src/imports.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::Ordering;
  12
  13 use config::lists::*;
  14 use syntax::ast::{self, UseTreeKind};
  15 use syntax::codemap::{self, BytePos, Span, DUMMY_SP};
  16
  17 use codemap::SpanUtils;
  18 use comment::combine_strs_with_missing_comments;
  19 use config::IndentStyle;
  20 use lists::{definitive_tactic, itemize_list, write_list, ListFormatting, ListItem, Separator};
  21 use rewrite::{Rewrite, RewriteContext};
  22 use shape::Shape;
  23 use spanned::Spanned;
  24 use utils::mk_sp;
  25 use visitor::FmtVisitor;
  26
  27 use std::borrow::Cow;
  28 use std::fmt;
  29
  30 /// Returns a name imported by a `use` declaration. e.g. returns `Ordering`
  31 /// for `std::cmp::Ordering` and `self` for `std::cmp::self`.
  32 pub fn path_to_imported_ident(path: &ast::Path) -> ast::Ident {
  33     path.segments.last().unwrap().ident
  34 }
  35
  36 impl<'a> FmtVisitor<'a> {
  37     pub fn format_import(&mut self, item: &ast::Item, tree: &ast::UseTree) {
  38         let span = item.span;
  39         let shape = self.shape();
  40         let rw = UseTree::from_ast(
  41             &self.get_context(),
  42             tree,
  43             None,
  44             Some(item.vis.clone()),
  45             Some(item.span.lo()),
  46             Some(item.attrs.clone()),
  47         ).rewrite_top_level(&self.get_context(), shape);
  48         match rw {
  49             Some(ref s) if s.is_empty() => {
  50                 // Format up to last newline
  51                 let prev_span = mk_sp(self.last_pos, source!(self, span).lo());
  52                 let trimmed_snippet = self.snippet(prev_span).trim_right();
  53                 let span_end = self.last_pos + BytePos(trimmed_snippet.len() as u32);
  54                 self.format_missing(span_end);
  55                 // We have an excessive newline from the removed import.
  56                 if self.buffer.ends_with('\n') {
  57                     self.buffer.pop();
  58                     self.line_number -= 1;
  59                 }
  60                 self.last_pos = source!(self, span).hi();
  61             }
  62             Some(ref s) => {
  63                 self.format_missing_with_indent(source!(self, span).lo());
  64                 self.push_str(s);
  65                 self.last_pos = source!(self, span).hi();
  66             }
  67             None => {
  68                 self.format_missing_with_indent(source!(self, span).lo());
  69                 self.format_missing(source!(self, span).hi());
  70             }
  71         }
  72     }
  73 }
  74
  75 // Ordering of imports
  76
  77 // We order imports by translating to our own representation and then sorting.
  78 // The Rust AST data structures are really bad for this. Rustfmt applies a bunch
  79 // of normalisations to imports and since we want to sort based on the result
  80 // of these (and to maintain idempotence) we must apply the same normalisations
  81 // to the data structures for sorting.
  82 //
  83 // We sort `self` and `super` before other imports, then identifier imports,
  84 // then glob imports, then lists of imports. We do not take aliases into account
  85 // when ordering unless the imports are identical except for the alias (rare in
  86 // practice).
  87
  88 // FIXME(#2531) - we should unify the comparison code here with the formatting
  89 // code elsewhere since we are essentially string-ifying twice. Furthermore, by
  90 // parsing to our own format on comparison, we repeat a lot of work when
  91 // sorting.
  92
  93 // FIXME we do a lot of allocation to make our own representation.
  94 #[derive(Clone, Eq, PartialEq)]
  95 pub enum UseSegment {
  96     Ident(String, Option<String>),
  97     Slf(Option<String>),
  98     Super(Option<String>),
  99     Glob,
 100     List(Vec<UseTree>),
 101 }
 102
 103 #[derive(Clone)]
 104 pub struct UseTree {
 105     pub path: Vec<UseSegment>,
 106     pub span: Span,
 107     // Comment information within nested use tree.
 108     pub list_item: Option<ListItem>,
 109     // Additional fields for top level use items.
 110     // Should we have another struct for top-level use items rather than reusing this?
 111     visibility: Option<ast::Visibility>,
 112     attrs: Option<Vec<ast::Attribute>>,
 113 }
 114
 115 impl PartialEq for UseTree {
 116     fn eq(&self, other: &UseTree) -> bool {
 117         self.path == other.path
 118     }
 119 }
 120 impl Eq for UseTree {}
 121
 122 impl Spanned for UseTree {
 123     fn span(&self) -> Span {
 124         let lo = if let Some(ref attrs) = self.attrs {
 125             attrs.iter().next().map_or(self.span.lo(), |a| a.span.lo())
 126         } else {
 127             self.span.lo()
 128         };
 129         mk_sp(lo, self.span.hi())
 130     }
 131 }
 132
 133 impl UseSegment {
 134     // Clone a version of self with any top-level alias removed.
