src/chains.rs

   1 //! Formatting of chained expressions, i.e., expressions that are chained by
   2 //! dots: struct and enum field access, method calls, and try shorthand (`?`).
   3 //!
   4 //! Instead of walking these subexpressions one-by-one, as is our usual strategy
   5 //! for expression formatting, we collect maximal sequences of these expressions
   6 //! and handle them simultaneously.
   7 //!
   8 //! Whenever possible, the entire chain is put on a single line. If that fails,
   9 //! we put each subexpression on a separate, much like the (default) function
  10 //! argument function argument strategy.
  11 //!
  12 //! Depends on config options: `chain_indent` is the indent to use for
  13 //! blocks in the parent/root/base of the chain (and the rest of the chain's
  14 //! alignment).
  15 //! E.g., `let foo = { aaaa; bbb; ccc }.bar.baz();`, we would layout for the
  16 //! following values of `chain_indent`:
  17 //! Block:
  18 //!
  19 //! ```ignore
  20 //! let foo = {
  21 //!     aaaa;
  22 //!     bbb;
  23 //!     ccc
  24 //! }.bar
  25 //!     .baz();
  26 //! ```
  27 //!
  28 //! Visual:
  29 //!
  30 //! ```ignore
  31 //! let foo = {
  32 //!               aaaa;
  33 //!               bbb;
  34 //!               ccc
  35 //!           }
  36 //!           .bar
  37 //!           .baz();
  38 //! ```
  39 //!
  40 //! If the first item in the chain is a block expression, we align the dots with
  41 //! the braces.
  42 //! Block:
  43 //!
  44 //! ```ignore
  45 //! let a = foo.bar
  46 //!     .baz()
  47 //!     .qux
  48 //! ```
  49 //!
  50 //! Visual:
  51 //!
  52 //! ```ignore
  53 //! let a = foo.bar
  54 //!            .baz()
  55 //!            .qux
  56 //! ```
  57
  58 use std::borrow::Cow;
  59 use std::cmp::min;
  60
  61 use syntax::source_map::{BytePos, Span};
  62 use syntax::{ast, ptr};
  63
  64 use crate::comment::{rewrite_comment, CharClasses, FullCodeCharKind, RichChar};
  65 use crate::config::IndentStyle;
  66 use crate::expr::rewrite_call;
  67 use crate::lists::extract_pre_comment;
  68 use crate::macros::convert_try_mac;
  69 use crate::rewrite::{Rewrite, RewriteContext};
  70 use crate::shape::Shape;
  71 use crate::source_map::SpanUtils;
  72 use crate::utils::{
  73     self, first_line_width, last_line_extendable, last_line_width, mk_sp, rewrite_ident,
  74     trimmed_last_line_width, wrap_str,
  75 };
  76
  77 pub(crate) fn rewrite_chain(
  78     expr: &ast::Expr,
  79     context: &RewriteContext<'_>,
  80     shape: Shape,
  81 ) -> Option<String> {
  82     let chain = Chain::from_ast(expr, context);
  83     debug!("rewrite_chain {:?} {:?}", chain, shape);
  84
  85     // If this is just an expression with some `?`s, then format it trivially and
  86     // return early.
  87     if chain.children.is_empty() {
  88         return chain.parent.rewrite(context, shape);
  89     }
  90
  91     chain.rewrite(context, shape)
  92 }
  93
  94 #[derive(Debug)]
  95 enum CommentPosition {
  96     Back,
  97     Top,
  98 }
  99
 100 // An expression plus trailing `?`s to be formatted together.
 101 #[derive(Debug)]
 102 struct ChainItem {
 103     kind: ChainItemKind,
 104     tries: usize,
 105     span: Span,
 106 }
 107
 108 // FIXME: we can't use a reference here because to convert `try!` to `?` we
 109 // synthesise the AST node. However, I think we could use `Cow` and that
 110 // would remove a lot of cloning.
