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
 235             .visibility
 236             .as_ref()
 237             .map_or(Cow::from(""), |vis| ::utils::format_visibility(&vis));
 238         let use_str = self
 239             .rewrite(context, shape.offset_left(vis.len())?)
 240             .map(|s| {
 241                 if s.is_empty() {
 242                     s.to_owned()
 243                 } else {
 244                     format!("{}use {};", vis, s)
 245                 }
 246             })?;
 247         if let Some(ref attrs) = self.attrs {
 248             let attr_str = attrs.rewrite(context, shape)?;
 249             let lo = attrs.last().as_ref()?.span().hi();
 250             let hi = self.span.lo();
 251             let span = mk_sp(lo, hi);
 252             combine_strs_with_missing_comments(context, &attr_str, &use_str, span, shape, false)
 253         } else {
 254             Some(use_str)
 255         }
 256     }
 257
 258     // FIXME: Use correct span?
 259     // The given span is essentially incorrect, since we are reconstructing
 260     // use statements. This should not be a problem, though, since we have
 261     // already tried to extract comment and observed that there are no comment
 262     // around the given use item, and the span will not be used afterward.
 263     fn from_path(path: Vec<UseSegment>, span: Span) -> UseTree {
 264         UseTree {
 265             path,
 266             span,
 267             list_item: None,
 268             visibility: None,
 269             attrs: None,
 270         }
 271     }
 272
 273     pub fn from_ast_with_normalization(
 274         context: &RewriteContext,
 275         item: &ast::Item,
 276     ) -> Option<UseTree> {
 277         match item.node {
 278             ast::ItemKind::Use(ref use_tree) => Some(
 279                 UseTree::from_ast(
 280                     context,
 281                     use_tree,
 282                     None,
 283                     Some(item.vis.clone()),
 284                     Some(item.span.lo()),
 285                     if item.attrs.is_empty() {
 286                         None
 287                     } else {
 288                         Some(item.attrs.clone())
 289                     },
 290                 ).normalize(),
 291             ),
 292             _ => None,
 293         }
 294     }
 295
 296     fn from_ast(
 297         context: &RewriteContext,
 298         a: &ast::UseTree,
 299         list_item: Option<ListItem>,
 300         visibility: Option<ast::Visibility>,
 301         opt_lo: Option<BytePos>,
 302         attrs: Option<Vec<ast::Attribute>>,
 303     ) -> UseTree {
 304         let span = if let Some(lo) = opt_lo {
 305             mk_sp(lo, a.span.hi())
 306         } else {
 307             a.span
 308         };
 309         let mut result = UseTree {
 310             path: vec![],
 311             span,
 312             list_item,
 313             visibility,
 314             attrs,
 315         };
 316         for p in &a.prefix.segments {
 317             if let Some(use_segment) = UseSegment::from_path_segment(p) {
 318                 result.path.push(use_segment);
 319             }
 320         }
 321         match a.kind {
 322             UseTreeKind::Glob => {
 323                 result.path.push(UseSegment::Glob);
 324             }
 325             UseTreeKind::Nested(ref list) => {
 326                 // Extract comments between nested use items.
 327                 // This needs to be done before sorting use items.
 328                 let items: Vec<_> = itemize_list(
 329                     context.snippet_provider,
 330                     list.iter().map(|(tree, _)| tree),
 331                     "}",
 332                     ",",
 333                     |tree| tree.span.lo(),
 334                     |tree| tree.span.hi(),
 335                     |_| Some("".to_owned()), // We only need comments for now.
 336                     context.snippet_provider.span_after(a.span, "{"),
 337                     a.span.hi(),
 338                     false,
 339                 ).collect();
 340                 result.path.push(UseSegment::List(
 341                     list.iter()
 342                         .zip(items.into_iter())
 343                         .map(|(t, list_item)| {
 344                             Self::from_ast(context, &t.0, Some(list_item), None, None, None)
 345                         })
 346                         .collect(),
 347                 ));
 348             }
 349             UseTreeKind::Simple(ref rename, ..) => {
 350                 let mut name = (*path_to_imported_ident(&a.prefix).name.as_str()).to_owned();
 351                 let alias = rename.and_then(|ident| {
 352                     if ident == path_to_imported_ident(&a.prefix) {
 353                         None
 354                     } else {
 355                         Some(ident.to_string())
 356                     }
 357                 });
 358
 359                 let segment = if &name == "self" {
 360                     UseSegment::Slf(alias)
 361                 } else if &name == "super" {
 362                     UseSegment::Super(alias)
 363                 } else {
 364                     UseSegment::Ident(name, alias)
 365                 };
 366
 367                 // `name` is already in result.