 135     fn remove_alias(&self) -> UseSegment {
 136         match *self {
 137             UseSegment::Ident(ref s, _) => UseSegment::Ident(s.clone(), None),
 138             UseSegment::Slf(_) => UseSegment::Slf(None),
 139             UseSegment::Super(_) => UseSegment::Super(None),
 140             _ => self.clone(),
 141         }
 142     }
 143
 144     fn from_path_segment(path_seg: &ast::PathSegment) -> Option<UseSegment> {
 145         let name = path_seg.ident.name.as_str();
 146         if name == "{{root}}" {
 147             return None;
 148         }
 149         Some(if name == "self" {
 150             UseSegment::Slf(None)
 151         } else if name == "super" {
 152             UseSegment::Super(None)
 153         } else {
 154             UseSegment::Ident((*name).to_owned(), None)
 155         })
 156     }
 157 }
 158
 159 pub fn merge_use_trees(use_trees: Vec<UseTree>) -> Vec<UseTree> {
 160     let mut result = Vec::with_capacity(use_trees.len());
 161     for use_tree in use_trees {
 162         if use_tree.has_comment() || use_tree.attrs.is_some() {
 163             result.push(use_tree);
 164             continue;
 165         }
 166
 167         for flattened in use_tree.flatten() {
 168             merge_use_trees_inner(&mut result, flattened);
 169         }
 170     }
 171     result
 172 }
 173
 174 fn merge_use_trees_inner(trees: &mut Vec<UseTree>, use_tree: UseTree) {
 175     for tree in trees.iter_mut() {
 176         if tree.share_prefix(&use_tree) {
 177             tree.merge(use_tree);
 178             return;
 179         }
 180     }
 181
 182     trees.push(use_tree);
 183 }
 184
 185 impl fmt::Debug for UseTree {
 186     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 187         fmt::Display::fmt(self, f)
 188     }
 189 }
 190
 191 impl fmt::Debug for UseSegment {
 192     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 193         fmt::Display::fmt(self, f)
 194     }
 195 }
 196
 197 impl fmt::Display for UseSegment {
 198     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 199         match *self {
 200             UseSegment::Glob => write!(f, "*"),
 201             UseSegment::Ident(ref s, _) => write!(f, "{}", s),
 202             UseSegment::Slf(..) => write!(f, "self"),
 203             UseSegment::Super(..) => write!(f, "super"),
 204             UseSegment::List(ref list) => {
 205                 write!(f, "{{")?;
 206                 for (i, item) in list.iter().enumerate() {
 207                     let is_last = i == list.len() - 1;
 208                     write!(f, "{}", item)?;
 209                     if !is_last {
 210                         write!(f, ", ")?;
 211                     }
 212                 }
 213                 write!(f, "}}")
 214             }
 215         }
 216     }
 217 }
 218 impl fmt::Display for UseTree {
 219     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 220         for (i, segment) in self.path.iter().enumerate() {
 221             let is_last = i == self.path.len() - 1;
 222             write!(f, "{}", segment)?;
 223             if !is_last {
 224                 write!(f, "::")?;
 225             }
 226         }
 227         write!(f, "")
 228     }
 229 }
 230
 231 impl UseTree {
 232     // Rewrite use tree with `use ` and a trailing `;`.
 233     pub fn rewrite_top_level(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 234         let vis = self.visibility
 235             .as_ref()
 236             .map_or(Cow::from(""), |vis| ::utils::format_visibility(&vis));
 237         let use_str = self.rewrite(context, shape.offset_left(vis.len())?)
 238             .map(|s| {
 239                 if s.is_empty() {
 240                     s.to_owned()
 241                 } else {
 242                     format!("{}use {};", vis, s)
 243                 }
 244             })?;
 245         if let Some(ref attrs) = self.attrs {
 246             let attr_str = attrs.rewrite(context, shape)?;
 247             let lo = attrs.last().as_ref()?.span().hi();
 248             let hi = self.span.lo();
 249             let span = mk_sp(lo, hi);
 250             combine_strs_with_missing_comments(context, &attr_str, &use_str, span, shape, false)
 251         } else {
 252             Some(use_str)
 253         }
 254     }
 255
 256     // FIXME: Use correct span?
 257     // The given span is essentially incorrect, since we are reconstructing
 258     // use statements. This should not be a problem, though, since we have
 259     // already tried to extract comment and observed that there are no comment
 260     // around the given use item, and the span will not be used afterward.
