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 //! ```text
  20 //! let foo = {
  21 //!     aaaa;
  22 //!     bbb;
  23 //!     ccc
  24 //! }.bar
  25 //!     .baz();
  26 //! ```
  27 //!
  28 //! Visual:
  29 //!
  30 //! ```text
  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 //! ```text
  45 //! let a = foo.bar
  46 //!     .baz()
  47 //!     .qux
  48 //! ```
  49 //!
  50 //! Visual:
  51 //!
  52 //! ```text
  53 //! let a = foo.bar
  54 //!            .baz()
  55 //!            .qux
  56 //! ```
  57
  58 use std::borrow::Cow;
  59 use std::cmp::min;
  60
  61 use rustc_ast::{ast, ptr};
  62 use rustc_span::{BytePos, Span};
  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     Await,
 122     Comment(String, CommentPosition),
 123 }
 124
 125 impl ChainItemKind {
 126     fn is_block_like(&self, context: &RewriteContext<'_>, reps: &str) -> bool {
 127         match self {
 128             ChainItemKind::Parent(ref expr) => utils::is_block_expr(context, expr, reps),
 129             ChainItemKind::MethodCall(..)
 130             | ChainItemKind::StructField(..)
 131             | ChainItemKind::TupleField(..)
 132             | ChainItemKind::Await
 133             | ChainItemKind::Comment(..) => false,
 134         }
 135     }
 136
 137     fn is_tup_field_access(expr: &ast::Expr) -> bool {
 138         match expr.kind {
 139             ast::ExprKind::Field(_, ref field) => {
 140                 field.name.to_string().chars().all(|c| c.is_digit(10))
 141             }
 142             _ => false,
 143         }
 144     }
 145
 146     fn from_ast(context: &RewriteContext<'_>, expr: &ast::Expr) -> (ChainItemKind, Span) {
 147         let (kind, span) = match expr.kind {
 148             ast::ExprKind::MethodCall(ref segment, ref expressions) => {
 149                 let types = if let Some(ref generic_args) = segment.args {
 150                     if let ast::GenericArgs::AngleBracketed(ref data) = **generic_args {
 151                         data.args
 152                             .iter()
 153                             .filter_map(|x| match x {
 154                                 ast::AngleBracketedArg::Arg(ref generic_arg) => {
 155                                     Some(generic_arg.clone())
 156                                 }
 157                                 _ => None,
 158                             })
 159                             .collect::<Vec<_>>()
 160                     } else {
 161                         vec![]
 162                     }
 163                 } else {
 164                     vec![]
 165                 };
 166                 let span = mk_sp(expressions[0].span.hi(), expr.span.hi());
 167                 let kind = ChainItemKind::MethodCall(segment.clone(), types, expressions.clone());
 168                 (kind, span)
 169             }
 170             ast::ExprKind::Field(ref nested, field) => {
 171                 let kind = if Self::is_tup_field_access(expr) {
 172                     ChainItemKind::TupleField(field, Self::is_tup_field_access(nested))
 173                 } else {
 174                     ChainItemKind::StructField(field)
 175                 };
 176                 let span = mk_sp(nested.span.hi(), field.span.hi());
 177                 (kind, span)
 178             }
 179             ast::ExprKind::Await(ref nested) => {
 180                 let span = mk_sp(nested.span.hi(), expr.span.hi());
 181                 (ChainItemKind::Await, span)
 182             }
 183             _ => return (ChainItemKind::Parent(expr.clone()), expr.span),
 184         };
 185
 186         // Remove comments from the span.
