit => offset,
1657         BlockIndentStyle::Tabbed => offset.block_indent(context.config),
1658         // 1 = <
1659         BlockIndentStyle::Visual => generics_offset + 1,
1660     };
1661
1662     let h_budget = try_opt!(width.checked_sub(generics_offset.width() + 2));
1663     // FIXME: might need to insert a newline if the generics are really long.
1664
1665     // Strings for the generics.
1666     let lt_strs = lifetimes.iter().map(|lt| lt.rewrite(&context, h_budget, offset));
1667     let ty_strs = tys.iter().map(|ty_param| ty_param.rewrite(&context, h_budget, offset));
1668
1669     // Extract comments between generics.
1670     let lt_spans = lifetimes.iter().map(|l| {
1671         let hi = if l.bounds.is_empty() {
1672             l.lifetime.span.hi
1673         } else {
1674             l.bounds[l.bounds.len() - 1].span.hi
1675         };
1676         mk_sp(l.lifetime.span.lo, hi)
1677     });
1678     let ty_spans = tys.iter().map(span_for_ty_param);
1679
1680     let items = itemize_list(context.codemap,
1681                              lt_spans.chain(ty_spans).zip(lt_strs.chain(ty_strs)),
1682                              ">",
1683                              |&(sp, _)| sp.lo,
1684                              |&(sp, _)| sp.hi,
1685                              // FIXME: don't clone
1686                              |&(_, ref str)| str.clone(),
1687                              context.codemap.span_after(span, "<"),
1688                              span.hi);
1689     let list_str = try_opt!(format_item_list(items, h_budget, offset, context.config));
1690
1691     Some(format!("<{}>", list_str))
1692 }
1693
1694 fn rewrite_trait_bounds(context: &RewriteContext,
1695                         type_param_bounds: &ast::TyParamBounds,
1696                         indent: Indent,
1697                         width: usize)
1698                         -> Option<String> {
1699     let bounds: &[_] = &type_param_bounds;
1700
1701     if bounds.is_empty() {
1702         return Some(String::new());
1703     }
1704
1705     let bound_str = bounds.iter()
1706         .filter_map(|ty_bound| ty_bound.rewrite(&context, width, indent))
1707         .collect::<Vec<String>>()
1708         .join(" + ");
1709
1710     let mut result = String::new();
1711     result.push_str(": ");
1712     result.push_str(&bound_str);
1713     Some(result)
1714 }
1715
1716 fn rewrite_where_clause(context: &RewriteContext,
1717                         where_clause: &ast::WhereClause,
1718                         config: &Config,
1719                         brace_style: BraceStyle,
1720                         indent: Indent,
1721                         width: usize,
1722                         density: Density,
1723                         terminator: &str,
1724                         allow_trailing_comma: bool,
1725                         span_end: Option<BytePos>)
1726                         -> Option<String> {
1727     if where_clause.predicates.is_empty() {
1728         return Some(String::new());
1729     }
1730
1731     let extra_indent = match context.config.where_indent {
1732         BlockIndentStyle::Inherit => Indent::empty(),
1733         BlockIndentStyle::Tabbed | BlockIndentStyle::Visual => Indent::new(config.tab_spaces, 0),
1734     };
1735
1736     let offset = match context.config.where_pred_indent {
1737         BlockIndentStyle::Inherit => indent + extra_indent,
1738         BlockIndentStyle::Tabbed => indent + extra_indent.block_indent(config),
1739         // 6 = "where ".len()
1740         BlockIndentStyle::Visual => indent + extra_indent + 6,
1741     };
1742     // FIXME: if where_pred_indent != Visual, then the budgets below might
1743     // be out by a char or two.
1744
1745     let budget = context.config.max_width - offset.width();
1746     let span_start = span_for_where_pred(&where_clause.predicates[0]).lo;
1747     // If we don't have the start of the next span, then use the end of the
1748     // predicates, but that means we miss comments.
