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 strings::string_buffer::StringBuffer;
  14 use syntax::{ast, visit};
  15 use syntax::attr::HasAttrs;
  16 use syntax::codemap::{self, BytePos, CodeMap, Pos, Span};
  17 use syntax::parse::ParseSess;
  18
  19 use expr::rewrite_literal;
  20 use spanned::Spanned;
  21 use codemap::{LineRangeUtils, SpanUtils};
  22 use comment::{combine_strs_with_missing_comments, contains_comment, remove_trailing_white_spaces,
  23               CodeCharKind, CommentCodeSlices, FindUncommented};
  24 use comment::rewrite_comment;
  25 use config::{BraceStyle, Config};
  26 use items::{format_impl, format_trait, rewrite_associated_impl_type, rewrite_associated_type,
  27             rewrite_type_alias, FnSig, StaticParts, StructParts};
  28 use lists::{itemize_list, write_list, DefinitiveListTactic, ListFormatting, SeparatorPlace,
  29             SeparatorTactic};
  30 use macros::{rewrite_macro, MacroPosition};
  31 use regex::Regex;
  32 use rewrite::{Rewrite, RewriteContext};
  33 use shape::{Indent, Shape};
  34 use utils::{self, contains_skip, inner_attributes, mk_sp, ptr_vec_to_ref_vec};
  35
  36 fn is_use_item(item: &ast::Item) -> bool {
  37     match item.node {
  38         ast::ItemKind::Use(_) => true,
  39         _ => false,
  40     }
  41 }
  42
  43 fn is_extern_crate(item: &ast::Item) -> bool {
  44     match item.node {
  45         ast::ItemKind::ExternCrate(..) => true,
  46         _ => false,
  47     }
  48 }
  49
  50 pub struct FmtVisitor<'a> {
  51     pub parse_session: &'a ParseSess,
  52     pub codemap: &'a CodeMap,
  53     pub buffer: StringBuffer,
  54     pub last_pos: BytePos,
  55     // FIXME: use an RAII util or closure for indenting
  56     pub block_indent: Indent,
  57     pub config: &'a Config,
  58     pub is_if_else_block: bool,
  59 }
  60
  61 impl<'a> FmtVisitor<'a> {
  62     pub fn shape(&self) -> Shape {
  63         Shape::indented(self.block_indent, self.config)
  64     }
  65
  66     fn visit_stmt(&mut self, stmt: &ast::Stmt) {
  67         debug!(
  68             "visit_stmt: {:?} {:?}",
  69             self.codemap.lookup_char_pos(stmt.span.lo()),
  70             self.codemap.lookup_char_pos(stmt.span.hi())
  71         );
  72
  73         match stmt.node {
  74             ast::StmtKind::Item(ref item) => {
  75                 self.visit_item(item);
  76             }
  77             ast::StmtKind::Local(..) | ast::StmtKind::Expr(..) | ast::StmtKind::Semi(..) => {
  78                 let rewrite = stmt.rewrite(&self.get_context(), self.shape());
  79                 self.push_rewrite(stmt.span(), rewrite)
  80             }
  81             ast::StmtKind::Mac(ref mac) => {
  82                 let (ref mac, _macro_style, ref attrs) = **mac;
  83                 if self.visit_attrs(attrs, ast::AttrStyle::Outer) {
  84                     self.push_rewrite(stmt.span(), None);
  85                 } else {
  86                     self.visit_mac(mac, None, MacroPosition::Statement);
  87                 }
  88                 self.format_missing(stmt.span.hi());
  89             }
  90         }
  91     }
  92
  93     pub fn visit_block(
  94         &mut self,
  95         b: &ast::Block,
  96         inner_attrs: Option<&[ast::Attribute]>,
  97         has_braces: bool,
  98     ) {
  99         debug!(
 100             "visit_block: {:?} {:?}",
 101             self.codemap.lookup_char_pos(b.span.lo()),
 102             self.codemap.lookup_char_pos(b.span.hi())
 103         );
 104
 105         // Check if this block has braces.
 106         let brace_compensation = BytePos(if has_braces { 1 } else { 0 });
 107
 108         self.last_pos = self.last_pos + brace_compensation;
 109         self.block_indent = self.block_indent.block_indent(self.config);
 110         self.buffer.push_str("{");
 111
 112         if self.config.remove_blank_lines_at_start_or_end_of_block() {
 113             if let Some(first_stmt) = b.stmts.first() {
 114                 let attr_lo = inner_attrs
 115                     .and_then(|attrs| inner_attributes(attrs).first().map(|attr| attr.span.lo()))
 116                     .or_else(|| {
 117                         // Attributes for an item in a statement position
 118                         // do not belong to the statement. (rust-lang/rust#34459)
 119                         if let ast::StmtKind::Item(ref item) = first_stmt.node {
 120                             item.attrs.first()
 121                         } else {
 122                             first_stmt.attrs().first()
 123                         }.and_then(|attr| {
 124                             // Some stmts can have embedded attributes.
