src/lists.rs

   1 //! Format list-like expressions and items.
   2
   3 use std::cmp;
   4 use std::iter::Peekable;
   5
   6 use rustc_span::BytePos;
   7
   8 use crate::comment::{find_comment_end, rewrite_comment, FindUncommented};
   9 use crate::config::lists::*;
  10 use crate::config::{Config, IndentStyle};
  11 use crate::rewrite::RewriteContext;
  12 use crate::shape::{Indent, Shape};
  13 use crate::utils::{
  14     count_newlines, first_line_width, last_line_width, mk_sp, starts_with_newline,
  15     unicode_str_width,
  16 };
  17 use crate::visitor::SnippetProvider;
  18
  19 pub(crate) struct ListFormatting<'a> {
  20     tactic: DefinitiveListTactic,
  21     separator: &'a str,
  22     trailing_separator: SeparatorTactic,
  23     separator_place: SeparatorPlace,
  24     shape: Shape,
  25     // Non-expressions, e.g., items, will have a new line at the end of the list.
  26     // Important for comment styles.
  27     ends_with_newline: bool,
  28     // Remove newlines between list elements for expressions.
  29     preserve_newline: bool,
  30     // Nested import lists get some special handling for the "Mixed" list type
  31     nested: bool,
  32     // Whether comments should be visually aligned.
  33     align_comments: bool,
  34     config: &'a Config,
  35 }
  36
  37 impl<'a> ListFormatting<'a> {
  38     pub(crate) fn new(shape: Shape, config: &'a Config) -> Self {
  39         ListFormatting {
  40             tactic: DefinitiveListTactic::Vertical,
  41             separator: ",",
  42             trailing_separator: SeparatorTactic::Never,
  43             separator_place: SeparatorPlace::Back,
  44             shape,
  45             ends_with_newline: true,
  46             preserve_newline: false,
  47             nested: false,
  48             align_comments: true,
  49             config,
  50         }
  51     }
  52
  53     pub(crate) fn tactic(mut self, tactic: DefinitiveListTactic) -> Self {
  54         self.tactic = tactic;
  55         self
  56     }
  57
  58     pub(crate) fn separator(mut self, separator: &'a str) -> Self {
  59         self.separator = separator;
  60         self
  61     }
  62
  63     pub(crate) fn trailing_separator(mut self, trailing_separator: SeparatorTactic) -> Self {
  64         self.trailing_separator = trailing_separator;
  65         self
  66     }
  67
  68     pub(crate) fn separator_place(mut self, separator_place: SeparatorPlace) -> Self {
  69         self.separator_place = separator_place;
  70         self
  71     }
  72
  73     pub(crate) fn ends_with_newline(mut self, ends_with_newline: bool) -> Self {
  74         self.ends_with_newline = ends_with_newline;
  75         self
  76     }
  77
  78     pub(crate) fn preserve_newline(mut self, preserve_newline: bool) -> Self {
  79         self.preserve_newline = preserve_newline;
  80         self
  81     }
  82
  83     pub(crate) fn nested(mut self, nested: bool) -> Self {
  84         self.nested = nested;
  85         self
  86     }
  87
  88     pub(crate) fn align_comments(mut self, align_comments: bool) -> Self {
  89         self.align_comments = align_comments;
  90         self
  91     }
  92
  93     pub(crate) fn needs_trailing_separator(&self) -> bool {
  94         match self.trailing_separator {
  95             // We always put separator in front.
  96             SeparatorTactic::Always => true,
  97             SeparatorTactic::Vertical => self.tactic == DefinitiveListTactic::Vertical,
  98             SeparatorTactic::Never => {
  99                 self.tactic == DefinitiveListTactic::Vertical && self.separator_place.is_front()
 100             }
 101         }
 102     }
 103 }
 104
 105 impl AsRef<ListItem> for ListItem {
 106     fn as_ref(&self) -> &ListItem {
 107         self
 108     }
 109 }
 110
 111 #[derive(PartialEq, Eq, Debug, Copy, Clone)]
 112 pub(crate) enum ListItemCommentStyle {
 113     // Try to keep the comment on the same line with the item.
 114     SameLine,
 115     // Put the comment on the previous or the next line of the item.
 116     DifferentLine,
 117     // No comment available.
 118     None,
 119 }
 120
 121 #[derive(Debug, Clone)]
 122 pub(crate) struct ListItem {
 123     // None for comments mean that they are not present.
