src/lists.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 //! Format list-like expressions and items.
  12
  13 use std::cmp;
  14 use std::iter::Peekable;
  15
  16 use config::lists::*;
  17 use syntax::codemap::BytePos;
  18
  19 use comment::{find_comment_end, rewrite_comment, FindUncommented};
  20 use config::{Config, IndentStyle};
  21 use rewrite::RewriteContext;
  22 use shape::{Indent, Shape};
  23 use utils::{count_newlines, first_line_width, last_line_width, mk_sp, starts_with_newline};
  24 use visitor::SnippetProvider;
  25
  26 pub struct ListFormatting<'a> {
  27     pub tactic: DefinitiveListTactic,
  28     pub separator: &'a str,
  29     pub trailing_separator: SeparatorTactic,
  30     pub separator_place: SeparatorPlace,
  31     pub shape: Shape,
  32     // Non-expressions, e.g. items, will have a new line at the end of the list.
  33     // Important for comment styles.
  34     pub ends_with_newline: bool,
  35     // Remove newlines between list elements for expressions.
  36     pub preserve_newline: bool,
  37     pub config: &'a Config,
  38 }
  39
  40 impl<'a> ListFormatting<'a> {
  41     pub fn needs_trailing_separator(&self) -> bool {
  42         match self.trailing_separator {
  43             // We always put separator in front.
  44             SeparatorTactic::Always => true,
  45             SeparatorTactic::Vertical => self.tactic == DefinitiveListTactic::Vertical,
  46             SeparatorTactic::Never => {
  47                 self.tactic == DefinitiveListTactic::Vertical && self.separator_place.is_front()
  48             }
  49         }
  50     }
  51 }
  52
  53 impl AsRef<ListItem> for ListItem {
  54     fn as_ref(&self) -> &ListItem {
  55         self
  56     }
  57 }
  58
  59 #[derive(PartialEq, Eq, Debug, Copy, Clone)]
  60 pub enum ListItemCommentStyle {
  61     // Try to keep the comment on the same line with the item.
  62     SameLine,
  63     // Put the comment on the previous or the next line of the item.
  64     DifferentLine,
  65     // No comment available.
  66     None,
  67 }
  68
  69 #[derive(Debug, Clone)]
  70 pub struct ListItem {
  71     // None for comments mean that they are not present.
  72     pub pre_comment: Option<String>,
  73     pub pre_comment_style: ListItemCommentStyle,
  74     // Item should include attributes and doc comments. None indicates a failed
  75     // rewrite.
  76     pub item: Option<String>,
  77     pub post_comment: Option<String>,
  78     // Whether there is extra whitespace before this item.
  79     pub new_lines: bool,
  80 }
  81
  82 impl ListItem {
  83     pub fn empty() -> ListItem {
  84         ListItem {
  85             pre_comment: None,
  86             pre_comment_style: ListItemCommentStyle::None,
  87             item: None,
  88             post_comment: None,
  89             new_lines: false,
  90         }
  91     }
  92
  93     pub fn inner_as_ref(&self) -> &str {
  94         self.item.as_ref().map_or("", |s| s)
  95     }
  96
  97     pub fn is_different_group(&self) -> bool {
  98         self.inner_as_ref().contains('\n') || self.pre_comment.is_some()
  99             || self.post_comment
 100                 .as_ref()
 101                 .map_or(false, |s| s.contains('\n'))
 102     }
 103
 104     pub fn is_multiline(&self) -> bool {
 105         self.inner_as_ref().contains('\n')
 106             || self.pre_comment
 107                 .as_ref()
 108                 .map_or(false, |s| s.contains('\n'))
 109             || self.post_comment
 110                 .as_ref()
 111                 .map_or(false, |s| s.contains('\n'))
 112     }
 113
 114     pub fn has_single_line_comment(&self) -> bool {
 115         self.pre_comment
 116             .as_ref()
 117             .map_or(false, |comment| comment.trim_left().starts_with("//"))
 118             || self.post_comment
 119                 .as_ref()
 120                 .map_or(false, |comment| comment.trim_left().starts_with("//"))
 121     }
 122
 123     pub fn has_comment(&self) -> bool {
 124         self.pre_comment.is_some() || self.post_comment.is_some()
 125     }
 126
 127     pub fn from_str<S: Into<String>>(s: S) -> ListItem {
 128         ListItem {
 129             pre_comment: None,
 130             pre_comment_style: ListItemCommentStyle::None,
 131             item: Some(s.into()),
 132             post_comment: None,
 133             new_lines: false,
 134         }
 135     }
 136
 137     // true if the item causes something to be written.