 125                             // e.g. `match { #![attr] ... }`
 126                             let attr_lo = attr.span.lo();
 127                             if attr_lo < first_stmt.span.lo() {
 128                                 Some(attr_lo)
 129                             } else {
 130                                 None
 131                             }
 132                         })
 133                     });
 134
 135                 let snippet = self.snippet(mk_sp(
 136                     self.last_pos,
 137                     attr_lo.unwrap_or(first_stmt.span.lo()),
 138                 ));
 139                 let len = CommentCodeSlices::new(&snippet)
 140                     .nth(0)
 141                     .and_then(|(kind, _, s)| {
 142                         if kind == CodeCharKind::Normal {
 143                             s.rfind('\n')
 144                         } else {
 145                             None
 146                         }
 147                     });
 148                 if let Some(len) = len {
 149                     self.last_pos = self.last_pos + BytePos::from_usize(len);
 150                 }
 151             }
 152         }
 153
 154         // Format inner attributes if available.
 155         let skip_rewrite = if let Some(attrs) = inner_attrs {
 156             self.visit_attrs(attrs, ast::AttrStyle::Inner)
 157         } else {
 158             false
 159         };
 160
 161         if skip_rewrite {
 162             self.push_rewrite(b.span, None);
 163             self.close_block(false);
 164             self.last_pos = source!(self, b.span).hi();
 165             return;
 166         }
 167
 168         self.walk_block_stmts(b);
 169
 170         if !b.stmts.is_empty() {
 171             if let Some(expr) = utils::stmt_expr(&b.stmts[b.stmts.len() - 1]) {
 172                 if utils::semicolon_for_expr(&self.get_context(), expr) {
 173                     self.buffer.push_str(";");
 174                 }
 175             }
 176         }
 177
 178         let mut remove_len = BytePos(0);
 179         if self.config.remove_blank_lines_at_start_or_end_of_block() {
 180             if let Some(stmt) = b.stmts.last() {
 181                 let snippet = self.snippet(mk_sp(
 182                     stmt.span.hi(),
 183                     source!(self, b.span).hi() - brace_compensation,
 184                 ));
 185                 let len = CommentCodeSlices::new(&snippet)
 186                     .last()
 187                     .and_then(|(kind, _, s)| {
 188                         if kind == CodeCharKind::Normal && s.trim().is_empty() {
 189                             Some(s.len())
 190                         } else {
 191                             None
 192                         }
 193                     });
 194                 if let Some(len) = len {
 195                     remove_len = BytePos::from_usize(len);
 196                 }
 197             }
 198         }
 199
 200         let unindent_comment = (self.is_if_else_block && !b.stmts.is_empty()) && {
 201             let end_pos = source!(self, b.span).hi() - brace_compensation - remove_len;
 202             let snippet = self.snippet(mk_sp(self.last_pos, end_pos));
 203             snippet.contains("//") || snippet.contains("/*")
 204         };
 205         // FIXME: we should compress any newlines here to just one
 206         if unindent_comment {
 207             self.block_indent = self.block_indent.block_unindent(self.config);
 208         }
 209         self.format_missing_with_indent(
 210             source!(self, b.span).hi() - brace_compensation - remove_len,
 211         );
 212         if unindent_comment {
 213             self.block_indent = self.block_indent.block_indent(self.config);
 214         }
 215         self.close_block(unindent_comment);
 216         self.last_pos = source!(self, b.span).hi();
 217     }
 218
 219     // FIXME: this is a terrible hack to indent the comments between the last
 220     // item in the block and the closing brace to the block's level.
 221     // The closing brace itself, however, should be indented at a shallower
 222     // level.
 223     fn close_block(&mut self, unindent_comment: bool) {
 224         let total_len = self.buffer.len;
 225         let chars_too_many = if unindent_comment {
 226             0
 227         } else if self.config.hard_tabs() {
 228             1
 229         } else {
 230             self.config.tab_spaces()
 231         };
 232         self.buffer.truncate(total_len - chars_too_many);
 233         self.buffer.push_str("}");
 234         self.block_indent = self.block_indent.block_unindent(self.config);
 235     }
 236
 237     // Note that this only gets called for function definitions. Required methods
 238     // on traits do not get handled here.
 239     fn visit_fn(
 240         &mut self,
 241         fk: visit::FnKind,
 242         generics: &ast::Generics,
 243         fd: &ast::FnDecl,
 244         s: Span,
 245         defaultness: ast::Defaultness,
 246         inner_attrs: Option<&[ast::Attribute]>,
 247     ) {
 248         let indent = self.block_indent;
 249         let block;
 250         let rewrite = match fk {
 251             visit::FnKind::ItemFn(ident, _, _, _, _, b) | visit::FnKind::Method(ident, _, _, b) => {
 252                 block = b;
 253                 self.rewrite_fn(
 254                     indent,
 255                     ident,
 256                     &FnSig::from_fn_kind(&fk, generics, fd, defaultness),
 257                     mk_sp(s.lo(), b.span.lo()),
 258                     b,
 259                 )
 260             }
 261             visit::FnKind::Closure(_) => unreachable!(),
 262         };
 263
 264         if let Some(fn_str) = rewrite {
 265             self.format_missing_with_indent(source!(self, s).lo());
 266             self.buffer.push_str(&fn_str);
 267             if let Some(c) = fn_str.chars().last() {
 268                 if c == '}' {
 269                     self.last_pos = source!(self, block.span).hi();
 270                     return;
 271                 }
 272             }
 273         } else {
 274             self.format_missing(source!(self, block.span).lo());
 275         }
 276
 277         self.last_pos = source!(self, block.span).lo();
 278         self.visit_block(block, inner_attrs, true)
 279     }
 280
 281     pub fn visit_item(&mut self, item: &ast::Item) {
 282         skip_out_of_file_lines_range_visitor!(self, item.span);
 283
 284         // This is where we bail out if there is a skip attribute. This is only
 285         // complex in the module case. It is complex because the module could be
 286         // in a separate file and there might be attributes in both files, but
 287         // the AST lumps them all together.
