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