 368                 result.path.pop();
 369                 result.path.push(segment);
 370             }
 371         }
 372         result
 373     }
 374
 375     // Do the adjustments that rustfmt does elsewhere to use paths.
 376     pub fn normalize(mut self) -> UseTree {
 377         let mut last = self.path.pop().expect("Empty use tree?");
 378         // Hack around borrow checker.
 379         let mut normalize_sole_list = false;
 380         let mut aliased_self = false;
 381
 382         // Remove foo::{} or self without attributes.
 383         match last {
 384             _ if self.attrs.is_some() => (),
 385             UseSegment::List(ref list) if list.is_empty() => {
 386                 self.path = vec![];
 387                 return self;
 388             }
 389             UseSegment::Slf(None) if self.path.is_empty() && self.visibility.is_some() => {
 390                 self.path = vec![];
 391                 return self;
 392             }
 393             _ => (),
 394         }
 395
 396         // Normalise foo::self -> foo.
 397         if let UseSegment::Slf(None) = last {
 398             if !self.path.is_empty() {
 399                 return self;
 400             }
 401         }
 402
 403         // Normalise foo::self as bar -> foo as bar.
 404         if let UseSegment::Slf(_) = last {
 405             match self.path.last() {
 406                 None => {}
 407                 Some(UseSegment::Ident(_, None)) => {
 408                     aliased_self = true;
 409                 }
 410                 _ => unreachable!(),
 411             }
 412         }
 413
 414         let mut done = false;
 415         if aliased_self {
 416             match self.path.last_mut() {
 417                 Some(UseSegment::Ident(_, ref mut old_rename)) => {
 418                     assert!(old_rename.is_none());
 419                     if let UseSegment::Slf(Some(rename)) = last.clone() {
 420                         *old_rename = Some(rename);
 421                         done = true;
 422                     }
 423                 }
 424                 _ => unreachable!(),
 425             }
 426         }
 427
 428         if done {
 429             return self;
 430         }
 431
 432         // Normalise foo::{bar} -> foo::bar
 433         if let UseSegment::List(ref list) = last {
 434             if list.len() == 1 {
 435                 normalize_sole_list = true;
 436             }
 437         }
 438
 439         if normalize_sole_list {
 440             match last {
 441                 UseSegment::List(list) => {
 442                     for seg in &list[0].path {
 443                         self.path.push(seg.clone());
 444                     }
 445                     return self.normalize();
 446                 }
 447                 _ => unreachable!(),
 448             }
 449         }
 450
 451         // Recursively normalize elements of a list use (including sorting the list).
 452         if let UseSegment::List(list) = last {
 453             let mut list = list
 454                 .into_iter()
 455                 .map(|ut| ut.normalize())
 456                 .collect::<Vec<_>>();
 457             list.sort();
 458             last = UseSegment::List(list);
 459         }
 460
 461         self.path.push(last);
 462         self
 463     }
 464
 465     fn has_comment(&self) -> bool {
 466         self.list_item.as_ref().map_or(false, ListItem::has_comment)
 467     }
 468
 469     fn same_visibility(&self, other: &UseTree) -> bool {
 470         match (&self.visibility, &other.visibility) {
 471             (
 472                 Some(codemap::Spanned {
 473                     node: ast::VisibilityKind::Inherited,
 474                     ..
 475                 }),
 476                 None,
 477             )
 478             | (
 479                 None,
 480                 Some(codemap::Spanned {
 481                     node: ast::VisibilityKind::Inherited,
 482                     ..