 138     fn is_substantial(&self) -> bool {
 139         fn empty(s: &Option<String>) -> bool {
 140             match *s {
 141                 Some(ref s) if !s.is_empty() => false,
 142                 _ => true,
 143             }
 144         }
 145
 146         !(empty(&self.pre_comment) && empty(&self.item) && empty(&self.post_comment))
 147     }
 148 }
 149
 150 /// The type of separator for lists.
 151 #[derive(Copy, Clone, Eq, PartialEq, Debug)]
 152 pub enum Separator {
 153     Comma,
 154     VerticalBar,
 155 }
 156
 157 impl Separator {
 158     pub fn len(&self) -> usize {
 159         match *self {
 160             // 2 = `, `
 161             Separator::Comma => 2,
 162             // 3 = ` | `
 163             Separator::VerticalBar => 3,
 164         }
 165     }
 166 }
 167
 168 pub fn definitive_tactic<I, T>(
 169     items: I,
 170     tactic: ListTactic,
 171     sep: Separator,
 172     width: usize,
 173 ) -> DefinitiveListTactic
 174 where
 175     I: IntoIterator<Item = T> + Clone,
 176     T: AsRef<ListItem>,
 177 {
 178     let pre_line_comments = items
 179         .clone()
 180         .into_iter()
 181         .any(|item| item.as_ref().has_single_line_comment());
 182
 183     let limit = match tactic {
 184         _ if pre_line_comments => return DefinitiveListTactic::Vertical,
 185         ListTactic::Horizontal => return DefinitiveListTactic::Horizontal,
 186         ListTactic::Vertical => return DefinitiveListTactic::Vertical,
 187         ListTactic::LimitedHorizontalVertical(limit) => ::std::cmp::min(width, limit),
 188         ListTactic::Mixed | ListTactic::HorizontalVertical => width,
 189     };
 190
 191     let (sep_count, total_width) = calculate_width(items.clone());
 192     let total_sep_len = sep.len() * sep_count.checked_sub(1).unwrap_or(0);
 193     let real_total = total_width + total_sep_len;
 194
 195     if real_total <= limit && !pre_line_comments
 196         && !items.into_iter().any(|item| item.as_ref().is_multiline())
 197     {
 198         DefinitiveListTactic::Horizontal
 199     } else {
 200         match tactic {
 201             ListTactic::Mixed => DefinitiveListTactic::Mixed,
 202             _ => DefinitiveListTactic::Vertical,
 203         }
 204     }
 205 }
 206
 207 // Format a list of commented items into a string.
 208 // TODO: add unit tests
 209 pub fn write_list<I, T>(items: I, formatting: &ListFormatting) -> Option<String>
 210 where
 211     I: IntoIterator<Item = T> + Clone,
 212     T: AsRef<ListItem>,
 213 {
 214     let tactic = formatting.tactic;
 215     let sep_len = formatting.separator.len();
 216
 217     // Now that we know how we will layout, we can decide for sure if there
 218     // will be a trailing separator.
 219     let mut trailing_separator = formatting.needs_trailing_separator();
 220     let mut result = String::with_capacity(128);
 221     let cloned_items = items.clone();
 222     let mut iter = items.into_iter().enumerate().peekable();
 223     let mut item_max_width: Option<usize> = None;
 224     let sep_place =
 225         SeparatorPlace::from_tactic(formatting.separator_place, tactic, formatting.separator);
 226
 227     let mut line_len = 0;
 228     let indent_str = &formatting.shape.indent.to_string(formatting.config);
 229     while let Some((i, item)) = iter.next() {
 230         let item = item.as_ref();
 231         let inner_item = item.item.as_ref()?;
 232         let first = i == 0;
 233         let last = iter.peek().is_none();
 234         let mut separate = match sep_place {
 235             SeparatorPlace::Front => !first,
 236             SeparatorPlace::Back => !last || trailing_separator,
 237         };
 238         let item_sep_len = if separate { sep_len } else { 0 };
 239
 240         // Item string may be multi-line. Its length (used for block comment alignment)
 241         // should be only the length of the last line.