1749     let len = where_clause.predicates.len();
1750     let end_of_preds = span_for_where_pred(&where_clause.predicates[len - 1]).hi;
1751     let span_end = span_end.unwrap_or(end_of_preds);
1752     let items = itemize_list(context.codemap,
1753                              where_clause.predicates.iter(),
1754                              terminator,
1755                              |pred| span_for_where_pred(pred).lo,
1756                              |pred| span_for_where_pred(pred).hi,
1757                              |pred| pred.rewrite(&context, budget, offset),
1758                              span_start,
1759                              span_end);
1760     let item_vec = items.collect::<Vec<_>>();
1761     // FIXME: we don't need to collect here if the where_layout isn't
1762     // HorizontalVertical.
1763     let tactic = definitive_tactic(&item_vec, context.config.where_layout, budget);
1764     let use_trailing_comma = allow_trailing_comma && context.config.where_trailing_comma;
1765
1766     let fmt = ListFormatting {
1767         tactic: tactic,
1768         separator: ",",
1769         trailing_separator: SeparatorTactic::from_bool(use_trailing_comma),
1770         indent: offset,
1771         width: budget,
1772         ends_with_newline: true,
1773         config: context.config,
1774     };
1775     let preds_str = try_opt!(write_list(&item_vec, &fmt));
1776
1777     let end_length = if terminator == "{" {
1778         // If the brace is on the next line we don't need to count it otherwise it needs two
1779         // characters " {"
1780         match brace_style {
1781             BraceStyle::AlwaysNextLine => 0,
1782             BraceStyle::PreferSameLine => 2,
1783             BraceStyle::SameLineWhere => 0,
1784         }
1785     } else if terminator == "=" {
1786         2
1787     } else {
1788         terminator.len()
1789     };
1790     if density == Density::Tall || preds_str.contains('\n') ||
1791        indent.width() + " where ".len() + preds_str.len() + end_length > width {
1792         Some(format!("\n{}where {}",
1793                      (indent + extra_indent).to_string(context.config),
1794                      preds_str))
1795     } else {
1796         Some(format!(" where {}", preds_str))
1797     }
1798 }
1799
1800 fn format_header(item_name: &str, ident: ast::Ident, vis: &ast::Visibility) -> String {
1801     format!("{}{}{}", format_visibility(vis), item_name, ident)
1802 }
1803
1804 fn format_generics(context: &RewriteContext,
1805                    generics: &ast::Generics,
1806                    opener: &str,
1807                    terminator: &str,
1808                    brace_style: BraceStyle,
1809                    force_same_line_brace: bool,
1810                    offset: Indent,
1811                    generics_offset: Indent,
1812                    span: Span)
1813                    -> Option<String> {
1814     let mut result = try_opt!(rewrite_generics(context,
1815                                                generics,
1816                                                offset,
1817                                                context.config.max_width,
1818                                                generics_offset,
1819                                                span));
1820
1821     if !generics.where_clause.predicates.is_empty() || result.contains('\n') {
1822         let budget = try_opt!(context.config.max_width.checked_sub(last_line_width(&result)));
1823         let where_clause_str = try_opt!(rewrite_where_clause(context,
1824                                                              &generics.where_clause,
1825                                                              context.config,
1826                                                              brace_style,
1827                                                              context.block_indent,
1828                                                              budget,
1829                                                              Density::Tall,
1830                                                              terminator,
1831                                                              true,
1832                                                              Some(span.hi)));
1833         result.push_str(&where_clause_str);
1834         if !force_same_line_brace &&
1835            (brace_style == BraceStyle::SameLineWhere || brace_style == BraceStyle::AlwaysNextLine) {
1836             result.push('\n');
1837             result.push_str(&context.block_indent.to_string(context.config));
1838         } else {
1839             result.push(' ');
1840         }
1841         result.push_str(opener);
1842     } else {
1843         if !force_same_line_brace && brace_style == BraceStyle::AlwaysNextLine {
1844             result.push('\n');
1845             result.push_str(&context.block_indent.to_string(context.config));
1846         } else {
1847             result.push(' ');
1848         }
1849         result.push_str(opener);
1850     }
1851
1852     Some(result)
1853 }