 124     pub(crate) pre_comment: Option<String>,
 125     pub(crate) pre_comment_style: ListItemCommentStyle,
 126     // Item should include attributes and doc comments. None indicates a failed
 127     // rewrite.
 128     pub(crate) item: Option<String>,
 129     pub(crate) post_comment: Option<String>,
 130     // Whether there is extra whitespace before this item.
 131     pub(crate) new_lines: bool,
 132 }
 133
 134 impl ListItem {
 135     pub(crate) fn empty() -> ListItem {
 136         ListItem {
 137             pre_comment: None,
 138             pre_comment_style: ListItemCommentStyle::None,
 139             item: None,
 140             post_comment: None,
 141             new_lines: false,
 142         }
 143     }
 144
 145     pub(crate) fn inner_as_ref(&self) -> &str {
 146         self.item.as_ref().map_or("", |s| s)
 147     }
 148
 149     pub(crate) fn is_different_group(&self) -> bool {
 150         self.inner_as_ref().contains('\n')
 151             || self.pre_comment.is_some()
 152             || self
 153                 .post_comment
 154                 .as_ref()
 155                 .map_or(false, |s| s.contains('\n'))
 156     }
 157
 158     pub(crate) fn is_multiline(&self) -> bool {
 159         self.inner_as_ref().contains('\n')
 160             || self
 161                 .pre_comment
 162                 .as_ref()
 163                 .map_or(false, |s| s.contains('\n'))
 164             || self
 165                 .post_comment
 166                 .as_ref()
 167                 .map_or(false, |s| s.contains('\n'))
 168     }
 169
 170     pub(crate) fn has_single_line_comment(&self) -> bool {
 171         self.pre_comment
 172             .as_ref()
 173             .map_or(false, |comment| comment.trim_start().starts_with("//"))
 174             || self
 175                 .post_comment
 176                 .as_ref()
 177                 .map_or(false, |comment| comment.trim_start().starts_with("//"))
 178     }
 179
 180     pub(crate) fn has_comment(&self) -> bool {
 181         self.pre_comment.is_some() || self.post_comment.is_some()
 182     }
 183
 184     pub(crate) fn from_str<S: Into<String>>(s: S) -> ListItem {
 185         ListItem {
 186             pre_comment: None,
 187             pre_comment_style: ListItemCommentStyle::None,
 188             item: Some(s.into()),
 189             post_comment: None,
 190             new_lines: false,
 191         }
 192     }
 193
 194     // Returns `true` if the item causes something to be written.
 195     fn is_substantial(&self) -> bool {
 196         fn empty(s: &Option<String>) -> bool {
 197             !matches!(*s, Some(ref s) if !s.is_empty())
 198         }
 199
 200         !(empty(&self.pre_comment) && empty(&self.item) && empty(&self.post_comment))
 201     }
 202 }
 203
 204 /// The type of separator for lists.
 205 #[derive(Copy, Clone, Eq, PartialEq, Debug)]
 206 pub(crate) enum Separator {
 207     Comma,
 208     VerticalBar,
 209 }
 210
 211 impl Separator {
 212     pub(crate) fn len(self) -> usize {
 213         match self {
 214             // 2 = `, `
 215             Separator::Comma => 2,
 216             // 3 = ` | `
 217             Separator::VerticalBar => 3,
 218         }
 219     }
 220 }
 221
 222 pub(crate) fn definitive_tactic<I, T>(
 223     items: I,
 224     tactic: ListTactic,
 225     sep: Separator,
 226     width: usize,
 227 ) -> DefinitiveListTactic
 228 where
 229     I: IntoIterator<Item = T> + Clone,
 230     T: AsRef<ListItem>,
 231 {
 232     let pre_line_comments = items
 233         .clone()
 234         .into_iter()
 235         .any(|item| item.as_ref().has_single_line_comment());
 236
 237     let limit = match tactic {
 238         _ if pre_line_comments => return DefinitiveListTactic::Vertical,
 239         ListTactic::Horizontal => return DefinitiveListTactic::Horizontal,
 240         ListTactic::Vertical => return DefinitiveListTactic::Vertical,
 241         ListTactic::LimitedHorizontalVertical(limit) => ::std::cmp::min(width, limit),
 242         ListTactic::Mixed | ListTactic::HorizontalVertical => width,
 243     };
 244
 245     let (sep_count, total_width) = calculate_width(items.clone());
 246     let total_sep_len = sep.len() * sep_count.saturating_sub(1);
 247     let real_total = total_width + total_sep_len;
 248
 249     if real_total <= limit && !items.into_iter().any(|item| item.as_ref().is_multiline()) {
 250         DefinitiveListTactic::Horizontal
 251     } else {
 252         match tactic {
 253             ListTactic::Mixed => DefinitiveListTactic::Mixed,
 254             _ => DefinitiveListTactic::Vertical,
 255         }
 256     }
 257 }
 258
 259 // Format a list of commented items into a string.