 242         let item_last_line = if item.is_multiline() {
 243             inner_item.lines().last().unwrap_or("")
 244         } else {
 245             inner_item.as_ref()
 246         };
 247         let mut item_last_line_width = item_last_line.len() + item_sep_len;
 248         if item_last_line.starts_with(&**indent_str) {
 249             item_last_line_width -= indent_str.len();
 250         }
 251
 252         if !item.is_substantial() {
 253             continue;
 254         }
 255
 256         match tactic {
 257             DefinitiveListTactic::Horizontal if !first => {
 258                 result.push(' ');
 259             }
 260             DefinitiveListTactic::SpecialMacro(num_args_before) => {
 261                 if i == 0 {
 262                     // Nothing
 263                 } else if i < num_args_before {
 264                     result.push(' ');
 265                 } else if i <= num_args_before + 1 {
 266                     result.push('\n');
 267                     result.push_str(indent_str);
 268                 } else {
 269                     result.push(' ');
 270                 }
 271             }
 272             DefinitiveListTactic::Vertical
 273                 if !first && !inner_item.is_empty() && !result.is_empty() =>
 274             {
 275                 result.push('\n');
 276                 result.push_str(indent_str);
 277             }
 278             DefinitiveListTactic::Mixed => {
 279                 let total_width = total_item_width(item) + item_sep_len;
 280
 281                 // 1 is space between separator and item.
 282                 if line_len > 0 && line_len + 1 + total_width > formatting.shape.width {
 283                     result.push('\n');
 284                     result.push_str(indent_str);
 285                     line_len = 0;
 286                     if formatting.ends_with_newline {
 287                         trailing_separator = true;
 288                     }
 289                 }
 290
 291                 if last && formatting.ends_with_newline {
 292                     match formatting.trailing_separator {
 293                         SeparatorTactic::Always | SeparatorTactic::Vertical => separate = true,
 294                         _ => (),
 295                     }
 296                 }
 297
 298                 if line_len > 0 {
 299                     result.push(' ');
 300                     line_len += 1;
 301                 }
 302
 303                 line_len += total_width;
 304             }
 305             _ => {}
 306         }
 307
 308         // Pre-comments
 309         if let Some(ref comment) = item.pre_comment {
 310             // Block style in non-vertical mode.
 311             let block_mode = tactic != DefinitiveListTactic::Vertical;
 312             // Width restriction is only relevant in vertical mode.
 313             let comment =
 314                 rewrite_comment(comment, block_mode, formatting.shape, formatting.config)?;
 315             result.push_str(&comment);
 316
 317             if !inner_item.is_empty() {
 318                 if tactic == DefinitiveListTactic::Vertical {
 319                     // We cannot keep pre-comments on the same line if the comment if normalized.
 320                     let keep_comment = if formatting.config.normalize_comments()
 321                         || item.pre_comment_style == ListItemCommentStyle::DifferentLine
 322                     {
 323                         false
 324                     } else {
 325                         // We will try to keep the comment on the same line with the item here.
 326                         // 1 = ` `
 327                         let total_width = total_item_width(item) + item_sep_len + 1;
 328                         total_width <= formatting.shape.width
 329                     };
 330                     if keep_comment {
 331                         result.push(' ');
 332                     } else {
 333                         result.push('\n');
 334                         result.push_str(indent_str);
 335                     }
 336                 } else {
 337                     result.push(' ');
 338                 }
 339             }
 340             item_max_width = None;
 341         }
 342
 343         if separate && sep_place.is_front() && !first {
 344             result.push_str(formatting.separator.trim());
 345             result.push(' ');
 346         }
 347         result.push_str(inner_item);
 348
 349         // Post-comments
 350         if tactic != DefinitiveListTactic::Vertical && item.post_comment.is_some() {
 351             let comment = item.post_comment.as_ref().unwrap();
 352             let formatted_comment = rewrite_comment(
 353                 comment,
 354                 true,
 355                 Shape::legacy(formatting.shape.width, Indent::empty()),
 356                 formatting.config,
 357             )?;
 358
 359             result.push(' ');
 360             result.push_str(&formatted_comment);
 361         }
 362
 363         if separate && sep_place.is_back() {
 364             result.push_str(formatting.separator);
 365         }
 366
 367         if tactic == DefinitiveListTactic::Vertical && item.post_comment.is_some() {
 368             let comment = item.post_comment.as_ref().unwrap();
 369             let overhead = last_line_width(&result) + first_line_width(comment.trim());
 370
 371             let rewrite_post_comment = |item_max_width: &mut Option<usize>| {
 372                 if item_max_width.is_none() && !last && !inner_item.contains('\n') {
 373                     *item_max_width = Some(max_width_of_item_with_post_comment(
 374                         &cloned_items,
 375                         i,
 376                         overhead,
 377                         formatting.config.max_width(),
 378                     ));
 379                 }
 380                 let overhead = if starts_with_newline(comment) {
 381                     0
 382                 } else if let Some(max_width) = *item_max_width {
 383                     max_width + 2
 384                 } else {
 385                     // 1 = space between item and comment.