 111 #[derive(Debug)]
 112 enum ChainItemKind {
 113     Parent(ast::Expr),
 114     MethodCall(
 115         ast::PathSegment,
 116         Vec<ast::GenericArg>,
 117         Vec<ptr::P<ast::Expr>>,
 118     ),
 119     StructField(ast::Ident),
 120     TupleField(ast::Ident, bool),
 121     Comment(String, CommentPosition),
 122 }
 123
 124 impl ChainItemKind {
 125     fn is_block_like(&self, context: &RewriteContext<'_>, reps: &str) -> bool {
 126         match self {
 127             ChainItemKind::Parent(ref expr) => utils::is_block_expr(context, expr, reps),
 128             ChainItemKind::MethodCall(..)
 129             | ChainItemKind::StructField(..)
 130             | ChainItemKind::TupleField(..)
 131             | ChainItemKind::Comment(..) => false,
 132         }
 133     }
 134
 135     fn is_tup_field_access(expr: &ast::Expr) -> bool {
 136         match expr.node {
 137             ast::ExprKind::Field(_, ref field) => {
 138                 field.name.to_string().chars().all(|c| c.is_digit(10))
 139             }
 140             _ => false,
 141         }
 142     }
 143
 144     fn from_ast(context: &RewriteContext<'_>, expr: &ast::Expr) -> (ChainItemKind, Span) {
 145         let (kind, span) = match expr.node {
 146             ast::ExprKind::MethodCall(ref segment, ref expressions) => {
 147                 let types = if let Some(ref generic_args) = segment.args {
 148                     if let ast::GenericArgs::AngleBracketed(ref data) = **generic_args {
 149                         data.args.clone()
 150                     } else {
 151                         vec![]
 152                     }
 153                 } else {
 154                     vec![]
 155                 };
 156                 let span = mk_sp(expressions[0].span.hi(), expr.span.hi());
 157                 let kind = ChainItemKind::MethodCall(segment.clone(), types, expressions.clone());
 158                 (kind, span)
 159             }
 160             ast::ExprKind::Field(ref nested, field) => {
 161                 let kind = if Self::is_tup_field_access(expr) {
 162                     ChainItemKind::TupleField(field, Self::is_tup_field_access(nested))
 163                 } else {
 164                     ChainItemKind::StructField(field)
 165                 };
 166                 let span = mk_sp(nested.span.hi(), field.span.hi());
 167                 (kind, span)
 168             }
 169             _ => return (ChainItemKind::Parent(expr.clone()), expr.span),
 170         };
 171
 172         // Remove comments from the span.
 173         let lo = context.snippet_provider.span_before(span, ".");
 174         (kind, mk_sp(lo, span.hi()))
 175     }
 176 }
 177
 178 impl Rewrite for ChainItem {
 179     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 180         let shape = shape.sub_width(self.tries)?;
 181         let rewrite = match self.kind {
 182             ChainItemKind::Parent(ref expr) => expr.rewrite(context, shape)?,
 183             ChainItemKind::MethodCall(ref segment, ref types, ref exprs) => {
 184                 Self::rewrite_method_call(segment.ident, types, exprs, self.span, context, shape)?
 185             }
 186             ChainItemKind::StructField(ident) => format!(".{}", rewrite_ident(context, ident)),
 187             ChainItemKind::TupleField(ident, nested) => format!(
 188                 "{}.{}",
 189                 if nested { " " } else { "" },
 190                 rewrite_ident(context, ident)
 191             ),
 192             ChainItemKind::Comment(ref comment, _) => {
 193                 rewrite_comment(comment, false, shape, context.config)?
