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::{is_same_visibility, mk_sp, rewrite_ident};
  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(
 145         context: &RewriteContext,
 146         path_seg: &ast::PathSegment,
 147     ) -> Option<UseSegment> {
 148         let name = rewrite_ident(context, path_seg.ident);
 149         if name.is_empty() || name == "{{root}}" {
 150             return None;
 151         }
 152         Some(if name == "self" {
 153             UseSegment::Slf(None)
 154         } else if name == "super" {
 155             UseSegment::Super(None)
 156         } else {
 157             UseSegment::Ident((*name).to_owned(), None)
 158         })
 159     }
 160 }
 161
 162 pub fn merge_use_trees(use_trees: Vec<UseTree>) -> Vec<UseTree> {
 163     let mut result = Vec::with_capacity(use_trees.len());
 164     for use_tree in use_trees {
 165         if use_tree.has_comment() || use_tree.attrs.is_some() {
 166             result.push(use_tree);
 167             continue;
 168         }
 169
 170         for flattened in use_tree.flatten() {
 171             merge_use_trees_inner(&mut result, flattened);
 172         }
 173     }
 174     result
 175 }
 176
 177 fn merge_use_trees_inner(trees: &mut Vec<UseTree>, use_tree: UseTree) {
 178     for tree in trees.iter_mut() {
 179         if tree.share_prefix(&use_tree) {
 180             tree.merge(use_tree);
 181             return;
 182         }
 183     }
 184
 185     trees.push(use_tree);
 186 }
 187
 188 impl fmt::Debug for UseTree {
 189     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 190         fmt::Display::fmt(self, f)
 191     }
 192 }
 193
 194 impl fmt::Debug for UseSegment {
 195     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 196         fmt::Display::fmt(self, f)
 197     }
 198 }
 199
 200 impl fmt::Display for UseSegment {
 201     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 202         match *self {
 203             UseSegment::Glob => write!(f, "*"),
 204             UseSegment::Ident(ref s, _) => write!(f, "{}", s),
 205             UseSegment::Slf(..) => write!(f, "self"),
 206             UseSegment::Super(..) => write!(f, "super"),
 207             UseSegment::List(ref list) => {
 208                 write!(f, "{{")?;
 209                 for (i, item) in list.iter().enumerate() {
 210                     let is_last = i == list.len() - 1;
 211                     write!(f, "{}", item)?;
 212                     if !is_last {
 213                         write!(f, ", ")?;
 214                     }
 215                 }
 216                 write!(f, "}}")
 217             }
 218         }
 219     }
 220 }
 221 impl fmt::Display for UseTree {
 222     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
 223         for (i, segment) in self.path.iter().enumerate() {
 224             let is_last = i == self.path.len() - 1;
 225             write!(f, "{}", segment)?;
 226             if !is_last {
 227                 write!(f, "::")?;
 228             }
 229         }
 230         write!(f, "")
 231     }
 232 }
 233
 234 impl UseTree {
 235     // Rewrite use tree with `use ` and a trailing `;`.
 236     pub fn rewrite_top_level(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 237         let vis = self.visibility.as_ref().map_or(Cow::from(""), |vis| {
 238             ::utils::format_visibility(context, &vis)
 239         });
 240         let use_str = self
 241             .rewrite(context, shape.offset_left(vis.len())?)
 242             .map(|s| {
 243                 if s.is_empty() {
 244                     s.to_owned()
 245                 } else {
 246                     format!("{}use {};", vis, s)
 247                 }
 248             })?;
 249         if let Some(ref attrs) = self.attrs {
 250             let attr_str = attrs.rewrite(context, shape)?;
 251             let lo = attrs.last().as_ref()?.span().hi();
 252             let hi = self.span.lo();
 253             let span = mk_sp(lo, hi);
 254             combine_strs_with_missing_comments(context, &attr_str, &use_str, span, shape, false)
 255         } else {
 256             Some(use_str)
 257         }
 258     }
 259
 260     // FIXME: Use correct span?