 260 pub(crate) fn write_list<I, T>(items: I, formatting: &ListFormatting<'_>) -> Option<String>
 261 where
 262     I: IntoIterator<Item = T> + Clone,
 263     T: AsRef<ListItem>,
 264 {
 265     let tactic = formatting.tactic;
 266     let sep_len = formatting.separator.len();
 267
 268     // Now that we know how we will layout, we can decide for sure if there
 269     // will be a trailing separator.
 270     let mut trailing_separator = formatting.needs_trailing_separator();
 271     let mut result = String::with_capacity(128);
 272     let cloned_items = items.clone();
 273     let mut iter = items.into_iter().enumerate().peekable();
 274     let mut item_max_width: Option<usize> = None;
 275     let sep_place =
 276         SeparatorPlace::from_tactic(formatting.separator_place, tactic, formatting.separator);
 277     let mut prev_item_had_post_comment = false;
 278     let mut prev_item_is_nested_import = false;
 279
 280     let mut line_len = 0;
 281     let indent_str = &formatting.shape.indent.to_string(formatting.config);
 282     while let Some((i, item)) = iter.next() {
 283         let item = item.as_ref();
 284         let inner_item = item.item.as_ref()?;
 285         let first = i == 0;
 286         let last = iter.peek().is_none();
 287         let mut separate = match sep_place {
 288             SeparatorPlace::Front => !first,
 289             SeparatorPlace::Back => !last || trailing_separator,
 290         };
 291         let item_sep_len = if separate { sep_len } else { 0 };
 292
 293         // Item string may be multi-line. Its length (used for block comment alignment)
 294         // should be only the length of the last line.
 295         let item_last_line = if item.is_multiline() {
 296             inner_item.lines().last().unwrap_or("")
 297         } else {
 298             inner_item.as_ref()
 299         };
 300         let mut item_last_line_width = item_last_line.len() + item_sep_len;
 301         if item_last_line.starts_with(&**indent_str) {
 302             item_last_line_width -= indent_str.len();
 303         }
 304
 305         if !item.is_substantial() {
 306             continue;
 307         }
 308
 309         match tactic {
 310             DefinitiveListTactic::Horizontal if !first => {
 311                 result.push(' ');
 312             }
 313             DefinitiveListTactic::SpecialMacro(num_args_before) => {
 314                 if i == 0 {
 315                     // Nothing
 316                 } else if i < num_args_before {
 317                     result.push(' ');
 318                 } else if i <= num_args_before + 1 {
 319                     result.push('\n');
 320                     result.push_str(indent_str);
 321                 } else {
 322                     result.push(' ');
 323                 }
 324             }
 325             DefinitiveListTactic::Vertical
 326                 if !first && !inner_item.is_empty() && !result.is_empty() =>
 327             {
 328                 result.push('\n');
 329                 result.push_str(indent_str);
 330             }
 331             DefinitiveListTactic::Mixed => {
 332                 let total_width = total_item_width(item) + item_sep_len;
 333
 334                 // 1 is space between separator and item.
 335                 if (line_len > 0 && line_len + 1 + total_width > formatting.shape.width)
 336                     || prev_item_had_post_comment
 337                     || (formatting.nested
 338                         && (prev_item_is_nested_import || (!first && inner_item.contains("::"))))
 339                 {
 340                     result.push('\n');
 341                     result.push_str(indent_str);
 342                     line_len = 0;
 343                     if formatting.ends_with_newline {
 344                         trailing_separator = true;
 345                     }
 346                 } else if line_len > 0 {
 347                     result.push(' ');
 348                     line_len += 1;
 349                 }
 350
 351                 if last && formatting.ends_with_newline {
 352                     separate = formatting.trailing_separator != SeparatorTactic::Never;
 353                 }
 354
 355                 line_len += total_width;
 356             }
 357             _ => {}
 358         }
 359
 360         // Pre-comments
 361         if let Some(ref comment) = item.pre_comment {
 362             // Block style in non-vertical mode.