 194             }
 195         };
 196         Some(format!("{}{}", rewrite, "?".repeat(self.tries)))
 197     }
 198 }
 199
 200 impl ChainItem {
 201     fn new(context: &RewriteContext<'_>, expr: &ast::Expr, tries: usize) -> ChainItem {
 202         let (kind, span) = ChainItemKind::from_ast(context, expr);
 203         ChainItem { kind, tries, span }
 204     }
 205
 206     fn comment(span: Span, comment: String, pos: CommentPosition) -> ChainItem {
 207         ChainItem {
 208             kind: ChainItemKind::Comment(comment, pos),
 209             tries: 0,
 210             span,
 211         }
 212     }
 213
 214     fn is_comment(&self) -> bool {
 215         match self.kind {
 216             ChainItemKind::Comment(..) => true,
 217             _ => false,
 218         }
 219     }
 220
 221     fn rewrite_method_call(
 222         method_name: ast::Ident,
 223         types: &[ast::GenericArg],
 224         args: &[ptr::P<ast::Expr>],
 225         span: Span,
 226         context: &RewriteContext<'_>,
 227         shape: Shape,
 228     ) -> Option<String> {
 229         let type_str = if types.is_empty() {
 230             String::new()
 231         } else {
 232             let type_list = types
 233                 .iter()
 234                 .map(|ty| ty.rewrite(context, shape))
 235                 .collect::<Option<Vec<_>>>()?;
 236
 237             format!("::<{}>", type_list.join(", "))
 238         };
 239         let callee_str = format!(".{}{}", rewrite_ident(context, method_name), type_str);
 240         rewrite_call(context, &callee_str, &args[1..], span, shape)
 241     }
 242 }
 243
 244 #[derive(Debug)]
 245 struct Chain {
 246     parent: ChainItem,
 247     children: Vec<ChainItem>,
 248 }
 249
 250 impl Chain {
 251     fn from_ast(expr: &ast::Expr, context: &RewriteContext<'_>) -> Chain {
 252         let subexpr_list = Self::make_subexpr_list(expr, context);
 253
 254         // Un-parse the expression tree into ChainItems
 255         let mut rev_children = vec![];
 256         let mut sub_tries = 0;
 257         for subexpr in &subexpr_list {
 258             match subexpr.node {
 259                 ast::ExprKind::Try(_) => sub_tries += 1,
 260                 _ => {
 261                     rev_children.push(ChainItem::new(context, subexpr, sub_tries));
 262                     sub_tries = 0;
 263                 }
 264             }
 265         }
 266
 267         fn is_tries(s: &str) -> bool {
 268             s.chars().all(|c| c == '?')
 269         }
 270
 271         fn is_post_comment(s: &str) -> bool {
 272             let comment_start_index = s.chars().position(|c| c == '/');
 273             if comment_start_index.is_none() {
 274                 return false;
 275             }
 276
 277             let newline_index = s.chars().position(|c| c == '\n');
 278             if newline_index.is_none() {
 279                 return true;
 280             }
 281
 282             comment_start_index.unwrap() < newline_index.unwrap()
 283         }
 284
 285         fn handle_post_comment(
 286             post_comment_span: Span,
 287             post_comment_snippet: &str,
 288             prev_span_end: &mut BytePos,
 289             children: &mut Vec<ChainItem>,
 290         ) {
 291             let white_spaces: &[_] = &[' ', '\t'];
 292             if post_comment_snippet
 293                 .trim_matches(white_spaces)
 294                 .starts_with('\n')
 295             {
 296                 // No post comment.
