src/visitor.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 use std::cmp;
  12
  13 use syntax::{ast, ptr, visit};
  14 use syntax::codemap::{self, CodeMap, Span, BytePos};
  15 use syntax::parse::ParseSess;
  16
  17 use strings::string_buffer::StringBuffer;
  18
  19 use {Indent, Shape};
  20 use utils;
  21 use codemap::{LineRangeUtils, SpanUtils};
  22 use config::Config;
  23 use rewrite::{Rewrite, RewriteContext};
  24 use comment::rewrite_comment;
  25 use macros::{rewrite_macro, MacroPosition};
  26 use items::{rewrite_static, rewrite_associated_type, rewrite_associated_impl_type,
  27             rewrite_type_alias, format_impl, format_trait};
  28
  29 fn is_use_item(item: &ast::Item) -> bool {
  30     match item.node {
  31         ast::ItemKind::Use(_) => true,
  32         _ => false,
  33     }
  34 }
  35
  36 fn item_bound(item: &ast::Item) -> Span {
  37     item.attrs
  38         .iter()
  39         .map(|attr| attr.span)
  40         .fold(item.span, |bound, span| {
  41             Span {
  42                 lo: cmp::min(bound.lo, span.lo),
  43                 hi: cmp::max(bound.hi, span.hi),
  44                 expn_id: span.expn_id,
  45             }
  46         })
  47 }
  48
  49 pub struct FmtVisitor<'a> {
  50     pub parse_session: &'a ParseSess,
  51     pub codemap: &'a CodeMap,
  52     pub buffer: StringBuffer,
  53     pub last_pos: BytePos,
  54     // FIXME: use an RAII util or closure for indenting
  55     pub block_indent: Indent,
  56     pub config: &'a Config,
  57     pub failed: bool,
  58 }
  59
  60 impl<'a> FmtVisitor<'a> {
  61     fn visit_stmt(&mut self, stmt: &ast::Stmt) {
  62         debug!("visit_stmt: {:?} {:?}",
  63                self.codemap.lookup_char_pos(stmt.span.lo),
  64                self.codemap.lookup_char_pos(stmt.span.hi));
  65
  66         // FIXME(#434): Move this check to somewhere more central, eg Rewrite.
  67         if !self.config
  68                .file_lines()
  69                .intersects(&self.codemap.lookup_line_range(stmt.span)) {
  70             return;
  71         }
  72
  73         match stmt.node {
  74             ast::StmtKind::Item(ref item) => {
  75                 self.visit_item(item);
  76             }
  77             ast::StmtKind::Local(..) |
  78             ast::StmtKind::Expr(..) |
  79             ast::StmtKind::Semi(..) => {
  80                 let rewrite =
  81                     stmt.rewrite(&self.get_context(),
  82                                  Shape::indented(self.block_indent, self.config));
  83                 self.push_rewrite(stmt.span, rewrite);
  84             }
  85             ast::StmtKind::Mac(ref mac) => {
  86                 let (ref mac, _macro_style, _) = **mac;
  87                 self.visit_mac(mac, None, MacroPosition::Statement);
  88                 self.format_missing(stmt.span.hi);
  89             }
  90         }
  91     }
  92
  93     pub fn visit_block(&mut self, b: &ast::Block) {
  94         debug!("visit_block: {:?} {:?}",
  95                self.codemap.lookup_char_pos(b.span.lo),
  96                self.codemap.lookup_char_pos(b.span.hi));
  97
  98         // Check if this block has braces.
  99         let snippet = self.snippet(b.span);
 100         let has_braces = snippet.starts_with('{') || snippet.starts_with("unsafe");
 101         let brace_compensation = if has_braces { BytePos(1) } else { BytePos(0) };
 102
 103         self.last_pos = self.last_pos + brace_compensation;
 104         self.block_indent = self.block_indent.block_indent(self.config);
 105         self.buffer.push_str("{");
 106
 107         for stmt in &b.stmts {
 108             self.visit_stmt(stmt)
 109         }
 110
 111         if !b.stmts.is_empty() {
 112             if let Some(expr) = utils::stmt_expr(&b.stmts[b.stmts.len() - 1]) {
 113                 if utils::semicolon_for_expr(expr) {
 114                     self.buffer.push_str(";");
 115                 }
 116             }
 117         }
 118
 119         // FIXME: we should compress any newlines here to just one
 120         self.format_missing_with_indent(source!(self, b.span).hi - brace_compensation);
 121         self.close_block();
 122         self.last_pos = source!(self, b.span).hi;
 123     }
 124
 125     // FIXME: this is a terrible hack to indent the comments between the last
 126     // item in the block and the closing brace to the block's level.
