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
 100                 .post_comment
 101                 .as_ref()
 102                 .map_or(false, |s| s.contains('\n'))
 103     }
 104
 105     pub fn is_multiline(&self) -> bool {
 106         self.inner_as_ref().contains('\n')
 107             || self
 108                 .pre_comment
 109                 .as_ref()
 110                 .map_or(false, |s| s.contains('\n'))
 111             || self
 112                 .post_comment
 113                 .as_ref()
 114                 .map_or(false, |s| s.contains('\n'))
 115     }
 116
 117     pub fn has_single_line_comment(&self) -> bool {
 118         self.pre_comment
 119             .as_ref()
 120             .map_or(false, |comment| comment.trim_left().starts_with("//"))
 121             || self
 122                 .post_comment
 123                 .as_ref()
 124                 .map_or(false, |comment| comment.trim_left().starts_with("//"))
 125     }
 126
 127     pub fn has_comment(&self) -> bool {
 128         self.pre_comment.is_some() || self.post_comment.is_some()
 129     }
 130
 131     pub fn from_str<S: Into<String>>(s: S) -> ListItem {
 132         ListItem {
 133             pre_comment: None,
 134             pre_comment_style: ListItemCommentStyle::None,
 135             item: Some(s.into()),
 136             post_comment: None,
 137             new_lines: false,
 138         }
 139     }
 140
 141     // true if the item causes something to be written.
 142     fn is_substantial(&self) -> bool {
 143         fn empty(s: &Option<String>) -> bool {
 144             match *s {
 145                 Some(ref s) if !s.is_empty() => false,
 146                 _ => true,
 147             }
 148         }
 149
 150         !(empty(&self.pre_comment) && empty(&self.item) && empty(&self.post_comment))
 151     }
 152 }
 153
 154 /// The type of separator for lists.
 155 #[derive(Copy, Clone, Eq, PartialEq, Debug)]
 156 pub enum Separator {
 157     Comma,
 158     VerticalBar,
 159 }
 160
 161 impl Separator {
 162     pub fn len(&self) -> usize {
 163         match *self {
 164             // 2 = `, `
 165             Separator::Comma => 2,
 166             // 3 = ` | `
 167             Separator::VerticalBar => 3,
 168         }
 169     }
 170 }
 171
 172 pub fn definitive_tactic<I, T>(
 173     items: I,
 174     tactic: ListTactic,
 175     sep: Separator,
 176     width: usize,
 177 ) -> DefinitiveListTactic
 178 where
 179     I: IntoIterator<Item = T> + Clone,
 180     T: AsRef<ListItem>,
 181 {
 182     let pre_line_comments = items
 183         .clone()
 184         .into_iter()
 185         .any(|item| item.as_ref().has_single_line_comment());
 186
 187     let limit = match tactic {
 188         _ if pre_line_comments => return DefinitiveListTactic::Vertical,
 189         ListTactic::Horizontal => return DefinitiveListTactic::Horizontal,
 190         ListTactic::Vertical => return DefinitiveListTactic::Vertical,
 191         ListTactic::LimitedHorizontalVertical(limit) => ::std::cmp::min(width, limit),
 192         ListTactic::Mixed | ListTactic::HorizontalVertical => width,
 193     };
 194
 195     let (sep_count, total_width) = calculate_width(items.clone());
 196     let total_sep_len = sep.len() * sep_count.checked_sub(1).unwrap_or(0);
 197     let real_total = total_width + total_sep_len;
 198
 199     if real_total <= limit
 200         && !pre_line_comments
 201         && !items.into_iter().any(|item| item.as_ref().is_multiline())
 202     {
 203         DefinitiveListTactic::Horizontal
 204     } else {
 205         match tactic {
 206             ListTactic::Mixed => DefinitiveListTactic::Mixed,
 207             _ => DefinitiveListTactic::Vertical,
 208         }
 209     }
 210 }
 211
 212 // Format a list of commented items into a string.
 213 // TODO: add unit tests
 214 pub fn write_list<I, T>(items: I, formatting: &ListFormatting) -> Option<String>
 215 where
 216     I: IntoIterator<Item = T> + Clone,
 217     T: AsRef<ListItem>,
 218 {
 219     let tactic = formatting.tactic;
 220     let sep_len = formatting.separator.len();
 221
 222     // Now that we know how we will layout, we can decide for sure if there
 223     // will be a trailing separator.