 483                 }),
 484             )
 485             | (None, None) => true,
 486             (
 487                 Some(codemap::Spanned { node: lnode, .. }),
 488                 Some(codemap::Spanned { node: rnode, .. }),
 489             ) => lnode == rnode,
 490             _ => false,
 491         }
 492     }
 493
 494     fn share_prefix(&self, other: &UseTree) -> bool {
 495         if self.path.is_empty()
 496             || other.path.is_empty()
 497             || self.attrs.is_some()
 498             || !self.same_visibility(other)
 499         {
 500             false
 501         } else {
 502             self.path[0] == other.path[0]
 503         }
 504     }
 505
 506     fn flatten(self) -> Vec<UseTree> {
 507         if self.path.is_empty() {
 508             return vec![self];
 509         }
 510         match self.path.clone().last().unwrap() {
 511             UseSegment::List(list) => {
 512                 let prefix = &self.path[..self.path.len() - 1];
 513                 let mut result = vec![];
 514                 for nested_use_tree in list {
 515                     for mut flattend in &mut nested_use_tree.clone().flatten() {
 516                         let mut new_path = prefix.to_vec();
 517                         new_path.append(&mut flattend.path);
 518                         result.push(UseTree {
 519                             path: new_path,
 520                             span: self.span,
 521                             list_item: None,
 522                             visibility: self.visibility.clone(),
 523                             attrs: None,
 524                         });
 525                     }
 526                 }
 527
 528                 result
 529             }
 530             _ => vec![self],
 531         }
 532     }
 533
 534     fn merge(&mut self, other: UseTree) {
 535         let mut new_path = vec![];
 536         for (mut a, b) in self
 537             .path
 538             .clone()
 539             .iter_mut()
 540             .zip(other.path.clone().into_iter())
 541         {
 542             if *a == b {
 543                 new_path.push(b);
 544             } else {
 545                 break;
 546             }
 547         }
 548         if let Some(merged) = merge_rest(&self.path, &other.path, new_path.len()) {
 549             new_path.push(merged);
 550             self.span = self.span.to(other.span);
 551         }
 552         self.path = new_path;
 553     }
 554 }
 555
 556 fn merge_rest(a: &[UseSegment], b: &[UseSegment], len: usize) -> Option<UseSegment> {
 557     let a_rest = &a[len..];
 558     let b_rest = &b[len..];
 559     if a_rest.is_empty() && b_rest.is_empty() {
 560         return None;
 561     }
 562     if a_rest.is_empty() {
 563         return Some(UseSegment::List(vec![
 564             UseTree::from_path(vec![UseSegment::Slf(None)], DUMMY_SP),
 565             UseTree::from_path(b_rest.to_vec(), DUMMY_SP),
 566         ]));
 567     }
 568     if b_rest.is_empty() {
 569         return Some(UseSegment::List(vec![
 570             UseTree::from_path(vec![UseSegment::Slf(None)], DUMMY_SP),
 571             UseTree::from_path(a_rest.to_vec(), DUMMY_SP),
 572         ]));
 573     }
 574     if let UseSegment::List(mut list) = a_rest[0].clone() {
 575         merge_use_trees_inner(&mut list, UseTree::from_path(b_rest.to_vec(), DUMMY_SP));
 576         list.sort();
 577         return Some(UseSegment::List(list.clone()));
 578     }
 579     let mut list = vec![
 580         UseTree::from_path(a_rest.to_vec(), DUMMY_SP),
 581         UseTree::from_path(b_rest.to_vec(), DUMMY_SP),
 582     ];
 583     list.sort();
 584     Some(UseSegment::List(list))
 585 }
 586
 587 impl PartialOrd for UseSegment {
 588     fn partial_cmp(&self, other: &UseSegment) -> Option<Ordering> {
 589         Some(self.cmp(other))
 590     }
 591 }
 592 impl PartialOrd for UseTree {
 593     fn partial_cmp(&self, other: &UseTree) -> Option<Ordering> {