 261     fn from_path(path: Vec<UseSegment>, span: Span) -> UseTree {
 262         UseTree {
 263             path,
 264             span,
 265             list_item: None,
 266             visibility: None,
 267             attrs: None,
 268         }
 269     }
 270
 271     pub fn from_ast_with_normalization(
 272         context: &RewriteContext,
 273         item: &ast::Item,
 274     ) -> Option<UseTree> {
 275         match item.node {
 276             ast::ItemKind::Use(ref use_tree) => Some(
 277                 UseTree::from_ast(
 278                     context,
 279                     use_tree,
 280                     None,
 281                     Some(item.vis.clone()),
 282                     Some(item.span.lo()),
 283                     if item.attrs.is_empty() {
 284                         None
 285                     } else {
 286                         Some(item.attrs.clone())
 287                     },
 288                 ).normalize(),
 289             ),
 290             _ => None,
 291         }
 292     }
 293
 294     fn from_ast(
 295         context: &RewriteContext,
 296         a: &ast::UseTree,
 297         list_item: Option<ListItem>,
 298         visibility: Option<ast::Visibility>,
 299         opt_lo: Option<BytePos>,
 300         attrs: Option<Vec<ast::Attribute>>,
 301     ) -> UseTree {
 302         let span = if let Some(lo) = opt_lo {
 303             mk_sp(lo, a.span.hi())
 304         } else {
 305             a.span
 306         };
 307         let mut result = UseTree {
 308             path: vec![],
 309             span,
 310             list_item,
 311             visibility,
 312             attrs,
 313         };
 314         for p in &a.prefix.segments {
 315             if let Some(use_segment) = UseSegment::from_path_segment(p) {
 316                 result.path.push(use_segment);
 317             }
 318         }
 319         match a.kind {
 320             UseTreeKind::Glob => {
 321                 result.path.push(UseSegment::Glob);
 322             }
 323             UseTreeKind::Nested(ref list) => {
 324                 // Extract comments between nested use items.
 325                 // This needs to be done before sorting use items.
 326                 let items: Vec<_> = itemize_list(
 327                     context.snippet_provider,
 328                     list.iter().map(|(tree, _)| tree),
 329                     "}",
 330                     ",",
 331                     |tree| tree.span.lo(),
 332                     |tree| tree.span.hi(),
 333                     |_| Some("".to_owned()), // We only need comments for now.
 334                     context.snippet_provider.span_after(a.span, "{"),
 335                     a.span.hi(),
 336                     false,
 337                 ).collect();
 338                 result.path.push(UseSegment::List(
 339                     list.iter()
 340                         .zip(items.into_iter())
 341                         .map(|(t, list_item)| {
 342                             Self::from_ast(context, &t.0, Some(list_item), None, None, None)
 343                         })
 344                         .collect(),
 345                 ));
 346             }
 347             UseTreeKind::Simple(ref rename) => {
 348                 let mut name = (*path_to_imported_ident(&a.prefix).name.as_str()).to_owned();
 349                 let alias = rename.and_then(|ident| {
 350                     if ident == path_to_imported_ident(&a.prefix) {
 351                         None
 352                     } else {
 353                         Some(ident.to_string())
 354                     }
 355                 });
 356
 357                 let segment = if &name == "self" {
 358                     UseSegment::Slf(alias)
 359                 } else if &name == "super" {
 360                     UseSegment::Super(alias)
 361                 } else {
 362                     UseSegment::Ident(name, alias)
 363                 };
 364
 365                 // `name` is already in result.
 366                 result.path.pop();
 367                 result.path.push(segment);
 368             }
 369         }
 370         result
 371     }
 372
 373     // Do the adjustments that rustfmt does elsewhere to use paths.
 374     pub fn normalize(mut self) -> UseTree {
 375         let mut last = self.path.pop().expect("Empty use tree?");
 376         // Hack around borrow checker.
 377         let mut normalize_sole_list = false;
 378         let mut aliased_self = false;
 379
 380         // Remove foo::{} or self without attributes.
 381         match last {
 382             _ if self.attrs.is_some() => (),
 383             UseSegment::List(ref list) if list.is_empty() => {
 384                 self.path = vec![];
 385                 return self;
 386             }
 387             UseSegment::Slf(None) if self.path.is_empty() && self.visibility.is_some() => {
 388                 self.path = vec![];
 389                 return self;
 390             }
 391             _ => (),
 392         }
 393
 394         // Normalise foo::self -> foo.
 395         if let UseSegment::Slf(None) = last {
 396             if !self.path.is_empty() {
 397                 return self;
 398             }
 399         }
 400
 401         // Normalise foo::self as bar -> foo as bar.
