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 if comment.trim().contains('\n') || comment.trim().len() > width {
 452                     true
 453                 } else {
 454                     false
 455                 };
 456
 457                 rewrite_comment(
 458                     comment.trim_start(),
 459                     block_style,
 460                     comment_shape,
 461                     formatting.config,
 462                 )
 463             };
 464
 465             let mut formatted_comment = rewrite_post_comment(&mut item_max_width)?;
 466
 467             if !starts_with_newline(comment) {
 468                 if formatting.align_comments {
 469                     let mut comment_alignment =
 470                         post_comment_alignment(item_max_width, inner_item.len());
 471                     if first_line_width(&formatted_comment)
 472                         + last_line_width(&result)
 473                         + comment_alignment
 474                         + 1
 475                         > formatting.config.max_width()
 476                     {
 477                         item_max_width = None;
 478                         formatted_comment = rewrite_post_comment(&mut item_max_width)?;
 479                         comment_alignment =
 480                             post_comment_alignment(item_max_width, inner_item.len());
 481                     }
 482                     for _ in 0..=comment_alignment {
 483                         result.push(' ');
 484                     }
 485                 }
 486                 // An additional space for the missing trailing separator (or
 487                 // if we skipped alignment above).
 488                 if !formatting.align_comments
 489                     || (last
 490                         && item_max_width.is_some()
 491                         && !separate
 492                         && !formatting.separator.is_empty())
 493                 {
 494                     result.push(' ');
 495                 }
 496             } else {
 497                 result.push('\n');
 498                 result.push_str(indent_str);
 499             }
 500             if formatted_comment.contains('\n') {
 501                 item_max_width = None;
 502             }
 503             result.push_str(&formatted_comment);
 504         } else {
 505             item_max_width = None;
 506         }
 507
 508         if formatting.preserve_newline
 509             && !last
 510             && tactic == DefinitiveListTactic::Vertical
 511             && item.new_lines
 512         {
 513             item_max_width = None;
 514             result.push('\n');
 515         }
 516
 517         prev_item_had_post_comment = item.post_comment.is_some();
 518         prev_item_is_nested_import = inner_item.contains("::");
 519     }
 520
 521     Some(result)
 522 }
 523
 524 fn max_width_of_item_with_post_comment<I, T>(
 525     items: &I,
 526     i: usize,
 527     overhead: usize,
 528     max_budget: usize,
 529 ) -> usize
 530 where
 531     I: IntoIterator<Item = T> + Clone,
 532     T: AsRef<ListItem>,
 533 {
 534     let mut max_width = 0;
 535     let mut first = true;
 536     for item in items.clone().into_iter().skip(i) {
 537         let item = item.as_ref();
 538         let inner_item_width = item.inner_as_ref().len();
 539         if !first
 540             && (item.is_different_group()
 541                 || item.post_comment.is_none()
 542                 || inner_item_width + overhead > max_budget)
 543         {
 544             return max_width;
 545         }
 546         if max_width < inner_item_width {
 547             max_width = inner_item_width;
 548         }
 549         if item.new_lines {
 550             return max_width;
 551         }
 552         first = false;
 553     }
 554     max_width
 555 }
 556
 557 fn post_comment_alignment(item_max_width: Option<usize>, inner_item_len: usize) -> usize {
 558     item_max_width.unwrap_or(0).saturating_sub(inner_item_len)
 559 }
 560
 561 pub(crate) struct ListItems<'a, I, F1, F2, F3>
 562 where
 563     I: Iterator,
 564 {
 565     snippet_provider: &'a SnippetProvider,
 566     inner: Peekable<I>,
 567     get_lo: F1,
 568     get_hi: F2,
 569     get_item_string: F3,
 570     prev_span_end: BytePos,
 571     next_span_start: BytePos,
 572     terminator: &'a str,
 573     separator: &'a str,
 574     leave_last: bool,
 575 }
 576
 577 pub(crate) fn extract_pre_comment(pre_snippet: &str) -> (Option<String>, ListItemCommentStyle) {
 578     let trimmed_pre_snippet = pre_snippet.trim();
 579     // Both start and end are checked to support keeping a block comment inline with
 580     // the item, even if there are preceeding line comments, while still supporting
 581     // a snippet that starts with a block comment but also contains one or more
 582     // trailing single line comments.