 187         let lo = context.snippet_provider.span_before(span, ".");
 188         (kind, mk_sp(lo, span.hi()))
 189     }
 190 }
 191
 192 impl Rewrite for ChainItem {
 193     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 194         let shape = shape.sub_width(self.tries)?;
 195         let rewrite = match self.kind {
 196             ChainItemKind::Parent(ref expr) => expr.rewrite(context, shape)?,
 197             ChainItemKind::MethodCall(ref segment, ref types, ref exprs) => {
 198                 Self::rewrite_method_call(segment.ident, types, exprs, self.span, context, shape)?
 199             }
 200             ChainItemKind::StructField(ident) => format!(".{}", rewrite_ident(context, ident)),
 201             ChainItemKind::TupleField(ident, nested) => format!(
 202                 "{}.{}",
 203                 if nested { " " } else { "" },
 204                 rewrite_ident(context, ident)
 205             ),
 206             ChainItemKind::Await => ".await".to_owned(),
 207             ChainItemKind::Comment(ref comment, _) => {
 208                 rewrite_comment(comment, false, shape, context.config)?
 209             }
 210         };
 211         Some(format!("{}{}", rewrite, "?".repeat(self.tries)))
 212     }
 213 }
 214
 215 impl ChainItem {
 216     fn new(context: &RewriteContext<'_>, expr: &ast::Expr, tries: usize) -> ChainItem {
 217         let (kind, span) = ChainItemKind::from_ast(context, expr);
 218         ChainItem { kind, tries, span }
 219     }
 220
 221     fn comment(span: Span, comment: String, pos: CommentPosition) -> ChainItem {
 222         ChainItem {
 223             kind: ChainItemKind::Comment(comment, pos),
 224             tries: 0,
 225             span,
 226         }
 227     }
 228
 229     fn is_comment(&self) -> bool {
 230         match self.kind {
 231             ChainItemKind::Comment(..) => true,
 232             _ => false,
 233         }
 234     }
 235
 236     fn rewrite_method_call(
 237         method_name: ast::Ident,
 238         types: &[ast::GenericArg],
 239         args: &[ptr::P<ast::Expr>],
 240         span: Span,
 241         context: &RewriteContext<'_>,
 242         shape: Shape,
 243     ) -> Option<String> {
 244         let type_str = if types.is_empty() {
 245             String::new()
 246         } else {
 247             let type_list = types
 248                 .iter()
 249                 .map(|ty| ty.rewrite(context, shape))
 250                 .collect::<Option<Vec<_>>>()?;
 251
 252             format!("::<{}>", type_list.join(", "))
 253         };
 254         let callee_str = format!(".{}{}", rewrite_ident(context, method_name), type_str);
 255         rewrite_call(context, &callee_str, &args[1..], span, shape)
 256     }
 257 }
 258
 259 #[derive(Debug)]
 260 struct Chain {
 261     parent: ChainItem,
 262     children: Vec<ChainItem>,
 263 }
 264
 265 impl Chain {
 266     fn from_ast(expr: &ast::Expr, context: &RewriteContext<'_>) -> Chain {
 267         let subexpr_list = Self::make_subexpr_list(expr, context);
 268
 269         // Un-parse the expression tree into ChainItems
 270         let mut rev_children = vec![];
 271         let mut sub_tries = 0;
 272         for subexpr in &subexpr_list {
 273             match subexpr.kind {
 274                 ast::ExprKind::Try(_) => sub_tries += 1,
 275                 _ => {
 276                     rev_children.push(ChainItem::new(context, subexpr, sub_tries));
 277                     sub_tries = 0;
 278                 }
 279             }
 280         }
 281
 282         fn is_tries(s: &str) -> bool {
 283             s.chars().all(|c| c == '?')
 284         }
 285
 286         fn is_post_comment(s: &str) -> bool {
 287             let comment_start_index = s.chars().position(|c| c == '/');
 288             if comment_start_index.is_none() {
 289                 return false;
 290             }
 291
 292             let newline_index = s.chars().position(|c| c == '\n');
 293             if newline_index.is_none() {
 294                 return true;
 295             }
 296
 297             comment_start_index.unwrap() < newline_index.unwrap()
 298         }
 299
 300         fn handle_post_comment(
 301             post_comment_span: Span,
 302             post_comment_snippet: &str,
 303             prev_span_end: &mut BytePos,
 304             children: &mut Vec<ChainItem>,
 305         ) {
 306             let white_spaces: &[_] = &[' ', '\t'];
 307             if post_comment_snippet
 308                 .trim_matches(white_spaces)
 309                 .starts_with('\n')
 310             {
 311                 // No post comment.