 224     let mut trailing_separator = formatting.needs_trailing_separator();
 225     let mut result = String::with_capacity(128);
 226     let cloned_items = items.clone();
 227     let mut iter = items.into_iter().enumerate().peekable();
 228     let mut item_max_width: Option<usize> = None;
 229     let sep_place =
 230         SeparatorPlace::from_tactic(formatting.separator_place, tactic, formatting.separator);
 231
 232     let mut line_len = 0;
 233     let indent_str = &formatting.shape.indent.to_string(formatting.config);
 234     while let Some((i, item)) = iter.next() {
 235         let item = item.as_ref();
 236         let inner_item = item.item.as_ref()?;
 237         let first = i == 0;
 238         let last = iter.peek().is_none();
 239         let mut separate = match sep_place {
 240             SeparatorPlace::Front => !first,
 241             SeparatorPlace::Back => !last || trailing_separator,
 242         };
 243         let item_sep_len = if separate { sep_len } else { 0 };
 244
 245         // Item string may be multi-line. Its length (used for block comment alignment)
 246         // should be only the length of the last line.
 247         let item_last_line = if item.is_multiline() {
 248             inner_item.lines().last().unwrap_or("")
 249         } else {
 250             inner_item.as_ref()
 251         };
 252         let mut item_last_line_width = item_last_line.len() + item_sep_len;
 253         if item_last_line.starts_with(&**indent_str) {
 254             item_last_line_width -= indent_str.len();
 255         }
 256
 257         if !item.is_substantial() {
 258             continue;
 259         }
 260
 261         match tactic {
 262             DefinitiveListTactic::Horizontal if !first => {
 263                 result.push(' ');
 264             }
 265             DefinitiveListTactic::SpecialMacro(num_args_before) => {
 266                 if i == 0 {
 267                     // Nothing
 268                 } else if i < num_args_before {
 269                     result.push(' ');
 270                 } else if i <= num_args_before + 1 {
 271                     result.push('\n');
 272                     result.push_str(indent_str);
 273                 } else {
 274                     result.push(' ');
 275                 }
 276             }
 277             DefinitiveListTactic::Vertical
 278                 if !first && !inner_item.is_empty() && !result.is_empty() =>
 279             {
 280                 result.push('\n');
 281                 result.push_str(indent_str);
 282             }
 283             DefinitiveListTactic::Mixed => {
 284                 let total_width = total_item_width(item) + item_sep_len;
 285
 286                 // 1 is space between separator and item.
 287                 if line_len > 0 && line_len + 1 + total_width > formatting.shape.width {
 288                     result.push('\n');
 289                     result.push_str(indent_str);
 290                     line_len = 0;
 291                     if formatting.ends_with_newline {
 292                         trailing_separator = true;
 293                     }
 294                 }
 295
 296                 if last && formatting.ends_with_newline {
 297                     separate = formatting.trailing_separator != SeparatorTactic::Never;
 298                 }
 299
 300                 if line_len > 0 {
 301                     result.push(' ');
 302                     line_len += 1;
 303                 }
 304
 305                 line_len += total_width;
 306             }
 307             _ => {}
 308         }
 309
 310         // Pre-comments
 311         if let Some(ref comment) = item.pre_comment {
 312             // Block style in non-vertical mode.
 313             let block_mode = tactic != DefinitiveListTactic::Vertical;
 314             // Width restriction is only relevant in vertical mode.
 315             let comment =
 316                 rewrite_comment(comment, block_mode, formatting.shape, formatting.config)?;
 317             result.push_str(&comment);
 318
 319             if !inner_item.is_empty() {
 320                 if tactic == DefinitiveListTactic::Vertical {
 321                     // We cannot keep pre-comments on the same line if the comment if normalized.
 322                     let keep_comment = if formatting.config.normalize_comments()
 323                         || item.pre_comment_style == ListItemCommentStyle::DifferentLine
 324                     {
 325                         false
 326                     } else {
 327                         // We will try to keep the comment on the same line with the item here.