 363             let block_mode = tactic == DefinitiveListTactic::Horizontal;
 364             // Width restriction is only relevant in vertical mode.
 365             let comment =
 366                 rewrite_comment(comment, block_mode, formatting.shape, formatting.config)?;
 367             result.push_str(&comment);
 368
 369             if !inner_item.is_empty() {
 370                 use DefinitiveListTactic::*;
 371                 if matches!(tactic, Vertical | Mixed | SpecialMacro(_)) {
 372                     // We cannot keep pre-comments on the same line if the comment is normalized.
 373                     let keep_comment = if formatting.config.normalize_comments()
 374                         || item.pre_comment_style == ListItemCommentStyle::DifferentLine
 375                     {
 376                         false
 377                     } else {
 378                         // We will try to keep the comment on the same line with the item here.
 379                         // 1 = ` `
 380                         let total_width = total_item_width(item) + item_sep_len + 1;
 381                         total_width <= formatting.shape.width
 382                     };
 383                     if keep_comment {
 384                         result.push(' ');
 385                     } else {
 386                         result.push('\n');
 387                         result.push_str(indent_str);
 388                         // This is the width of the item (without comments).
 389                         line_len = item.item.as_ref().map_or(0, |s| unicode_str_width(s));
 390                     }
 391                 } else {
 392                     result.push(' ')
 393                 }
 394             }
 395             item_max_width = None;
 396         }
 397
 398         if separate && sep_place.is_front() && !first {
 399             result.push_str(formatting.separator.trim());
 400             result.push(' ');
 401         }
 402         result.push_str(inner_item);
 403
 404         // Post-comments
 405         if tactic == DefinitiveListTactic::Horizontal && item.post_comment.is_some() {
 406             let comment = item.post_comment.as_ref().unwrap();
 407             let formatted_comment = rewrite_comment(
 408                 comment,
 409                 true,
 410                 Shape::legacy(formatting.shape.width, Indent::empty()),
 411                 formatting.config,
 412             )?;
 413
 414             result.push(' ');
 415             result.push_str(&formatted_comment);
 416         }
 417
 418         if separate && sep_place.is_back() {
 419             result.push_str(formatting.separator);
 420         }
 421
 422         if tactic != DefinitiveListTactic::Horizontal && item.post_comment.is_some() {
 423             let comment = item.post_comment.as_ref().unwrap();
 424             let overhead = last_line_width(&result) + first_line_width(comment.trim());
 425
 426             let rewrite_post_comment = |item_max_width: &mut Option<usize>| {
 427                 if item_max_width.is_none() && !last && !inner_item.contains('\n') {
 428                     *item_max_width = Some(max_width_of_item_with_post_comment(
 429                         &cloned_items,
 430                         i,
 431                         overhead,
 432                         formatting.config.max_width(),
 433                     ));
 434                 }
 435                 let overhead = if starts_with_newline(comment) {
 436                     0
 437                 } else if let Some(max_width) = *item_max_width {
 438                     max_width + 2
 439                 } else {
 440                     // 1 = space between item and comment.
 441                     item_last_line_width + 1
 442                 };
 443                 let width = formatting.shape.width.checked_sub(overhead).unwrap_or(1);
 444                 let offset = formatting.shape.indent + overhead;
 445                 let comment_shape = Shape::legacy(width, offset);
 446
 447                 let block_style = if !formatting.ends_with_newline && last {
 448                     true
 449                 } else if starts_with_newline(comment) {
 450                     false
 451                 } else {
 452                     comment.trim().contains('\n') || comment.trim().len() > width
 453                 };
 454
 455                 rewrite_comment(
 456                     comment.trim_start(),
 457                     block_style,
 458                     comment_shape,
 459                     formatting.config,
 460                 )
 461             };
 462
 463             let mut formatted_comment = rewrite_post_comment(&mut item_max_width)?;
 464
 465             if !starts_with_newline(comment) {
 466                 if formatting.align_comments {
 467                     let mut comment_alignment =
 468                         post_comment_alignment(item_max_width, inner_item.len());
 469                     if first_line_width(&formatted_comment)
 470                         + last_line_width(&result)
 471                         + comment_alignment
 472                         + 1
 473                         > formatting.config.max_width()
 474                     {
 475                         item_max_width = None;
 476                         formatted_comment = rewrite_post_comment(&mut item_max_width)?;
 477                         comment_alignment =
 478                             post_comment_alignment(item_max_width, inner_item.len());
 479                     }
 480                     for _ in 0..=comment_alignment {
 481                         result.push(' ');
 482                     }
 483                 }
 484                 // An additional space for the missing trailing separator (or
 485                 // if we skipped alignment above).