 297                 return;
 298             }
 299             let trimmed_snippet = trim_tries(post_comment_snippet);
 300             if is_post_comment(&trimmed_snippet) {
 301                 children.push(ChainItem::comment(
 302                     post_comment_span,
 303                     trimmed_snippet.trim().to_owned(),
 304                     CommentPosition::Back,
 305                 ));
 306                 *prev_span_end = post_comment_span.hi();
 307             }
 308         }
 309
 310         let parent = rev_children.pop().unwrap();
 311         let mut children = vec![];
 312         let mut prev_span_end = parent.span.hi();
 313         let mut iter = rev_children.into_iter().rev().peekable();
 314         if let Some(first_chain_item) = iter.peek() {
 315             let comment_span = mk_sp(prev_span_end, first_chain_item.span.lo());
 316             let comment_snippet = context.snippet(comment_span);
 317             if !is_tries(comment_snippet.trim()) {
 318                 handle_post_comment(
 319                     comment_span,
 320                     comment_snippet,
 321                     &mut prev_span_end,
 322                     &mut children,
 323                 );
 324             }
 325         }
 326         while let Some(chain_item) = iter.next() {
 327             let comment_snippet = context.snippet(chain_item.span);
 328             // FIXME: Figure out the way to get a correct span when converting `try!` to `?`.
 329             let handle_comment =
 330                 !(context.config.use_try_shorthand() || is_tries(comment_snippet.trim()));
 331
 332             // Pre-comment
 333             if handle_comment {
 334                 let pre_comment_span = mk_sp(prev_span_end, chain_item.span.lo());
 335                 let pre_comment_snippet = trim_tries(context.snippet(pre_comment_span));
 336                 let (pre_comment, _) = extract_pre_comment(&pre_comment_snippet);
 337                 match pre_comment {
 338                     Some(ref comment) if !comment.is_empty() => {
 339                         children.push(ChainItem::comment(
 340                             pre_comment_span,
 341                             comment.to_owned(),
 342                             CommentPosition::Top,
 343                         ));
 344                     }
 345                     _ => (),
 346                 }
 347             }
 348
 349             prev_span_end = chain_item.span.hi();
 350             children.push(chain_item);
 351
 352             // Post-comment
 353             if !handle_comment || iter.peek().is_none() {
 354                 continue;
 355             }
 356
 357             let next_lo = iter.peek().unwrap().span.lo();
 358             let post_comment_span = mk_sp(prev_span_end, next_lo);
 359             let post_comment_snippet = context.snippet(post_comment_span);
 360             handle_post_comment(
 361                 post_comment_span,
 362                 post_comment_snippet,
 363                 &mut prev_span_end,
 364                 &mut children,
 365             );
 366         }
 367
 368         Chain { parent, children }
 369     }
 370
 371     // Returns a Vec of the prefixes of the chain.
 372     // E.g., for input `a.b.c` we return [`a.b.c`, `a.b`, 'a']
 373     fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext<'_>) -> Vec<ast::Expr> {
 374         let mut subexpr_list = vec![expr.clone()];
 375
 376         while let Some(subexpr) = Self::pop_expr_chain(subexpr_list.last().unwrap(), context) {
 377             subexpr_list.push(subexpr.clone());
 378         }
 379
 380         subexpr_list
 381     }
 382
 383     // Returns the expression's subexpression, if it exists. When the subexpr
 384     // is a try! macro, we'll convert it to shorthand when the option is set.
 385     fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext<'_>) -> Option<ast::Expr> {
 386         match expr.node {
 387             ast::ExprKind::MethodCall(_, ref expressions) => {
 388                 Some(Self::convert_try(&expressions[0], context))
 389             }
 390             ast::ExprKind::Field(ref subexpr, _) | ast::ExprKind::Try(ref subexpr) => {
 391                 Some(Self::convert_try(subexpr, context))
 392             }
 393             _ => None,
 394         }
 395     }
 396
 397     fn convert_try(expr: &ast::Expr, context: &RewriteContext<'_>) -> ast::Expr {
 398         match expr.node {
 399             ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
 400                 if let Some(subexpr) = convert_try_mac(mac, context) {
 401                     subexpr
 402                 } else {
 403                     expr.clone()
 404                 }
 405             }
 406             _ => expr.clone(),
 407         }
 408     }
 409 }
 410
 411 impl Rewrite for Chain {
 412     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 413         debug!("rewrite chain {:?} {:?}", self, shape);
 414
 415         let mut formatter = match context.config.indent_style() {
 416             IndentStyle::Block => {
 417                 Box::new(ChainFormatterBlock::new(self)) as Box<dyn ChainFormatter>
 418             }
 419             IndentStyle::Visual => {
 420                 Box::new(ChainFormatterVisual::new(self)) as Box<dyn ChainFormatter>
 421             }
 422         };
 423
 424         formatter.format_root(&self.parent, context, shape)?;
 425         if let Some(result) = formatter.pure_root() {
 426             return wrap_str(result, context.config.max_width(), shape);
 427         }
 428
 429         // Decide how to layout the rest of the chain.