 288         let filtered_attrs;
 289         let mut attrs = &item.attrs;
 290         match item.node {
 291             ast::ItemKind::Mod(ref m) => {
 292                 let outer_file = self.codemap.lookup_char_pos(item.span.lo()).file;
 293                 let inner_file = self.codemap.lookup_char_pos(m.inner.lo()).file;
 294                 if outer_file.name == inner_file.name {
 295                     // Module is inline, in this case we treat modules like any
 296                     // other item.
 297                     if self.visit_attrs(&item.attrs, ast::AttrStyle::Outer) {
 298                         self.push_rewrite(item.span, None);
 299                         return;
 300                     }
 301                 } else if contains_skip(&item.attrs) {
 302                     // Module is not inline, but should be skipped.
 303                     return;
 304                 } else {
 305                     // Module is not inline and should not be skipped. We want
 306                     // to process only the attributes in the current file.
 307                     filtered_attrs = item.attrs
 308                         .iter()
 309                         .filter_map(|a| {
 310                             let attr_file = self.codemap.lookup_char_pos(a.span.lo()).file;
 311                             if attr_file.name == outer_file.name {
 312                                 Some(a.clone())
 313                             } else {
 314                                 None
 315                             }
 316                         })
 317                         .collect::<Vec<_>>();
 318                     // Assert because if we should skip it should be caught by
 319                     // the above case.
 320                     assert!(!self.visit_attrs(&filtered_attrs, ast::AttrStyle::Outer));
 321                     attrs = &filtered_attrs;
 322                 }
 323             }
 324             _ => if self.visit_attrs(&item.attrs, ast::AttrStyle::Outer) {
 325                 self.push_rewrite(item.span, None);
 326                 return;
 327             },
 328         }
 329
 330         match item.node {
 331             ast::ItemKind::Use(ref vp) => self.format_import(item, vp),
 332             ast::ItemKind::Impl(..) => {
 333                 let snippet = self.snippet(item.span);
 334                 let where_span_end = snippet
 335                     .find_uncommented("{")
 336                     .map(|x| (BytePos(x as u32)) + source!(self, item.span).lo());
 337                 let rw = format_impl(&self.get_context(), item, self.block_indent, where_span_end);
 338                 self.push_rewrite(item.span, rw);
 339             }
 340             ast::ItemKind::Trait(..) => {
 341                 let rw = format_trait(&self.get_context(), item, self.block_indent);
 342                 self.push_rewrite(item.span, rw);
 343             }
 344             ast::ItemKind::ExternCrate(_) => {
 345                 let rw = rewrite_extern_crate(&self.get_context(), item);
 346                 self.push_rewrite(item.span, rw);
 347             }
 348             ast::ItemKind::Struct(..) | ast::ItemKind::Union(..) => {
 349                 self.visit_struct(&StructParts::from_item(item));
 350             }
 351             ast::ItemKind::Enum(ref def, ref generics) => {
 352                 self.format_missing_with_indent(source!(self, item.span).lo());
 353                 self.visit_enum(item.ident, &item.vis, def, generics, item.span);
 354                 self.last_pos = source!(self, item.span).hi();
 355             }
 356             ast::ItemKind::Mod(ref module) => {
 357                 self.format_missing_with_indent(source!(self, item.span).lo());
 358                 self.format_mod(module, &item.vis, item.span, item.ident, attrs);
 359             }
 360             ast::ItemKind::Mac(ref mac) => {
 361                 self.visit_mac(mac, Some(item.ident), MacroPosition::Item);
 362             }
 363             ast::ItemKind::ForeignMod(ref foreign_mod) => {
 364                 self.format_missing_with_indent(source!(self, item.span).lo());
 365                 self.format_foreign_mod(foreign_mod, item.span);
 366             }
 367             ast::ItemKind::Static(..) | ast::ItemKind::Const(..) => {
 368                 self.visit_static(&StaticParts::from_item(item));
 369             }
 370             ast::ItemKind::AutoImpl(..) => {
 371                 // FIXME(#78): format impl definitions.