 486                 if !formatting.align_comments
 487                     || (last
 488                         && item_max_width.is_some()
 489                         && !separate
 490                         && !formatting.separator.is_empty())
 491                 {
 492                     result.push(' ');
 493                 }
 494             } else {
 495                 result.push('\n');
 496                 result.push_str(indent_str);
 497             }
 498             if formatted_comment.contains('\n') {
 499                 item_max_width = None;
 500             }
 501             result.push_str(&formatted_comment);
 502         } else {
 503             item_max_width = None;
 504         }
 505
 506         if formatting.preserve_newline
 507             && !last
 508             && tactic == DefinitiveListTactic::Vertical
 509             && item.new_lines
 510         {
 511             item_max_width = None;
 512             result.push('\n');
 513         }
 514
 515         prev_item_had_post_comment = item.post_comment.is_some();
 516         prev_item_is_nested_import = inner_item.contains("::");
 517     }
 518
 519     Some(result)
 520 }
 521
 522 fn max_width_of_item_with_post_comment<I, T>(
 523     items: &I,
 524     i: usize,
 525     overhead: usize,
 526     max_budget: usize,
 527 ) -> usize
 528 where
 529     I: IntoIterator<Item = T> + Clone,
 530     T: AsRef<ListItem>,
 531 {
 532     let mut max_width = 0;
 533     let mut first = true;
 534     for item in items.clone().into_iter().skip(i) {
 535         let item = item.as_ref();
 536         let inner_item_width = item.inner_as_ref().len();
 537         if !first
 538             && (item.is_different_group()
 539                 || item.post_comment.is_none()
 540                 || inner_item_width + overhead > max_budget)
 541         {
 542             return max_width;
 543         }
 544         if max_width < inner_item_width {
 545             max_width = inner_item_width;
 546         }
 547         if item.new_lines {
 548             return max_width;
 549         }
 550         first = false;
 551     }
 552     max_width
 553 }
 554
 555 fn post_comment_alignment(item_max_width: Option<usize>, inner_item_len: usize) -> usize {
 556     item_max_width.unwrap_or(0).saturating_sub(inner_item_len)
 557 }
 558
 559 pub(crate) struct ListItems<'a, I, F1, F2, F3>
 560 where
 561     I: Iterator,
 562 {
 563     snippet_provider: &'a SnippetProvider,
 564     inner: Peekable<I>,
 565     get_lo: F1,
 566     get_hi: F2,
 567     get_item_string: F3,
 568     prev_span_end: BytePos,
 569     next_span_start: BytePos,
 570     terminator: &'a str,
 571     separator: &'a str,
 572     leave_last: bool,
 573 }
 574
 575 pub(crate) fn extract_pre_comment(pre_snippet: &str) -> (Option<String>, ListItemCommentStyle) {
 576     let trimmed_pre_snippet = pre_snippet.trim();
 577     // Both start and end are checked to support keeping a block comment inline with
 578     // the item, even if there are preceeding line comments, while still supporting
 579     // a snippet that starts with a block comment but also contains one or more
 580     // trailing single line comments.