 402         if let UseSegment::Slf(_) = last {
 403             match self.path.last() {
 404                 None => {}
 405                 Some(UseSegment::Ident(_, None)) => {
 406                     aliased_self = true;
 407                 }
 408                 _ => unreachable!(),
 409             }
 410         }
 411
 412         let mut done = false;
 413         if aliased_self {
 414             match self.path.last_mut() {
 415                 Some(UseSegment::Ident(_, ref mut old_rename)) => {
 416                     assert!(old_rename.is_none());
 417                     if let UseSegment::Slf(Some(rename)) = last.clone() {
 418                         *old_rename = Some(rename);
 419                         done = true;
 420                     }
 421                 }
 422                 _ => unreachable!(),
 423             }
 424         }
 425
 426         if done {
 427             return self;
 428         }
 429
 430         // Normalise foo::{bar} -> foo::bar
 431         if let UseSegment::List(ref list) = last {
 432             if list.len() == 1 {
 433                 normalize_sole_list = true;
 434             }
 435         }
 436
 437         if normalize_sole_list {
 438             match last {
 439                 UseSegment::List(list) => {
 440                     for seg in &list[0].path {
 441                         self.path.push(seg.clone());
 442                     }
 443                     return self.normalize();
 444                 }
 445                 _ => unreachable!(),
 446             }
 447         }
 448
 449         // Recursively normalize elements of a list use (including sorting the list).
 450         if let UseSegment::List(list) = last {
 451             let mut list = list.into_iter()
 452                 .map(|ut| ut.normalize())
 453                 .collect::<Vec<_>>();
 454             list.sort();
 455             last = UseSegment::List(list);
 456         }
 457
 458         self.path.push(last);
 459         self
 460     }
 461
 462     fn has_comment(&self) -> bool {
 463         self.list_item.as_ref().map_or(false, ListItem::has_comment)
 464     }
 465
 466     fn same_visibility(&self, other: &UseTree) -> bool {
 467         match (&self.visibility, &other.visibility) {
 468             (
 469                 Some(codemap::Spanned {
 470                     node: ast::VisibilityKind::Inherited,
 471                     ..
 472                 }),
 473                 None,
 474             )
 475             | (
 476                 None,
 477                 Some(codemap::Spanned {
 478                     node: ast::VisibilityKind::Inherited,
 479                     ..
 480                 }),
 481             )
 482             | (None, None) => true,
 483             (
 484                 Some(codemap::Spanned { node: lnode, .. }),
 485                 Some(codemap::Spanned { node: rnode, .. }),
 486             ) => lnode == rnode,
 487             _ => false,
 488         }
 489     }
 490
 491     fn share_prefix(&self, other: &UseTree) -> bool {
 492         if self.path.is_empty()
 493             || other.path.is_empty()
 494             || self.attrs.is_some()
 495             || !self.same_visibility(other)
 496         {
 497             false
 498         } else {
 499             self.path[0] == other.path[0]
 500         }
 501     }
 502
 503     fn flatten(self) -> Vec<UseTree> {
 504         if self.path.is_empty() {
 505             return vec![self];
 506         }
 507         match self.path.clone().last().unwrap() {
 508             UseSegment::List(list) => {
 509                 let prefix = &self.path[..self.path.len() - 1];
 510                 let mut result = vec![];
 511                 for nested_use_tree in list {
 512                     for mut flattend in &mut nested_use_tree.clone().flatten() {
 513                         let mut new_path = prefix.to_vec();
 514                         new_path.append(&mut flattend.path);
 515                         result.push(UseTree {
 516                             path: new_path,
 517                             span: self.span,
 518                             list_item: None,
 519                             visibility: self.visibility.clone(),
 520                             attrs: None,
 521                         });
 522                     }
 523                 }
 524
 525                 result
 526             }
 527             _ => vec![self],
 528         }
 529     }
 530
 531     fn merge(&mut self, other: UseTree) {
 532         let mut new_path = vec![];
 533         for (mut a, b) in self.path
 534             .clone()
 535             .iter_mut()
 536             .zip(other.path.clone().into_iter())
 537         {
 538             if *a == b {
 539                 new_path.push(b);