 312                 return;
 313             }
 314             let trimmed_snippet = trim_tries(post_comment_snippet);
 315             if is_post_comment(&trimmed_snippet) {
 316                 children.push(ChainItem::comment(
 317                     post_comment_span,
 318                     trimmed_snippet.trim().to_owned(),
 319                     CommentPosition::Back,
 320                 ));
 321                 *prev_span_end = post_comment_span.hi();
 322             }
 323         }
 324
 325         let parent = rev_children.pop().unwrap();
 326         let mut children = vec![];
 327         let mut prev_span_end = parent.span.hi();
 328         let mut iter = rev_children.into_iter().rev().peekable();
 329         if let Some(first_chain_item) = iter.peek() {
 330             let comment_span = mk_sp(prev_span_end, first_chain_item.span.lo());
 331             let comment_snippet = context.snippet(comment_span);
 332             if !is_tries(comment_snippet.trim()) {
 333                 handle_post_comment(
 334                     comment_span,
 335                     comment_snippet,
 336                     &mut prev_span_end,
 337                     &mut children,
 338                 );
 339             }
 340         }
 341         while let Some(chain_item) = iter.next() {
 342             let comment_snippet = context.snippet(chain_item.span);
 343             // FIXME: Figure out the way to get a correct span when converting `try!` to `?`.
 344             let handle_comment =
 345                 !(context.config.use_try_shorthand() || is_tries(comment_snippet.trim()));
 346
 347             // Pre-comment
 348             if handle_comment {
 349                 let pre_comment_span = mk_sp(prev_span_end, chain_item.span.lo());
 350                 let pre_comment_snippet = trim_tries(context.snippet(pre_comment_span));
 351                 let (pre_comment, _) = extract_pre_comment(&pre_comment_snippet);
 352                 match pre_comment {
 353                     Some(ref comment) if !comment.is_empty() => {
 354                         children.push(ChainItem::comment(
 355                             pre_comment_span,
 356                             comment.to_owned(),
 357                             CommentPosition::Top,
 358                         ));
 359                     }
 360                     _ => (),
 361                 }
 362             }
 363
 364             prev_span_end = chain_item.span.hi();
 365             children.push(chain_item);
 366
 367             // Post-comment
 368             if !handle_comment || iter.peek().is_none() {
 369                 continue;
 370             }
 371
 372             let next_lo = iter.peek().unwrap().span.lo();
 373             let post_comment_span = mk_sp(prev_span_end, next_lo);
 374             let post_comment_snippet = context.snippet(post_comment_span);
 375             handle_post_comment(
 376                 post_comment_span,
 377                 post_comment_snippet,
 378                 &mut prev_span_end,
 379                 &mut children,
 380             );
 381         }
 382
 383         Chain { parent, children }
 384     }
 385
 386     // Returns a Vec of the prefixes of the chain.
 387     // E.g., for input `a.b.c` we return [`a.b.c`, `a.b`, 'a']
 388     fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext<'_>) -> Vec<ast::Expr> {
 389         let mut subexpr_list = vec![expr.clone()];
 390
 391         while let Some(subexpr) = Self::pop_expr_chain(subexpr_list.last().unwrap(), context) {
 392             subexpr_list.push(subexpr.clone());
 393         }
 394
 395         subexpr_list
 396     }
 397
 398     // Returns the expression's subexpression, if it exists. When the subexpr
 399     // is a try! macro, we'll convert it to shorthand when the option is set.