 581     // https://github.com/rust-lang/rustfmt/issues/3025
 582     // https://github.com/rust-lang/rustfmt/pull/3048
 583     // https://github.com/rust-lang/rustfmt/issues/3839
 584     let starts_with_block_comment = trimmed_pre_snippet.starts_with("/*");
 585     let ends_with_block_comment = trimmed_pre_snippet.ends_with("*/");
 586     let starts_with_single_line_comment = trimmed_pre_snippet.starts_with("//");
 587     if ends_with_block_comment {
 588         let comment_end = pre_snippet.rfind(|c| c == '/').unwrap();
 589         if pre_snippet[comment_end..].contains('\n') {
 590             (
 591                 Some(trimmed_pre_snippet.to_owned()),
 592                 ListItemCommentStyle::DifferentLine,
 593             )
 594         } else {
 595             (
 596                 Some(trimmed_pre_snippet.to_owned()),
 597                 ListItemCommentStyle::SameLine,
 598             )
 599         }
 600     } else if starts_with_single_line_comment || starts_with_block_comment {
 601         (
 602             Some(trimmed_pre_snippet.to_owned()),
 603             ListItemCommentStyle::DifferentLine,
 604         )
 605     } else {
 606         (None, ListItemCommentStyle::None)
 607     }
 608 }
 609
 610 pub(crate) fn extract_post_comment(
 611     post_snippet: &str,
 612     comment_end: usize,
 613     separator: &str,
 614 ) -> Option<String> {
 615     let white_space: &[_] = &[' ', '\t'];
 616
 617     // Cleanup post-comment: strip separators and whitespace.
 618     let post_snippet = post_snippet[..comment_end].trim();
 619     let post_snippet_trimmed = if post_snippet.starts_with(|c| c == ',' || c == ':') {
 620         post_snippet[1..].trim_matches(white_space)
 621     } else if let Some(stripped) = post_snippet.strip_prefix(separator) {
 622         stripped.trim_matches(white_space)
 623     }
 624     // not comment or over two lines
 625     else if post_snippet.ends_with(',')
 626         && (!post_snippet.trim().starts_with("//") || post_snippet.trim().contains('\n'))
 627     {
 628         post_snippet[..(post_snippet.len() - 1)].trim_matches(white_space)
 629     } else {
 630         post_snippet
 631     };
 632     // FIXME(#3441): post_snippet includes 'const' now
 633     // it should not include here
 634     let removed_newline_snippet = post_snippet_trimmed.trim();
 635     if !post_snippet_trimmed.is_empty()
 636         && (removed_newline_snippet.starts_with("//") || removed_newline_snippet.starts_with("/*"))
 637     {
 638         Some(post_snippet_trimmed.to_owned())
 639     } else {
 640         None
 641     }
 642 }
 643
 644 pub(crate) fn get_comment_end(
 645     post_snippet: &str,
 646     separator: &str,
 647     terminator: &str,
 648     is_last: bool,
 649 ) -> usize {
 650     if is_last {
 651         return post_snippet
 652             .find_uncommented(terminator)
 653             .unwrap_or_else(|| post_snippet.len());
 654     }
 655
 656     let mut block_open_index = post_snippet.find("/*");
 657     // check if it really is a block comment (and not `//*` or a nested comment)
 658     if let Some(i) = block_open_index {
 659         match post_snippet.find('/') {
 660             Some(j) if j < i => block_open_index = None,
 661             _ if post_snippet[..i].ends_with('/') => block_open_index = None,
 662             _ => (),
 663         }
 664     }
 665     let newline_index = post_snippet.find('\n');
 666     if let Some(separator_index) = post_snippet.find_uncommented(separator) {
 667         match (block_open_index, newline_index) {
 668             // Separator before comment, with the next item on same line.
 669             // Comment belongs to next item.
 670             (Some(i), None) if i > separator_index => separator_index + 1,
 671             // Block-style post-comment before the separator.
 672             (Some(i), None) => cmp::max(
 673                 find_comment_end(&post_snippet[i..]).unwrap() + i,
 674                 separator_index + 1,
 675             ),
 676             // Block-style post-comment. Either before or after the separator.
 677             (Some(i), Some(j)) if i < j => cmp::max(
 678                 find_comment_end(&post_snippet[i..]).unwrap() + i,
 679                 separator_index + 1,
 680             ),
 681             // Potential *single* line comment.
 682             (_, Some(j)) if j > separator_index => j + 1,
 683             _ => post_snippet.len(),
 684         }
 685     } else if let Some(newline_index) = newline_index {
 686         // Match arms may not have trailing comma. In any case, for match arms,
 687         // we will assume that the post comment belongs to the next arm if they
 688         // do not end with trailing comma.
 689         newline_index + 1
 690     } else {
 691         0
 692     }
 693 }
 694
 695 // Account for extra whitespace between items. This is fiddly
 696 // because of the way we divide pre- and post- comments.
 697 pub(crate) fn has_extra_newline(post_snippet: &str, comment_end: usize) -> bool {
 698     if post_snippet.is_empty() || comment_end == 0 {
 699         return false;
 700     }
 701
 702     let len_last = post_snippet[..comment_end]
 703         .chars()
 704         .last()
 705         .unwrap()
 706         .len_utf8();
 707     // Everything from the separator to the next item.
