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::rc::Rc;
  12 use std::cmp;
  13 use std::mem;
  14
  15 use strings::string_buffer::StringBuffer;
  16 use syntax::{ast, visit};
  17 use syntax::attr::HasAttrs;
  18 use syntax::codemap::{self, BytePos, CodeMap, Pos, Span};
  19 use syntax::parse::ParseSess;
  20
  21 use expr::rewrite_literal;
  22 use spanned::Spanned;
  23 use codemap::{LineRangeUtils, SpanUtils};
  24 use comment::{combine_strs_with_missing_comments, contains_comment, remove_trailing_white_spaces,
  25               CodeCharKind, CommentCodeSlices, FindUncommented};
  26 use comment::rewrite_comment;
  27 use config::{BraceStyle, Config};
  28 use items::{format_impl, format_trait, rewrite_associated_impl_type, rewrite_associated_type,
  29             rewrite_type_alias, FnSig, StaticParts, StructParts};
  30 use lists::{itemize_list, write_list, DefinitiveListTactic, ListFormatting, SeparatorPlace,
  31             SeparatorTactic};
  32 use macros::{rewrite_macro, MacroPosition};
  33 use regex::Regex;
  34 use rewrite::{Rewrite, RewriteContext};
  35 use shape::{Indent, Shape};
  36 use utils::{self, contains_skip, count_newlines, inner_attributes, mk_sp, ptr_vec_to_ref_vec};
  37
  38 fn is_use_item(item: &ast::Item) -> bool {
  39     match item.node {
  40         ast::ItemKind::Use(_) => true,
  41         _ => false,
  42     }
  43 }
  44
  45 fn is_extern_crate(item: &ast::Item) -> bool {
  46     match item.node {
  47         ast::ItemKind::ExternCrate(..) => true,
  48         _ => false,
  49     }
  50 }
  51
  52 /// Creates a string slice corresponding to the specified span.
  53 pub struct SnippetProvider {
  54     /// A pointer to the content of the file we are formatting.
  55     big_snippet: *const Rc<String>,
  56     /// A position of the start of `big_snippet`, used as an offset.
  57     start_pos: usize,
  58 }
  59
  60 impl SnippetProvider {
  61     pub fn span_to_snippet(&self, span: Span) -> Option<&str> {
  62         let start_index = span.lo().to_usize().checked_sub(self.start_pos)?;
  63         let end_index = span.hi().to_usize().checked_sub(self.start_pos)?;
  64         unsafe { Some(&(*self.big_snippet)[start_index..end_index]) }
  65     }
  66
  67     pub fn from_codemap(codemap: &CodeMap, span: Span) -> Self {
  68         let filemap = codemap.lookup_char_pos(span.lo()).file;
  69         let big_snippet = unsafe { mem::transmute(&filemap.src) };
  70         let start_pos = filemap.start_pos.to_usize();
  71         SnippetProvider {
  72             big_snippet,
  73             start_pos,
  74         }
  75     }
  76 }
  77
  78 pub struct FmtVisitor<'a> {
  79     pub parse_session: &'a ParseSess,
  80     pub codemap: &'a CodeMap,
  81     pub buffer: StringBuffer,
  82     pub last_pos: BytePos,
  83     // FIXME: use an RAII util or closure for indenting
  84     pub block_indent: Indent,
  85     pub config: &'a Config,
  86     pub is_if_else_block: bool,
  87     pub snippet_provier: SnippetProvider,
  88 }
  89
  90 impl<'a> FmtVisitor<'a> {
  91     pub fn shape(&self) -> Shape {
  92         Shape::indented(self.block_indent, self.config)
  93     }
  94
  95     fn visit_stmt(&mut self, stmt: &ast::Stmt) {
  96         debug!(
  97             "visit_stmt: {:?} {:?}",
  98             self.codemap.lookup_char_pos(stmt.span.lo()),
  99             self.codemap.lookup_char_pos(stmt.span.hi())
 100         );
 101
 102         match stmt.node {
 103             ast::StmtKind::Item(ref item) => {
 104                 self.visit_item(item);
 105             }
 106             ast::StmtKind::Local(..) | ast::StmtKind::Expr(..) | ast::StmtKind::Semi(..) => {
 107                 let rewrite = stmt.rewrite(&self.get_context(), self.shape());
 108                 self.push_rewrite(stmt.span(), rewrite)
 109             }
 110             ast::StmtKind::Mac(ref mac) => {
 111                 let (ref mac, _macro_style, ref attrs) = **mac;
 112                 if self.visit_attrs(attrs, ast::AttrStyle::Outer) {
 113                     self.push_rewrite(stmt.span(), None);
 114                 } else {
 115                     self.visit_mac(mac, None, MacroPosition::Statement);
 116                 }
 117                 self.format_missing(stmt.span.hi());
 118             }
 119         }
 120     }
 121
 122     pub fn visit_block(
 123         &mut self,
 124         b: &ast::Block,
 125         inner_attrs: Option<&[ast::Attribute]>,
 126         has_braces: bool,
 127     ) {
 128         debug!(
 129             "visit_block: {:?} {:?}",
 130             self.codemap.lookup_char_pos(b.span.lo()),
 131             self.codemap.lookup_char_pos(b.span.hi())
 132         );
 133
 134         // Check if this block has braces.
