src/lists.rs

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