 540             } else {
 541                 break;
 542             }
 543         }
 544         if let Some(merged) = merge_rest(&self.path, &other.path, new_path.len()) {
 545             new_path.push(merged);
 546             self.span = self.span.to(other.span);
 547         }
 548         self.path = new_path;
 549     }
 550 }
 551
 552 fn merge_rest(a: &[UseSegment], b: &[UseSegment], len: usize) -> Option<UseSegment> {
 553     let a_rest = &a[len..];
 554     let b_rest = &b[len..];
 555     if a_rest.is_empty() && b_rest.is_empty() {
 556         return None;
 557     }
 558     if a_rest.is_empty() {
 559         return Some(UseSegment::List(vec![
 560             UseTree::from_path(vec![UseSegment::Slf(None)], DUMMY_SP),
 561             UseTree::from_path(b_rest.to_vec(), DUMMY_SP),
 562         ]));
 563     }
 564     if b_rest.is_empty() {
 565         return Some(UseSegment::List(vec![
 566             UseTree::from_path(vec![UseSegment::Slf(None)], DUMMY_SP),
 567             UseTree::from_path(a_rest.to_vec(), DUMMY_SP),
 568         ]));
 569     }
 570     if let UseSegment::List(mut list) = a_rest[0].clone() {
 571         merge_use_trees_inner(&mut list, UseTree::from_path(b_rest.to_vec(), DUMMY_SP));
 572         list.sort();
 573         return Some(UseSegment::List(list.clone()));
 574     }
 575     let mut list = vec![
 576         UseTree::from_path(a_rest.to_vec(), DUMMY_SP),
 577         UseTree::from_path(b_rest.to_vec(), DUMMY_SP),
 578     ];
 579     list.sort();
 580     Some(UseSegment::List(list))
 581 }
 582
 583 impl PartialOrd for UseSegment {
 584     fn partial_cmp(&self, other: &UseSegment) -> Option<Ordering> {
 585         Some(self.cmp(other))
 586     }
 587 }
 588 impl PartialOrd for UseTree {
 589     fn partial_cmp(&self, other: &UseTree) -> Option<Ordering> {
 590         Some(self.cmp(other))
 591     }
 592 }
 593 impl Ord for UseSegment {
 594     fn cmp(&self, other: &UseSegment) -> Ordering {
 595         use self::UseSegment::*;
 596
 597         fn is_upper_snake_case(s: &str) -> bool {
 598             s.chars().all(|c| c.is_uppercase() || c == '_')
 599         }
 600
 601         match (self, other) {
 602             (&Slf(ref a), &Slf(ref b)) | (&Super(ref a), &Super(ref b)) => a.cmp(b),
 603             (&Glob, &Glob) => Ordering::Equal,
 604             (&Ident(ref ia, ref aa), &Ident(ref ib, ref ab)) => {
 605                 // snake_case < CamelCase < UPPER_SNAKE_CASE
 606                 if ia.starts_with(char::is_uppercase) && ib.starts_with(char::is_lowercase) {
 607                     return Ordering::Greater;
 608                 }
 609                 if ia.starts_with(char::is_lowercase) && ib.starts_with(char::is_uppercase) {
 610                     return Ordering::Less;
 611                 }
 612                 if is_upper_snake_case(ia) && !is_upper_snake_case(ib) {
 613                     return Ordering::Greater;
 614                 }
 615                 if !is_upper_snake_case(ia) && is_upper_snake_case(ib) {
 616                     return Ordering::Less;
 617                 }
 618                 let ident_ord = ia.cmp(ib);
 619                 if ident_ord != Ordering::Equal {
 620                     return ident_ord;
 621                 }
 622                 if aa.is_none() && ab.is_some() {
 623                     return Ordering::Less;
 624                 }
 625                 if aa.is_some() && ab.is_none() {
 626                     return Ordering::Greater;
 627                 }
 628                 aa.cmp(ab)
 629             }
 630             (&List(ref a), &List(ref b)) => {
 631                 for (a, b) in a.iter().zip(b.iter()) {
 632                     let ord = a.cmp(b);
 633                     if ord != Ordering::Equal {
 634                         return ord;
 635                     }
 636                 }
 637
 638                 a.len().cmp(&b.len())
 639             }
 640             (&Slf(_), _) => Ordering::Less,
 641             (_, &Slf(_)) => Ordering::Greater,
 642             (&Super(_), _) => Ordering::Less,
 643             (_, &Super(_)) => Ordering::Greater,
 644             (&Ident(..), _) => Ordering::Less,
 645             (_, &Ident(..)) => Ordering::Greater,
 646             (&Glob, _) => Ordering::Less,
 647             (_, &Glob) => Ordering::Greater,
 648         }
 649     }
 650 }
 651 impl Ord for UseTree {
 652     fn cmp(&self, other: &UseTree) -> Ordering {
 653         for (a, b) in self.path.iter().zip(other.path.iter()) {
 654             let ord = a.cmp(b);
 655             // The comparison without aliases is a hack to avoid situations like
 656             // comparing `a::b` to `a as c` - where the latter should be ordered
 657             // first since it is shorter.