 372             }
 373             ast::ItemKind::Fn(ref decl, unsafety, constness, abi, ref generics, ref body) => {
 374                 self.visit_fn(
 375                     visit::FnKind::ItemFn(item.ident, unsafety, constness, abi, &item.vis, body),
 376                     generics,
 377                     decl,
 378                     item.span,
 379                     ast::Defaultness::Final,
 380                     Some(&item.attrs),
 381                 )
 382             }
 383             ast::ItemKind::Ty(ref ty, ref generics) => {
 384                 let rewrite = rewrite_type_alias(
 385                     &self.get_context(),
 386                     self.block_indent,
 387                     item.ident,
 388                     ty,
 389                     generics,
 390                     &item.vis,
 391                     item.span,
 392                 );
 393                 self.push_rewrite(item.span, rewrite);
 394             }
 395             ast::ItemKind::GlobalAsm(..) => {
 396                 let snippet = Some(self.snippet(item.span));
 397                 self.push_rewrite(item.span, snippet);
 398             }
 399             ast::ItemKind::MacroDef(..) => {
 400                 // FIXME(#1539): macros 2.0
 401                 let mac_snippet = Some(remove_trailing_white_spaces(&self.snippet(item.span)));
 402                 self.push_rewrite(item.span, mac_snippet);
 403             }
 404         }
 405     }
 406
 407     pub fn visit_trait_item(&mut self, ti: &ast::TraitItem) {
 408         skip_out_of_file_lines_range_visitor!(self, ti.span);
 409
 410         if self.visit_attrs(&ti.attrs, ast::AttrStyle::Outer) {
 411             self.push_rewrite(ti.span, None);
 412             return;
 413         }
 414
 415         match ti.node {
 416             ast::TraitItemKind::Const(..) => self.visit_static(&StaticParts::from_trait_item(ti)),
 417             ast::TraitItemKind::Method(ref sig, None) => {
 418                 let indent = self.block_indent;
 419                 let rewrite =
 420                     self.rewrite_required_fn(indent, ti.ident, sig, &ti.generics, ti.span);
 421                 self.push_rewrite(ti.span, rewrite);
 422             }
 423             ast::TraitItemKind::Method(ref sig, Some(ref body)) => {
 424                 self.visit_fn(
 425                     visit::FnKind::Method(ti.ident, sig, None, body),
 426                     &ti.generics,
 427                     &sig.decl,
 428                     ti.span,
 429                     ast::Defaultness::Final,
 430                     Some(&ti.attrs),
 431                 );
 432             }
 433             ast::TraitItemKind::Type(ref type_param_bounds, ref type_default) => {
 434                 let rewrite = rewrite_associated_type(
 435                     ti.ident,
 436                     type_default.as_ref(),
 437                     Some(type_param_bounds),
 438                     &self.get_context(),
 439                     self.block_indent,
 440                 );
 441                 self.push_rewrite(ti.span, rewrite);
 442             }
 443             ast::TraitItemKind::Macro(ref mac) => {
 444                 self.visit_mac(mac, Some(ti.ident), MacroPosition::Item);
 445             }
 446         }
 447     }
 448
 449     pub fn visit_impl_item(&mut self, ii: &ast::ImplItem) {
 450         skip_out_of_file_lines_range_visitor!(self, ii.span);
 451
 452         if self.visit_attrs(&ii.attrs, ast::AttrStyle::Outer) {
 453             self.push_rewrite(ii.span, None);
 454             return;
 455         }
 456
 457         match ii.node {
 458             ast::ImplItemKind::Method(ref sig, ref body) => {
 459                 self.visit_fn(
 460                     visit::FnKind::Method(ii.ident, sig, Some(&ii.vis), body),
 461                     &ii.generics,
 462                     &sig.decl,
 463                     ii.span,
 464                     ii.defaultness,
 465                     Some(&ii.attrs),
 466                 );
 467             }
 468             ast::ImplItemKind::Const(..) => self.visit_static(&StaticParts::from_impl_item(ii)),
 469             ast::ImplItemKind::Type(ref ty) => {
 470                 let rewrite = rewrite_associated_impl_type(
 471                     ii.ident,
 472                     ii.defaultness,
 473                     Some(ty),
 474                     None,
 475                     &self.get_context(),
 476                     self.block_indent,
 477                 );
 478                 self.push_rewrite(ii.span, rewrite);
 479             }
 480             ast::ImplItemKind::Macro(ref mac) => {
 481                 self.visit_mac(mac, Some(ii.ident), MacroPosition::Item);
 482             }
 483         }
 484     }
 485
 486     fn visit_mac(&mut self, mac: &ast::Mac, ident: Option<ast::Ident>, pos: MacroPosition) {
 487         skip_out_of_file_lines_range_visitor!(self, mac.span);
 488
 489         // 1 = ;
 490         let shape = self.shape().sub_width(1).unwrap();
 491         let rewrite = rewrite_macro(mac, ident, &self.get_context(), shape, pos);
 492         self.push_rewrite(mac.span, rewrite);
 493     }
 494
 495     pub fn push_rewrite(&mut self, span: Span, rewrite: Option<String>) {
 496         self.format_missing_with_indent(source!(self, span).lo());
 497         let result = rewrite.unwrap_or_else(|| self.snippet(span));
 498         self.buffer.push_str(&result);
 499         self.last_pos = source!(self, span).hi();
 500     }
 501
 502     pub fn from_codemap(parse_session: &'a ParseSess, config: &'a Config) -> FmtVisitor<'a> {
 503         FmtVisitor {
 504             parse_session: parse_session,
 505             codemap: parse_session.codemap(),
 506             buffer: StringBuffer::new(),
 507             last_pos: BytePos(0),
 508             block_indent: Indent::empty(),
 509             config: config,
 510             is_if_else_block: false,
 511         }
 512     }
 513
 514     pub fn opt_snippet(&self, span: Span) -> Option<String> {
 515         self.codemap.span_to_snippet(span).ok()
 516     }
 517
 518     pub fn snippet(&self, span: Span) -> String {
 519         match self.codemap.span_to_snippet(span) {
 520             Ok(s) => s,
 521             Err(_) => {
 522                 eprintln!(
 523                     "Couldn't make snippet for span {:?}->{:?}",
 524                     self.codemap.lookup_char_pos(span.lo()),
 525                     self.codemap.lookup_char_pos(span.hi())
 526                 );
 527                 "".to_owned()
 528             }
 529         }
 530     }
 531
 532     // Returns true if we should skip the following item.