 400     fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext<'_>) -> Option<ast::Expr> {
 401         match expr.kind {
 402             ast::ExprKind::MethodCall(_, ref expressions) => {
 403                 Some(Self::convert_try(&expressions[0], context))
 404             }
 405             ast::ExprKind::Field(ref subexpr, _)
 406             | ast::ExprKind::Try(ref subexpr)
 407             | ast::ExprKind::Await(ref subexpr) => Some(Self::convert_try(subexpr, context)),
 408             _ => None,
 409         }
 410     }
 411
 412     fn convert_try(expr: &ast::Expr, context: &RewriteContext<'_>) -> ast::Expr {
 413         match expr.kind {
 414             ast::ExprKind::MacCall(ref mac) if context.config.use_try_shorthand() => {
 415                 if let Some(subexpr) = convert_try_mac(mac, context) {
 416                     subexpr
 417                 } else {
 418                     expr.clone()
 419                 }
 420             }
 421             _ => expr.clone(),
 422         }
 423     }
 424 }
 425
 426 impl Rewrite for Chain {
 427     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 428         debug!("rewrite chain {:?} {:?}", self, shape);
 429
 430         let mut formatter = match context.config.indent_style() {
 431             IndentStyle::Block => {
 432                 Box::new(ChainFormatterBlock::new(self)) as Box<dyn ChainFormatter>
 433             }
 434             IndentStyle::Visual => {
 435                 Box::new(ChainFormatterVisual::new(self)) as Box<dyn ChainFormatter>
 436             }
 437         };
 438
 439         formatter.format_root(&self.parent, context, shape)?;
 440         if let Some(result) = formatter.pure_root() {
 441             return wrap_str(result, context.config.max_width(), shape);
 442         }
 443
 444         // Decide how to layout the rest of the chain.
 445         let child_shape = formatter.child_shape(context, shape)?;
 446
 447         formatter.format_children(context, child_shape)?;
 448         formatter.format_last_child(context, shape, child_shape)?;
 449
 450         let result = formatter.join_rewrites(context, child_shape)?;
 451         wrap_str(result, context.config.max_width(), shape)
 452     }
 453 }
 454
 455 // There are a few types for formatting chains. This is because there is a lot
 456 // in common between formatting with block vs visual indent, but they are
 457 // different enough that branching on the indent all over the place gets ugly.
 458 // Anything that can format a chain is a ChainFormatter.
 459 trait ChainFormatter {
 460     // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
 461     // Root is the parent plus any other chain items placed on the first line to
 462     // avoid an orphan. E.g.,
 463     // ```text
 464     // foo.bar
 465     //     .baz()
 466     // ```
 467     // If `bar` were not part of the root, then foo would be orphaned and 'float'.
 468     fn format_root(
 469         &mut self,
 470         parent: &ChainItem,
 471         context: &RewriteContext<'_>,
 472         shape: Shape,
 473     ) -> Option<()>;
 474     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape>;
 475     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()>;
 476     fn format_last_child(
 477         &mut self,
 478         context: &RewriteContext<'_>,
 479         shape: Shape,
 480         child_shape: Shape,
 481     ) -> Option<()>;
 482     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String>;
 483     // Returns `Some` if the chain is only a root, None otherwise.
 484     fn pure_root(&mut self) -> Option<String>;
 485 }
 486
 487 // Data and behaviour that is shared by both chain formatters. The concrete
 488 // formatters can delegate much behaviour to `ChainFormatterShared`.
 489 struct ChainFormatterShared<'a> {
 490     // The current working set of child items.
 491     children: &'a [ChainItem],
 492     // The current rewrites of items (includes trailing `?`s, but not any way to
 493     // connect the rewrites together).
 494     rewrites: Vec<String>,
 495     // Whether the chain can fit on one line.
 496     fits_single_line: bool,
 497     // The number of children in the chain. This is not equal to `self.children.len()`
 498     // because `self.children` will change size as we process the chain.