 658             if ord != Ordering::Equal && a.remove_alias().cmp(&b.remove_alias()) != Ordering::Equal
 659             {
 660                 return ord;
 661             }
 662         }
 663
 664         self.path.len().cmp(&other.path.len())
 665     }
 666 }
 667
 668 fn rewrite_nested_use_tree(
 669     context: &RewriteContext,
 670     use_tree_list: &[UseTree],
 671     shape: Shape,
 672 ) -> Option<String> {
 673     let mut list_items = Vec::with_capacity(use_tree_list.len());
 674     let nested_shape = match context.config.imports_indent() {
 675         IndentStyle::Block => shape
 676             .block_indent(context.config.tab_spaces())
 677             .with_max_width(context.config)
 678             .sub_width(1)?,
 679         IndentStyle::Visual => shape.visual_indent(0),
 680     };
 681     for use_tree in use_tree_list {
 682         if let Some(mut list_item) = use_tree.list_item.clone() {
 683             list_item.item = use_tree.rewrite(context, nested_shape);
 684             list_items.push(list_item);
 685         } else {
 686             list_items.push(ListItem::from_str(use_tree.rewrite(context, nested_shape)?));
 687         }
 688     }
 689     let has_nested_list = use_tree_list.iter().any(|use_segment| {
 690         use_segment
 691             .path
 692             .last()
 693             .map_or(false, |last_segment| match last_segment {
 694                 UseSegment::List(..) => true,
 695                 _ => false,
 696             })
 697     });
 698
 699     let remaining_width = if has_nested_list {
 700         0
 701     } else {
 702         shape.width.checked_sub(2).unwrap_or(0)
 703     };
 704
 705     let tactic = definitive_tactic(
 706         &list_items,
 707         context.config.imports_layout(),
 708         Separator::Comma,
 709         remaining_width,
 710     );
 711
 712     let ends_with_newline = context.config.imports_indent() == IndentStyle::Block
 713         && tactic != DefinitiveListTactic::Horizontal;
 714     let fmt = ListFormatting {
 715         tactic,
 716         separator: ",",
 717         trailing_separator: if ends_with_newline {
 718             context.config.trailing_comma()
 719         } else {
 720             SeparatorTactic::Never
 721         },
 722         separator_place: SeparatorPlace::Back,
 723         shape: nested_shape,
 724         ends_with_newline,
 725         preserve_newline: true,
 726         config: context.config,
 727     };
 728
 729     let list_str = write_list(&list_items, &fmt)?;
 730
 731     let result = if (list_str.contains('\n') || list_str.len() > remaining_width)
 732         && context.config.imports_indent() == IndentStyle::Block
 733     {
 734         format!(
 735             "{{\n{}{}\n{}}}",
 736             nested_shape.indent.to_string(context.config),
 737             list_str,
 738             shape.indent.to_string(context.config)
 739         )
 740     } else {
 741         format!("{{{}}}", list_str)
 742     };
 743
 744     Some(result)
 745 }
 746
 747 impl Rewrite for UseSegment {
 748     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 749         Some(match *self {
 750             UseSegment::Ident(ref ident, Some(ref rename)) => format!("{} as {}", ident, rename),
 751             UseSegment::Ident(ref ident, None) => ident.clone(),
 752             UseSegment::Slf(Some(ref rename)) => format!("self as {}", rename),
 753             UseSegment::Slf(None) => "self".to_owned(),
 754             UseSegment::Super(Some(ref rename)) => format!("super as {}", rename),
 755             UseSegment::Super(None) => "super".to_owned(),
 756             UseSegment::Glob => "*".to_owned(),
 757             UseSegment::List(ref use_tree_list) => rewrite_nested_use_tree(
 758                 context,
 759                 use_tree_list,
 760                 // 1 = "{" and "}"
 761                 shape.offset_left(1)?.sub_width(1)?,
 762             )?,
 763         })
 764     }
 765 }
 766
 767 impl Rewrite for UseTree {
 768     // This does NOT format attributes and visibility or add a trailing `;`.
 769     fn rewrite(&self, context: &RewriteContext, mut shape: Shape) -> Option<String> {
 770         let mut result = String::with_capacity(256);
 771         let mut iter = self.path.iter().peekable();
 772         while let Some(ref segment) = iter.next() {
 773             let segment_str = segment.rewrite(context, shape)?;
 774             result.push_str(&segment_str);
 775             if iter.peek().is_some() {
 776                 result.push_str("::");
 777                 // 2 = "::"
 778                 shape = shape.offset_left(2 + segment_str.len())?;
 779             }
 780         }
 781         Some(result)
 782     }
 783 }
 784
 785 #[cfg(test)]
 786 mod test {
 787     use super::*;
 788     use syntax::codemap::DUMMY_SP;
 789
 790     // Parse the path part of an import. This parser is not robust and is only
 791     // suitable for use in a test harness.