 261     // The given span is essentially incorrect, since we are reconstructing
 262     // use statements. This should not be a problem, though, since we have
 263     // already tried to extract comment and observed that there are no comment
 264     // around the given use item, and the span will not be used afterward.
 265     fn from_path(path: Vec<UseSegment>, span: Span) -> UseTree {
 266         UseTree {
 267             path,
 268             span,
 269             list_item: None,
 270             visibility: None,
 271             attrs: None,
 272         }
 273     }
 274
 275     pub fn from_ast_with_normalization(
 276         context: &RewriteContext,
 277         item: &ast::Item,
 278     ) -> Option<UseTree> {
 279         match item.node {
 280             ast::ItemKind::Use(ref use_tree) => Some(
 281                 UseTree::from_ast(
 282                     context,
 283                     use_tree,
 284                     None,
 285                     Some(item.vis.clone()),
 286                     Some(item.span.lo()),
 287                     if item.attrs.is_empty() {
 288                         None
 289                     } else {
 290                         Some(item.attrs.clone())
 291                     },
 292                 ).normalize(),
 293             ),
 294             _ => None,
 295         }
 296     }
 297
 298     fn from_ast(
 299         context: &RewriteContext,
 300         a: &ast::UseTree,
 301         list_item: Option<ListItem>,
 302         visibility: Option<ast::Visibility>,
 303         opt_lo: Option<BytePos>,
 304         attrs: Option<Vec<ast::Attribute>>,
 305     ) -> UseTree {
 306         let span = if let Some(lo) = opt_lo {
 307             mk_sp(lo, a.span.hi())
 308         } else {
 309             a.span
 310         };
 311         let mut result = UseTree {
 312             path: vec![],
 313             span,
 314             list_item,
 315             visibility,
 316             attrs,
 317         };
 318         for p in &a.prefix.segments {
 319             if let Some(use_segment) = UseSegment::from_path_segment(context, p) {
 320                 result.path.push(use_segment);
 321             }
 322         }
 323         match a.kind {
 324             UseTreeKind::Glob => {
 325                 result.path.push(UseSegment::Glob);
 326             }
 327             UseTreeKind::Nested(ref list) => {
 328                 // Extract comments between nested use items.
 329                 // This needs to be done before sorting use items.
 330                 let items: Vec<_> = itemize_list(
 331                     context.snippet_provider,
 332                     list.iter().map(|(tree, _)| tree),
 333                     "}",
 334                     ",",
 335                     |tree| tree.span.lo(),
 336                     |tree| tree.span.hi(),
 337                     |_| Some("".to_owned()), // We only need comments for now.
 338                     context.snippet_provider.span_after(a.span, "{"),
 339                     a.span.hi(),
 340                     false,
 341                 ).collect();
 342                 result.path.push(UseSegment::List(
 343                     list.iter()
 344                         .zip(items.into_iter())
 345                         .map(|(t, list_item)| {
 346                             Self::from_ast(context, &t.0, Some(list_item), None, None, None)
 347                         })
 348                         .collect(),
 349                 ));
 350             }
 351             UseTreeKind::Simple(ref rename, ..) => {
 352                 let mut name = rewrite_ident(context, path_to_imported_ident(&a.prefix)).to_owned();
 353                 let alias = rename.and_then(|ident| {
 354                     if ident == path_to_imported_ident(&a.prefix) {
 355                         None
 356                     } else {
 357                         Some(rewrite_ident(context, ident).to_owned())
 358                     }
 359                 });
 360
 361                 let segment = if &name == "self" {
 362                     UseSegment::Slf(alias)
 363                 } else if &name == "super" {
 364                     UseSegment::Super(alias)
 365                 } else {
 366                     UseSegment::Ident(name, alias)
 367                 };
 368
 369                 // `name` is already in result.
 370                 result.path.pop();
 371                 result.path.push(segment);
 372             }
 373         }
 374         result
 375     }
 376
 377     // Do the adjustments that rustfmt does elsewhere to use paths.
 378     pub fn normalize(mut self) -> UseTree {
 379         let mut last = self.path.pop().expect("Empty use tree?");
 380         // Hack around borrow checker.