 386                     item_last_line_width + 1
 387                 };
 388                 let width = formatting.shape.width.checked_sub(overhead).unwrap_or(1);
 389                 let offset = formatting.shape.indent + overhead;
 390                 let comment_shape = Shape::legacy(width, offset);
 391
 392                 // Use block-style only for the last item or multiline comments.
 393                 let block_style = !formatting.ends_with_newline && last
 394                     || comment.trim().contains('\n')
 395                     || comment.trim().len() > width;
 396
 397                 rewrite_comment(
 398                     comment.trim_left(),
 399                     block_style,
 400                     comment_shape,
 401                     formatting.config,
 402                 )
 403             };
 404
 405             let mut formatted_comment = rewrite_post_comment(&mut item_max_width)?;
 406
 407             if !starts_with_newline(comment) {
 408                 let mut comment_alignment =
 409                     post_comment_alignment(item_max_width, inner_item.len());
 410                 if first_line_width(&formatted_comment) + last_line_width(&result)
 411                     + comment_alignment + 1 > formatting.config.max_width()
 412                 {
 413                     item_max_width = None;
 414                     formatted_comment = rewrite_post_comment(&mut item_max_width)?;
 415                     comment_alignment = post_comment_alignment(item_max_width, inner_item.len());
 416                 }
 417                 for _ in 0..(comment_alignment + 1) {
 418                     result.push(' ');
 419                 }
 420                 // An additional space for the missing trailing separator.
 421                 if last && item_max_width.is_some() && !separate && !formatting.separator.is_empty()
 422                 {
 423                     result.push(' ');
 424                 }
 425             } else {
 426                 result.push('\n');
 427                 result.push_str(indent_str);
 428             }
 429             if formatted_comment.contains('\n') {
 430                 item_max_width = None;
 431             }
 432             result.push_str(&formatted_comment);
 433         } else {
 434             item_max_width = None;
 435         }
 436
 437         if formatting.preserve_newline && !last && tactic == DefinitiveListTactic::Vertical
 438             && item.new_lines
 439         {
 440             item_max_width = None;
 441             result.push('\n');
 442         }
 443     }
 444
 445     Some(result)
 446 }
 447
 448 fn max_width_of_item_with_post_comment<I, T>(
 449     items: &I,
 450     i: usize,
 451     overhead: usize,
 452     max_budget: usize,
 453 ) -> usize
 454 where
 455     I: IntoIterator<Item = T> + Clone,
 456     T: AsRef<ListItem>,
 457 {
 458     let mut max_width = 0;
 459     let mut first = true;
 460     for item in items.clone().into_iter().skip(i) {
 461         let item = item.as_ref();
 462         let inner_item_width = item.inner_as_ref().len();
 463         if !first
 464             && (item.is_different_group() || !item.post_comment.is_some()
 465                 || inner_item_width + overhead > max_budget)
 466         {
 467             return max_width;
 468         }
 469         if max_width < inner_item_width {
 470             max_width = inner_item_width;
 471         }
 472         if item.new_lines {
 473             return max_width;
 474         }
 475         first = false;
 476     }
 477     max_width
 478 }
 479
 480 fn post_comment_alignment(item_max_width: Option<usize>, inner_item_len: usize) -> usize {
 481     item_max_width
 482         .and_then(|max_line_width| max_line_width.checked_sub(inner_item_len))
 483         .unwrap_or(0)
 484 }
 485
 486 pub struct ListItems<'a, I, F1, F2, F3>
 487 where
 488     I: Iterator,
 489 {
 490     snippet_provider: &'a SnippetProvider<'a>,
 491     inner: Peekable<I>,
 492     get_lo: F1,
 493     get_hi: F2,
 494     get_item_string: F3,
 495     prev_span_end: BytePos,
 496     next_span_start: BytePos,
 497     terminator: &'a str,
 498     separator: &'a str,
 499     leave_last: bool,
 500 }
 501
 502 impl<'a, T, I, F1, F2, F3> Iterator for ListItems<'a, I, F1, F2, F3>