 792     fn parse_use_tree(s: &str) -> UseTree {
 793         use std::iter::Peekable;
 794         use std::mem::swap;
 795         use std::str::Chars;
 796
 797         struct Parser<'a> {
 798             input: Peekable<Chars<'a>>,
 799         }
 800
 801         impl<'a> Parser<'a> {
 802             fn bump(&mut self) {
 803                 self.input.next().unwrap();
 804             }
 805
 806             fn eat(&mut self, c: char) {
 807                 assert!(self.input.next().unwrap() == c);
 808             }
 809
 810             fn push_segment(
 811                 result: &mut Vec<UseSegment>,
 812                 buf: &mut String,
 813                 alias_buf: &mut Option<String>,
 814             ) {
 815                 if !buf.is_empty() {
 816                     let mut alias = None;
 817                     swap(alias_buf, &mut alias);
 818                     if buf == "self" {
 819                         result.push(UseSegment::Slf(alias));
 820                         *buf = String::new();
 821                         *alias_buf = None;
 822                     } else if buf == "super" {
 823                         result.push(UseSegment::Super(alias));
 824                         *buf = String::new();
 825                         *alias_buf = None;
 826                     } else {
 827                         let mut name = String::new();
 828                         swap(buf, &mut name);
 829                         result.push(UseSegment::Ident(name, alias));
 830                     }
 831                 }
 832             }
 833
 834             fn parse_in_list(&mut self) -> UseTree {
 835                 let mut result = vec![];
 836                 let mut buf = String::new();
 837                 let mut alias_buf = None;
 838                 while let Some(&c) = self.input.peek() {
 839                     match c {
 840                         '{' => {
 841                             assert!(buf.is_empty());
 842                             self.bump();
 843                             result.push(UseSegment::List(self.parse_list()));
 844                             self.eat('}');
 845                         }
 846                         '*' => {
 847                             assert!(buf.is_empty());
 848                             self.bump();
 849                             result.push(UseSegment::Glob);
 850                         }
 851                         ':' => {
 852                             self.bump();
 853                             self.eat(':');
 854                             Self::push_segment(&mut result, &mut buf, &mut alias_buf);
 855                         }
 856                         '}' | ',' => {
 857                             Self::push_segment(&mut result, &mut buf, &mut alias_buf);
 858                             return UseTree {
 859                                 path: result,
 860                                 span: DUMMY_SP,
 861                                 list_item: None,
 862                                 visibility: None,
 863                                 attrs: None,
 864                             };
 865                         }
 866                         ' ' => {
 867                             self.bump();
 868                             self.eat('a');
 869                             self.eat('s');
 870                             self.eat(' ');
 871                             alias_buf = Some(String::new());
 872                         }
 873                         c => {
 874                             self.bump();
 875                             if let Some(ref mut buf) = alias_buf {
 876                                 buf.push(c);
 877                             } else {
 878                                 buf.push(c);
 879                             }
 880                         }
 881                     }
 882                 }
 883                 Self::push_segment(&mut result, &mut buf, &mut alias_buf);
 884                 UseTree {
 885                     path: result,
 886                     span: DUMMY_SP,
 887                     list_item: None,
 888                     visibility: None,
 889                     attrs: None,
 890                 }
 891             }
 892
 893             fn parse_list(&mut self) -> Vec<UseTree> {
 894                 let mut result = vec![];
 895                 loop {
 896                     match self.input.peek().unwrap() {
 897                         ',' | ' ' => self.bump(),
 898                         '}' => {
 899                             return result;
 900                         }
 901                         _ => result.push(self.parse_in_list()),
 902                     }
 903                 }
 904             }
 905         }
 906
 907         let mut parser = Parser {
 908             input: s.chars().peekable(),