 381         let mut normalize_sole_list = false;
 382         let mut aliased_self = false;
 383
 384         // Remove foo::{} or self without attributes.
 385         match last {
 386             _ if self.attrs.is_some() => (),
 387             UseSegment::List(ref list) if list.is_empty() => {
 388                 self.path = vec![];
 389                 return self;
 390             }
 391             UseSegment::Slf(None) if self.path.is_empty() && self.visibility.is_some() => {
 392                 self.path = vec![];
 393                 return self;
 394             }
 395             _ => (),
 396         }
 397
 398         // Normalise foo::self -> foo.
 399         if let UseSegment::Slf(None) = last {
 400             if !self.path.is_empty() {
 401                 return self;
 402             }
 403         }
 404
 405         // Normalise foo::self as bar -> foo as bar.
 406         if let UseSegment::Slf(_) = last {
 407             match self.path.last() {
 408                 None => {}
 409                 Some(UseSegment::Ident(_, None)) => {
 410                     aliased_self = true;
 411                 }
 412                 _ => unreachable!(),
 413             }
 414         }
 415
 416         let mut done = false;
 417         if aliased_self {
 418             match self.path.last_mut() {
 419                 Some(UseSegment::Ident(_, ref mut old_rename)) => {
 420                     assert!(old_rename.is_none());
 421                     if let UseSegment::Slf(Some(rename)) = last.clone() {
 422                         *old_rename = Some(rename);
 423                         done = true;
 424                     }
 425                 }
 426                 _ => unreachable!(),
 427             }
 428         }
 429
 430         if done {
 431             return self;
 432         }
 433
 434         // Normalise foo::{bar} -> foo::bar
 435         if let UseSegment::List(ref list) = last {
 436             if list.len() == 1 {
 437                 normalize_sole_list = true;
 438             }
 439         }
 440
 441         if normalize_sole_list {
 442             match last {
 443                 UseSegment::List(list) => {
 444                     for seg in &list[0].path {
 445                         self.path.push(seg.clone());
 446                     }
 447                     return self.normalize();
 448                 }
 449                 _ => unreachable!(),
 450             }
 451         }
 452
 453         // Recursively normalize elements of a list use (including sorting the list).
 454         if let UseSegment::List(list) = last {
 455             let mut list = list
 456                 .into_iter()
 457                 .map(|ut| ut.normalize())
 458                 .collect::<Vec<_>>();
 459             list.sort();
 460             last = UseSegment::List(list);
 461         }
 462
 463         self.path.push(last);
 464         self
 465     }
 466
 467     fn has_comment(&self) -> bool {
 468         self.list_item.as_ref().map_or(false, ListItem::has_comment)
 469     }
 470
 471     fn same_visibility(&self, other: &UseTree) -> bool {
 472         match (&self.visibility, &other.visibility) {
 473             (
 474                 Some(codemap::Spanned {
 475                     node: ast::VisibilityKind::Inherited,
 476                     ..
 477                 }),
 478                 None,
 479             )
 480             | (
 481                 None,
 482                 Some(codemap::Spanned {
 483                     node: ast::VisibilityKind::Inherited,
 484                     ..