 127     // The closing brace itself, however, should be indented at a shallower
 128     // level.
 129     fn close_block(&mut self) {
 130         let total_len = self.buffer.len;
 131         let chars_too_many = if self.config.hard_tabs() {
 132             1
 133         } else {
 134             self.config.tab_spaces()
 135         };
 136         self.buffer.truncate(total_len - chars_too_many);
 137         self.buffer.push_str("}");
 138         self.block_indent = self.block_indent.block_unindent(self.config);
 139     }
 140
 141     // Note that this only gets called for function definitions. Required methods
 142     // on traits do not get handled here.
 143     fn visit_fn(&mut self,
 144                 fk: visit::FnKind,
 145                 fd: &ast::FnDecl,
 146                 s: Span,
 147                 _: ast::NodeId,
 148                 defaultness: ast::Defaultness) {
 149         let indent = self.block_indent;
 150         let block;
 151         let rewrite = match fk {
 152             visit::FnKind::ItemFn(ident, generics, unsafety, constness, abi, vis, b) => {
 153                 block = b;
 154                 self.rewrite_fn(indent,
 155                                 ident,
 156                                 fd,
 157                                 generics,
 158                                 unsafety,
 159                                 constness.node,
 160                                 defaultness,
 161                                 abi,
 162                                 vis,
 163                                 codemap::mk_sp(s.lo, b.span.lo),
 164                                 &b)
 165             }
 166             visit::FnKind::Method(ident, sig, vis, b) => {
 167                 block = b;
 168                 self.rewrite_fn(indent,
 169                                 ident,
 170                                 fd,
 171                                 &sig.generics,
 172                                 sig.unsafety,
 173                                 sig.constness.node,
 174                                 defaultness,
 175                                 sig.abi,
 176                                 vis.unwrap_or(&ast::Visibility::Inherited),
 177                                 codemap::mk_sp(s.lo, b.span.lo),
 178                                 &b)
 179             }
 180             visit::FnKind::Closure(_) => unreachable!(),
 181         };
 182
 183         if let Some(fn_str) = rewrite {
 184             self.format_missing_with_indent(source!(self, s).lo);
 185             self.buffer.push_str(&fn_str);
 186             if let Some(c) = fn_str.chars().last() {
 187                 if c == '}' {
 188                     self.last_pos = source!(self, block.span).hi;
 189                     return;
 190                 }
 191             }
 192         } else {
 193             self.format_missing(source!(self, block.span).lo);
 194         }
 195
 196         self.last_pos = source!(self, block.span).lo;
 197         self.visit_block(block)
 198     }
 199
 200     pub fn visit_item(&mut self, item: &ast::Item) {
 201         // This is where we bail out if there is a skip attribute. This is only
 202         // complex in the module case. It is complex because the module could be
 203         // in a separate file and there might be attributes in both files, but
 204         // the AST lumps them all together.
 205         match item.node {
 206             ast::ItemKind::Mod(ref m) => {
 207                 let outer_file = self.codemap.lookup_char_pos(item.span.lo).file;
 208                 let inner_file = self.codemap.lookup_char_pos(m.inner.lo).file;
 209                 if outer_file.name == inner_file.name {
 210                     // Module is inline, in this case we treat modules like any
 211                     // other item.
 212                     if self.visit_attrs(&item.attrs) {
 213                         self.push_rewrite(item.span, None);
 214                         return;
 215                     }
 216                 } else if utils::contains_skip(&item.attrs) {
 217                     // Module is not inline, but should be skipped.
 218                     return;
 219                 } else {
 220                     // Module is not inline and should not be skipped. We want
 221                     // to process only the attributes in the current file.
 222                     let attrs = item.attrs
 223                         .iter()
 224                         .filter_map(|a| {
 225                             let attr_file = self.codemap.lookup_char_pos(a.span.lo).file;
 226                             if attr_file.name == outer_file.name {
 227                                 Some(a.clone())
 228                             } else {
 229                                 None
 230                             }
 231                         })
 232                         .collect::<Vec<_>>();
 233                     // Assert because if we should skip it should be caught by
 234                     // the above case.