 328                         // 1 = ` `
 329                         let total_width = total_item_width(item) + item_sep_len + 1;
 330                         total_width <= formatting.shape.width
 331                     };
 332                     if keep_comment {
 333                         result.push(' ');
 334                     } else {
 335                         result.push('\n');
 336                         result.push_str(indent_str);
 337                     }
 338                 } else {
 339                     result.push(' ');
 340                 }
 341             }
 342             item_max_width = None;
 343         }
 344
 345         if separate && sep_place.is_front() && !first {
 346             result.push_str(formatting.separator.trim());
 347             result.push(' ');
 348         }
 349         result.push_str(inner_item);
 350
 351         // Post-comments
 352         if tactic != DefinitiveListTactic::Vertical && item.post_comment.is_some() {
 353             let comment = item.post_comment.as_ref().unwrap();
 354             let formatted_comment = rewrite_comment(
 355                 comment,
 356                 true,
 357                 Shape::legacy(formatting.shape.width, Indent::empty()),
 358                 formatting.config,
 359             )?;
 360
 361             result.push(' ');
 362             result.push_str(&formatted_comment);
 363         }
 364
 365         if separate && sep_place.is_back() {
 366             result.push_str(formatting.separator);
 367         }
 368
 369         if tactic == DefinitiveListTactic::Vertical && item.post_comment.is_some() {
 370             let comment = item.post_comment.as_ref().unwrap();
 371             let overhead = last_line_width(&result) + first_line_width(comment.trim());
 372
 373             let rewrite_post_comment = |item_max_width: &mut Option<usize>| {
 374                 if item_max_width.is_none() && !last && !inner_item.contains('\n') {
 375                     *item_max_width = Some(max_width_of_item_with_post_comment(
 376                         &cloned_items,
 377                         i,
 378                         overhead,
 379                         formatting.config.max_width(),
 380                     ));
 381                 }
 382                 let overhead = if starts_with_newline(comment) {
 383                     0
 384                 } else if let Some(max_width) = *item_max_width {
 385                     max_width + 2
 386                 } else {
 387                     // 1 = space between item and comment.
 388                     item_last_line_width + 1
 389                 };
 390                 let width = formatting.shape.width.checked_sub(overhead).unwrap_or(1);
 391                 let offset = formatting.shape.indent + overhead;
 392                 let comment_shape = Shape::legacy(width, offset);
 393
 394                 // Use block-style only for the last item or multiline comments.
 395                 let block_style = !formatting.ends_with_newline && last
 396                     || comment.trim().contains('\n')
 397                     || comment.trim().len() > width;
 398
 399                 rewrite_comment(
 400                     comment.trim_left(),
 401                     block_style,
 402                     comment_shape,
 403                     formatting.config,
 404                 )
 405             };
 406
 407             let mut formatted_comment = rewrite_post_comment(&mut item_max_width)?;
 408
 409             if !starts_with_newline(comment) {
 410                 let mut comment_alignment =
 411                     post_comment_alignment(item_max_width, inner_item.len());
 412                 if first_line_width(&formatted_comment)
 413                     + last_line_width(&result)
 414                     + comment_alignment
 415                     + 1 > formatting.config.max_width()
 416                 {
 417                     item_max_width = None;
 418                     formatted_comment = rewrite_post_comment(&mut item_max_width)?;
 419                     comment_alignment = post_comment_alignment(item_max_width, inner_item.len());
 420                 }
 421                 for _ in 0..(comment_alignment + 1) {
 422                     result.push(' ');
 423                 }
 424                 // An additional space for the missing trailing separator.
 425                 if last && item_max_width.is_some() && !separate && !formatting.separator.is_empty()
 426                 {
 427                     result.push(' ');
 428                 }
 429             } else {
 430                 result.push('\n');
 431                 result.push_str(indent_str);
 432             }
 433             if formatted_comment.contains('\n') {
 434                 item_max_width = None;
 435             }
 436             result.push_str(&formatted_comment);
 437         } else {
 438             item_max_width = None;
 439         }
 440
 441         if formatting.preserve_newline
 442             && !last
 443             && tactic == DefinitiveListTactic::Vertical
 444             && item.new_lines
 445         {
 446             item_max_width = None;
 447             result.push('\n');
 448         }
 449     }
 450
 451     Some(result)
 452 }
 453
 454 fn max_width_of_item_with_post_comment<I, T>(
 455     items: &I,
 456     i: usize,
 457     overhead: usize,
 458     max_budget: usize,
 459 ) -> usize
 460 where
 461     I: IntoIterator<Item = T> + Clone,