 485                 }),
 486             )
 487             | (None, None) => true,
 488             (Some(ref a), Some(ref b)) => is_same_visibility(a, b),
 489             _ => false,
 490         }
 491     }
 492
 493     fn share_prefix(&self, other: &UseTree) -> bool {
 494         if self.path.is_empty()
 495             || other.path.is_empty()
 496             || self.attrs.is_some()
 497             || !self.same_visibility(other)
 498         {
 499             false
 500         } else {
 501             self.path[0] == other.path[0]
 502         }
 503     }
 504
 505     fn flatten(self) -> Vec<UseTree> {
 506         if self.path.is_empty() {
 507             return vec![self];
 508         }
 509         match self.path.clone().last().unwrap() {
 510             UseSegment::List(list) => {
 511                 let prefix = &self.path[..self.path.len() - 1];
 512                 let mut result = vec![];
 513                 for nested_use_tree in list {
 514                     for mut flattend in &mut nested_use_tree.clone().flatten() {
 515                         let mut new_path = prefix.to_vec();
 516                         new_path.append(&mut flattend.path);
 517                         result.push(UseTree {
 518                             path: new_path,
 519                             span: self.span,
 520                             list_item: None,
 521                             visibility: self.visibility.clone(),
 522                             attrs: None,
 523                         });
 524                     }
 525                 }
 526
 527                 result
 528             }
 529             _ => vec![self],
 530         }
 531     }
 532
 533     fn merge(&mut self, other: UseTree) {
 534         let mut new_path = vec![];
 535         for (mut a, b) in self
 536             .path
 537             .clone()
 538             .iter_mut()
 539             .zip(other.path.clone().into_iter())
 540         {
 541             if *a == b {
 542                 new_path.push(b);
 543             } else {
 544                 break;
 545             }
 546         }
 547         if let Some(merged) = merge_rest(&self.path, &other.path, new_path.len()) {
 548             new_path.push(merged);
 549             self.span = self.span.to(other.span);
 550         }
 551         self.path = new_path;
 552     }
 553 }
 554
 555 fn merge_rest(a: &[UseSegment], b: &[UseSegment], len: usize) -> Option<UseSegment> {
 556     let a_rest = &a[len..];
 557     let b_rest = &b[len..];
 558     if a_rest.is_empty() && b_rest.is_empty() {
 559         return None;
 560     }
 561     if a_rest.is_empty() {
 562         return Some(UseSegment::List(vec![
 563             UseTree::from_path(vec![UseSegment::Slf(None)], DUMMY_SP),
 564             UseTree::from_path(b_rest.to_vec(), DUMMY_SP),
 565         ]));
 566     }
 567     if b_rest.is_empty() {
 568         return Some(UseSegment::List(vec![
 569             UseTree::from_path(vec![UseSegment::Slf(None)], DUMMY_SP),
 570             UseTree::from_path(a_rest.to_vec(), DUMMY_SP),
 571         ]));
 572     }
 573     if let UseSegment::List(mut list) = a_rest[0].clone() {
 574         merge_use_trees_inner(&mut list, UseTree::from_path(b_rest.to_vec(), DUMMY_SP));
 575         list.sort();
 576         return Some(UseSegment::List(list.clone()));
 577     }
 578     let mut list = vec![
 579         UseTree::from_path(a_rest.to_vec(), DUMMY_SP),
 580         UseTree::from_path(b_rest.to_vec(), DUMMY_SP),
 581     ];
 582     list.sort();
 583     Some(UseSegment::List(list))
 584 }
 585
 586 impl PartialOrd for UseSegment {
 587     fn partial_cmp(&self, other: &UseSegment) -> Option<Ordering> {
 588         Some(self.cmp(other))
 589     }
 590 }
 591 impl PartialOrd for UseTree {
 592     fn partial_cmp(&self, other: &UseTree) -> Option<Ordering> {
 593         Some(self.cmp(other))
 594     }
 595 }
 596 impl Ord for UseSegment {