 235                     assert!(!self.visit_attrs(&attrs));
 236                 }
 237             }
 238             _ => {
 239                 if self.visit_attrs(&item.attrs) {
 240                     self.push_rewrite(item.span, None);
 241                     return;
 242                 }
 243             }
 244         }
 245
 246         match item.node {
 247             ast::ItemKind::Use(ref vp) => {
 248                 self.format_import(&item.vis, vp, item.span);
 249             }
 250             ast::ItemKind::Impl(..) => {
 251                 self.format_missing_with_indent(source!(self, item.span).lo);
 252                 if let Some(impl_str) = format_impl(&self.get_context(), item, self.block_indent) {
 253                     self.buffer.push_str(&impl_str);
 254                     self.last_pos = source!(self, item.span).hi;
 255                 }
 256             }
 257             ast::ItemKind::Trait(..) => {
 258                 self.format_missing_with_indent(item.span.lo);
 259                 if let Some(trait_str) = format_trait(&self.get_context(),
 260                                                       item,
 261                                                       self.block_indent) {
 262                     self.buffer.push_str(&trait_str);
 263                     self.last_pos = source!(self, item.span).hi;
 264                 }
 265             }
 266             ast::ItemKind::ExternCrate(_) => {
 267                 self.format_missing_with_indent(source!(self, item.span).lo);
 268                 let new_str = self.snippet(item.span);
 269                 self.buffer.push_str(&new_str);
 270                 self.last_pos = source!(self, item.span).hi;
 271             }
 272             ast::ItemKind::Struct(ref def, ref generics) => {
 273                 let rewrite = {
 274                     let indent = self.block_indent;
 275                     let context = self.get_context();
 276                     ::items::format_struct(&context,
 277                                            "struct ",
 278                                            item.ident,
 279                                            &item.vis,
 280                                            def,
 281                                            Some(generics),
 282                                            item.span,
 283                                            indent,
 284                                            None)
 285                         .map(|s| match *def {
 286                                  ast::VariantData::Tuple(..) => s + ";",
 287                                  _ => s,
 288                              })
 289                 };
 290                 self.push_rewrite(item.span, rewrite);
 291             }
 292             ast::ItemKind::Enum(ref def, ref generics) => {
 293                 self.format_missing_with_indent(source!(self, item.span).lo);
 294                 self.visit_enum(item.ident, &item.vis, def, generics, item.span);
 295                 self.last_pos = source!(self, item.span).hi;
 296             }
 297             ast::ItemKind::Mod(ref module) => {
 298                 self.format_missing_with_indent(source!(self, item.span).lo);
 299                 self.format_mod(module, &item.vis, item.span, item.ident);
 300             }
 301             ast::ItemKind::Mac(ref mac) => {
 302                 self.visit_mac(mac, Some(item.ident), MacroPosition::Item);
 303             }
 304             ast::ItemKind::ForeignMod(ref foreign_mod) => {
 305                 self.format_missing_with_indent(source!(self, item.span).lo);
 306                 self.format_foreign_mod(foreign_mod, item.span);
 307             }
 308             ast::ItemKind::Static(ref ty, mutability, ref expr) => {
 309                 let rewrite = rewrite_static("static",
 310                                              &item.vis,
 311                                              item.ident,
 312                                              ty,
 313                                              mutability,
 314                                              Some(expr),
 315                                              self.block_indent,
 316                                              &self.get_context());
 317                 self.push_rewrite(item.span, rewrite);
 318             }
 319             ast::ItemKind::Const(ref ty, ref expr) => {
 320                 let rewrite = rewrite_static("const",
 321                                              &item.vis,
 322                                              item.ident,
 323                                              ty,
 324                                              ast::Mutability::Immutable,
 325                                              Some(expr),
 326                                              self.block_indent,
 327                                              &self.get_context());
 328                 self.push_rewrite(item.span, rewrite);
 329             }
 330             ast::ItemKind::DefaultImpl(..) => {
 331                 // FIXME(#78): format impl definitions.