 135         let brace_compensation = BytePos(if has_braces { 1 } else { 0 });
 136
 137         self.last_pos = self.last_pos + brace_compensation;
 138         self.block_indent = self.block_indent.block_indent(self.config);
 139         self.buffer.push_str("{");
 140
 141         if self.config.remove_blank_lines_at_start_or_end_of_block() {
 142             if let Some(first_stmt) = b.stmts.first() {
 143                 let attr_lo = inner_attrs
 144                     .and_then(|attrs| inner_attributes(attrs).first().map(|attr| attr.span.lo()))
 145                     .or_else(|| {
 146                         // Attributes for an item in a statement position
 147                         // do not belong to the statement. (rust-lang/rust#34459)
 148                         if let ast::StmtKind::Item(ref item) = first_stmt.node {
 149                             item.attrs.first()
 150                         } else {
 151                             first_stmt.attrs().first()
 152                         }.and_then(|attr| {
 153                             // Some stmts can have embedded attributes.
 154                             // e.g. `match { #![attr] ... }`
 155                             let attr_lo = attr.span.lo();
 156                             if attr_lo < first_stmt.span.lo() {
 157                                 Some(attr_lo)
 158                             } else {
 159                                 None
 160                             }
 161                         })
 162                     });
 163
 164                 let snippet = self.snippet(mk_sp(
 165                     self.last_pos,
 166                     attr_lo.unwrap_or(first_stmt.span.lo()),
 167                 ));
 168                 let len = CommentCodeSlices::new(&snippet)
 169                     .nth(0)
 170                     .and_then(|(kind, _, s)| {
 171                         if kind == CodeCharKind::Normal {
 172                             s.rfind('\n')
 173                         } else {
 174                             None
 175                         }
 176                     });
 177                 if let Some(len) = len {
 178                     self.last_pos = self.last_pos + BytePos::from_usize(len);
 179                 }
 180             }
 181         }
 182
 183         // Format inner attributes if available.
 184         let skip_rewrite = if let Some(attrs) = inner_attrs {
 185             self.visit_attrs(attrs, ast::AttrStyle::Inner)
 186         } else {
 187             false
 188         };
 189
 190         if skip_rewrite {
 191             self.push_rewrite(b.span, None);
 192             self.close_block(false);
 193             self.last_pos = source!(self, b.span).hi();
 194             return;
 195         }
 196
 197         self.walk_block_stmts(b);
 198
 199         if !b.stmts.is_empty() {
 200             if let Some(expr) = utils::stmt_expr(&b.stmts[b.stmts.len() - 1]) {
 201                 if utils::semicolon_for_expr(&self.get_context(), expr) {
 202                     self.buffer.push_str(";");
 203                 }
 204             }
 205         }
 206
 207         let mut remove_len = BytePos(0);
 208         if self.config.remove_blank_lines_at_start_or_end_of_block() {
 209             if let Some(stmt) = b.stmts.last() {
 210                 let snippet = self.snippet(mk_sp(
 211                     stmt.span.hi(),
 212                     source!(self, b.span).hi() - brace_compensation,
 213                 ));
 214                 let len = CommentCodeSlices::new(&snippet)
 215                     .last()
 216                     .and_then(|(kind, _, s)| {
 217                         if kind == CodeCharKind::Normal && s.trim().is_empty() {
 218                             Some(s.len())
 219                         } else {
 220                             None
 221                         }
 222                     });
 223                 if let Some(len) = len {
 224                     remove_len = BytePos::from_usize(len);
 225                 }
 226             }
 227         }
 228
 229         let unindent_comment = (self.is_if_else_block && !b.stmts.is_empty()) && {
 230             let end_pos = source!(self, b.span).hi() - brace_compensation - remove_len;
 231             let snippet = self.snippet(mk_sp(self.last_pos, end_pos));
 232             snippet.contains("//") || snippet.contains("/*")
 233         };
 234         // FIXME: we should compress any newlines here to just one
 235         if unindent_comment {
 236             self.block_indent = self.block_indent.block_unindent(self.config);
 237         }
 238         self.format_missing_with_indent(
 239             source!(self, b.span).hi() - brace_compensation - remove_len,
 240         );
 241         if unindent_comment {
 242             self.block_indent = self.block_indent.block_indent(self.config);
 243         }
 244         self.close_block(unindent_comment);
 245         self.last_pos = source!(self, b.span).hi();
 246     }
 247
 248     // FIXME: this is a terrible hack to indent the comments between the last
 249     // item in the block and the closing brace to the block's level.
 250     // The closing brace itself, however, should be indented at a shallower
 251     // level.
 252     fn close_block(&mut self, unindent_comment: bool) {
 253         let total_len = self.buffer.len;
 254         let chars_too_many = if unindent_comment {
 255             0
 256         } else if self.config.hard_tabs() {
 257             1
 258         } else {
 259             self.config.tab_spaces()
 260         };
 261         self.buffer.truncate(total_len - chars_too_many);
 262         self.buffer.push_str("}");
 263         self.block_indent = self.block_indent.block_unindent(self.config);
 264     }
 265
 266     // Note that this only gets called for function definitions. Required methods
 267     // on traits do not get handled here.