 708     let test_snippet = &post_snippet[comment_end - len_last..];
 709     let first_newline = test_snippet
 710         .find('\n')
 711         .unwrap_or_else(|| test_snippet.len());
 712     // From the end of the first line of comments.
 713     let test_snippet = &test_snippet[first_newline..];
 714     let first = test_snippet
 715         .find(|c: char| !c.is_whitespace())
 716         .unwrap_or_else(|| test_snippet.len());
 717     // From the end of the first line of comments to the next non-whitespace char.
 718     let test_snippet = &test_snippet[..first];
 719
 720     // There were multiple line breaks which got trimmed to nothing.
 721     count_newlines(test_snippet) > 1
 722 }
 723
 724 impl<'a, T, I, F1, F2, F3> Iterator for ListItems<'a, I, F1, F2, F3>
 725 where
 726     I: Iterator<Item = T>,
 727     F1: Fn(&T) -> BytePos,
 728     F2: Fn(&T) -> BytePos,
 729     F3: Fn(&T) -> Option<String>,
 730 {
 731     type Item = ListItem;
 732
 733     fn next(&mut self) -> Option<Self::Item> {
 734         self.inner.next().map(|item| {
 735             // Pre-comment
 736             let pre_snippet = self
 737                 .snippet_provider
 738                 .span_to_snippet(mk_sp(self.prev_span_end, (self.get_lo)(&item)))
 739                 .unwrap_or("");
 740             let (pre_comment, pre_comment_style) = extract_pre_comment(pre_snippet);
 741
 742             // Post-comment
 743             let next_start = match self.inner.peek() {
 744                 Some(next_item) => (self.get_lo)(next_item),
 745                 None => self.next_span_start,
 746             };
 747             let post_snippet = self
 748                 .snippet_provider
 749                 .span_to_snippet(mk_sp((self.get_hi)(&item), next_start))
 750                 .unwrap_or("");
 751             let comment_end = get_comment_end(
 752                 post_snippet,
 753                 self.separator,
 754                 self.terminator,
 755                 self.inner.peek().is_none(),
 756             );
 757             let new_lines = has_extra_newline(post_snippet, comment_end);
 758             let post_comment = extract_post_comment(post_snippet, comment_end, self.separator);
 759
 760             self.prev_span_end = (self.get_hi)(&item) + BytePos(comment_end as u32);
 761
 762             ListItem {
 763                 pre_comment,
 764                 pre_comment_style,
 765                 item: if self.inner.peek().is_none() && self.leave_last {
 766                     None
 767                 } else {
 768                     (self.get_item_string)(&item)
 769                 },
 770                 post_comment,
 771                 new_lines,
 772             }
 773         })
 774     }
 775 }
 776
 777 #[allow(clippy::too_many_arguments)]
 778 // Creates an iterator over a list's items with associated comments.
 779 pub(crate) fn itemize_list<'a, T, I, F1, F2, F3>(
 780     snippet_provider: &'a SnippetProvider,
 781     inner: I,
 782     terminator: &'a str,
 783     separator: &'a str,
 784     get_lo: F1,
 785     get_hi: F2,
 786     get_item_string: F3,
 787     prev_span_end: BytePos,
 788     next_span_start: BytePos,
 789     leave_last: bool,
 790 ) -> ListItems<'a, I, F1, F2, F3>
 791 where
 792     I: Iterator<Item = T>,
 793     F1: Fn(&T) -> BytePos,
 794     F2: Fn(&T) -> BytePos,
 795     F3: Fn(&T) -> Option<String>,
 796 {
 797     ListItems {
 798         snippet_provider,
 799         inner: inner.peekable(),
 800         get_lo,
 801         get_hi,
 802         get_item_string,
 803         prev_span_end,
 804         next_span_start,
 805         terminator,
 806         separator,
 807         leave_last,
 808     }
 809 }
 810
 811 /// Returns the count and total width of the list items.
 812 fn calculate_width<I, T>(items: I) -> (usize, usize)
 813 where
 814     I: IntoIterator<Item = T>,
 815     T: AsRef<ListItem>,
 816 {
 817     items
 818         .into_iter()
 819         .map(|item| total_item_width(item.as_ref()))
 820         .fold((0, 0), |acc, l| (acc.0 + 1, acc.1 + l))
 821 }
 822
 823 pub(crate) fn total_item_width(item: &ListItem) -> usize {
 824     comment_len(item.pre_comment.as_ref().map(|x| &(*x)[..]))