 533     pub fn visit_attrs(&mut self, attrs: &[ast::Attribute], style: ast::AttrStyle) -> bool {
 534         if contains_skip(attrs) {
 535             return true;
 536         }
 537
 538         let attrs: Vec<_> = attrs.iter().filter(|a| a.style == style).cloned().collect();
 539         if attrs.is_empty() {
 540             return false;
 541         }
 542
 543         let rewrite = attrs.rewrite(&self.get_context(), self.shape());
 544         let span = mk_sp(attrs[0].span.lo(), attrs[attrs.len() - 1].span.hi());
 545         self.push_rewrite(span, rewrite);
 546
 547         false
 548     }
 549
 550     fn reorder_items<F>(&mut self, items_left: &[&ast::Item], is_item: &F, in_group: bool) -> usize
 551     where
 552         F: Fn(&ast::Item) -> bool,
 553     {
 554         let mut last = self.codemap.lookup_line_range(items_left[0].span());
 555         let item_length = items_left
 556             .iter()
 557             .take_while(|ppi| {
 558                 is_item(&***ppi) && (!in_group || {
 559                     let current = self.codemap.lookup_line_range(ppi.span());
 560                     let in_same_group = current.lo < last.hi + 2;
 561                     last = current;
 562                     in_same_group
 563                 })
 564             })
 565             .count();
 566         let items = &items_left[..item_length];
 567
 568         let at_least_one_in_file_lines = items
 569             .iter()
 570             .any(|item| !out_of_file_lines_range!(self, item.span));
 571
 572         if at_least_one_in_file_lines {
 573             self.format_imports(items);
 574         } else {
 575             for item in items {
 576                 self.push_rewrite(item.span, None);
 577             }
 578         }
 579
 580         item_length
 581     }
 582
 583     fn walk_items(&mut self, mut items_left: &[&ast::Item]) {
 584         while !items_left.is_empty() {
 585             // If the next item is a `use` declaration, then extract it and any subsequent `use`s
 586             // to be potentially reordered within `format_imports`. Otherwise, just format the
 587             // next item for output.
 588             if self.config.reorder_imports() && is_use_item(&*items_left[0]) {
 589                 let used_items_len = self.reorder_items(
 590                     items_left,
 591                     &is_use_item,
 592                     self.config.reorder_imports_in_group(),
 593                 );
 594                 let (_, rest) = items_left.split_at(used_items_len);
 595                 items_left = rest;
 596             } else if self.config.reorder_extern_crates() && is_extern_crate(&*items_left[0]) {
 597                 let used_items_len = self.reorder_items(
 598                     items_left,
 599                     &is_extern_crate,
 600                     self.config.reorder_extern_crates_in_group(),
 601                 );
 602                 let (_, rest) = items_left.split_at(used_items_len);
 603                 items_left = rest;
 604             } else {
 605                 // `unwrap()` is safe here because we know `items_left`
 606                 // has elements from the loop condition
 607                 let (item, rest) = items_left.split_first().unwrap();
 608                 self.visit_item(item);
 609                 items_left = rest;
 610             }
 611         }
 612     }
 613
 614     fn walk_mod_items(&mut self, m: &ast::Mod) {
 615         self.walk_items(&ptr_vec_to_ref_vec(&m.items));
 616     }
 617
 618     fn walk_stmts(&mut self, stmts: &[ast::Stmt]) {
 619         fn to_stmt_item(stmt: &ast::Stmt) -> Option<&ast::Item> {
 620             match stmt.node {
 621                 ast::StmtKind::Item(ref item) => Some(&**item),
 622                 _ => None,
 623             }
 624         }
 625
 626         if stmts.is_empty() {
 627             return;
 628         }
 629
 630         // Extract leading `use ...;`.