 268     fn visit_fn(
 269         &mut self,
 270         fk: visit::FnKind,
 271         generics: &ast::Generics,
 272         fd: &ast::FnDecl,
 273         s: Span,
 274         defaultness: ast::Defaultness,
 275         inner_attrs: Option<&[ast::Attribute]>,
 276     ) {
 277         let indent = self.block_indent;
 278         let block;
 279         let rewrite = match fk {
 280             visit::FnKind::ItemFn(ident, _, _, _, _, b) | visit::FnKind::Method(ident, _, _, b) => {
 281                 block = b;
 282                 self.rewrite_fn(
 283                     indent,
 284                     ident,
 285                     &FnSig::from_fn_kind(&fk, generics, fd, defaultness),
 286                     mk_sp(s.lo(), b.span.lo()),
 287                     b,
 288                 )
 289             }
 290             visit::FnKind::Closure(_) => unreachable!(),
 291         };
 292
 293         if let Some(fn_str) = rewrite {
 294             self.format_missing_with_indent(source!(self, s).lo());
 295             self.buffer.push_str(&fn_str);
 296             if let Some(c) = fn_str.chars().last() {
 297                 if c == '}' {
 298                     self.last_pos = source!(self, block.span).hi();
 299                     return;
 300                 }
 301             }
 302         } else {
 303             self.format_missing(source!(self, block.span).lo());
 304         }
 305
 306         self.last_pos = source!(self, block.span).lo();
 307         self.visit_block(block, inner_attrs, true)
 308     }
 309
 310     pub fn visit_item(&mut self, item: &ast::Item) {
 311         skip_out_of_file_lines_range_visitor!(self, item.span);
 312
 313         // This is where we bail out if there is a skip attribute. This is only
 314         // complex in the module case. It is complex because the module could be
 315         // in a separate file and there might be attributes in both files, but
 316         // the AST lumps them all together.
 317         let filtered_attrs;
 318         let mut attrs = &item.attrs;
 319         match item.node {
 320             ast::ItemKind::Mod(ref m) => {
 321                 let outer_file = self.codemap.lookup_char_pos(item.span.lo()).file;
 322                 let inner_file = self.codemap.lookup_char_pos(m.inner.lo()).file;
 323                 if outer_file.name == inner_file.name {
 324                     // Module is inline, in this case we treat modules like any
 325                     // other item.
 326                     if self.visit_attrs(&item.attrs, ast::AttrStyle::Outer) {
 327                         self.push_rewrite(item.span, None);
 328                         return;
 329                     }
 330                 } else if contains_skip(&item.attrs) {
 331                     // Module is not inline, but should be skipped.
 332                     return;
 333                 } else {
 334                     // Module is not inline and should not be skipped. We want
 335                     // to process only the attributes in the current file.
 336                     filtered_attrs = item.attrs
 337                         .iter()
 338                         .filter_map(|a| {
 339                             let attr_file = self.codemap.lookup_char_pos(a.span.lo()).file;
 340                             if attr_file.name == outer_file.name {
 341                                 Some(a.clone())
 342                             } else {
 343                                 None
 344                             }
 345                         })
 346                         .collect::<Vec<_>>();
 347                     // Assert because if we should skip it should be caught by
 348                     // the above case.
 349                     assert!(!self.visit_attrs(&filtered_attrs, ast::AttrStyle::Outer));
 350                     attrs = &filtered_attrs;
 351                 }
 352             }
 353             _ => {
 354                 if self.visit_attrs(&item.attrs, ast::AttrStyle::Outer) {
 355                     self.push_rewrite(item.span, None);
 356                     return;
 357                 }
 358             }
 359         }
 360
 361         match item.node {
 362             ast::ItemKind::Use(ref tree) => self.format_import(item, tree),
 363             ast::ItemKind::Impl(..) => {
 364                 let snippet = self.snippet(item.span);
 365                 let where_span_end = snippet
 366                     .find_uncommented("{")
 367                     .map(|x| (BytePos(x as u32)) + source!(self, item.span).lo());
 368                 let rw = format_impl(&self.get_context(), item, self.block_indent, where_span_end);
 369                 self.push_rewrite(item.span, rw);
 370             }
 371             ast::ItemKind::Trait(..) => {
 372                 let rw = format_trait(&self.get_context(), item, self.block_indent);
 373                 self.push_rewrite(item.span, rw);
 374             }
 375             ast::ItemKind::ExternCrate(_) => {
 376                 let rw = rewrite_extern_crate(&self.get_context(), item);
 377                 self.push_rewrite(item.span, rw);
 378             }
 379             ast::ItemKind::Struct(..) | ast::ItemKind::Union(..) => {
 380                 self.visit_struct(&StructParts::from_item(item));
 381             }
 382             ast::ItemKind::Enum(ref def, ref generics) => {
 383                 self.format_missing_with_indent(source!(self, item.span).lo());
 384                 self.visit_enum(item.ident, &item.vis, def, generics, item.span);
 385                 self.last_pos = source!(self, item.span).hi();
 386             }
 387             ast::ItemKind::Mod(ref module) => {
 388                 self.format_missing_with_indent(source!(self, item.span).lo());
 389                 self.format_mod(module, &item.vis, item.span, item.ident, attrs);
 390             }
 391             ast::ItemKind::Mac(ref mac) => {
 392                 self.visit_mac(mac, Some(item.ident), MacroPosition::Item);
 393             }
 394             ast::ItemKind::ForeignMod(ref foreign_mod) => {
 395                 self.format_missing_with_indent(source!(self, item.span).lo());
 396                 self.format_foreign_mod(foreign_mod, item.span);
 397             }
 398             ast::ItemKind::Static(..) | ast::ItemKind::Const(..) => {
 399                 self.visit_static(&StaticParts::from_item(item));
 400             }
 401             ast::ItemKind::AutoImpl(..) => {
 402                 // FIXME(#78): format impl definitions.