 503 where
 504     I: Iterator<Item = T>,
 505     F1: Fn(&T) -> BytePos,
 506     F2: Fn(&T) -> BytePos,
 507     F3: Fn(&T) -> Option<String>,
 508 {
 509     type Item = ListItem;
 510
 511     fn next(&mut self) -> Option<Self::Item> {
 512         let white_space: &[_] = &[' ', '\t'];
 513
 514         self.inner.next().map(|item| {
 515             let mut new_lines = false;
 516             // Pre-comment
 517             let pre_snippet = self.snippet_provider
 518                 .span_to_snippet(mk_sp(self.prev_span_end, (self.get_lo)(&item)))
 519                 .unwrap();
 520             let trimmed_pre_snippet = pre_snippet.trim();
 521             let has_single_line_comment = trimmed_pre_snippet.starts_with("//");
 522             let has_block_comment = trimmed_pre_snippet.starts_with("/*");
 523             let (pre_comment, pre_comment_style) = if has_single_line_comment {
 524                 (
 525                     Some(trimmed_pre_snippet.to_owned()),
 526                     ListItemCommentStyle::DifferentLine,
 527                 )
 528             } else if has_block_comment {
 529                 let comment_end = pre_snippet.chars().rev().position(|c| c == '/').unwrap();
 530                 if pre_snippet
 531                     .chars()
 532                     .rev()
 533                     .take(comment_end + 1)
 534                     .any(|c| c == '\n')
 535                 {
 536                     (
 537                         Some(trimmed_pre_snippet.to_owned()),
 538                         ListItemCommentStyle::DifferentLine,
 539                     )
 540                 } else {
 541                     (
 542                         Some(trimmed_pre_snippet.to_owned()),
 543                         ListItemCommentStyle::SameLine,
 544                     )
 545                 }
 546             } else {
 547                 (None, ListItemCommentStyle::None)
 548             };
 549
 550             // Post-comment
 551             let next_start = match self.inner.peek() {
 552                 Some(next_item) => (self.get_lo)(next_item),
 553                 None => self.next_span_start,
 554             };
 555             let post_snippet = self.snippet_provider
 556                 .span_to_snippet(mk_sp((self.get_hi)(&item), next_start))
 557                 .unwrap();
 558
 559             let comment_end = match self.inner.peek() {
 560                 Some(..) => {
 561                     let mut block_open_index = post_snippet.find("/*");
 562                     // check if it really is a block comment (and not `//*` or a nested comment)
 563                     if let Some(i) = block_open_index {
 564                         match post_snippet.find('/') {
 565                             Some(j) if j < i => block_open_index = None,
 566                             _ if i > 0 && &post_snippet[i - 1..i] == "/" => block_open_index = None,
 567                             _ => (),
 568                         }
 569                     }
 570                     let newline_index = post_snippet.find('\n');
 571                     if let Some(separator_index) = post_snippet.find_uncommented(self.separator) {
 572                         match (block_open_index, newline_index) {
 573                             // Separator before comment, with the next item on same line.
 574                             // Comment belongs to next item.
 575                             (Some(i), None) if i > separator_index => separator_index + 1,
 576                             // Block-style post-comment before the separator.
 577                             (Some(i), None) => cmp::max(
 578                                 find_comment_end(&post_snippet[i..]).unwrap() + i,
 579                                 separator_index + 1,
 580                             ),
 581                             // Block-style post-comment. Either before or after the separator.
 582                             (Some(i), Some(j)) if i < j => cmp::max(
 583                                 find_comment_end(&post_snippet[i..]).unwrap() + i,
 584                                 separator_index + 1,
 585                             ),
 586                             // Potential *single* line comment.