 583     // https://github.com/rust-lang/rustfmt/issues/3025
 584     // https://github.com/rust-lang/rustfmt/pull/3048
 585     // https://github.com/rust-lang/rustfmt/issues/3839
 586     let starts_with_block_comment = trimmed_pre_snippet.starts_with("/*");
 587     let ends_with_block_comment = trimmed_pre_snippet.ends_with("*/");
 588     let starts_with_single_line_comment = trimmed_pre_snippet.starts_with("//");
 589     if ends_with_block_comment {
 590         let comment_end = pre_snippet.rfind(|c| c == '/').unwrap();
 591         if pre_snippet[comment_end..].contains('\n') {
 592             (
 593                 Some(trimmed_pre_snippet.to_owned()),
 594                 ListItemCommentStyle::DifferentLine,
 595             )
 596         } else {
 597             (
 598                 Some(trimmed_pre_snippet.to_owned()),
 599                 ListItemCommentStyle::SameLine,
 600             )
 601         }
 602     } else if starts_with_single_line_comment || starts_with_block_comment {
 603         (
 604             Some(trimmed_pre_snippet.to_owned()),
 605             ListItemCommentStyle::DifferentLine,
 606         )
 607     } else {
 608         (None, ListItemCommentStyle::None)
 609     }
 610 }
 611
 612 pub(crate) fn extract_post_comment(
 613     post_snippet: &str,
 614     comment_end: usize,
 615     separator: &str,
 616 ) -> Option<String> {
 617     let white_space: &[_] = &[' ', '\t'];
 618
 619     // Cleanup post-comment: strip separators and whitespace.
 620     let post_snippet = post_snippet[..comment_end].trim();
 621     let post_snippet_trimmed = if post_snippet.starts_with(|c| c == ',' || c == ':') {
 622         post_snippet[1..].trim_matches(white_space)
 623     } else if let Some(stripped) = post_snippet.strip_prefix(separator) {
 624         stripped.trim_matches(white_space)
 625     }
 626     // not comment or over two lines
 627     else if post_snippet.ends_with(',')
 628         && (!post_snippet.trim().starts_with("//") || post_snippet.trim().contains('\n'))
 629     {
 630         post_snippet[..(post_snippet.len() - 1)].trim_matches(white_space)
 631     } else {
 632         post_snippet
 633     };
 634     // FIXME(#3441): post_snippet includes 'const' now
 635     // it should not include here
 636     let removed_newline_snippet = post_snippet_trimmed.trim();
 637     if !post_snippet_trimmed.is_empty()
 638         && (removed_newline_snippet.starts_with("//") || removed_newline_snippet.starts_with("/*"))
 639     {
 640         Some(post_snippet_trimmed.to_owned())
 641     } else {
 642         None
 643     }
 644 }
 645
 646 pub(crate) fn get_comment_end(
 647     post_snippet: &str,
 648     separator: &str,
 649     terminator: &str,
 650     is_last: bool,
 651 ) -> usize {
 652     if is_last {
 653         return post_snippet
 654             .find_uncommented(terminator)
 655             .unwrap_or_else(|| post_snippet.len());
 656     }
 657
 658     let mut block_open_index = post_snippet.find("/*");
 659     // check if it really is a block comment (and not `//*` or a nested comment)
 660     if let Some(i) = block_open_index {
 661         match post_snippet.find('/') {
 662             Some(j) if j < i => block_open_index = None,
 663             _ if post_snippet[..i].ends_with('/') => block_open_index = None,
 664             _ => (),
 665         }
 666     }
 667     let newline_index = post_snippet.find('\n');
 668     if let Some(separator_index) = post_snippet.find_uncommented(separator) {
 669         match (block_open_index, newline_index) {
 670             // Separator before comment, with the next item on same line.
 671             // Comment belongs to next item.
 672             (Some(i), None) if i > separator_index => separator_index + 1,
 673             // Block-style post-comment before the separator.
 674             (Some(i), None) => cmp::max(
 675                 find_comment_end(&post_snippet[i..]).unwrap() + i,
 676                 separator_index + 1,
 677             ),
 678             // Block-style post-comment. Either before or after the separator.
 679             (Some(i), Some(j)) if i < j => cmp::max(
 680                 find_comment_end(&post_snippet[i..]).unwrap() + i,
 681                 separator_index + 1,
 682             ),
 683             // Potential *single* line comment.
 684             (_, Some(j)) if j > separator_index => j + 1,
 685             _ => post_snippet.len(),
 686         }
 687     } else if let Some(newline_index) = newline_index {
 688         // Match arms may not have trailing comma. In any case, for match arms,
 689         // we will assume that the post comment belongs to the next arm if they
 690         // do not end with trailing comma.