 597     fn cmp(&self, other: &UseSegment) -> Ordering {
 598         use self::UseSegment::*;
 599
 600         fn is_upper_snake_case(s: &str) -> bool {
 601             s.chars().all(|c| c.is_uppercase() || c == '_')
 602         }
 603
 604         match (self, other) {
 605             (&Slf(ref a), &Slf(ref b)) | (&Super(ref a), &Super(ref b)) => a.cmp(b),
 606             (&Glob, &Glob) => Ordering::Equal,
 607             (&Ident(ref ia, ref aa), &Ident(ref ib, ref ab)) => {
 608                 // snake_case < CamelCase < UPPER_SNAKE_CASE
 609                 if ia.starts_with(char::is_uppercase) && ib.starts_with(char::is_lowercase) {
 610                     return Ordering::Greater;
 611                 }
 612                 if ia.starts_with(char::is_lowercase) && ib.starts_with(char::is_uppercase) {
 613                     return Ordering::Less;
 614                 }
 615                 if is_upper_snake_case(ia) && !is_upper_snake_case(ib) {
 616                     return Ordering::Greater;
 617                 }
 618                 if !is_upper_snake_case(ia) && is_upper_snake_case(ib) {
 619                     return Ordering::Less;
 620                 }
 621                 let ident_ord = ia.cmp(ib);
 622                 if ident_ord != Ordering::Equal {
 623                     return ident_ord;
 624                 }
 625                 if aa.is_none() && ab.is_some() {
 626                     return Ordering::Less;
 627                 }
 628                 if aa.is_some() && ab.is_none() {
 629                     return Ordering::Greater;
 630                 }
 631                 aa.cmp(ab)
 632             }
 633             (&List(ref a), &List(ref b)) => {
 634                 for (a, b) in a.iter().zip(b.iter()) {
 635                     let ord = a.cmp(b);
 636                     if ord != Ordering::Equal {
 637                         return ord;
 638                     }
 639                 }
 640
 641                 a.len().cmp(&b.len())
 642             }
 643             (&Slf(_), _) => Ordering::Less,
 644             (_, &Slf(_)) => Ordering::Greater,
 645             (&Super(_), _) => Ordering::Less,
 646             (_, &Super(_)) => Ordering::Greater,
 647             (&Ident(..), _) => Ordering::Less,
 648             (_, &Ident(..)) => Ordering::Greater,
 649             (&Glob, _) => Ordering::Less,
 650             (_, &Glob) => Ordering::Greater,
 651         }
 652     }
 653 }
 654 impl Ord for UseTree {
 655     fn cmp(&self, other: &UseTree) -> Ordering {
 656         for (a, b) in self.path.iter().zip(other.path.iter()) {
 657             let ord = a.cmp(b);
 658             // The comparison without aliases is a hack to avoid situations like
 659             // comparing `a::b` to `a as c` - where the latter should be ordered
 660             // first since it is shorter.
 661             if ord != Ordering::Equal && a.remove_alias().cmp(&b.remove_alias()) != Ordering::Equal
 662             {
 663                 return ord;
 664             }
 665         }
 666
 667         self.path.len().cmp(&other.path.len())
 668     }
 669 }
 670
 671 fn rewrite_nested_use_tree(
 672     context: &RewriteContext,
 673     use_tree_list: &[UseTree],
 674     shape: Shape,
 675 ) -> Option<String> {
 676     let mut list_items = Vec::with_capacity(use_tree_list.len());
 677     let nested_shape = match context.config.imports_indent() {
 678         IndentStyle::Block => shape
 679             .block_indent(context.config.tab_spaces())
 680             .with_max_width(context.config)
 681             .sub_width(1)?,
 682         IndentStyle::Visual => shape.visual_indent(0),
 683     };
 684     for use_tree in use_tree_list {
 685         if let Some(mut list_item) = use_tree.list_item.clone() {
 686             list_item.item = use_tree.rewrite(context, nested_shape);
 687             list_items.push(list_item);
 688         } else {