 594         Some(self.cmp(other))
 595     }
 596 }
 597 impl Ord for UseSegment {
 598     fn cmp(&self, other: &UseSegment) -> Ordering {
 599         use self::UseSegment::*;
 600
 601         fn is_upper_snake_case(s: &str) -> bool {
 602             s.chars().all(|c| c.is_uppercase() || c == '_')
 603         }
 604
 605         match (self, other) {
 606             (&Slf(ref a), &Slf(ref b)) | (&Super(ref a), &Super(ref b)) => a.cmp(b),
 607             (&Glob, &Glob) => Ordering::Equal,
 608             (&Ident(ref ia, ref aa), &Ident(ref ib, ref ab)) => {
 609                 // snake_case < CamelCase < UPPER_SNAKE_CASE
 610                 if ia.starts_with(char::is_uppercase) && ib.starts_with(char::is_lowercase) {
 611                     return Ordering::Greater;
 612                 }
 613                 if ia.starts_with(char::is_lowercase) && ib.starts_with(char::is_uppercase) {
 614                     return Ordering::Less;
 615                 }
 616                 if is_upper_snake_case(ia) && !is_upper_snake_case(ib) {
 617                     return Ordering::Greater;
 618                 }
 619                 if !is_upper_snake_case(ia) && is_upper_snake_case(ib) {
 620                     return Ordering::Less;
 621                 }
 622                 let ident_ord = ia.cmp(ib);
 623                 if ident_ord != Ordering::Equal {
 624                     return ident_ord;
 625                 }
 626                 if aa.is_none() && ab.is_some() {
 627                     return Ordering::Less;
 628                 }
 629                 if aa.is_some() && ab.is_none() {
 630                     return Ordering::Greater;
 631                 }
 632                 aa.cmp(ab)
 633             }
 634             (&List(ref a), &List(ref b)) => {
 635                 for (a, b) in a.iter().zip(b.iter()) {
 636                     let ord = a.cmp(b);
 637                     if ord != Ordering::Equal {
 638                         return ord;
 639                     }
 640                 }
 641
 642                 a.len().cmp(&b.len())
 643             }
 644             (&Slf(_), _) => Ordering::Less,
 645             (_, &Slf(_)) => Ordering::Greater,
 646             (&Super(_), _) => Ordering::Less,
 647             (_, &Super(_)) => Ordering::Greater,
 648             (&Ident(..), _) => Ordering::Less,
 649             (_, &Ident(..)) => Ordering::Greater,
 650             (&Glob, _) => Ordering::Less,
 651             (_, &Glob) => Ordering::Greater,
 652         }
 653     }
 654 }
 655 impl Ord for UseTree {
 656     fn cmp(&self, other: &UseTree) -> Ordering {
 657         for (a, b) in self.path.iter().zip(other.path.iter()) {
 658             let ord = a.cmp(b);
 659             // The comparison without aliases is a hack to avoid situations like
 660             // comparing `a::b` to `a as c` - where the latter should be ordered
 661             // first since it is shorter.
 662             if ord != Ordering::Equal && a.remove_alias().cmp(&b.remove_alias()) != Ordering::Equal
 663             {
 664                 return ord;
 665             }
 666         }
 667
 668         self.path.len().cmp(&other.path.len())
 669     }
 670 }
 671
 672 fn rewrite_nested_use_tree(
 673     context: &RewriteContext,
 674     use_tree_list: &[UseTree],
 675     shape: Shape,
 676 ) -> Option<String> {
 677     let mut list_items = Vec::with_capacity(use_tree_list.len());
 678     let nested_shape = match context.config.imports_indent() {
 679         IndentStyle::Block => shape
 680             .block_indent(context.config.tab_spaces())
 681             .with_max_width(context.config)
 682             .sub_width(1)?,
 683         IndentStyle::Visual => shape.visual_indent(0),
 684     };
 685     for use_tree in use_tree_list {
 686         if let Some(mut list_item) = use_tree.list_item.clone() {
 687             list_item.item = use_tree.rewrite(context, nested_shape);
 688             list_items.push(list_item);