 499     child_count: usize,
 500 }
 501
 502 impl<'a> ChainFormatterShared<'a> {
 503     fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
 504         ChainFormatterShared {
 505             children: &chain.children,
 506             rewrites: Vec::with_capacity(chain.children.len() + 1),
 507             fits_single_line: false,
 508             child_count: chain.children.len(),
 509         }
 510     }
 511
 512     fn pure_root(&mut self) -> Option<String> {
 513         if self.children.is_empty() {
 514             assert_eq!(self.rewrites.len(), 1);
 515             Some(self.rewrites.pop().unwrap())
 516         } else {
 517             None
 518         }
 519     }
 520
 521     // Rewrite the last child. The last child of a chain requires special treatment. We need to
 522     // know whether 'overflowing' the last child make a better formatting:
 523     //
 524     // A chain with overflowing the last child:
 525     // ```text
 526     // parent.child1.child2.last_child(
 527     //     a,
 528     //     b,
 529     //     c,
 530     // )
 531     // ```
 532     //
 533     // A chain without overflowing the last child (in vertical layout):
 534     // ```text
 535     // parent
 536     //     .child1
 537     //     .child2
 538     //     .last_child(a, b, c)
 539     // ```
 540     //
 541     // In particular, overflowing is effective when the last child is a method with a multi-lined
 542     // block-like argument (e.g., closure):
 543     // ```text
 544     // parent.child1.child2.last_child(|a, b, c| {
 545     //     let x = foo(a, b, c);
 546     //     let y = bar(a, b, c);
 547     //
 548     //     // ...
 549     //
 550     //     result
 551     // })
 552     // ```
 553     fn format_last_child(
 554         &mut self,
 555         may_extend: bool,
 556         context: &RewriteContext<'_>,
 557         shape: Shape,
 558         child_shape: Shape,
 559     ) -> Option<()> {
 560         let last = self.children.last()?;
 561         let extendable = may_extend && last_line_extendable(&self.rewrites[0]);
 562         let prev_last_line_width = last_line_width(&self.rewrites[0]);
 563
 564         // Total of all items excluding the last.
 565         let almost_total = if extendable {
 566             prev_last_line_width
 567         } else {
 568             self.rewrites
 569                 .iter()
 570                 .map(|rw| utils::unicode_str_width(&rw))
 571                 .sum()
 572         } + last.tries;
 573         let one_line_budget = if self.child_count == 1 {
 574             shape.width
 575         } else {
 576             min(shape.width, context.config.width_heuristics().chain_width)
 577         }
 578         .saturating_sub(almost_total);
 579
 580         let all_in_one_line = !self.children.iter().any(ChainItem::is_comment)
 581             && self.rewrites.iter().all(|s| !s.contains('\n'))
 582             && one_line_budget > 0;
 583         let last_shape = if all_in_one_line {
 584             shape.sub_width(last.tries)?
 585         } else if extendable {
 586             child_shape.sub_width(last.tries)?
 587         } else {
 588             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 589         };
 590
 591         let mut last_subexpr_str = None;
 592         if all_in_one_line || extendable {
 593             // First we try to 'overflow' the last child and see if it looks better than using
 594             // vertical layout.
 595             let one_line_shape = if context.use_block_indent() {
 596                 last_shape.offset_left(almost_total)
 597             } else {
 598                 last_shape
 599                     .visual_indent(almost_total)
 600                     .sub_width(almost_total)
 601             };
 602
 603             if let Some(one_line_shape) = one_line_shape {
 604                 if let Some(rw) = last.rewrite(context, one_line_shape) {
 605                     // We allow overflowing here only if both of the following conditions match:
 606                     // 1. The entire chain fits in a single line except the last child.
 607                     // 2. `last_child_str.lines().count() >= 5`.
 608                     let line_count = rw.lines().count();
 609                     let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
 610                     if could_fit_single_line && line_count >= 5 {
 611                         last_subexpr_str = Some(rw);
 612                         self.fits_single_line = all_in_one_line;
 613                     } else {
 614                         // We could not know whether overflowing is better than using vertical
 615                         // layout, just by looking at the overflowed rewrite. Now we rewrite the
 616                         // last child on its own line, and compare two rewrites to choose which is
 617                         // better.