 403             }
 404             ast::ItemKind::Fn(ref decl, unsafety, constness, abi, ref generics, ref body) => {
 405                 self.visit_fn(
 406                     visit::FnKind::ItemFn(item.ident, unsafety, constness, abi, &item.vis, body),
 407                     generics,
 408                     decl,
 409                     item.span,
 410                     ast::Defaultness::Final,
 411                     Some(&item.attrs),
 412                 )
 413             }
 414             ast::ItemKind::Ty(ref ty, ref generics) => {
 415                 let rewrite = rewrite_type_alias(
 416                     &self.get_context(),
 417                     self.block_indent,
 418                     item.ident,
 419                     ty,
 420                     generics,
 421                     &item.vis,
 422                     item.span,
 423                 );
 424                 self.push_rewrite(item.span, rewrite);
 425             }
 426             ast::ItemKind::GlobalAsm(..) => {
 427                 let snippet = Some(self.snippet(item.span));
 428                 self.push_rewrite(item.span, snippet);
 429             }
 430             ast::ItemKind::MacroDef(..) => {
 431                 // FIXME(#1539): macros 2.0
 432                 let mac_snippet = Some(remove_trailing_white_spaces(&self.snippet(item.span)));
 433                 self.push_rewrite(item.span, mac_snippet);
 434             }
 435         }
 436     }
 437
 438     pub fn visit_trait_item(&mut self, ti: &ast::TraitItem) {
 439         skip_out_of_file_lines_range_visitor!(self, ti.span);
 440
 441         if self.visit_attrs(&ti.attrs, ast::AttrStyle::Outer) {
 442             self.push_rewrite(ti.span, None);
 443             return;
 444         }
 445
 446         match ti.node {
 447             ast::TraitItemKind::Const(..) => self.visit_static(&StaticParts::from_trait_item(ti)),
 448             ast::TraitItemKind::Method(ref sig, None) => {
 449                 let indent = self.block_indent;
 450                 let rewrite =
 451                     self.rewrite_required_fn(indent, ti.ident, sig, &ti.generics, ti.span);
 452                 self.push_rewrite(ti.span, rewrite);
 453             }
 454             ast::TraitItemKind::Method(ref sig, Some(ref body)) => {
 455                 self.visit_fn(
 456                     visit::FnKind::Method(ti.ident, sig, None, body),
 457                     &ti.generics,
 458                     &sig.decl,
 459                     ti.span,
 460                     ast::Defaultness::Final,
 461                     Some(&ti.attrs),
 462                 );
 463             }
 464             ast::TraitItemKind::Type(ref type_param_bounds, ref type_default) => {
 465                 let rewrite = rewrite_associated_type(
 466                     ti.ident,
 467                     type_default.as_ref(),
 468                     Some(type_param_bounds),
 469                     &self.get_context(),
 470                     self.block_indent,
 471                 );
 472                 self.push_rewrite(ti.span, rewrite);
 473             }
 474             ast::TraitItemKind::Macro(ref mac) => {
 475                 self.visit_mac(mac, Some(ti.ident), MacroPosition::Item);
 476             }
 477         }
 478     }
 479
 480     pub fn visit_impl_item(&mut self, ii: &ast::ImplItem) {
 481         skip_out_of_file_lines_range_visitor!(self, ii.span);
 482
 483         if self.visit_attrs(&ii.attrs, ast::AttrStyle::Outer) {
 484             self.push_rewrite(ii.span, None);
 485             return;
 486         }
 487
 488         match ii.node {
 489             ast::ImplItemKind::Method(ref sig, ref body) => {
 490                 self.visit_fn(
 491                     visit::FnKind::Method(ii.ident, sig, Some(&ii.vis), body),
 492                     &ii.generics,
 493                     &sig.decl,
 494                     ii.span,
 495                     ii.defaultness,
 496                     Some(&ii.attrs),
 497                 );
 498             }
 499             ast::ImplItemKind::Const(..) => self.visit_static(&StaticParts::from_impl_item(ii)),
 500             ast::ImplItemKind::Type(ref ty) => {
 501                 let rewrite = rewrite_associated_impl_type(
 502                     ii.ident,
 503                     ii.defaultness,
 504                     Some(ty),
 505                     None,
 506                     &self.get_context(),
 507                     self.block_indent,
 508                 );
 509                 self.push_rewrite(ii.span, rewrite);
 510             }
 511             ast::ImplItemKind::Macro(ref mac) => {
 512                 self.visit_mac(mac, Some(ii.ident), MacroPosition::Item);
 513             }
 514         }
 515     }
 516
 517     fn visit_mac(&mut self, mac: &ast::Mac, ident: Option<ast::Ident>, pos: MacroPosition) {
 518         skip_out_of_file_lines_range_visitor!(self, mac.span);
 519
 520         // 1 = ;
 521         let shape = self.shape().sub_width(1).unwrap();
 522         let rewrite = rewrite_macro(mac, ident, &self.get_context(), shape, pos);
 523         self.push_rewrite(mac.span, rewrite);
 524     }
 525
 526     pub fn push_rewrite(&mut self, span: Span, rewrite: Option<String>) {