 430         let child_shape = formatter.child_shape(context, shape)?;
 431
 432         formatter.format_children(context, child_shape)?;
 433         formatter.format_last_child(context, shape, child_shape)?;
 434
 435         let result = formatter.join_rewrites(context, child_shape)?;
 436         wrap_str(result, context.config.max_width(), shape)
 437     }
 438 }
 439
 440 // There are a few types for formatting chains. This is because there is a lot
 441 // in common between formatting with block vs visual indent, but they are
 442 // different enough that branching on the indent all over the place gets ugly.
 443 // Anything that can format a chain is a ChainFormatter.
 444 trait ChainFormatter {
 445     // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
 446     // Root is the parent plus any other chain items placed on the first line to
 447     // avoid an orphan. E.g.,
 448     // ```ignore
 449     // foo.bar
 450     //     .baz()
 451     // ```
 452     // If `bar` were not part of the root, then foo would be orphaned and 'float'.
 453     fn format_root(
 454         &mut self,
 455         parent: &ChainItem,
 456         context: &RewriteContext<'_>,
 457         shape: Shape,
 458     ) -> Option<()>;
 459     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape>;
 460     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()>;
 461     fn format_last_child(
 462         &mut self,
 463         context: &RewriteContext<'_>,
 464         shape: Shape,
 465         child_shape: Shape,
 466     ) -> Option<()>;
 467     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String>;
 468     // Returns `Some` if the chain is only a root, None otherwise.
 469     fn pure_root(&mut self) -> Option<String>;
 470 }
 471
 472 // Data and behaviour that is shared by both chain formatters. The concrete
 473 // formatters can delegate much behaviour to `ChainFormatterShared`.
 474 struct ChainFormatterShared<'a> {
 475     // The current working set of child items.
 476     children: &'a [ChainItem],
 477     // The current rewrites of items (includes trailing `?`s, but not any way to
 478     // connect the rewrites together).
 479     rewrites: Vec<String>,
 480     // Whether the chain can fit on one line.
 481     fits_single_line: bool,
 482     // The number of children in the chain. This is not equal to `self.children.len()`
 483     // because `self.children` will change size as we process the chain.
 484     child_count: usize,
 485 }
 486
 487 impl<'a> ChainFormatterShared<'a> {
 488     fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
 489         ChainFormatterShared {
 490             children: &chain.children,
 491             rewrites: Vec::with_capacity(chain.children.len() + 1),
 492             fits_single_line: false,
 493             child_count: chain.children.len(),
 494         }
 495     }
 496
 497     fn pure_root(&mut self) -> Option<String> {
 498         if self.children.is_empty() {
 499             assert_eq!(self.rewrites.len(), 1);
 500             Some(self.rewrites.pop().unwrap())
 501         } else {
 502             None
 503         }
 504     }
 505
 506     // Rewrite the last child. The last child of a chain requires special treatment. We need to
 507     // know whether 'overflowing' the last child make a better formatting:
 508     //
 509     // A chain with overflowing the last child:
 510     // ```ignore
 511     // parent.child1.child2.last_child(
 512     //     a,
 513     //     b,
 514     //     c,
 515     // )
 516     // ```
 517     //
 518     // A chain without overflowing the last child (in vertical layout):
 519     // ```ignore
 520     // parent
 521     //     .child1
 522     //     .child2
 523     //     .last_child(a, b, c)
 524     // ```
 525     //
 526     // In particular, overflowing is effective when the last child is a method with a multi-lined
 527     // block-like argument (e.g., closure):
 528     // ```ignore
 529     // parent.child1.child2.last_child(|a, b, c| {
 530     //     let x = foo(a, b, c);
 531     //     let y = bar(a, b, c);
 532     //
 533     //     // ...