 332             }
 333             ast::ItemKind::Fn(ref decl, unsafety, constness, abi, ref generics, ref body) => {
 334                 self.visit_fn(visit::FnKind::ItemFn(item.ident,
 335                                                     generics,
 336                                                     unsafety,
 337                                                     constness,
 338                                                     abi,
 339                                                     &item.vis,
 340                                                     body),
 341                               decl,
 342                               item.span,
 343                               item.id,
 344                               ast::Defaultness::Final)
 345             }
 346             ast::ItemKind::Ty(ref ty, ref generics) => {
 347                 let rewrite = rewrite_type_alias(&self.get_context(),
 348                                                  self.block_indent,
 349                                                  item.ident,
 350                                                  ty,
 351                                                  generics,
 352                                                  &item.vis,
 353                                                  item.span);
 354                 self.push_rewrite(item.span, rewrite);
 355             }
 356             ast::ItemKind::Union(..) => {
 357                 // FIXME(#1157): format union definitions.
 358             }
 359         }
 360     }
 361
 362     pub fn visit_trait_item(&mut self, ti: &ast::TraitItem) {
 363         if self.visit_attrs(&ti.attrs) {
 364             self.push_rewrite(ti.span, None);
 365             return;
 366         }
 367
 368         match ti.node {
 369             ast::TraitItemKind::Const(ref ty, ref expr_opt) => {
 370                 let rewrite = rewrite_static("const",
 371                                              &ast::Visibility::Inherited,
 372                                              ti.ident,
 373                                              ty,
 374                                              ast::Mutability::Immutable,
 375                                              expr_opt.as_ref(),
 376                                              self.block_indent,
 377                                              &self.get_context());
 378                 self.push_rewrite(ti.span, rewrite);
 379             }
 380             ast::TraitItemKind::Method(ref sig, None) => {
 381                 let indent = self.block_indent;
 382                 let rewrite = self.rewrite_required_fn(indent, ti.ident, sig, ti.span);
 383                 self.push_rewrite(ti.span, rewrite);
 384             }
 385             ast::TraitItemKind::Method(ref sig, Some(ref body)) => {
 386                 self.visit_fn(visit::FnKind::Method(ti.ident, sig, None, body),
 387                               &sig.decl,
 388                               ti.span,
 389                               ti.id,
 390                               ast::Defaultness::Final);
 391             }
 392             ast::TraitItemKind::Type(ref type_param_bounds, ref type_default) => {
 393                 let rewrite = rewrite_associated_type(ti.ident,
 394                                                       type_default.as_ref(),
 395                                                       Some(type_param_bounds),
 396                                                       &self.get_context(),
 397                                                       self.block_indent);
 398                 self.push_rewrite(ti.span, rewrite);
 399             }
 400             ast::TraitItemKind::Macro(ref mac) => {
 401                 self.visit_mac(mac, Some(ti.ident), MacroPosition::Item);
 402             }
 403         }
 404     }
 405
 406     pub fn visit_impl_item(&mut self, ii: &ast::ImplItem) {
 407         if self.visit_attrs(&ii.attrs) {
 408             self.push_rewrite(ii.span, None);
 409             return;
 410         }
 411
 412         match ii.node {
 413             ast::ImplItemKind::Method(ref sig, ref body) => {
 414                 self.visit_fn(visit::FnKind::Method(ii.ident, sig, Some(&ii.vis), body),
 415                               &sig.decl,
 416                               ii.span,
 417                               ii.id,
 418                               ii.defaultness);
 419             }
 420             ast::ImplItemKind::Const(ref ty, ref expr) => {
 421                 let rewrite = rewrite_static("const",
 422                                              &ii.vis,
 423                                              ii.ident,
 424                                              ty,
 425                                              ast::Mutability::Immutable,
 426                                              Some(expr),
 427                                              self.block_indent,
 428                                              &self.get_context());
 429                 self.push_rewrite(ii.span, rewrite);
 430             }
 431             ast::ImplItemKind::Type(ref ty) => {
 432                 let rewrite = rewrite_associated_impl_type(ii.ident,
 433                                                            ii.defaultness,
 434                                                            Some(ty),
 435                                                            None,