 462     T: AsRef<ListItem>,
 463 {
 464     let mut max_width = 0;
 465     let mut first = true;
 466     for item in items.clone().into_iter().skip(i) {
 467         let item = item.as_ref();
 468         let inner_item_width = item.inner_as_ref().len();
 469         if !first
 470             && (item.is_different_group()
 471                 || item.post_comment.is_none()
 472                 || inner_item_width + overhead > max_budget)
 473         {
 474             return max_width;
 475         }
 476         if max_width < inner_item_width {
 477             max_width = inner_item_width;
 478         }
 479         if item.new_lines {
 480             return max_width;
 481         }
 482         first = false;
 483     }
 484     max_width
 485 }
 486
 487 fn post_comment_alignment(item_max_width: Option<usize>, inner_item_len: usize) -> usize {
 488     item_max_width
 489         .and_then(|max_line_width| max_line_width.checked_sub(inner_item_len))
 490         .unwrap_or(0)
 491 }
 492
 493 pub struct ListItems<'a, I, F1, F2, F3>
 494 where
 495     I: Iterator,
 496 {
 497     snippet_provider: &'a SnippetProvider<'a>,
 498     inner: Peekable<I>,
 499     get_lo: F1,
 500     get_hi: F2,
 501     get_item_string: F3,
 502     prev_span_end: BytePos,
 503     next_span_start: BytePos,
 504     terminator: &'a str,
 505     separator: &'a str,
 506     leave_last: bool,
 507 }
 508
 509 impl<'a, T, I, F1, F2, F3> Iterator for ListItems<'a, I, F1, F2, F3>
 510 where
 511     I: Iterator<Item = T>,
 512     F1: Fn(&T) -> BytePos,
 513     F2: Fn(&T) -> BytePos,
 514     F3: Fn(&T) -> Option<String>,
 515 {
 516     type Item = ListItem;
 517
 518     fn next(&mut self) -> Option<Self::Item> {
 519         let white_space: &[_] = &[' ', '\t'];
 520
 521         self.inner.next().map(|item| {
 522             let mut new_lines = false;
 523             // Pre-comment
 524             let pre_snippet = self
 525                 .snippet_provider
 526                 .span_to_snippet(mk_sp(self.prev_span_end, (self.get_lo)(&item)))
 527                 .unwrap();
 528             let trimmed_pre_snippet = pre_snippet.trim();
 529             let has_single_line_comment = trimmed_pre_snippet.starts_with("//");
 530             let has_block_comment = trimmed_pre_snippet.starts_with("/*");
 531             let (pre_comment, pre_comment_style) = if has_single_line_comment {
 532                 (
 533                     Some(trimmed_pre_snippet.to_owned()),
 534                     ListItemCommentStyle::DifferentLine,
 535                 )
 536             } else if has_block_comment {
 537                 let comment_end = pre_snippet.chars().rev().position(|c| c == '/').unwrap();
 538                 if pre_snippet
 539                     .chars()
 540                     .rev()
 541                     .take(comment_end + 1)
 542                     .any(|c| c == '\n')
 543                 {
 544                     (
 545                         Some(trimmed_pre_snippet.to_owned()),
 546                         ListItemCommentStyle::DifferentLine,
 547                     )
 548                 } else {
 549                     (
 550                         Some(trimmed_pre_snippet.to_owned()),
 551                         ListItemCommentStyle::SameLine,
 552                     )
 553                 }
 554             } else {
 555                 (None, ListItemCommentStyle::None)
 556             };
 557
 558             // Post-comment
 559             let next_start = match self.inner.peek() {
 560                 Some(next_item) => (self.get_lo)(next_item),
 561                 None => self.next_span_start,
 562             };
 563             let post_snippet = self
 564                 .snippet_provider
 565                 .span_to_snippet(mk_sp((self.get_hi)(&item), next_start))
 566                 .unwrap();
 567
 568             let comment_end = match self.inner.peek() {
 569                 Some(..) => {
 570                     let mut block_open_index = post_snippet.find("/*");
 571                     // check if it really is a block comment (and not `//*` or a nested comment)
 572                     if let Some(i) = block_open_index {
 573                         match post_snippet.find('/') {
 574                             Some(j) if j < i => block_open_index = None,
 575                             _ if i > 0 && &post_snippet[i - 1..i] == "/" => block_open_index = None,
 576                             _ => (),
 577                         }
 578                     }
 579                     let newline_index = post_snippet.find('\n');
 580                     if let Some(separator_index) = post_snippet.find_uncommented(self.separator) {
 581                         match (block_open_index, newline_index) {
 582                             // Separator before comment, with the next item on same line.
 583                             // Comment belongs to next item.
 584                             (Some(i), None) if i > separator_index => separator_index + 1,
 585                             // Block-style post-comment before the separator.
 586                             (Some(i), None) => cmp::max(
 587                                 find_comment_end(&post_snippet[i..]).unwrap() + i,
 588                                 separator_index + 1,
 589                             ),
 590                             // Block-style post-comment. Either before or after the separator.