 587                             (_, Some(j)) if j > separator_index => j + 1,
 588                             _ => post_snippet.len(),
 589                         }
 590                     } else if let Some(newline_index) = newline_index {
 591                         // Match arms may not have trailing comma. In any case, for match arms,
 592                         // we will assume that the post comment belongs to the next arm if they
 593                         // do not end with trailing comma.
 594                         newline_index + 1
 595                     } else {
 596                         0
 597                     }
 598                 }
 599                 None => post_snippet
 600                     .find_uncommented(self.terminator)
 601                     .unwrap_or_else(|| post_snippet.len()),
 602             };
 603
 604             if !post_snippet.is_empty() && comment_end > 0 {
 605                 // Account for extra whitespace between items. This is fiddly
 606                 // because of the way we divide pre- and post- comments.
 607
 608                 // Everything from the separator to the next item.
 609                 let test_snippet = &post_snippet[comment_end - 1..];
 610                 let first_newline = test_snippet
 611                     .find('\n')
 612                     .unwrap_or_else(|| test_snippet.len());
 613                 // From the end of the first line of comments.
 614                 let test_snippet = &test_snippet[first_newline..];
 615                 let first = test_snippet
 616                     .find(|c: char| !c.is_whitespace())
 617                     .unwrap_or_else(|| test_snippet.len());
 618                 // From the end of the first line of comments to the next non-whitespace char.
 619                 let test_snippet = &test_snippet[..first];
 620
 621                 if count_newlines(test_snippet) > 1 {
 622                     // There were multiple line breaks which got trimmed to nothing.
 623                     new_lines = true;
 624                 }
 625             }
 626
 627             // Cleanup post-comment: strip separators and whitespace.
 628             self.prev_span_end = (self.get_hi)(&item) + BytePos(comment_end as u32);
 629             let post_snippet = post_snippet[..comment_end].trim();
 630
 631             let post_snippet_trimmed = if post_snippet.starts_with(|c| c == ',' || c == ':') {
 632                 post_snippet[1..].trim_matches(white_space)
 633             } else if post_snippet.starts_with(self.separator) {
 634                 post_snippet[self.separator.len()..].trim_matches(white_space)
 635             } else if post_snippet.ends_with(',') {
 636                 post_snippet[..(post_snippet.len() - 1)].trim_matches(white_space)
 637             } else {
 638                 post_snippet
 639             };
 640
 641             let post_comment = if !post_snippet_trimmed.is_empty() {
 642                 Some(post_snippet_trimmed.to_owned())
 643             } else {
 644                 None
 645             };
 646
 647             ListItem {
 648                 pre_comment,
 649                 pre_comment_style,
 650                 item: if self.inner.peek().is_none() && self.leave_last {
 651                     None
 652                 } else {
 653                     (self.get_item_string)(&item)
 654                 },
 655                 post_comment,
 656                 new_lines,
 657             }
 658         })
 659     }
 660 }
 661
 662 #[cfg_attr(feature = "cargo-clippy", allow(too_many_arguments))]
 663 // Creates an iterator over a list's items with associated comments.
 664 pub fn itemize_list<'a, T, I, F1, F2, F3>(
 665     snippet_provider: &'a SnippetProvider,
 666     inner: I,
 667     terminator: &'a str,
 668     separator: &'a str,
 669     get_lo: F1,
 670     get_hi: F2,
 671     get_item_string: F3,
 672     prev_span_end: BytePos,
 673     next_span_start: BytePos,
 674     leave_last: bool,
 675 ) -> ListItems<'a, I, F1, F2, F3>
 676 where
 677     I: Iterator<Item = T>,
 678     F1: Fn(&T) -> BytePos,
 679     F2: Fn(&T) -> BytePos,
 680     F3: Fn(&T) -> Option<String>,
 681 {
 682     ListItems {
 683         snippet_provider,
 684         inner: inner.peekable(),
 685         get_lo,
 686         get_hi,
 687         get_item_string,
 688         prev_span_end,
 689         next_span_start,
 690         terminator,
 691         separator,
 692         leave_last,
 693     }
 694 }
 695
 696 /// Returns the count and total width of the list items.