 436                                                            &self.get_context(),
 437                                                            self.block_indent);
 438                 self.push_rewrite(ii.span, rewrite);
 439             }
 440             ast::ImplItemKind::Macro(ref mac) => {
 441                 self.visit_mac(mac, Some(ii.ident), MacroPosition::Item);
 442             }
 443         }
 444     }
 445
 446     fn visit_mac(&mut self, mac: &ast::Mac, ident: Option<ast::Ident>, pos: MacroPosition) {
 447         // 1 = ;
 448         let shape = Shape::indented(self.block_indent, self.config)
 449             .sub_width(1)
 450             .unwrap();
 451         let rewrite = rewrite_macro(mac, ident, &self.get_context(), shape, pos);
 452         self.push_rewrite(mac.span, rewrite);
 453     }
 454
 455     fn push_rewrite(&mut self, span: Span, rewrite: Option<String>) {
 456         self.format_missing_with_indent(source!(self, span).lo);
 457         self.failed = match rewrite {
 458             Some(ref s) if s.rewrite(&self.get_context(),
 459                                      Shape::indented(self.block_indent, self.config))
 460                                .is_none() => true,
 461             None => true,
 462             _ => self.failed,
 463         };
 464         let result = rewrite.unwrap_or_else(|| self.snippet(span));
 465         self.buffer.push_str(&result);
 466         self.last_pos = source!(self, span).hi;
 467     }
 468
 469     pub fn from_codemap(parse_session: &'a ParseSess, config: &'a Config) -> FmtVisitor<'a> {
 470         FmtVisitor {
 471             parse_session: parse_session,
 472             codemap: parse_session.codemap(),
 473             buffer: StringBuffer::new(),
 474             last_pos: BytePos(0),
 475             block_indent: Indent::empty(),
 476             config: config,
 477             failed: false,
 478         }
 479     }
 480
 481     pub fn snippet(&self, span: Span) -> String {
 482         match self.codemap.span_to_snippet(span) {
 483             Ok(s) => s,
 484             Err(_) => {
 485                 println!("Couldn't make snippet for span {:?}->{:?}",
 486                          self.codemap.lookup_char_pos(span.lo),
 487                          self.codemap.lookup_char_pos(span.hi));
 488                 "".to_owned()
 489             }
 490         }
 491     }
 492
 493     // Returns true if we should skip the following item.
 494     pub fn visit_attrs(&mut self, attrs: &[ast::Attribute]) -> bool {
 495         if utils::contains_skip(attrs) {
 496             return true;
 497         }
 498
 499         let outers: Vec<_> = attrs
 500             .iter()
 501             .filter(|a| a.style == ast::AttrStyle::Outer)
 502             .cloned()
 503             .collect();
 504         if outers.is_empty() {
 505             return false;
 506         }
 507
 508         let first = &outers[0];
 509         self.format_missing_with_indent(source!(self, first.span).lo);
 510
 511         let rewrite = outers
 512             .rewrite(&self.get_context(),
 513                      Shape::indented(self.block_indent, self.config))
 514             .unwrap();
 515         self.buffer.push_str(&rewrite);
 516         let last = outers.last().unwrap();
 517         self.last_pos = source!(self, last.span).hi;
 518         false
 519     }
 520
 521     fn walk_mod_items(&mut self, m: &ast::Mod) {
 522         let mut items_left: &[ptr::P<ast::Item>] = &m.items;
 523         while !items_left.is_empty() {
 524             // If the next item is a `use` declaration, then extract it and any subsequent `use`s
 525             // to be potentially reordered within `format_imports`. Otherwise, just format the
 526             // next item for output.
 527             if self.config.reorder_imports() && is_use_item(&*items_left[0]) {
 528                 let reorder_imports_in_group = self.config.reorder_imports_in_group();
 529                 let mut last = self.codemap.lookup_line_range(item_bound(&items_left[0]));
 530                 let use_item_length = items_left
 531                     .iter()
 532                     .take_while(|ppi| {
 533                         is_use_item(&***ppi) &&
 534                         (!reorder_imports_in_group ||
 535                          {
 536                              let current = self.codemap.lookup_line_range(item_bound(&ppi));
 537                              let in_same_group = current.lo < last.hi + 2;
 538                              last = current;
 539                              in_same_group
 540                          })
 541                     })
 542                     .count();
 543                 let (use_items, rest) = items_left.split_at(use_item_length);
 544                 self.format_imports(use_items);
 545                 items_left = rest;
 546             } else {
 547                 // `unwrap()` is safe here because we know `items_left`
 548                 // has elements from the loop condition
 549                 let (item, rest) = items_left.split_first().unwrap();
 550                 self.visit_item(item);
 551                 items_left = rest;
 552             }
 553         }
 554     }
 555
 556     fn format_mod(&mut self, m: &ast::Mod, vis: &ast::Visibility, s: Span, ident: ast::Ident) {
 557         // Decide whether this is an inline mod or an external mod.