 691         newline_index + 1
 692     } else {
 693         0
 694     }
 695 }
 696
 697 // Account for extra whitespace between items. This is fiddly
 698 // because of the way we divide pre- and post- comments.
 699 pub(crate) fn has_extra_newline(post_snippet: &str, comment_end: usize) -> bool {
 700     if post_snippet.is_empty() || comment_end == 0 {
 701         return false;
 702     }
 703
 704     let len_last = post_snippet[..comment_end]
 705         .chars()
 706         .last()
 707         .unwrap()
 708         .len_utf8();
 709     // Everything from the separator to the next item.
 710     let test_snippet = &post_snippet[comment_end - len_last..];
 711     let first_newline = test_snippet
 712         .find('\n')
 713         .unwrap_or_else(|| test_snippet.len());
 714     // From the end of the first line of comments.
 715     let test_snippet = &test_snippet[first_newline..];
 716     let first = test_snippet
 717         .find(|c: char| !c.is_whitespace())
 718         .unwrap_or_else(|| test_snippet.len());
 719     // From the end of the first line of comments to the next non-whitespace char.
 720     let test_snippet = &test_snippet[..first];
 721
 722     // There were multiple line breaks which got trimmed to nothing.
 723     count_newlines(test_snippet) > 1
 724 }
 725
 726 impl<'a, T, I, F1, F2, F3> Iterator for ListItems<'a, I, F1, F2, F3>
 727 where
 728     I: Iterator<Item = T>,
 729     F1: Fn(&T) -> BytePos,
 730     F2: Fn(&T) -> BytePos,
 731     F3: Fn(&T) -> Option<String>,
 732 {
 733     type Item = ListItem;
 734
 735     fn next(&mut self) -> Option<Self::Item> {
 736         self.inner.next().map(|item| {
 737             // Pre-comment
 738             let pre_snippet = self
 739                 .snippet_provider
 740                 .span_to_snippet(mk_sp(self.prev_span_end, (self.get_lo)(&item)))
 741                 .unwrap_or("");
 742             let (pre_comment, pre_comment_style) = extract_pre_comment(pre_snippet);
 743
 744             // Post-comment
 745             let next_start = match self.inner.peek() {
 746                 Some(next_item) => (self.get_lo)(next_item),
 747                 None => self.next_span_start,
 748             };
 749             let post_snippet = self
 750                 .snippet_provider
 751                 .span_to_snippet(mk_sp((self.get_hi)(&item), next_start))
 752                 .unwrap_or("");
 753             let comment_end = get_comment_end(
 754                 post_snippet,
 755                 self.separator,
 756                 self.terminator,
 757                 self.inner.peek().is_none(),
 758             );
 759             let new_lines = has_extra_newline(post_snippet, comment_end);
 760             let post_comment = extract_post_comment(post_snippet, comment_end, self.separator);
 761
 762             self.prev_span_end = (self.get_hi)(&item) + BytePos(comment_end as u32);
 763
 764             ListItem {
 765                 pre_comment,
 766                 pre_comment_style,
 767                 item: if self.inner.peek().is_none() && self.leave_last {
 768                     None
 769                 } else {
 770                     (self.get_item_string)(&item)
 771                 },
 772                 post_comment,
 773                 new_lines,
 774             }
 775         })
 776     }
 777 }
 778
 779 #[allow(clippy::too_many_arguments)]
 780 // Creates an iterator over a list's items with associated comments.
 781 pub(crate) fn itemize_list<'a, T, I, F1, F2, F3>(
 782     snippet_provider: &'a SnippetProvider,
 783     inner: I,
 784     terminator: &'a str,
 785     separator: &'a str,
 786     get_lo: F1,
 787     get_hi: F2,
 788     get_item_string: F3,
 789     prev_span_end: BytePos,
 790     next_span_start: BytePos,
 791     leave_last: bool,
 792 ) -> ListItems<'a, I, F1, F2, F3>
 793 where
 794     I: Iterator<Item = T>,
 795     F1: Fn(&T) -> BytePos,
 796     F2: Fn(&T) -> BytePos,
 797     F3: Fn(&T) -> Option<String>,
 798 {
 799     ListItems {
 800         snippet_provider,
 801         inner: inner.peekable(),
 802         get_lo,
 803         get_hi,
 804         get_item_string,
 805         prev_span_end,
 806         next_span_start,
 807         terminator,
 808         separator,
 809         leave_last,
 810     }
 811 }
 812
 813 /// Returns the count and total width of the list items.