 591                             (Some(i), Some(j)) if i < j => cmp::max(
 592                                 find_comment_end(&post_snippet[i..]).unwrap() + i,
 593                                 separator_index + 1,
 594                             ),
 595                             // Potential *single* line comment.
 596                             (_, Some(j)) if j > separator_index => j + 1,
 597                             _ => post_snippet.len(),
 598                         }
 599                     } else if let Some(newline_index) = newline_index {
 600                         // Match arms may not have trailing comma. In any case, for match arms,
 601                         // we will assume that the post comment belongs to the next arm if they
 602                         // do not end with trailing comma.
 603                         newline_index + 1
 604                     } else {
 605                         0
 606                     }
 607                 }
 608                 None => post_snippet
 609                     .find_uncommented(self.terminator)
 610                     .unwrap_or_else(|| post_snippet.len()),
 611             };
 612
 613             if !post_snippet.is_empty() && comment_end > 0 {
 614                 // Account for extra whitespace between items. This is fiddly
 615                 // because of the way we divide pre- and post- comments.
 616
 617                 // Everything from the separator to the next item.
 618                 let test_snippet = &post_snippet[comment_end - 1..];
 619                 let first_newline = test_snippet
 620                     .find('\n')
 621                     .unwrap_or_else(|| test_snippet.len());
 622                 // From the end of the first line of comments.
 623                 let test_snippet = &test_snippet[first_newline..];
 624                 let first = test_snippet
 625                     .find(|c: char| !c.is_whitespace())
 626                     .unwrap_or_else(|| test_snippet.len());
 627                 // From the end of the first line of comments to the next non-whitespace char.
 628                 let test_snippet = &test_snippet[..first];
 629
 630                 if count_newlines(test_snippet) > 1 {
 631                     // There were multiple line breaks which got trimmed to nothing.
 632                     new_lines = true;
 633                 }
 634             }
 635
 636             // Cleanup post-comment: strip separators and whitespace.
 637             self.prev_span_end = (self.get_hi)(&item) + BytePos(comment_end as u32);
 638             let post_snippet = post_snippet[..comment_end].trim();
 639
 640             let post_snippet_trimmed = if post_snippet.starts_with(|c| c == ',' || c == ':') {
 641                 post_snippet[1..].trim_matches(white_space)
 642             } else if post_snippet.starts_with(self.separator) {
 643                 post_snippet[self.separator.len()..].trim_matches(white_space)
 644             } else if post_snippet.ends_with(',') {
 645                 post_snippet[..(post_snippet.len() - 1)].trim_matches(white_space)
 646             } else {
 647                 post_snippet
 648             };
 649
 650             let post_comment = if !post_snippet_trimmed.is_empty() {
 651                 Some(post_snippet_trimmed.to_owned())
 652             } else {
 653                 None
 654             };
 655
 656             ListItem {
 657                 pre_comment,
 658                 pre_comment_style,
 659                 item: if self.inner.peek().is_none() && self.leave_last {
 660                     None
 661                 } else {
 662                     (self.get_item_string)(&item)
 663                 },
 664                 post_comment,
 665                 new_lines,
 666             }
 667         })
 668     }
 669 }
 670
 671 #[cfg_attr(feature = "cargo-clippy", allow(too_many_arguments))]
 672 // Creates an iterator over a list's items with associated comments.
 673 pub fn itemize_list<'a, T, I, F1, F2, F3>(
 674     snippet_provider: &'a SnippetProvider,
 675     inner: I,
 676     terminator: &'a str,
 677     separator: &'a str,
 678     get_lo: F1,
 679     get_hi: F2,
 680     get_item_string: F3,
 681     prev_span_end: BytePos,
 682     next_span_start: BytePos,
 683     leave_last: bool,
 684 ) -> ListItems<'a, I, F1, F2, F3>
 685 where
 686     I: Iterator<Item = T>,
 687     F1: Fn(&T) -> BytePos,
 688     F2: Fn(&T) -> BytePos,
 689     F3: Fn(&T) -> Option<String>,
 690 {
 691     ListItems {
 692         snippet_provider,
 693         inner: inner.peekable(),
 694         get_lo,
 695         get_hi,
 696         get_item_string,
 697         prev_span_end,
 698         next_span_start,
 699         terminator,
 700         separator,
 701         leave_last,
 702     }
 703 }
 704
 705 /// Returns the count and total width of the list items.