 689             list_items.push(ListItem::from_str(use_tree.rewrite(context, nested_shape)?));
 690         }
 691     }
 692     let has_nested_list = use_tree_list.iter().any(|use_segment| {
 693         use_segment
 694             .path
 695             .last()
 696             .map_or(false, |last_segment| match last_segment {
 697                 UseSegment::List(..) => true,
 698                 _ => false,
 699             })
 700     });
 701
 702     let remaining_width = if has_nested_list {
 703         0
 704     } else {
 705         shape.width.saturating_sub(2)
 706     };
 707
 708     let tactic = definitive_tactic(
 709         &list_items,
 710         context.config.imports_layout(),
 711         Separator::Comma,
 712         remaining_width,
 713     );
 714
 715     let ends_with_newline = context.config.imports_indent() == IndentStyle::Block
 716         && tactic != DefinitiveListTactic::Horizontal;
 717     let fmt = ListFormatting {
 718         tactic,
 719         separator: ",",
 720         trailing_separator: if ends_with_newline {
 721             context.config.trailing_comma()
 722         } else {
 723             SeparatorTactic::Never
 724         },
 725         separator_place: SeparatorPlace::Back,
 726         shape: nested_shape,
 727         ends_with_newline,
 728         preserve_newline: true,
 729         nested: has_nested_list,
 730         config: context.config,
 731     };
 732
 733     let list_str = write_list(&list_items, &fmt)?;
 734
 735     let result = if (list_str.contains('\n') || list_str.len() > remaining_width)
 736         && context.config.imports_indent() == IndentStyle::Block
 737     {
 738         format!(
 739             "{{\n{}{}\n{}}}",
 740             nested_shape.indent.to_string(context.config),
 741             list_str,
 742             shape.indent.to_string(context.config)
 743         )
 744     } else {
 745         format!("{{{}}}", list_str)
 746     };
 747
 748     Some(result)
 749 }
 750
 751 impl Rewrite for UseSegment {
 752     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 753         Some(match *self {
 754             UseSegment::Ident(ref ident, Some(ref rename)) => format!("{} as {}", ident, rename),
 755             UseSegment::Ident(ref ident, None) => ident.clone(),
 756             UseSegment::Slf(Some(ref rename)) => format!("self as {}", rename),
 757             UseSegment::Slf(None) => "self".to_owned(),
 758             UseSegment::Super(Some(ref rename)) => format!("super as {}", rename),
 759             UseSegment::Super(None) => "super".to_owned(),
 760             UseSegment::Glob => "*".to_owned(),
 761             UseSegment::List(ref use_tree_list) => rewrite_nested_use_tree(
 762                 context,
 763                 use_tree_list,
 764                 // 1 = "{" and "}"
 765                 shape.offset_left(1)?.sub_width(1)?,
 766             )?,
 767         })
 768     }
 769 }
 770
 771 impl Rewrite for UseTree {
 772     // This does NOT format attributes and visibility or add a trailing `;`.
 773     fn rewrite(&self, context: &RewriteContext, mut shape: Shape) -> Option<String> {
 774         let mut result = String::with_capacity(256);
 775         let mut iter = self.path.iter().peekable();
 776         while let Some(ref segment) = iter.next() {
 777             let segment_str = segment.rewrite(context, shape)?;
 778             result.push_str(&segment_str);
 779             if iter.peek().is_some() {
 780                 result.push_str("::");
 781                 // 2 = "::"
 782                 shape = shape.offset_left(2 + segment_str.len())?;
 783             }
 784         }
 785         Some(result)
 786     }
 787 }
 788
 789 #[cfg(test)]
 790 mod test {
 791     use super::*;
 792     use syntax::codemap::DUMMY_SP;
 793
 794     // Parse the path part of an import. This parser is not robust and is only
 795     // suitable for use in a test harness.