 814 fn calculate_width<I, T>(items: I) -> (usize, usize)
 815 where
 816     I: IntoIterator<Item = T>,
 817     T: AsRef<ListItem>,
 818 {
 819     items
 820         .into_iter()
 821         .map(|item| total_item_width(item.as_ref()))
 822         .fold((0, 0), |acc, l| (acc.0 + 1, acc.1 + l))
 823 }
 824
 825 pub(crate) fn total_item_width(item: &ListItem) -> usize {
 826     comment_len(item.pre_comment.as_ref().map(|x| &(*x)[..]))
 827         + comment_len(item.post_comment.as_ref().map(|x| &(*x)[..]))
 828         + item.item.as_ref().map_or(0, |s| unicode_str_width(s))
 829 }
 830
 831 fn comment_len(comment: Option<&str>) -> usize {
 832     match comment {
 833         Some(s) => {
 834             let text_len = s.trim().len();
 835             if text_len > 0 {
 836                 // We'll put " /*" before and " */" after inline comments.
 837                 text_len + 6
 838             } else {
 839                 text_len
 840             }
 841         }
 842         None => 0,
 843     }
 844 }
 845
 846 // Compute horizontal and vertical shapes for a struct-lit-like thing.
 847 pub(crate) fn struct_lit_shape(
 848     shape: Shape,
 849     context: &RewriteContext<'_>,
 850     prefix_width: usize,
 851     suffix_width: usize,
 852 ) -> Option<(Option<Shape>, Shape)> {
 853     let v_shape = match context.config.indent_style() {
 854         IndentStyle::Visual => shape
 855             .visual_indent(0)
 856             .shrink_left(prefix_width)?
 857             .sub_width(suffix_width)?,
 858         IndentStyle::Block => {
 859             let shape = shape.block_indent(context.config.tab_spaces());
 860             Shape {
 861                 width: context.budget(shape.indent.width()),
 862                 ..shape
 863             }
 864         }
 865     };
 866     let shape_width = shape.width.checked_sub(prefix_width + suffix_width);
 867     if let Some(w) = shape_width {
 868         let shape_width = cmp::min(w, context.config.struct_lit_width());
 869         Some((Some(Shape::legacy(shape_width, shape.indent)), v_shape))
 870     } else {
 871         Some((None, v_shape))
 872     }
 873 }
 874
 875 // Compute the tactic for the internals of a struct-lit-like thing.
 876 pub(crate) fn struct_lit_tactic(
 877     h_shape: Option<Shape>,
 878     context: &RewriteContext<'_>,
 879     items: &[ListItem],
 880 ) -> DefinitiveListTactic {
 881     if let Some(h_shape) = h_shape {
 882         let prelim_tactic = match (context.config.indent_style(), items.len()) {
 883             (IndentStyle::Visual, 1) => ListTactic::HorizontalVertical,
 884             _ if context.config.struct_lit_single_line() => ListTactic::HorizontalVertical,
 885             _ => ListTactic::Vertical,
 886         };
 887         definitive_tactic(items, prelim_tactic, Separator::Comma, h_shape.width)
 888     } else {
 889         DefinitiveListTactic::Vertical
 890     }
 891 }
 892
 893 // Given a tactic and possible shapes for horizontal and vertical layout,
 894 // come up with the actual shape to use.
 895 pub(crate) fn shape_for_tactic(
 896     tactic: DefinitiveListTactic,
 897     h_shape: Option<Shape>,
 898     v_shape: Shape,
 899 ) -> Shape {
 900     match tactic {
 901         DefinitiveListTactic::Horizontal => h_shape.unwrap(),
 902         _ => v_shape,
 903     }
 904 }
 905
 906 // Create a ListFormatting object for formatting the internals of a
 907 // struct-lit-like thing, that is a series of fields.
 908 pub(crate) fn struct_lit_formatting<'a>(
 909     shape: Shape,
 910     tactic: DefinitiveListTactic,
 911     context: &'a RewriteContext<'_>,
 912     force_no_trailing_comma: bool,
 913 ) -> ListFormatting<'a> {
 914     let ends_with_newline = context.config.indent_style() != IndentStyle::Visual
 915         && tactic == DefinitiveListTactic::Vertical;
 916     ListFormatting {
 917         tactic,
 918         separator: ",",
 919         trailing_separator: if force_no_trailing_comma {
 920             SeparatorTactic::Never
 921         } else {
 922             context.config.trailing_comma()
 923         },
 924         separator_place: SeparatorPlace::Back,
 925         shape,
 926         ends_with_newline,
 927         preserve_newline: true,
 928         nested: false,
 929         align_comments: true,
 930         config: context.config,
 931     }
 932 }