 697 fn calculate_width<I, T>(items: I) -> (usize, usize)
 698 where
 699     I: IntoIterator<Item = T>,
 700     T: AsRef<ListItem>,
 701 {
 702     items
 703         .into_iter()
 704         .map(|item| total_item_width(item.as_ref()))
 705         .fold((0, 0), |acc, l| (acc.0 + 1, acc.1 + l))
 706 }
 707
 708 pub fn total_item_width(item: &ListItem) -> usize {
 709     comment_len(item.pre_comment.as_ref().map(|x| &(*x)[..]))
 710         + comment_len(item.post_comment.as_ref().map(|x| &(*x)[..]))
 711         + item.item.as_ref().map_or(0, |str| str.len())
 712 }
 713
 714 fn comment_len(comment: Option<&str>) -> usize {
 715     match comment {
 716         Some(s) => {
 717             let text_len = s.trim().len();
 718             if text_len > 0 {
 719                 // We'll put " /*" before and " */" after inline comments.
 720                 text_len + 6
 721             } else {
 722                 text_len
 723             }
 724         }
 725         None => 0,
 726     }
 727 }
 728
 729 // Compute horizontal and vertical shapes for a struct-lit-like thing.
 730 pub fn struct_lit_shape(
 731     shape: Shape,
 732     context: &RewriteContext,
 733     prefix_width: usize,
 734     suffix_width: usize,
 735 ) -> Option<(Option<Shape>, Shape)> {
 736     let v_shape = match context.config.indent_style() {
 737         IndentStyle::Visual => shape
 738             .visual_indent(0)
 739             .shrink_left(prefix_width)?
 740             .sub_width(suffix_width)?,
 741         IndentStyle::Block => {
 742             let shape = shape.block_indent(context.config.tab_spaces());
 743             Shape {
 744                 width: context.budget(shape.indent.width()),
 745                 ..shape
 746             }
 747         }
 748     };
 749     let shape_width = shape.width.checked_sub(prefix_width + suffix_width);
 750     if let Some(w) = shape_width {
 751         let shape_width = cmp::min(w, context.config.width_heuristics().struct_lit_width);
 752         Some((Some(Shape::legacy(shape_width, shape.indent)), v_shape))
 753     } else {
 754         Some((None, v_shape))
 755     }
 756 }
 757
 758 // Compute the tactic for the internals of a struct-lit-like thing.
 759 pub fn struct_lit_tactic(
 760     h_shape: Option<Shape>,
 761     context: &RewriteContext,
 762     items: &[ListItem],
 763 ) -> DefinitiveListTactic {
 764     if let Some(h_shape) = h_shape {
 765         let prelim_tactic = match (context.config.indent_style(), items.len()) {
 766             (IndentStyle::Visual, 1) => ListTactic::HorizontalVertical,
 767             _ if context.config.struct_lit_single_line() => ListTactic::HorizontalVertical,
 768             _ => ListTactic::Vertical,
 769         };
 770         definitive_tactic(items, prelim_tactic, Separator::Comma, h_shape.width)
 771     } else {
 772         DefinitiveListTactic::Vertical
 773     }
 774 }
 775
 776 // Given a tactic and possible shapes for horizontal and vertical layout,
 777 // come up with the actual shape to use.
 778 pub fn shape_for_tactic(
 779     tactic: DefinitiveListTactic,
 780     h_shape: Option<Shape>,
 781     v_shape: Shape,
 782 ) -> Shape {
 783     match tactic {
 784         DefinitiveListTactic::Horizontal => h_shape.unwrap(),
 785         _ => v_shape,
 786     }
 787 }
 788
 789 // Create a ListFormatting object for formatting the internals of a
 790 // struct-lit-like thing, that is a series of fields.
 791 pub fn struct_lit_formatting<'a>(
 792     shape: Shape,
 793     tactic: DefinitiveListTactic,
 794     context: &'a RewriteContext,
 795     force_no_trailing_comma: bool,
 796 ) -> ListFormatting<'a> {
 797     let ends_with_newline = context.config.indent_style() != IndentStyle::Visual
 798         && tactic == DefinitiveListTactic::Vertical;
 799     ListFormatting {
 800         tactic,
 801         separator: ",",
 802         trailing_separator: if force_no_trailing_comma {
 803             SeparatorTactic::Never
 804         } else {
 805             context.config.trailing_comma()
 806         },
 807         separator_place: SeparatorPlace::Back,
 808         shape,
 809         ends_with_newline,
 810         preserve_newline: true,
 811         config: context.config,
 812     }
 813 }