 706 fn calculate_width<I, T>(items: I) -> (usize, usize)
 707 where
 708     I: IntoIterator<Item = T>,
 709     T: AsRef<ListItem>,
 710 {
 711     items
 712         .into_iter()
 713         .map(|item| total_item_width(item.as_ref()))
 714         .fold((0, 0), |acc, l| (acc.0 + 1, acc.1 + l))
 715 }
 716
 717 pub fn total_item_width(item: &ListItem) -> usize {
 718     comment_len(item.pre_comment.as_ref().map(|x| &(*x)[..]))
 719         + comment_len(item.post_comment.as_ref().map(|x| &(*x)[..]))
 720         + item.item.as_ref().map_or(0, |str| str.len())
 721 }
 722
 723 fn comment_len(comment: Option<&str>) -> usize {
 724     match comment {
 725         Some(s) => {
 726             let text_len = s.trim().len();
 727             if text_len > 0 {
 728                 // We'll put " /*" before and " */" after inline comments.
 729                 text_len + 6
 730             } else {
 731                 text_len
 732             }
 733         }
 734         None => 0,
 735     }
 736 }
 737
 738 // Compute horizontal and vertical shapes for a struct-lit-like thing.
 739 pub fn struct_lit_shape(
 740     shape: Shape,
 741     context: &RewriteContext,
 742     prefix_width: usize,
 743     suffix_width: usize,
 744 ) -> Option<(Option<Shape>, Shape)> {
 745     let v_shape = match context.config.indent_style() {
 746         IndentStyle::Visual => shape
 747             .visual_indent(0)
 748             .shrink_left(prefix_width)?
 749             .sub_width(suffix_width)?,
 750         IndentStyle::Block => {
 751             let shape = shape.block_indent(context.config.tab_spaces());
 752             Shape {
 753                 width: context.budget(shape.indent.width()),
 754                 ..shape
 755             }
 756         }
 757     };
 758     let shape_width = shape.width.checked_sub(prefix_width + suffix_width);
 759     if let Some(w) = shape_width {
 760         let shape_width = cmp::min(w, context.config.width_heuristics().struct_lit_width);
 761         Some((Some(Shape::legacy(shape_width, shape.indent)), v_shape))
 762     } else {
 763         Some((None, v_shape))
 764     }
 765 }
 766
 767 // Compute the tactic for the internals of a struct-lit-like thing.
 768 pub fn struct_lit_tactic(
 769     h_shape: Option<Shape>,
 770     context: &RewriteContext,
 771     items: &[ListItem],
 772 ) -> DefinitiveListTactic {
 773     if let Some(h_shape) = h_shape {
 774         let prelim_tactic = match (context.config.indent_style(), items.len()) {
 775             (IndentStyle::Visual, 1) => ListTactic::HorizontalVertical,
 776             _ if context.config.struct_lit_single_line() => ListTactic::HorizontalVertical,
 777             _ => ListTactic::Vertical,
 778         };
 779         definitive_tactic(items, prelim_tactic, Separator::Comma, h_shape.width)
 780     } else {
 781         DefinitiveListTactic::Vertical
 782     }
 783 }
 784
 785 // Given a tactic and possible shapes for horizontal and vertical layout,
 786 // come up with the actual shape to use.
 787 pub fn shape_for_tactic(
 788     tactic: DefinitiveListTactic,
 789     h_shape: Option<Shape>,
 790     v_shape: Shape,
 791 ) -> Shape {
 792     match tactic {
 793         DefinitiveListTactic::Horizontal => h_shape.unwrap(),
 794         _ => v_shape,
 795     }
 796 }
 797
 798 // Create a ListFormatting object for formatting the internals of a
 799 // struct-lit-like thing, that is a series of fields.
 800 pub fn struct_lit_formatting<'a>(
 801     shape: Shape,
 802     tactic: DefinitiveListTactic,
 803     context: &'a RewriteContext,
 804     force_no_trailing_comma: bool,
 805 ) -> ListFormatting<'a> {
 806     let ends_with_newline = context.config.indent_style() != IndentStyle::Visual
 807         && tactic == DefinitiveListTactic::Vertical;
 808     ListFormatting {
 809         tactic,
 810         separator: ",",
 811         trailing_separator: if force_no_trailing_comma {
 812             SeparatorTactic::Never
 813         } else {
 814             context.config.trailing_comma()
 815         },
 816         separator_place: SeparatorPlace::Back,
 817         shape,
 818         ends_with_newline,
 819         preserve_newline: true,
 820         config: context.config,
 821     }
 822 }