 534     //
 535     //     result
 536     // })
 537     // ```
 538     fn format_last_child(
 539         &mut self,
 540         may_extend: bool,
 541         context: &RewriteContext<'_>,
 542         shape: Shape,
 543         child_shape: Shape,
 544     ) -> Option<()> {
 545         let last = self.children.last()?;
 546         let extendable = may_extend && last_line_extendable(&self.rewrites[0]);
 547         let prev_last_line_width = last_line_width(&self.rewrites[0]);
 548
 549         // Total of all items excluding the last.
 550         let almost_total = if extendable {
 551             prev_last_line_width
 552         } else {
 553             self.rewrites.iter().map(String::len).sum()
 554         } + last.tries;
 555         let one_line_budget = if self.child_count == 1 {
 556             shape.width
 557         } else {
 558             min(shape.width, context.config.width_heuristics().chain_width)
 559         }
 560         .saturating_sub(almost_total);
 561
 562         let all_in_one_line = !self.children.iter().any(ChainItem::is_comment)
 563             && self.rewrites.iter().all(|s| !s.contains('\n'))
 564             && one_line_budget > 0;
 565         let last_shape = if all_in_one_line {
 566             shape.sub_width(last.tries)?
 567         } else if extendable {
 568             child_shape.sub_width(last.tries)?
 569         } else {
 570             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 571         };
 572
 573         let mut last_subexpr_str = None;
 574         if all_in_one_line || extendable {
 575             // First we try to 'overflow' the last child and see if it looks better than using
 576             // vertical layout.
 577             let one_line_shape = if context.use_block_indent() {
 578                 last_shape.offset_left(almost_total)
 579             } else {
 580                 last_shape
 581                     .visual_indent(almost_total)
 582                     .sub_width(almost_total)
 583             };
 584
 585             if let Some(one_line_shape) = one_line_shape {
 586                 if let Some(rw) = last.rewrite(context, one_line_shape) {
 587                     // We allow overflowing here only if both of the following conditions match:
 588                     // 1. The entire chain fits in a single line except the last child.
 589                     // 2. `last_child_str.lines().count() >= 5`.
 590                     let line_count = rw.lines().count();
 591                     let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
 592                     if could_fit_single_line && line_count >= 5 {
 593                         last_subexpr_str = Some(rw);
 594                         self.fits_single_line = all_in_one_line;
 595                     } else {
 596                         // We could not know whether overflowing is better than using vertical
 597                         // layout, just by looking at the overflowed rewrite. Now we rewrite the
 598                         // last child on its own line, and compare two rewrites to choose which is
 599                         // better.
 600                         let last_shape = child_shape
 601                             .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
 602                         match last.rewrite(context, last_shape) {
 603                             Some(ref new_rw) if !could_fit_single_line => {
 604                                 last_subexpr_str = Some(new_rw.clone());
 605                             }
 606                             Some(ref new_rw) if new_rw.lines().count() >= line_count => {
 607                                 last_subexpr_str = Some(rw);
 608                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 609                             }
 610                             new_rw @ Some(..) => {
 611                                 last_subexpr_str = new_rw;
 612                             }
 613                             _ => {
 614                                 last_subexpr_str = Some(rw);
 615                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 616                             }
 617                         }
 618                     }
 619                 }
 620             }
 621         }
 622
 623         let last_shape = if context.use_block_indent() {
 624             last_shape
 625         } else {
 626             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 627         };
 628
 629         last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
 630         self.rewrites.push(last_subexpr_str?);
 631         Some(())
 632     }
 633
 634     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 635         let connector = if self.fits_single_line {
 636             // Yay, we can put everything on one line.