 631         let items: Vec<_> = stmts
 632             .iter()
 633             .take_while(|stmt| to_stmt_item(stmt).is_some())
 634             .filter_map(|stmt| to_stmt_item(stmt))
 635             .take_while(|item| is_use_item(item))
 636             .collect();
 637
 638         if items.is_empty() {
 639             self.visit_stmt(&stmts[0]);
 640             self.walk_stmts(&stmts[1..]);
 641         } else {
 642             self.walk_items(&items);
 643             self.walk_stmts(&stmts[items.len()..]);
 644         }
 645     }
 646
 647     fn walk_block_stmts(&mut self, b: &ast::Block) {
 648         self.walk_stmts(&b.stmts)
 649     }
 650
 651     fn format_mod(
 652         &mut self,
 653         m: &ast::Mod,
 654         vis: &ast::Visibility,
 655         s: Span,
 656         ident: ast::Ident,
 657         attrs: &[ast::Attribute],
 658     ) {
 659         // Decide whether this is an inline mod or an external mod.
 660         let local_file_name = self.codemap.span_to_filename(s);
 661         let inner_span = source!(self, m.inner);
 662         let is_internal = !(inner_span.lo().0 == 0 && inner_span.hi().0 == 0)
 663             && local_file_name == self.codemap.span_to_filename(inner_span);
 664
 665         self.buffer.push_str(&*utils::format_visibility(vis));
 666         self.buffer.push_str("mod ");
 667         self.buffer.push_str(&ident.to_string());
 668
 669         if is_internal {
 670             match self.config.brace_style() {
 671                 BraceStyle::AlwaysNextLine => self.buffer
 672                     .push_str(&format!("\n{}{{", self.block_indent.to_string(self.config))),
 673                 _ => self.buffer.push_str(" {"),
 674             }
 675             // Hackery to account for the closing }.
 676             let mod_lo = self.codemap.span_after(source!(self, s), "{");
 677             let body_snippet =
 678                 self.snippet(mk_sp(mod_lo, source!(self, m.inner).hi() - BytePos(1)));
 679             let body_snippet = body_snippet.trim();
 680             if body_snippet.is_empty() {
 681                 self.buffer.push_str("}");
 682             } else {
 683                 self.last_pos = mod_lo;
 684                 self.block_indent = self.block_indent.block_indent(self.config);
 685                 self.visit_attrs(attrs, ast::AttrStyle::Inner);
 686                 self.walk_mod_items(m);
 687                 self.format_missing_with_indent(source!(self, m.inner).hi() - BytePos(1));
 688                 self.close_block(false);
 689             }
 690             self.last_pos = source!(self, m.inner).hi();
 691         } else {
 692             self.buffer.push_str(";");
 693             self.last_pos = source!(self, s).hi();
 694         }
 695     }
 696
 697     pub fn format_separate_mod(&mut self, m: &ast::Mod, filemap: &codemap::FileMap) {
 698         self.block_indent = Indent::empty();
 699         self.walk_mod_items(m);
 700         self.format_missing_with_indent(filemap.end_pos);
 701     }
 702
 703     pub fn skip_empty_lines(&mut self, end_pos: BytePos) {
 704         while let Some(pos) = self.codemap
 705             .opt_span_after(mk_sp(self.last_pos, end_pos), "\n")
 706         {
 707             if let Some(snippet) = self.opt_snippet(mk_sp(self.last_pos, pos)) {
 708                 if snippet.trim().is_empty() {
 709                     self.last_pos = pos;
 710                 } else {
 711                     return;
 712                 }
 713             }
 714         }
 715     }
 716
 717     pub fn get_context(&self) -> RewriteContext {
 718         RewriteContext {
 719             parse_session: self.parse_session,
 720             codemap: self.codemap,
 721             config: self.config,
 722             inside_macro: false,
 723             use_block: false,
 724             is_if_else_block: false,
 725             force_one_line_chain: false,
 726         }
 727     }
 728 }
 729
 730 impl Rewrite for ast::NestedMetaItem {
 731     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 732         match self.node {
 733             ast::NestedMetaItemKind::MetaItem(ref meta_item) => meta_item.rewrite(context, shape),
 734             ast::NestedMetaItemKind::Literal(ref l) => rewrite_literal(context, l, shape),
 735         }
 736     }
 737 }
 738
 739 impl Rewrite for ast::MetaItem {
 740     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 741         Some(match self.node {
 742             ast::MetaItemKind::Word => String::from(&*self.name.as_str()),
 743             ast::MetaItemKind::List(ref list) => {
 744                 let name = self.name.as_str();
 745                 // 1 = `(`, 2 = `]` and `)`
 746                 let item_shape = shape
 747                     .visual_indent(0)
 748                     .shrink_left(name.len() + 1)
 749                     .and_then(|s| s.sub_width(2))?;
 750                 let items = itemize_list(
 751                     context.codemap,
 752                     list.iter(),
 753                     ")",
 754                     ",",
 755                     |nested_meta_item| nested_meta_item.span.lo(),
 756                     |nested_meta_item| nested_meta_item.span.hi(),
 757                     |nested_meta_item| nested_meta_item.rewrite(context, item_shape),
 758                     self.span.lo(),
 759                     self.span.hi(),
 760                     false,
 761                 );
 762                 let item_vec = items.collect::<Vec<_>>();
 763                 let fmt = ListFormatting {
 764                     tactic: DefinitiveListTactic::Mixed,
 765                     separator: ",",
 766                     trailing_separator: SeparatorTactic::Never,
 767                     separator_place: SeparatorPlace::Back,
 768                     shape: item_shape,
 769                     ends_with_newline: false,
 770                     preserve_newline: false,
 771                     config: context.config,
 772                 };
 773                 format!("{}({})", name, write_list(&item_vec, &fmt)?)