 527         self.format_missing_with_indent(source!(self, span).lo());
 528         let result = rewrite.unwrap_or_else(|| self.snippet(span));
 529         self.buffer.push_str(&result);
 530         self.last_pos = source!(self, span).hi();
 531     }
 532
 533     pub fn from_codemap(parse_session: &'a ParseSess, config: &'a Config) -> FmtVisitor<'a> {
 534         FmtVisitor {
 535             parse_session: parse_session,
 536             codemap: parse_session.codemap(),
 537             buffer: StringBuffer::new(),
 538             last_pos: BytePos(0),
 539             block_indent: Indent::empty(),
 540             config: config,
 541             is_if_else_block: false,
 542             snippet_provier: SnippetProvider::from_codemap(parse_session.codemap(), span),
 543         }
 544     }
 545
 546     pub fn opt_snippet<'b: 'a>(&'a self, span: Span) -> Option<&'b str> {
 547         self.snippet_provier
 548             .span_to_snippet(span)
 549             .map(|s| unsafe { mem::transmute::<&'a str, &'b str>(s) })
 550     }
 551
 552     pub fn snippet<'b: 'a>(&'a self, span: Span) -> &'b str {
 553         self.opt_snippet(span).unwrap()
 554     }
 555
 556     // Returns true if we should skip the following item.
 557     pub fn visit_attrs(&mut self, attrs: &[ast::Attribute], style: ast::AttrStyle) -> bool {
 558         if contains_skip(attrs) {
 559             return true;
 560         }
 561
 562         let attrs: Vec<_> = attrs.iter().filter(|a| a.style == style).cloned().collect();
 563         if attrs.is_empty() {
 564             return false;
 565         }
 566
 567         let rewrite = attrs.rewrite(&self.get_context(), self.shape());
 568         let span = mk_sp(attrs[0].span.lo(), attrs[attrs.len() - 1].span.hi());
 569         self.push_rewrite(span, rewrite);
 570
 571         false
 572     }
 573
 574     fn reorder_items<F>(&mut self, items_left: &[&ast::Item], is_item: &F, in_group: bool) -> usize
 575     where
 576         F: Fn(&ast::Item) -> bool,
 577     {
 578         let mut last = self.codemap.lookup_line_range(items_left[0].span());
 579         let item_length = items_left
 580             .iter()
 581             .take_while(|ppi| {
 582                 is_item(&***ppi) && (!in_group || {
 583                     let current = self.codemap.lookup_line_range(ppi.span());
 584                     let in_same_group = current.lo < last.hi + 2;
 585                     last = current;
 586                     in_same_group
 587                 })
 588             })
 589             .count();
 590         let items = &items_left[..item_length];
 591
 592         let at_least_one_in_file_lines = items
 593             .iter()
 594             .any(|item| !out_of_file_lines_range!(self, item.span));
 595
 596         if at_least_one_in_file_lines {
 597             self.format_imports(items);
 598         } else {
 599             for item in items {
 600                 self.push_rewrite(item.span, None);
 601             }
 602         }
 603
 604         item_length
 605     }
 606
 607     fn walk_items(&mut self, mut items_left: &[&ast::Item]) {
 608         while !items_left.is_empty() {
 609             // If the next item is a `use` declaration, then extract it and any subsequent `use`s
 610             // to be potentially reordered within `format_imports`. Otherwise, just format the
 611             // next item for output.
 612             if self.config.reorder_imports() && is_use_item(&*items_left[0]) {
 613                 let used_items_len = self.reorder_items(
 614                     items_left,
 615                     &is_use_item,
 616                     self.config.reorder_imports_in_group(),
 617                 );
 618                 let (_, rest) = items_left.split_at(used_items_len);
 619                 items_left = rest;
 620             } else if self.config.reorder_extern_crates() && is_extern_crate(&*items_left[0]) {
 621                 let used_items_len = self.reorder_items(
 622                     items_left,
 623                     &is_extern_crate,
 624                     self.config.reorder_extern_crates_in_group(),
 625                 );
 626                 let (_, rest) = items_left.split_at(used_items_len);
 627                 items_left = rest;
 628             } else {
 629                 // `unwrap()` is safe here because we know `items_left`
 630                 // has elements from the loop condition
 631                 let (item, rest) = items_left.split_first().unwrap();
 632                 self.visit_item(item);
 633                 items_left = rest;
 634             }
 635         }
 636     }
 637
 638     fn walk_mod_items(&mut self, m: &ast::Mod) {
 639         self.walk_items(&ptr_vec_to_ref_vec(&m.items));
 640     }
 641
 642     fn walk_stmts(&mut self, stmts: &[ast::Stmt]) {
 643         fn to_stmt_item(stmt: &ast::Stmt) -> Option<&ast::Item> {
 644             match stmt.node {
 645                 ast::StmtKind::Item(ref item) => Some(&**item),
 646                 _ => None,
 647             }
 648         }
 649
 650         if stmts.is_empty() {
 651             return;
 652         }
 653
 654         // Extract leading `use ...;`.