 637             Cow::from("")
 638         } else {
 639             // Use new lines.
 640             if *context.force_one_line_chain.borrow() {
 641                 return None;
 642             }
 643             child_shape.to_string_with_newline(context.config)
 644         };
 645
 646         let mut rewrite_iter = self.rewrites.iter();
 647         let mut result = rewrite_iter.next().unwrap().clone();
 648         let children_iter = self.children.iter();
 649         let iter = rewrite_iter.zip(children_iter);
 650
 651         for (rewrite, chain_item) in iter {
 652             match chain_item.kind {
 653                 ChainItemKind::Comment(_, CommentPosition::Back) => result.push(' '),
 654                 ChainItemKind::Comment(_, CommentPosition::Top) => result.push_str(&connector),
 655                 _ => result.push_str(&connector),
 656             }
 657             result.push_str(&rewrite);
 658         }
 659
 660         Some(result)
 661     }
 662 }
 663
 664 // Formats a chain using block indent.
 665 struct ChainFormatterBlock<'a> {
 666     shared: ChainFormatterShared<'a>,
 667     root_ends_with_block: bool,
 668 }
 669
 670 impl<'a> ChainFormatterBlock<'a> {
 671     fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
 672         ChainFormatterBlock {
 673             shared: ChainFormatterShared::new(chain),
 674             root_ends_with_block: false,
 675         }
 676     }
 677 }
 678
 679 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
 680     fn format_root(
 681         &mut self,
 682         parent: &ChainItem,
 683         context: &RewriteContext<'_>,
 684         shape: Shape,
 685     ) -> Option<()> {
 686         let mut root_rewrite: String = parent.rewrite(context, shape)?;
 687
 688         let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
 689         let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
 690
 691         while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
 692             let item = &self.shared.children[0];
 693             if let ChainItemKind::Comment(..) = item.kind {
 694                 break;
 695             }
 696             let shape = shape.offset_left(root_rewrite.len())?;
 697             match &item.rewrite(context, shape) {
 698                 Some(rewrite) => root_rewrite.push_str(rewrite),
 699                 None => break,
 700             }
 701
 702             root_ends_with_block = last_line_extendable(&root_rewrite);
 703
 704             self.shared.children = &self.shared.children[1..];
 705             if self.shared.children.is_empty() {
 706                 break;
 707             }
 708         }
 709         self.shared.rewrites.push(root_rewrite);
 710         self.root_ends_with_block = root_ends_with_block;
 711         Some(())
 712     }
 713
 714     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
 715         Some(
 716             if self.root_ends_with_block {
 717                 shape.block_indent(0)
 718             } else {
 719                 shape.block_indent(context.config.tab_spaces())
 720             }
 721             .with_max_width(context.config),
 722         )
 723     }
 724
 725     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
 726         for item in &self.shared.children[..self.shared.children.len() - 1] {
 727             let rewrite = item.rewrite(context, child_shape)?;
 728             self.shared.rewrites.push(rewrite);
 729         }
 730         Some(())
 731     }
 732
 733     fn format_last_child(
 734         &mut self,
 735         context: &RewriteContext<'_>,
 736         shape: Shape,
 737         child_shape: Shape,
 738     ) -> Option<()> {
 739         self.shared
 740             .format_last_child(true, context, shape, child_shape)
 741     }
 742
 743     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 744         self.shared.join_rewrites(context, child_shape)
 745     }
 746
 747     fn pure_root(&mut self) -> Option<String> {
 748         self.shared.pure_root()
 749     }
 750 }
 751
 752 // Format a chain using visual indent.