 689         } else {
 690             list_items.push(ListItem::from_str(use_tree.rewrite(context, nested_shape)?));
 691         }
 692     }
 693     let has_nested_list = use_tree_list.iter().any(|use_segment| {
 694         use_segment
 695             .path
 696             .last()
 697             .map_or(false, |last_segment| match last_segment {
 698                 UseSegment::List(..) => true,
 699                 _ => false,
 700             })
 701     });
 702
 703     let remaining_width = if has_nested_list {
 704         0
 705     } else {
 706         shape.width.saturating_sub(2)
 707     };
 708
 709     let tactic = definitive_tactic(
 710         &list_items,
 711         context.config.imports_layout(),
 712         Separator::Comma,
 713         remaining_width,
 714     );
 715
 716     let ends_with_newline = context.config.imports_indent() == IndentStyle::Block
 717         && tactic != DefinitiveListTactic::Horizontal;
 718     let fmt = ListFormatting {
 719         tactic,
 720         separator: ",",
 721         trailing_separator: if ends_with_newline {
 722             context.config.trailing_comma()
 723         } else {
 724             SeparatorTactic::Never
 725         },
 726         separator_place: SeparatorPlace::Back,
 727         shape: nested_shape,
 728         ends_with_newline,
 729         preserve_newline: true,
 730         nested: has_nested_list,
 731         config: context.config,
 732     };
 733
 734     let list_str = write_list(&list_items, &fmt)?;
 735
 736     let result = if (list_str.contains('\n') || list_str.len() > remaining_width)
 737         && context.config.imports_indent() == IndentStyle::Block
 738     {
 739         format!(
 740             "{{\n{}{}\n{}}}",
 741             nested_shape.indent.to_string(context.config),
 742             list_str,
 743             shape.indent.to_string(context.config)
 744         )
 745     } else {
 746         format!("{{{}}}", list_str)
 747     };
 748
 749     Some(result)
 750 }
 751
 752 impl Rewrite for UseSegment {
 753     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 754         Some(match *self {
 755             UseSegment::Ident(ref ident, Some(ref rename)) => format!("{} as {}", ident, rename),
 756             UseSegment::Ident(ref ident, None) => ident.clone(),
 757             UseSegment::Slf(Some(ref rename)) => format!("self as {}", rename),
 758             UseSegment::Slf(None) => "self".to_owned(),
 759             UseSegment::Super(Some(ref rename)) => format!("super as {}", rename),
 760             UseSegment::Super(None) => "super".to_owned(),
 761             UseSegment::Glob => "*".to_owned(),
 762             UseSegment::List(ref use_tree_list) => rewrite_nested_use_tree(
 763                 context,
 764                 use_tree_list,
 765                 // 1 = "{" and "}"
 766                 shape.offset_left(1)?.sub_width(1)?,
 767             )?,
 768         })
 769     }
 770 }
 771
 772 impl Rewrite for UseTree {
 773     // This does NOT format attributes and visibility or add a trailing `;`.
 774     fn rewrite(&self, context: &RewriteContext, mut shape: Shape) -> Option<String> {
 775         let mut result = String::with_capacity(256);
 776         let mut iter = self.path.iter().peekable();
 777         while let Some(ref segment) = iter.next() {
 778             let segment_str = segment.rewrite(context, shape)?;
 779             result.push_str(&segment_str);
 780             if iter.peek().is_some() {
 781                 result.push_str("::");
 782                 // 2 = "::"
 783                 shape = shape.offset_left(2 + segment_str.len())?;
 784             }
 785         }
 786         Some(result)
 787     }
 788 }
 789
 790 #[cfg(test)]
 791 mod test {
 792     use super::*;
 793     use syntax::codemap::DUMMY_SP;
 794
 795     // Parse the path part of an import. This parser is not robust and is only
 796     // suitable for use in a test harness.