 655         let items: Vec<_> = stmts
 656             .iter()
 657             .take_while(|stmt| to_stmt_item(stmt).is_some())
 658             .filter_map(|stmt| to_stmt_item(stmt))
 659             .take_while(|item| is_use_item(item))
 660             .collect();
 661
 662         if items.is_empty() {
 663             self.visit_stmt(&stmts[0]);
 664             self.walk_stmts(&stmts[1..]);
 665         } else {
 666             self.walk_items(&items);
 667             self.walk_stmts(&stmts[items.len()..]);
 668         }
 669     }
 670
 671     fn walk_block_stmts(&mut self, b: &ast::Block) {
 672         self.walk_stmts(&b.stmts)
 673     }
 674
 675     fn format_mod(
 676         &mut self,
 677         m: &ast::Mod,
 678         vis: &ast::Visibility,
 679         s: Span,
 680         ident: ast::Ident,
 681         attrs: &[ast::Attribute],
 682     ) {
 683         // Decide whether this is an inline mod or an external mod.
 684         let local_file_name = self.codemap.span_to_filename(s);
 685         let inner_span = source!(self, m.inner);
 686         let is_internal = !(inner_span.lo().0 == 0 && inner_span.hi().0 == 0)
 687             && local_file_name == self.codemap.span_to_filename(inner_span);
 688
 689         self.buffer.push_str(&*utils::format_visibility(vis));
 690         self.buffer.push_str("mod ");
 691         self.buffer.push_str(&ident.to_string());
 692
 693         if is_internal {
 694             match self.config.brace_style() {
 695                 BraceStyle::AlwaysNextLine => self.buffer
 696                     .push_str(&format!("\n{}{{", self.block_indent.to_string(self.config))),
 697                 _ => self.buffer.push_str(" {"),
 698             }
 699             // Hackery to account for the closing }.
 700             let mod_lo = self.codemap.span_after(source!(self, s), "{");
 701             let body_snippet =
 702                 self.snippet(mk_sp(mod_lo, source!(self, m.inner).hi() - BytePos(1)));
 703             let body_snippet = body_snippet.trim();
 704             if body_snippet.is_empty() {
 705                 self.buffer.push_str("}");
 706             } else {
 707                 self.last_pos = mod_lo;
 708                 self.block_indent = self.block_indent.block_indent(self.config);
 709                 self.visit_attrs(attrs, ast::AttrStyle::Inner);
 710                 self.walk_mod_items(m);
 711                 self.format_missing_with_indent(source!(self, m.inner).hi() - BytePos(1));
 712                 self.close_block(false);
 713             }
 714             self.last_pos = source!(self, m.inner).hi();
 715         } else {
 716             self.buffer.push_str(";");
 717             self.last_pos = source!(self, s).hi();
 718         }
 719     }
 720
 721     pub fn format_separate_mod(&mut self, m: &ast::Mod, filemap: &codemap::FileMap) {
 722         self.block_indent = Indent::empty();
 723         self.walk_mod_items(m);
 724         self.format_missing_with_indent(filemap.end_pos);
 725     }
 726
 727     pub fn skip_empty_lines(&mut self, end_pos: BytePos) {
 728         while let Some(pos) = self.codemap
 729             .opt_span_after(mk_sp(self.last_pos, end_pos), "\n")
 730         {
 731             if let Some(snippet) = self.opt_snippet(mk_sp(self.last_pos, pos)) {
 732                 if snippet.trim().is_empty() {
 733                     self.last_pos = pos;
 734                 } else {
 735                     return;
 736                 }
 737             }
 738         }
 739     }
 740
 741     pub fn get_context(&self) -> RewriteContext {
 742         RewriteContext {
 743             parse_session: self.parse_session,
 744             codemap: self.codemap,
 745             config: self.config,
 746             inside_macro: false,
 747             use_block: false,
 748             is_if_else_block: false,
 749             force_one_line_chain: false,
 750             snippet_provider: &self.snippet_provier,
 751         }
 752     }
 753 }
 754
 755 impl Rewrite for ast::NestedMetaItem {
 756     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 757         match self.node {
 758             ast::NestedMetaItemKind::MetaItem(ref meta_item) => meta_item.rewrite(context, shape),
 759             ast::NestedMetaItemKind::Literal(ref l) => rewrite_literal(context, l, shape),
 760         }
 761     }
 762 }
 763
 764 impl Rewrite for ast::MetaItem {
 765     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 766         Some(match self.node {
 767             ast::MetaItemKind::Word => String::from(&*self.name.as_str()),
 768             ast::MetaItemKind::List(ref list) => {
 769                 let name = self.name.as_str();
 770                 // 1 = `(`, 2 = `]` and `)`
 771                 let item_shape = shape
 772                     .visual_indent(0)
 773                     .shrink_left(name.len() + 1)
 774                     .and_then(|s| s.sub_width(2))?;
 775                 let items = itemize_list(
 776                     context.codemap,
 777                     list.iter(),
 778                     ")",
 779                     ",",
 780                     |nested_meta_item| nested_meta_item.span.lo(),
 781                     |nested_meta_item| nested_meta_item.span.hi(),
 782                     |nested_meta_item| nested_meta_item.rewrite(context, item_shape),
 783                     self.span.lo(),
 784                     self.span.hi(),
 785                     false,
 786                 );
 787                 let item_vec = items.collect::<Vec<_>>();
 788                 let fmt = ListFormatting {
 789                     tactic: DefinitiveListTactic::Mixed,
 790                     separator: ",",
 791                     trailing_separator: SeparatorTactic::Never,
 792                     separator_place: SeparatorPlace::Back,
 793                     shape: item_shape,
 794                     ends_with_newline: false,
 795                     preserve_newline: false,
 796                     config: context.config,
 797                 };
 798                 format!("{}({})", name, write_list(&item_vec, &fmt)?)