 753 struct ChainFormatterVisual<'a> {
 754     shared: ChainFormatterShared<'a>,
 755     // The extra offset from the chain's shape to the position of the `.`
 756     offset: usize,
 757 }
 758
 759 impl<'a> ChainFormatterVisual<'a> {
 760     fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
 761         ChainFormatterVisual {
 762             shared: ChainFormatterShared::new(chain),
 763             offset: 0,
 764         }
 765     }
 766 }
 767
 768 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
 769     fn format_root(
 770         &mut self,
 771         parent: &ChainItem,
 772         context: &RewriteContext<'_>,
 773         shape: Shape,
 774     ) -> Option<()> {
 775         let parent_shape = shape.visual_indent(0);
 776         let mut root_rewrite = parent.rewrite(context, parent_shape)?;
 777         let multiline = root_rewrite.contains('\n');
 778         self.offset = if multiline {
 779             last_line_width(&root_rewrite).saturating_sub(shape.used_width())
 780         } else {
 781             trimmed_last_line_width(&root_rewrite)
 782         };
 783
 784         if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
 785             let item = &self.shared.children[0];
 786             if let ChainItemKind::Comment(..) = item.kind {
 787                 self.shared.rewrites.push(root_rewrite);
 788                 return Some(());
 789             }
 790             let child_shape = parent_shape
 791                 .visual_indent(self.offset)
 792                 .sub_width(self.offset)?;
 793             let rewrite = item.rewrite(context, child_shape)?;
 794             match wrap_str(rewrite, context.config.max_width(), shape) {
 795                 Some(rewrite) => root_rewrite.push_str(&rewrite),
 796                 None => {
 797                     // We couldn't fit in at the visual indent, try the last
 798                     // indent.
 799                     let rewrite = item.rewrite(context, parent_shape)?;
 800                     root_rewrite.push_str(&rewrite);
 801                     self.offset = 0;
 802                 }
 803             }
 804
 805             self.shared.children = &self.shared.children[1..];
 806         }
 807
 808         self.shared.rewrites.push(root_rewrite);
 809         Some(())
 810     }
 811
 812     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
 813         shape
 814             .with_max_width(context.config)
 815             .offset_left(self.offset)
 816             .map(|s| s.visual_indent(0))
 817     }
 818
 819     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
 820         for item in &self.shared.children[..self.shared.children.len() - 1] {
 821             let rewrite = item.rewrite(context, child_shape)?;
 822             self.shared.rewrites.push(rewrite);
 823         }
 824         Some(())
 825     }
 826
 827     fn format_last_child(
 828         &mut self,
 829         context: &RewriteContext<'_>,
 830         shape: Shape,
 831         child_shape: Shape,
 832     ) -> Option<()> {
 833         self.shared
 834             .format_last_child(false, context, shape, child_shape)
 835     }
 836
 837     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 838         self.shared.join_rewrites(context, child_shape)
 839     }
 840
 841     fn pure_root(&mut self) -> Option<String> {
 842         self.shared.pure_root()
 843     }
 844 }
 845
 846 /// Removes try operators (`?`s) that appear in the given string. If removing
 847 /// them leaves an empty line, remove that line as well unless it is the first
 848 /// line (we need the first newline for detecting pre/post comment).
 849 fn trim_tries(s: &str) -> String {
 850     let mut result = String::with_capacity(s.len());
 851     let mut line_buffer = String::with_capacity(s.len());
 852     for (kind, rich_char) in CharClasses::new(s.chars()) {
 853         match rich_char.get_char() {
 854             '\n' => {
 855                 if result.is_empty() || !line_buffer.trim().is_empty() {
 856                     result.push_str(&line_buffer);
 857                     result.push('\n')
 858                 }
 859                 line_buffer.clear();
 860             }
 861             '?' if kind == FullCodeCharKind::Normal => continue,
 862             c => line_buffer.push(c),
 863         }
 864     }
 865     if !line_buffer.trim().is_empty() {
 866         result.push_str(&line_buffer);
 867     }
 868     result
 869 }