 774             }
 775             ast::MetaItemKind::NameValue(ref literal) => {
 776                 let name = self.name.as_str();
 777                 // 3 = ` = `
 778                 let lit_shape = shape.shrink_left(name.len() + 3)?;
 779                 let value = rewrite_literal(context, literal, lit_shape)?;
 780                 format!("{} = {}", name, value)
 781             }
 782         })
 783     }
 784 }
 785
 786 impl Rewrite for ast::Attribute {
 787     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 788         let prefix = match self.style {
 789             ast::AttrStyle::Inner => "#!",
 790             ast::AttrStyle::Outer => "#",
 791         };
 792         let snippet = context.snippet(self.span);
 793         if self.is_sugared_doc {
 794             let doc_shape = Shape {
 795                 width: cmp::min(shape.width, context.config.comment_width())
 796                     .checked_sub(shape.indent.width())
 797                     .unwrap_or(0),
 798                 ..shape
 799             };
 800             rewrite_comment(&snippet, false, doc_shape, context.config)
 801         } else {
 802             if contains_comment(&snippet) {
 803                 return Some(snippet);
 804             }
 805             // 1 = `[`
 806             let shape = shape.offset_left(prefix.len() + 1)?;
 807             self.meta()?
 808                 .rewrite(context, shape)
 809                 .map(|rw| format!("{}[{}]", prefix, rw))
 810         }
 811     }
 812 }
 813
 814 /// Returns the first group of attributes that fills the given predicate.
 815 /// We consider two doc comments are in different group if they are separated by normal comments.
 816 fn take_while_with_pred<'a, P>(
 817     context: &RewriteContext,
 818     attrs: &'a [ast::Attribute],
 819     pred: P,
 820 ) -> &'a [ast::Attribute]
 821 where
 822     P: Fn(&ast::Attribute) -> bool,
 823 {
 824     let mut last_index = 0;
 825     let mut iter = attrs.iter().enumerate().peekable();
 826     while let Some((i, attr)) = iter.next() {
 827         if !pred(attr) {
 828             break;
 829         }
 830         if let Some(&(_, next_attr)) = iter.peek() {
 831             // Extract comments between two attributes.
 832             let span_between_attr = mk_sp(attr.span.hi(), next_attr.span.lo());
 833             let snippet = context.snippet(span_between_attr);
 834             if snippet.chars().filter(|c| *c == '\n').count() >= 2 || snippet.contains('/') {
 835                 break;
 836             }
 837         }
 838         last_index = i;
 839     }
 840     if last_index == 0 {
 841         &[]
 842     } else {
 843         &attrs[..last_index + 1]
 844     }
 845 }
 846
 847 fn rewrite_first_group_attrs(
 848     context: &RewriteContext,
 849     attrs: &[ast::Attribute],
 850     shape: Shape,
 851 ) -> Option<(usize, String)> {
 852     if attrs.is_empty() {
 853         return Some((0, String::new()));
 854     }
 855     // Rewrite doc comments
 856     let sugared_docs = take_while_with_pred(context, attrs, |a| a.is_sugared_doc);
 857     if !sugared_docs.is_empty() {
 858         let snippet = sugared_docs
 859             .iter()
 860             .map(|a| context.snippet(a.span))
 861             .collect::<Vec<_>>()
 862             .join("\n");
 863         return Some((
 864             sugared_docs.len(),
 865             rewrite_comment(&snippet, false, shape, context.config)?,
 866         ));
 867     }
 868     // Rewrite `#[derive(..)]`s.
 869     if context.config.merge_derives() {
 870         let derives = take_while_with_pred(context, attrs, is_derive);
 871         if !derives.is_empty() {
 872             let mut derive_args = vec![];
 873             for derive in derives {
 874                 derive_args.append(&mut get_derive_args(context, derive)?);
 875             }
 876             return Some((derives.len(), format_derive(context, &derive_args, shape)?));
 877         }
 878     }
 879     // Rewrite the first attribute.
 880     Some((1, attrs[0].rewrite(context, shape)?))
 881 }
 882
 883 fn has_newlines_before_after_comment(comment: &str) -> (&str, &str) {
 884     // Look at before and after comment and see if there are any empty lines.