 799             }
 800             ast::MetaItemKind::NameValue(ref literal) => {
 801                 let name = self.name.as_str();
 802                 // 3 = ` = `
 803                 let lit_shape = shape.shrink_left(name.len() + 3)?;
 804                 let value = rewrite_literal(context, literal, lit_shape)?;
 805                 format!("{} = {}", name, value)
 806             }
 807         })
 808     }
 809 }
 810
 811 impl Rewrite for ast::Attribute {
 812     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 813         let prefix = match self.style {
 814             ast::AttrStyle::Inner => "#!",
 815             ast::AttrStyle::Outer => "#",
 816         };
 817         let snippet = context.snippet(self.span);
 818         if self.is_sugared_doc {
 819             let doc_shape = Shape {
 820                 width: cmp::min(shape.width, context.config.comment_width())
 821                     .checked_sub(shape.indent.width())
 822                     .unwrap_or(0),
 823                 ..shape
 824             };
 825             rewrite_comment(&snippet, false, doc_shape, context.config)
 826         } else {
 827             if contains_comment(&snippet) {
 828                 return Some(snippet);
 829             }
 830             // 1 = `[`
 831             let shape = shape.offset_left(prefix.len() + 1)?;
 832             self.meta()?
 833                 .rewrite(context, shape)
 834                 .map(|rw| format!("{}[{}]", prefix, rw))
 835         }
 836     }
 837 }
 838
 839 /// Returns the first group of attributes that fills the given predicate.
 840 /// We consider two doc comments are in different group if they are separated by normal comments.
 841 fn take_while_with_pred<'a, P>(
 842     context: &RewriteContext,
 843     attrs: &'a [ast::Attribute],
 844     pred: P,
 845 ) -> &'a [ast::Attribute]
 846 where
 847     P: Fn(&ast::Attribute) -> bool,
 848 {
 849     let mut last_index = 0;
 850     let mut iter = attrs.iter().enumerate().peekable();
 851     while let Some((i, attr)) = iter.next() {
 852         if !pred(attr) {
 853             break;
 854         }
 855         if let Some(&(_, next_attr)) = iter.peek() {
 856             // Extract comments between two attributes.
 857             let span_between_attr = mk_sp(attr.span.hi(), next_attr.span.lo());
 858             let snippet = context.snippet(span_between_attr);
 859             if count_newlines(&snippet) >= 2 || snippet.contains('/') {
 860                 break;
 861             }
 862         }
 863         last_index = i;
 864     }
 865     if last_index == 0 {
 866         &[]
 867     } else {
 868         &attrs[..last_index + 1]
 869     }
 870 }
 871
 872 fn rewrite_first_group_attrs(
 873     context: &RewriteContext,
 874     attrs: &[ast::Attribute],
 875     shape: Shape,
 876 ) -> Option<(usize, String)> {
 877     if attrs.is_empty() {
 878         return Some((0, String::new()));
 879     }
 880     // Rewrite doc comments
 881     let sugared_docs = take_while_with_pred(context, attrs, |a| a.is_sugared_doc);
 882     if !sugared_docs.is_empty() {
 883         let snippet = sugared_docs
 884             .iter()
 885             .map(|a| context.snippet(a.span))
 886             .collect::<Vec<_>>()
 887             .join("\n");
 888         return Some((
 889             sugared_docs.len(),
 890             rewrite_comment(&snippet, false, shape, context.config)?,
 891         ));
 892     }
 893     // Rewrite `#[derive(..)]`s.
 894     if context.config.merge_derives() {
 895         let derives = take_while_with_pred(context, attrs, is_derive);
 896         if !derives.is_empty() {
 897             let mut derive_args = vec![];
 898             for derive in derives {
 899                 derive_args.append(&mut get_derive_args(context, derive)?);
 900             }
 901             return Some((derives.len(), format_derive(context, &derive_args, shape)?));
 902         }
 903     }
 904     // Rewrite the first attribute.
 905     Some((1, attrs[0].rewrite(context, shape)?))
 906 }
 907
 908 fn has_newlines_before_after_comment(comment: &str) -> (&str, &str) {
 909     // Look at before and after comment and see if there are any empty lines.