 796     fn parse_use_tree(s: &str) -> UseTree {
 797         use std::iter::Peekable;
 798         use std::mem::swap;
 799         use std::str::Chars;
 800
 801         struct Parser<'a> {
 802             input: Peekable<Chars<'a>>,
 803         }
 804
 805         impl<'a> Parser<'a> {
 806             fn bump(&mut self) {
 807                 self.input.next().unwrap();
 808             }
 809
 810             fn eat(&mut self, c: char) {
 811                 assert!(self.input.next().unwrap() == c);
 812             }
 813
 814             fn push_segment(
 815                 result: &mut Vec<UseSegment>,
 816                 buf: &mut String,
 817                 alias_buf: &mut Option<String>,
 818             ) {
 819                 if !buf.is_empty() {
 820                     let mut alias = None;
 821                     swap(alias_buf, &mut alias);
 822                     if buf == "self" {
 823                         result.push(UseSegment::Slf(alias));
 824                         *buf = String::new();
 825                         *alias_buf = None;
 826                     } else if buf == "super" {
 827                         result.push(UseSegment::Super(alias));
 828                         *buf = String::new();
 829                         *alias_buf = None;
 830                     } else {
 831                         let mut name = String::new();
 832                         swap(buf, &mut name);
 833                         result.push(UseSegment::Ident(name, alias));
 834                     }
 835                 }
 836             }
 837
 838             fn parse_in_list(&mut self) -> UseTree {
 839                 let mut result = vec![];
 840                 let mut buf = String::new();
 841                 let mut alias_buf = None;
 842                 while let Some(&c) = self.input.peek() {
 843                     match c {
 844                         '{' => {
 845                             assert!(buf.is_empty());
 846                             self.bump();
 847                             result.push(UseSegment::List(self.parse_list()));
 848                             self.eat('}');
 849                         }
 850                         '*' => {
 851                             assert!(buf.is_empty());
 852                             self.bump();
 853                             result.push(UseSegment::Glob);
 854                         }
 855                         ':' => {
 856                             self.bump();
 857                             self.eat(':');
 858                             Self::push_segment(&mut result, &mut buf, &mut alias_buf);
 859                         }
 860                         '}' | ',' => {
 861                             Self::push_segment(&mut result, &mut buf, &mut alias_buf);
 862                             return UseTree {
 863                                 path: result,
 864                                 span: DUMMY_SP,
 865                                 list_item: None,
 866                                 visibility: None,
 867                                 attrs: None,
 868                             };
 869                         }
 870                         ' ' => {
 871                             self.bump();
 872                             self.eat('a');
 873                             self.eat('s');
 874                             self.eat(' ');
 875                             alias_buf = Some(String::new());
 876                         }
 877                         c => {
 878                             self.bump();
 879                             if let Some(ref mut buf) = alias_buf {
 880                                 buf.push(c);
 881                             } else {
 882                                 buf.push(c);
 883                             }
 884                         }
 885                     }
 886                 }
 887                 Self::push_segment(&mut result, &mut buf, &mut alias_buf);
 888                 UseTree {
 889                     path: result,
 890                     span: DUMMY_SP,
 891                     list_item: None,
 892                     visibility: None,
 893                     attrs: None,
 894                 }
 895             }
 896
 897             fn parse_list(&mut self) -> Vec<UseTree> {
 898                 let mut result = vec![];
 899                 loop {
 900                     match self.input.peek().unwrap() {
 901                         ',' | ' ' => self.bump(),
 902                         '}' => {
 903                             return result;
 904                         }
 905                         _ => result.push(self.parse_in_list()),
 906                     }
 907                 }
 908             }
 909         }
 910
 911         let mut parser = Parser {
 912             input: s.chars().peekable(),