 558         let local_file_name = self.codemap.span_to_filename(s);
 559         let inner_span = source!(self, m.inner);
 560         let is_internal = !(inner_span.lo.0 == 0 && inner_span.hi.0 == 0) &&
 561                           local_file_name == self.codemap.span_to_filename(inner_span);
 562
 563         self.buffer.push_str(&*utils::format_visibility(vis));
 564         self.buffer.push_str("mod ");
 565         self.buffer.push_str(&ident.to_string());
 566
 567         if is_internal {
 568             self.buffer.push_str(" {");
 569             // Hackery to account for the closing }.
 570             let mod_lo = self.codemap.span_after(source!(self, s), "{");
 571             let body_snippet =
 572                 self.snippet(codemap::mk_sp(mod_lo, source!(self, m.inner).hi - BytePos(1)));
 573             let body_snippet = body_snippet.trim();
 574             if body_snippet.is_empty() {
 575                 self.buffer.push_str("}");
 576             } else {
 577                 self.last_pos = mod_lo;
 578                 self.block_indent = self.block_indent.block_indent(self.config);
 579                 self.walk_mod_items(m);
 580                 self.format_missing_with_indent(source!(self, m.inner).hi - BytePos(1));
 581                 self.close_block();
 582             }
 583             self.last_pos = source!(self, m.inner).hi;
 584         } else {
 585             self.buffer.push_str(";");
 586             self.last_pos = source!(self, s).hi;
 587         }
 588     }
 589
 590     pub fn format_separate_mod(&mut self, m: &ast::Mod) {
 591         let filemap = self.codemap.lookup_char_pos(m.inner.lo).file;
 592         self.last_pos = filemap.start_pos;
 593         self.block_indent = Indent::empty();
 594         self.walk_mod_items(m);
 595         self.format_missing_with_indent(filemap.end_pos);
 596     }
 597
 598     pub fn get_context(&self) -> RewriteContext {
 599         RewriteContext {
 600             parse_session: self.parse_session,
 601             codemap: self.codemap,
 602             config: self.config,
 603             inside_macro: false,
 604         }
 605     }
 606 }
 607
 608 impl<'a> Rewrite for [ast::Attribute] {
 609     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 610         let mut result = String::new();
 611         if self.is_empty() {
 612             return Some(result);
 613         }
 614         let indent = shape.indent.to_string(context.config);
 615
 616         for (i, a) in self.iter().enumerate() {
 617             let mut a_str = context.snippet(a.span);
 618
 619             // Write comments and blank lines between attributes.
 620             if i > 0 {
 621                 let comment = context.snippet(codemap::mk_sp(self[i - 1].span.hi, a.span.lo));
 622                 // This particular horror show is to preserve line breaks in between doc
 623                 // comments. An alternative would be to force such line breaks to start
 624                 // with the usual doc comment token.
 625                 let multi_line = a_str.starts_with("//") && comment.matches('\n').count() > 1;
 626                 let comment = comment.trim();
 627                 if !comment.is_empty() {
 628                     let comment =
 629                         try_opt!(rewrite_comment(comment,
 630                                                  false,
 631                                                  Shape::legacy(context.config.comment_width() -
 632                                                                shape.indent.width(),
 633                                                                shape.indent),
 634                                                  context.config));
 635                     result.push_str(&indent);
 636                     result.push_str(&comment);
 637                     result.push('\n');
 638                 } else if multi_line {
 639                     result.push('\n');
 640                 }
 641                 result.push_str(&indent);
 642             }
 643
 644             if a_str.starts_with("//") {
 645                 a_str = try_opt!(rewrite_comment(&a_str,
 646                                                  false,
 647                                                  Shape::legacy(context.config.comment_width() -
 648                                                                shape.indent.width(),
 649                                                                shape.indent),
 650                                                  context.config));
 651             }
 652
 653             // Write the attribute itself.
 654             result.push_str(&a_str);
 655
 656             if i < self.len() - 1 {
 657                 result.push('\n');
 658             }
 659         }
 660
 661         Some(result)
 662     }
 663 }