 797     fn parse_use_tree(s: &str) -> UseTree {
 798         use std::iter::Peekable;
 799         use std::mem::swap;
 800         use std::str::Chars;
 801
 802         struct Parser<'a> {
 803             input: Peekable<Chars<'a>>,
 804         }
 805
 806         impl<'a> Parser<'a> {
 807             fn bump(&mut self) {
 808                 self.input.next().unwrap();
 809             }
 810
 811             fn eat(&mut self, c: char) {
 812                 assert!(self.input.next().unwrap() == c);
 813             }
 814
 815             fn push_segment(
 816                 result: &mut Vec<UseSegment>,
 817                 buf: &mut String,
 818                 alias_buf: &mut Option<String>,
 819             ) {
 820                 if !buf.is_empty() {
 821                     let mut alias = None;
 822                     swap(alias_buf, &mut alias);
 823                     if buf == "self" {
 824                         result.push(UseSegment::Slf(alias));
 825                         *buf = String::new();
 826                         *alias_buf = None;
 827                     } else if buf == "super" {
 828                         result.push(UseSegment::Super(alias));
 829                         *buf = String::new();
 830                         *alias_buf = None;
 831                     } else {
 832                         let mut name = String::new();
 833                         swap(buf, &mut name);
 834                         result.push(UseSegment::Ident(name, alias));
 835                     }
 836                 }
 837             }
 838
 839             fn parse_in_list(&mut self) -> UseTree {
 840                 let mut result = vec![];
 841                 let mut buf = String::new();
 842                 let mut alias_buf = None;
 843                 while let Some(&c) = self.input.peek() {
 844                     match c {
 845                         '{' => {
 846                             assert!(buf.is_empty());
 847                             self.bump();
 848                             result.push(UseSegment::List(self.parse_list()));
 849                             self.eat('}');
 850                         }
 851                         '*' => {
 852                             assert!(buf.is_empty());
 853                             self.bump();
 854                             result.push(UseSegment::Glob);
 855                         }
 856                         ':' => {
 857                             self.bump();
 858                             self.eat(':');
 859                             Self::push_segment(&mut result, &mut buf, &mut alias_buf);
 860                         }
 861                         '}' | ',' => {
 862                             Self::push_segment(&mut result, &mut buf, &mut alias_buf);
 863                             return UseTree {
 864                                 path: result,
 865                                 span: DUMMY_SP,
 866                                 list_item: None,
 867                                 visibility: None,
 868                                 attrs: None,
 869                             };
 870                         }
 871                         ' ' => {
 872                             self.bump();
 873                             self.eat('a');
 874                             self.eat('s');
 875                             self.eat(' ');
 876                             alias_buf = Some(String::new());
 877                         }
 878                         c => {
 879                             self.bump();
 880                             if let Some(ref mut buf) = alias_buf {
 881                                 buf.push(c);
 882                             } else {
 883                                 buf.push(c);
 884                             }
 885                         }
 886                     }
 887                 }
 888                 Self::push_segment(&mut result, &mut buf, &mut alias_buf);
 889                 UseTree {
 890                     path: result,
 891                     span: DUMMY_SP,
 892                     list_item: None,
 893                     visibility: None,
 894                     attrs: None,
 895                 }
 896             }
 897
 898             fn parse_list(&mut self) -> Vec<UseTree> {
 899                 let mut result = vec![];
 900                 loop {
 901                     match self.input.peek().unwrap() {
 902                         ',' | ' ' => self.bump(),
 903                         '}' => {
 904                             return result;
 905                         }
 906                         _ => result.push(self.parse_in_list()),
 907                     }
 908                 }
 909             }
 910         }
 911
 912         let mut parser = Parser {
 913             input: s.chars().peekable(),