 909         };
 910         parser.parse_in_list()
 911     }
 912
 913     macro parse_use_trees($($s:expr),* $(,)*) {
 914         vec![
 915             $(parse_use_tree($s),)*
 916         ]
 917     }
 918
 919     #[test]
 920     fn test_use_tree_merge() {
 921         macro test_merge([$($input:expr),* $(,)*], [$($output:expr),* $(,)*]) {
 922             assert_eq!(
 923                 merge_use_trees(parse_use_trees!($($input,)*)),
 924                 parse_use_trees!($($output,)*),
 925             );
 926         }
 927
 928         test_merge!(["a::b::{c, d}", "a::b::{e, f}"], ["a::b::{c, d, e, f}"]);
 929         test_merge!(["a::b::c", "a::b"], ["a::b::{self, c}"]);
 930         test_merge!(["a::b", "a::b"], ["a::b"]);
 931         test_merge!(["a", "a::b", "a::b::c"], ["a::{self, b::{self, c}}"]);
 932         test_merge!(
 933             ["a::{b::{self, c}, d::e}", "a::d::f"],
 934             ["a::{b::{self, c}, d::{e, f}}"]
 935         );
 936         test_merge!(
 937             ["a::d::f", "a::{b::{self, c}, d::e}"],
 938             ["a::{b::{self, c}, d::{e, f}}"]
 939         );
 940         test_merge!(
 941             ["a::{c, d, b}", "a::{d, e, b, a, f}", "a::{f, g, c}"],
 942             ["a::{a, b, c, d, e, f, g}"]
 943         );
 944     }
 945
 946     #[test]
 947     fn test_use_tree_flatten() {
 948         assert_eq!(
 949             parse_use_tree("a::b::{c, d, e, f}").flatten(),
 950             parse_use_trees!("a::b::c", "a::b::d", "a::b::e", "a::b::f",)
 951         );
 952
 953         assert_eq!(
 954             parse_use_tree("a::b::{c::{d, e, f}, g, h::{i, j, k}}").flatten(),
 955             parse_use_trees![
 956                 "a::b::c::d",
 957                 "a::b::c::e",
 958                 "a::b::c::f",
 959                 "a::b::g",
 960                 "a::b::h::i",
 961                 "a::b::h::j",
 962                 "a::b::h::k",
 963             ]
 964         );
 965     }
 966
 967     #[test]
 968     fn test_use_tree_normalize() {
 969         assert_eq!(parse_use_tree("a::self").normalize(), parse_use_tree("a"));
 970         assert_eq!(
 971             parse_use_tree("a::self as foo").normalize(),
 972             parse_use_tree("a as foo")
 973         );
 974         assert_eq!(parse_use_tree("a::{self}").normalize(), parse_use_tree("a"));
 975         assert_eq!(parse_use_tree("a::{b}").normalize(), parse_use_tree("a::b"));
 976         assert_eq!(
 977             parse_use_tree("a::{b, c::self}").normalize(),
 978             parse_use_tree("a::{b, c}")
 979         );
 980         assert_eq!(
 981             parse_use_tree("a::{b as bar, c::self}").normalize(),
 982             parse_use_tree("a::{b as bar, c}")
 983         );
 984     }
 985
 986     #[test]
 987     fn test_use_tree_ord() {
 988         assert!(parse_use_tree("a").normalize() < parse_use_tree("aa").normalize());
 989         assert!(parse_use_tree("a").normalize() < parse_use_tree("a::a").normalize());
 990         assert!(parse_use_tree("a").normalize() < parse_use_tree("*").normalize());
 991         assert!(parse_use_tree("a").normalize() < parse_use_tree("{a, b}").normalize());
 992         assert!(parse_use_tree("*").normalize() < parse_use_tree("{a, b}").normalize());
 993
 994         assert!(
 995             parse_use_tree("aaaaaaaaaaaaaaa::{bb, cc, dddddddd}").normalize()
 996                 < parse_use_tree("aaaaaaaaaaaaaaa::{bb, cc, ddddddddd}").normalize()
 997         );
 998         assert!(
 999             parse_use_tree("serde::de::{Deserialize}").normalize()
1000                 < parse_use_tree("serde_json").normalize()
1001         );
1002         assert!(parse_use_tree("a::b::c").normalize() < parse_use_tree("a::b::*").normalize());
1003         assert!(
1004             parse_use_tree("foo::{Bar, Baz}").normalize()
1005                 < parse_use_tree("{Bar, Baz}").normalize()
1006         );
1007
1008         assert!(
1009             parse_use_tree("foo::{self as bar}").normalize()
1010                 < parse_use_tree("foo::{qux as bar}").normalize()
1011         );
1012         assert!(
1013             parse_use_tree("foo::{qux as bar}").normalize()
1014                 < parse_use_tree("foo::{baz, qux as bar}").normalize()
1015         );
1016         assert!(
1017             parse_use_tree("foo::{self as bar, baz}").normalize()
1018                 < parse_use_tree("foo::{baz, qux as bar}").normalize()
1019         );
1020
1021         assert!(parse_use_tree("foo").normalize() < parse_use_tree("Foo").normalize());
1022         assert!(parse_use_tree("foo").normalize() < parse_use_tree("foo::Bar").normalize());
1023
1024         assert!(
1025             parse_use_tree("std::cmp::{d, c, b, a}").normalize()
1026                 < parse_use_tree("std::cmp::{b, e, g, f}").normalize()
1027         );
1028     }
1029 }