 913         };
 914         parser.parse_in_list()
 915     }
 916
 917     macro parse_use_trees($($s:expr),* $(,)*) {
 918         vec![
 919             $(parse_use_tree($s),)*
 920         ]
 921     }
 922
 923     #[test]
 924     fn test_use_tree_merge() {
 925         macro test_merge([$($input:expr),* $(,)*], [$($output:expr),* $(,)*]) {
 926             assert_eq!(
 927                 merge_use_trees(parse_use_trees!($($input,)*)),
 928                 parse_use_trees!($($output,)*),
 929             );
 930         }
 931
 932         test_merge!(["a::b::{c, d}", "a::b::{e, f}"], ["a::b::{c, d, e, f}"]);
 933         test_merge!(["a::b::c", "a::b"], ["a::b::{self, c}"]);
 934         test_merge!(["a::b", "a::b"], ["a::b"]);
 935         test_merge!(["a", "a::b", "a::b::c"], ["a::{self, b::{self, c}}"]);
 936         test_merge!(
 937             ["a::{b::{self, c}, d::e}", "a::d::f"],
 938             ["a::{b::{self, c}, d::{e, f}}"]
 939         );
 940         test_merge!(
 941             ["a::d::f", "a::{b::{self, c}, d::e}"],
 942             ["a::{b::{self, c}, d::{e, f}}"]
 943         );
 944         test_merge!(
 945             ["a::{c, d, b}", "a::{d, e, b, a, f}", "a::{f, g, c}"],
 946             ["a::{a, b, c, d, e, f, g}"]
 947         );
 948     }
 949
 950     #[test]
 951     fn test_use_tree_flatten() {
 952         assert_eq!(
 953             parse_use_tree("a::b::{c, d, e, f}").flatten(),
 954             parse_use_trees!("a::b::c", "a::b::d", "a::b::e", "a::b::f",)
 955         );
 956
 957         assert_eq!(
 958             parse_use_tree("a::b::{c::{d, e, f}, g, h::{i, j, k}}").flatten(),
 959             parse_use_trees![
 960                 "a::b::c::d",
 961                 "a::b::c::e",
 962                 "a::b::c::f",
 963                 "a::b::g",
 964                 "a::b::h::i",
 965                 "a::b::h::j",
 966                 "a::b::h::k",
 967             ]
 968         );
 969     }
 970
 971     #[test]
 972     fn test_use_tree_normalize() {
 973         assert_eq!(parse_use_tree("a::self").normalize(), parse_use_tree("a"));
 974         assert_eq!(
 975             parse_use_tree("a::self as foo").normalize(),
 976             parse_use_tree("a as foo")
 977         );
 978         assert_eq!(parse_use_tree("a::{self}").normalize(), parse_use_tree("a"));
 979         assert_eq!(parse_use_tree("a::{b}").normalize(), parse_use_tree("a::b"));
 980         assert_eq!(
 981             parse_use_tree("a::{b, c::self}").normalize(),
 982             parse_use_tree("a::{b, c}")
 983         );
 984         assert_eq!(
 985             parse_use_tree("a::{b as bar, c::self}").normalize(),
 986             parse_use_tree("a::{b as bar, c}")
 987         );
 988     }
 989
 990     #[test]
 991     fn test_use_tree_ord() {
 992         assert!(parse_use_tree("a").normalize() < parse_use_tree("aa").normalize());
 993         assert!(parse_use_tree("a").normalize() < parse_use_tree("a::a").normalize());
 994         assert!(parse_use_tree("a").normalize() < parse_use_tree("*").normalize());
 995         assert!(parse_use_tree("a").normalize() < parse_use_tree("{a, b}").normalize());
 996         assert!(parse_use_tree("*").normalize() < parse_use_tree("{a, b}").normalize());
 997
 998         assert!(
 999             parse_use_tree("aaaaaaaaaaaaaaa::{bb, cc, dddddddd}").normalize()
1000                 < parse_use_tree("aaaaaaaaaaaaaaa::{bb, cc, ddddddddd}").normalize()
1001         );
1002         assert!(
1003             parse_use_tree("serde::de::{Deserialize}").normalize()
1004                 < parse_use_tree("serde_json").normalize()
1005         );
1006         assert!(parse_use_tree("a::b::c").normalize() < parse_use_tree("a::b::*").normalize());
1007         assert!(
1008             parse_use_tree("foo::{Bar, Baz}").normalize()
1009                 < parse_use_tree("{Bar, Baz}").normalize()
1010         );
1011
1012         assert!(
1013             parse_use_tree("foo::{self as bar}").normalize()
1014                 < parse_use_tree("foo::{qux as bar}").normalize()
1015         );
1016         assert!(
1017             parse_use_tree("foo::{qux as bar}").normalize()
1018                 < parse_use_tree("foo::{baz, qux as bar}").normalize()
1019         );
1020         assert!(
1021             parse_use_tree("foo::{self as bar, baz}").normalize()
1022                 < parse_use_tree("foo::{baz, qux as bar}").normalize()
1023         );
1024
1025         assert!(parse_use_tree("foo").normalize() < parse_use_tree("Foo").normalize());
1026         assert!(parse_use_tree("foo").normalize() < parse_use_tree("foo::Bar").normalize());
1027
1028         assert!(
1029             parse_use_tree("std::cmp::{d, c, b, a}").normalize()
1030                 < parse_use_tree("std::cmp::{b, e, g, f}").normalize()
1031         );
1032     }
1033 }