 910     let comment_begin = comment.chars().position(|c| c == '/');
 911     let len = comment_begin.unwrap_or_else(|| comment.len());
 912     let mlb = count_newlines(&comment[..len]) > 1;
 913     let mla = if comment_begin.is_none() {
 914         mlb
 915     } else {
 916         let comment_end = comment.chars().rev().position(|c| !c.is_whitespace());
 917         let len = comment_end.unwrap();
 918         comment
 919             .chars()
 920             .rev()
 921             .take(len)
 922             .filter(|c| *c == '\n')
 923             .count() > 1
 924     };
 925     (if mlb { "\n" } else { "" }, if mla { "\n" } else { "" })
 926 }
 927
 928 impl<'a> Rewrite for [ast::Attribute] {
 929     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 930         if self.is_empty() {
 931             return Some(String::new());
 932         }
 933         let (first_group_len, first_group_str) = rewrite_first_group_attrs(context, self, shape)?;
 934         if self.len() == 1 || first_group_len == self.len() {
 935             Some(first_group_str)
 936         } else {
 937             let rest_str = self[first_group_len..].rewrite(context, shape)?;
 938             let missing_span = mk_sp(
 939                 self[first_group_len - 1].span.hi(),
 940                 self[first_group_len].span.lo(),
 941             );
 942             // Preserve an empty line before/after doc comments.
 943             if self[0].is_sugared_doc || self[first_group_len].is_sugared_doc {
 944                 let snippet = context.snippet(missing_span);
 945                 let (mla, mlb) = has_newlines_before_after_comment(&snippet);
 946                 let comment = ::comment::recover_missing_comment_in_span(
 947                     missing_span,
 948                     shape.with_max_width(context.config),
 949                     context,
 950                     0,
 951                 )?;
 952                 let comment = if comment.is_empty() {
 953                     format!("\n{}", mlb)
 954                 } else {
 955                     format!("{}{}\n{}", mla, comment, mlb)
 956                 };
 957                 Some(format!(
 958                     "{}{}{}{}",
 959                     first_group_str,
 960                     comment,
 961                     shape.indent.to_string(context.config),
 962                     rest_str
 963                 ))
 964             } else {
 965                 combine_strs_with_missing_comments(
 966                     context,
 967                     &first_group_str,
 968                     &rest_str,
 969                     missing_span,
 970                     shape,
 971                     false,
 972                 )
 973             }
 974         }
 975     }
 976 }
 977
 978 // Format `#[derive(..)]`, using visual indent & mixed style when we need to go multiline.
 979 fn format_derive(context: &RewriteContext, derive_args: &[String], shape: Shape) -> Option<String> {
 980     let mut result = String::with_capacity(128);
 981     result.push_str("#[derive(");
 982     // 11 = `#[derive()]`
 983     let initial_budget = shape.width.checked_sub(11)?;
 984     let mut budget = initial_budget;
 985     let num = derive_args.len();
 986     for (i, a) in derive_args.iter().enumerate() {
 987         // 2 = `, ` or `)]`
 988         let width = a.len() + 2;
 989         if width > budget {
 990             if i > 0 {
 991                 // Remove trailing whitespace.
 992                 result.pop();
 993             }
 994             result.push('\n');
 995             // 9 = `#[derive(`
 996             result.push_str(&(shape.indent + 9).to_string(context.config));
 997             budget = initial_budget;
 998         } else {
 999             budget = budget.checked_sub(width).unwrap_or(0);
1000         }
1001         result.push_str(a);
1002         if i != num - 1 {
1003             result.push_str(", ")
1004         }
1005     }
1006     result.push_str(")]");
1007     Some(result)
1008 }
1009
1010 fn is_derive(attr: &ast::Attribute) -> bool {
1011     match attr.meta() {
1012         Some(meta_item) => match meta_item.node {
1013             ast::MetaItemKind::List(..) => meta_item.name.as_str() == "derive",
1014             _ => false,
1015         },
1016         _ => false,
1017     }
1018 }
1019
1020 /// Returns the arguments of `#[derive(...)]`.
1021 fn get_derive_args(context: &RewriteContext, attr: &ast::Attribute) -> Option<Vec<String>> {
1022     attr.meta().and_then(|meta_item| match meta_item.node {
1023         ast::MetaItemKind::List(ref args) if meta_item.name.as_str() == "derive" => {
1024             // Every argument of `derive` should be `NestedMetaItemKind::Literal`.
1025             Some(
1026                 args.iter()
1027                     .map(|a| context.snippet(a.span))
1028                     .collect::<Vec<_>>(),
1029             )
1030         }
1031         _ => None,
1032     })
1033 }
1034
1035 // Rewrite `extern crate foo;` WITHOUT attributes.
1036 pub fn rewrite_extern_crate(context: &RewriteContext, item: &ast::Item) -> Option<String> {
1037     assert!(is_extern_crate(item));
1038     let new_str = context.snippet(item.span);
1039     Some(if contains_comment(&new_str) {
1040         new_str
1041     } else {
1042         let no_whitespace = &new_str.split_whitespace().collect::<Vec<&str>>().join(" ");
1043         String::from(&*Regex::new(r"\s;").unwrap().replace(no_whitespace, ";"))
1044     })
1045 }