 618                         let last_shape = child_shape
 619                             .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
 620                         match last.rewrite(context, last_shape) {
 621                             Some(ref new_rw) if !could_fit_single_line => {
 622                                 last_subexpr_str = Some(new_rw.clone());
 623                             }
 624                             Some(ref new_rw) if new_rw.lines().count() >= line_count => {
 625                                 last_subexpr_str = Some(rw);
 626                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 627                             }
 628                             new_rw @ Some(..) => {
 629                                 last_subexpr_str = new_rw;
 630                             }
 631                             _ => {
 632                                 last_subexpr_str = Some(rw);
 633                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 634                             }
 635                         }
 636                     }
 637                 }
 638             }
 639         }
 640
 641         let last_shape = if context.use_block_indent() {
 642             last_shape
 643         } else {
 644             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 645         };
 646
 647         last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
 648         self.rewrites.push(last_subexpr_str?);
 649         Some(())
 650     }
 651
 652     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 653         let connector = if self.fits_single_line {
 654             // Yay, we can put everything on one line.
 655             Cow::from("")
 656         } else {
 657             // Use new lines.
 658             if context.force_one_line_chain.get() {
 659                 return None;
 660             }
 661             child_shape.to_string_with_newline(context.config)
 662         };
 663
 664         let mut rewrite_iter = self.rewrites.iter();
 665         let mut result = rewrite_iter.next().unwrap().clone();
 666         let children_iter = self.children.iter();
 667         let iter = rewrite_iter.zip(children_iter);
 668
 669         for (rewrite, chain_item) in iter {
 670             match chain_item.kind {
 671                 ChainItemKind::Comment(_, CommentPosition::Back) => result.push(' '),
 672                 ChainItemKind::Comment(_, CommentPosition::Top) => result.push_str(&connector),
 673                 _ => result.push_str(&connector),
 674             }
 675             result.push_str(&rewrite);
 676         }
 677
 678         Some(result)
 679     }
 680 }
 681
 682 // Formats a chain using block indent.
 683 struct ChainFormatterBlock<'a> {
 684     shared: ChainFormatterShared<'a>,
 685     root_ends_with_block: bool,
 686 }
 687
 688 impl<'a> ChainFormatterBlock<'a> {
 689     fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
 690         ChainFormatterBlock {
 691             shared: ChainFormatterShared::new(chain),
 692             root_ends_with_block: false,
 693         }
 694     }
 695 }
 696
 697 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
 698     fn format_root(
 699         &mut self,
 700         parent: &ChainItem,
 701         context: &RewriteContext<'_>,
 702         shape: Shape,
 703     ) -> Option<()> {
 704         let mut root_rewrite: String = parent.rewrite(context, shape)?;
 705
 706         let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
 707         let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
 708
 709         while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
 710             let item = &self.shared.children[0];
 711             if let ChainItemKind::Comment(..) = item.kind {
 712                 break;
 713             }
 714             let shape = shape.offset_left(root_rewrite.len())?;
 715             match &item.rewrite(context, shape) {
 716                 Some(rewrite) => root_rewrite.push_str(rewrite),
 717                 None => break,
 718             }
 719
 720             root_ends_with_block = last_line_extendable(&root_rewrite);
 721
 722             self.shared.children = &self.shared.children[1..];
 723             if self.shared.children.is_empty() {
 724                 break;
 725             }
 726         }
 727         self.shared.rewrites.push(root_rewrite);
 728         self.root_ends_with_block = root_ends_with_block;
 729         Some(())
 730     }
 731
 732     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
 733         Some(
 734             if self.root_ends_with_block {
 735                 shape.block_indent(0)
 736             } else {
 737                 shape.block_indent(context.config.tab_spaces())
 738             }
 739             .with_max_width(context.config),
 740         )
 741     }
 742
 743     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
 744         for item in &self.shared.children[..self.shared.children.len() - 1] {
 745             let rewrite = item.rewrite(context, child_shape)?;
 746             self.shared.rewrites.push(rewrite);
 747         }
 748         Some(())
 749     }
 750
 751     fn format_last_child(
 752         &mut self,
 753         context: &RewriteContext<'_>,
 754         shape: Shape,
 755         child_shape: Shape,
 756     ) -> Option<()> {
 757         self.shared
 758             .format_last_child(true, context, shape, child_shape)
 759     }
 760
 761     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 762         self.shared.join_rewrites(context, child_shape)
 763     }
 764
 765     fn pure_root(&mut self) -> Option<String> {
 766         self.shared.pure_root()
 767     }
 768 }
 769
 770 // Format a chain using visual indent.