 825         + comment_len(item.post_comment.as_ref().map(|x| &(*x)[..]))
 826         + item.item.as_ref().map_or(0, |s| unicode_str_width(s))
 827 }
 828
 829 fn comment_len(comment: Option<&str>) -> usize {
 830     match comment {
 831         Some(s) => {
 832             let text_len = s.trim().len();
 833             if text_len > 0 {
 834                 // We'll put " /*" before and " */" after inline comments.
 835                 text_len + 6
 836             } else {
 837                 text_len
 838             }
 839         }
 840         None => 0,
 841     }
 842 }
 843
 844 // Compute horizontal and vertical shapes for a struct-lit-like thing.
 845 pub(crate) fn struct_lit_shape(
 846     shape: Shape,
 847     context: &RewriteContext<'_>,
 848     prefix_width: usize,
 849     suffix_width: usize,
 850 ) -> Option<(Option<Shape>, Shape)> {
 851     let v_shape = match context.config.indent_style() {
 852         IndentStyle::Visual => shape
 853             .visual_indent(0)
 854             .shrink_left(prefix_width)?
 855             .sub_width(suffix_width)?,
 856         IndentStyle::Block => {
 857             let shape = shape.block_indent(context.config.tab_spaces());
 858             Shape {
 859                 width: context.budget(shape.indent.width()),
 860                 ..shape
 861             }
 862         }
 863     };
 864     let shape_width = shape.width.checked_sub(prefix_width + suffix_width);
 865     if let Some(w) = shape_width {
 866         let shape_width = cmp::min(w, context.config.struct_lit_width());
 867         Some((Some(Shape::legacy(shape_width, shape.indent)), v_shape))
 868     } else {
 869         Some((None, v_shape))
 870     }
 871 }
 872
 873 // Compute the tactic for the internals of a struct-lit-like thing.
 874 pub(crate) fn struct_lit_tactic(
 875     h_shape: Option<Shape>,
 876     context: &RewriteContext<'_>,
 877     items: &[ListItem],
 878 ) -> DefinitiveListTactic {
 879     if let Some(h_shape) = h_shape {
 880         let prelim_tactic = match (context.config.indent_style(), items.len()) {
 881             (IndentStyle::Visual, 1) => ListTactic::HorizontalVertical,
 882             _ if context.config.struct_lit_single_line() => ListTactic::HorizontalVertical,
 883             _ => ListTactic::Vertical,
 884         };
 885         definitive_tactic(items, prelim_tactic, Separator::Comma, h_shape.width)
 886     } else {
 887         DefinitiveListTactic::Vertical
 888     }
 889 }
 890
 891 // Given a tactic and possible shapes for horizontal and vertical layout,
 892 // come up with the actual shape to use.
 893 pub(crate) fn shape_for_tactic(
 894     tactic: DefinitiveListTactic,
 895     h_shape: Option<Shape>,
 896     v_shape: Shape,
 897 ) -> Shape {
 898     match tactic {
 899         DefinitiveListTactic::Horizontal => h_shape.unwrap(),
 900         _ => v_shape,
 901     }
 902 }
 903
 904 // Create a ListFormatting object for formatting the internals of a
 905 // struct-lit-like thing, that is a series of fields.
 906 pub(crate) fn struct_lit_formatting<'a>(
 907     shape: Shape,
 908     tactic: DefinitiveListTactic,
 909     context: &'a RewriteContext<'_>,
 910     force_no_trailing_comma: bool,
 911 ) -> ListFormatting<'a> {
 912     let ends_with_newline = context.config.indent_style() != IndentStyle::Visual
 913         && tactic == DefinitiveListTactic::Vertical;
 914     ListFormatting {
 915         tactic,
 916         separator: ",",
 917         trailing_separator: if force_no_trailing_comma {
 918             SeparatorTactic::Never
 919         } else {
 920             context.config.trailing_comma()
 921         },
 922         separator_place: SeparatorPlace::Back,
 923         shape,
 924         ends_with_newline,
 925         preserve_newline: true,
 926         nested: false,
 927         align_comments: true,
 928         config: context.config,
 929     }
 930 }