 914         };
 915         parser.parse_in_list()
 916     }
 917
 918     macro parse_use_trees($($s:expr),* $(,)*) {
 919         vec![
 920             $(parse_use_tree($s),)*
 921         ]
 922     }
 923
 924     #[test]
 925     fn test_use_tree_merge() {
 926         macro test_merge([$($input:expr),* $(,)*], [$($output:expr),* $(,)*]) {
 927             assert_eq!(
 928                 merge_use_trees(parse_use_trees!($($input,)*)),
 929                 parse_use_trees!($($output,)*),
 930             );
 931         }
 932
 933         test_merge!(["a::b::{c, d}", "a::b::{e, f}"], ["a::b::{c, d, e, f}"]);
 934         test_merge!(["a::b::c", "a::b"], ["a::b::{self, c}"]);
 935         test_merge!(["a::b", "a::b"], ["a::b"]);
 936         test_merge!(["a", "a::b", "a::b::c"], ["a::{self, b::{self, c}}"]);
 937         test_merge!(
 938             ["a::{b::{self, c}, d::e}", "a::d::f"],
 939             ["a::{b::{self, c}, d::{e, f}}"]
 940         );
 941         test_merge!(
 942             ["a::d::f", "a::{b::{self, c}, d::e}"],
 943             ["a::{b::{self, c}, d::{e, f}}"]
 944         );
 945         test_merge!(
 946             ["a::{c, d, b}", "a::{d, e, b, a, f}", "a::{f, g, c}"],
 947             ["a::{a, b, c, d, e, f, g}"]
 948         );
 949     }
 950
 951     #[test]
 952     fn test_use_tree_flatten() {
 953         assert_eq!(
 954             parse_use_tree("a::b::{c, d, e, f}").flatten(),
 955             parse_use_trees!("a::b::c", "a::b::d", "a::b::e", "a::b::f",)
 956         );
 957
 958         assert_eq!(
 959             parse_use_tree("a::b::{c::{d, e, f}, g, h::{i, j, k}}").flatten(),
 960             parse_use_trees![
 961                 "a::b::c::d",
 962                 "a::b::c::e",
 963                 "a::b::c::f",
 964                 "a::b::g",
 965                 "a::b::h::i",
 966                 "a::b::h::j",
 967                 "a::b::h::k",
 968             ]
 969         );
 970     }
 971
 972     #[test]
 973     fn test_use_tree_normalize() {
 974         assert_eq!(parse_use_tree("a::self").normalize(), parse_use_tree("a"));
 975         assert_eq!(
 976             parse_use_tree("a::self as foo").normalize(),
 977             parse_use_tree("a as foo")
 978         );
 979         assert_eq!(parse_use_tree("a::{self}").normalize(), parse_use_tree("a"));
 980         assert_eq!(parse_use_tree("a::{b}").normalize(), parse_use_tree("a::b"));
 981         assert_eq!(
 982             parse_use_tree("a::{b, c::self}").normalize(),
 983             parse_use_tree("a::{b, c}")
 984         );
 985         assert_eq!(
 986             parse_use_tree("a::{b as bar, c::self}").normalize(),
 987             parse_use_tree("a::{b as bar, c}")
 988         );
 989     }
 990
 991     #[test]
 992     fn test_use_tree_ord() {
 993         assert!(parse_use_tree("a").normalize() < parse_use_tree("aa").normalize());
 994         assert!(parse_use_tree("a").normalize() < parse_use_tree("a::a").normalize());
 995         assert!(parse_use_tree("a").normalize() < parse_use_tree("*").normalize());
 996         assert!(parse_use_tree("a").normalize() < parse_use_tree("{a, b}").normalize());
 997         assert!(parse_use_tree("*").normalize() < parse_use_tree("{a, b}").normalize());
 998
 999         assert!(
1000             parse_use_tree("aaaaaaaaaaaaaaa::{bb, cc, dddddddd}").normalize()
1001                 < parse_use_tree("aaaaaaaaaaaaaaa::{bb, cc, ddddddddd}").normalize()
1002         );
1003         assert!(
1004             parse_use_tree("serde::de::{Deserialize}").normalize()
1005                 < parse_use_tree("serde_json").normalize()
1006         );
1007         assert!(parse_use_tree("a::b::c").normalize() < parse_use_tree("a::b::*").normalize());
1008         assert!(
1009             parse_use_tree("foo::{Bar, Baz}").normalize()
1010                 < parse_use_tree("{Bar, Baz}").normalize()
1011         );
1012
1013         assert!(
1014             parse_use_tree("foo::{self as bar}").normalize()
1015                 < parse_use_tree("foo::{qux as bar}").normalize()
1016         );
1017         assert!(
1018             parse_use_tree("foo::{qux as bar}").normalize()
1019                 < parse_use_tree("foo::{baz, qux as bar}").normalize()
1020         );
1021         assert!(
1022             parse_use_tree("foo::{self as bar, baz}").normalize()
1023                 < parse_use_tree("foo::{baz, qux as bar}").normalize()
1024         );
1025
1026         assert!(parse_use_tree("foo").normalize() < parse_use_tree("Foo").normalize());
1027         assert!(parse_use_tree("foo").normalize() < parse_use_tree("foo::Bar").normalize());
1028
1029         assert!(
1030             parse_use_tree("std::cmp::{d, c, b, a}").normalize()
1031                 < parse_use_tree("std::cmp::{b, e, g, f}").normalize()
1032         );
1033     }
1034 }