 885     let comment_begin = comment.chars().position(|c| c == '/');
 886     let len = comment_begin.unwrap_or_else(|| comment.len());
 887     let mlb = comment.chars().take(len).filter(|c| *c == '\n').count() > 1;
 888     let mla = if comment_begin.is_none() {
 889         mlb
 890     } else {
 891         let comment_end = comment.chars().rev().position(|c| !c.is_whitespace());
 892         let len = comment_end.unwrap();
 893         comment
 894             .chars()
 895             .rev()
 896             .take(len)
 897             .filter(|c| *c == '\n')
 898             .count() > 1
 899     };
 900     (if mlb { "\n" } else { "" }, if mla { "\n" } else { "" })
 901 }
 902
 903 impl<'a> Rewrite for [ast::Attribute] {
 904     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 905         if self.is_empty() {
 906             return Some(String::new());
 907         }
 908         let (first_group_len, first_group_str) = rewrite_first_group_attrs(context, self, shape)?;
 909         if self.len() == 1 || first_group_len == self.len() {
 910             Some(first_group_str)
 911         } else {
 912             let rest_str = self[first_group_len..].rewrite(context, shape)?;
 913             let missing_span = mk_sp(
 914                 self[first_group_len - 1].span.hi(),
 915                 self[first_group_len].span.lo(),
 916             );
 917             // Preserve an empty line before/after doc comments.
 918             if self[0].is_sugared_doc || self[first_group_len].is_sugared_doc {
 919                 let snippet = context.snippet(missing_span);
 920                 let (mla, mlb) = has_newlines_before_after_comment(&snippet);
 921                 let comment = ::comment::recover_missing_comment_in_span(
 922                     missing_span,
 923                     shape.with_max_width(context.config),
 924                     context,
 925                     0,
 926                 )?;
 927                 let comment = if comment.is_empty() {
 928                     format!("\n{}", mlb)
 929                 } else {
 930                     format!("{}{}\n{}", mla, comment, mlb)
 931                 };
 932                 Some(format!(
 933                     "{}{}{}{}",
 934                     first_group_str,
 935                     comment,
 936                     shape.indent.to_string(context.config),
 937                     rest_str
 938                 ))
 939             } else {
 940                 combine_strs_with_missing_comments(
 941                     context,
 942                     &first_group_str,
 943                     &rest_str,
 944                     missing_span,
 945                     shape,
 946                     false,
 947                 )
 948             }
 949         }
 950     }
 951 }
 952
 953 // Format `#[derive(..)]`, using visual indent & mixed style when we need to go multiline.
 954 fn format_derive(context: &RewriteContext, derive_args: &[String], shape: Shape) -> Option<String> {
 955     let mut result = String::with_capacity(128);
 956     result.push_str("#[derive(");
 957     // 11 = `#[derive()]`
 958     let initial_budget = shape.width.checked_sub(11)?;
 959     let mut budget = initial_budget;
 960     let num = derive_args.len();
 961     for (i, a) in derive_args.iter().enumerate() {
 962         // 2 = `, ` or `)]`
 963         let width = a.len() + 2;
 964         if width > budget {
 965             if i > 0 {
 966                 // Remove trailing whitespace.
 967                 result.pop();
 968             }
 969             result.push('\n');
 970             // 9 = `#[derive(`
 971             result.push_str(&(shape.indent + 9).to_string(context.config));
 972             budget = initial_budget;
 973         } else {
 974             budget = budget.checked_sub(width).unwrap_or(0);
 975         }
 976         result.push_str(a);
 977         if i != num - 1 {
 978             result.push_str(", ")
 979         }
 980     }
 981     result.push_str(")]");
 982     Some(result)
 983 }
 984
 985 fn is_derive(attr: &ast::Attribute) -> bool {
 986     match attr.meta() {
 987         Some(meta_item) => match meta_item.node {
 988             ast::MetaItemKind::List(..) => meta_item.name.as_str() == "derive",
 989             _ => false,
 990         },
 991         _ => false,
 992     }
 993 }
 994
 995 /// Returns the arguments of `#[derive(...)]`.
 996 fn get_derive_args(context: &RewriteContext, attr: &ast::Attribute) -> Option<Vec<String>> {
 997     attr.meta().and_then(|meta_item| match meta_item.node {
 998         ast::MetaItemKind::List(ref args) if meta_item.name.as_str() == "derive" => {
 999             // Every argument of `derive` should be `NestedMetaItemKind::Literal`.
1000             Some(
1001                 args.iter()
1002                     .map(|a| context.snippet(a.span))
1003                     .collect::<Vec<_>>(),
1004             )
1005         }
1006         _ => None,
1007     })
1008 }
1009
1010 // Rewrite `extern crate foo;` WITHOUT attributes.
1011 pub fn rewrite_extern_crate(context: &RewriteContext, item: &ast::Item) -> Option<String> {
1012     assert!(is_extern_crate(item));
1013     let new_str = context.snippet(item.span);
1014     Some(if contains_comment(&new_str) {
1015         new_str
1016     } else {
1017         let no_whitespace = &new_str.split_whitespace().collect::<Vec<&str>>().join(" ");
1018         String::from(&*Regex::new(r"\s;").unwrap().replace(no_whitespace, ";"))
1019     })
1020 }