 771 struct ChainFormatterVisual<'a> {
 772     shared: ChainFormatterShared<'a>,
 773     // The extra offset from the chain's shape to the position of the `.`
 774     offset: usize,
 775 }
 776
 777 impl<'a> ChainFormatterVisual<'a> {
 778     fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
 779         ChainFormatterVisual {
 780             shared: ChainFormatterShared::new(chain),
 781             offset: 0,
 782         }
 783     }
 784 }
 785
 786 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
 787     fn format_root(
 788         &mut self,
 789         parent: &ChainItem,
 790         context: &RewriteContext<'_>,
 791         shape: Shape,
 792     ) -> Option<()> {
 793         let parent_shape = shape.visual_indent(0);
 794         let mut root_rewrite = parent.rewrite(context, parent_shape)?;
 795         let multiline = root_rewrite.contains('\n');
 796         self.offset = if multiline {
 797             last_line_width(&root_rewrite).saturating_sub(shape.used_width())
 798         } else {
 799             trimmed_last_line_width(&root_rewrite)
 800         };
 801
 802         if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
 803             let item = &self.shared.children[0];
 804             if let ChainItemKind::Comment(..) = item.kind {
 805                 self.shared.rewrites.push(root_rewrite);
 806                 return Some(());
 807             }
 808             let child_shape = parent_shape
 809                 .visual_indent(self.offset)
 810                 .sub_width(self.offset)?;
 811             let rewrite = item.rewrite(context, child_shape)?;
 812             match wrap_str(rewrite, context.config.max_width(), shape) {
 813                 Some(rewrite) => root_rewrite.push_str(&rewrite),
 814                 None => {
 815                     // We couldn't fit in at the visual indent, try the last
 816                     // indent.
 817                     let rewrite = item.rewrite(context, parent_shape)?;
 818                     root_rewrite.push_str(&rewrite);
 819                     self.offset = 0;
 820                 }
 821             }
 822
 823             self.shared.children = &self.shared.children[1..];
 824         }
 825
 826         self.shared.rewrites.push(root_rewrite);
 827         Some(())
 828     }
 829
 830     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
 831         shape
 832             .with_max_width(context.config)
 833             .offset_left(self.offset)
 834             .map(|s| s.visual_indent(0))
 835     }
 836
 837     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
 838         for item in &self.shared.children[..self.shared.children.len() - 1] {
 839             let rewrite = item.rewrite(context, child_shape)?;
 840             self.shared.rewrites.push(rewrite);
 841         }
 842         Some(())
 843     }
 844
 845     fn format_last_child(
 846         &mut self,
 847         context: &RewriteContext<'_>,
 848         shape: Shape,
 849         child_shape: Shape,
 850     ) -> Option<()> {
 851         self.shared
 852             .format_last_child(false, context, shape, child_shape)
 853     }
 854
 855     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 856         self.shared.join_rewrites(context, child_shape)
 857     }
 858
 859     fn pure_root(&mut self) -> Option<String> {
 860         self.shared.pure_root()
 861     }
 862 }
 863
 864 /// Removes try operators (`?`s) that appear in the given string. If removing
 865 /// them leaves an empty line, remove that line as well unless it is the first
 866 /// line (we need the first newline for detecting pre/post comment).
 867 fn trim_tries(s: &str) -> String {
 868     let mut result = String::with_capacity(s.len());
 869     let mut line_buffer = String::with_capacity(s.len());
 870     for (kind, rich_char) in CharClasses::new(s.chars()) {
 871         match rich_char.get_char() {
 872             '\n' => {
 873                 if result.is_empty() || !line_buffer.trim().is_empty() {
 874                     result.push_str(&line_buffer);
 875                     result.push('\n')
 876                 }
 877                 line_buffer.clear();
 878             }
 879             '?' if kind == FullCodeCharKind::Normal => continue,
 880             c => line_buffer.push(c),
 881         }
 882     }
 883     if !line_buffer.trim().is_empty() {
 884         result.push_str(&line_buffer);
 885     }
 886     result
 887 }