src/chains.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! Formatting of chained expressions, i.e. expressions which are chained by
  12 //! dots: struct and enum field access, method calls, and try shorthand (?).
  13 //!
  14 //! Instead of walking these subexpressions one-by-one, as is our usual strategy
  15 //! for expression formatting, we collect maximal sequences of these expressions
  16 //! and handle them simultaneously.
  17 //!
  18 //! Whenever possible, the entire chain is put on a single line. If that fails,
  19 //! we put each subexpression on a separate, much like the (default) function
  20 //! argument function argument strategy.
  21 //!
  22 //! Depends on config options: `chain_indent` is the indent to use for
  23 //! blocks in the parent/root/base of the chain (and the rest of the chain's
  24 //! alignment).
  25 //! E.g., `let foo = { aaaa; bbb; ccc }.bar.baz();`, we would layout for the
  26 //! following values of `chain_indent`:
  27 //! Block:
  28 //!
  29 //! ```ignore
  30 //! let foo = {
  31 //!     aaaa;
  32 //!     bbb;
  33 //!     ccc
  34 //! }.bar
  35 //!     .baz();
  36 //! ```
  37 //!
  38 //! Visual:
  39 //!
  40 //! ```ignore
  41 //! let foo = {
  42 //!               aaaa;
  43 //!               bbb;
  44 //!               ccc
  45 //!           }
  46 //!           .bar
  47 //!           .baz();
  48 //! ```
  49 //!
  50 //! If the first item in the chain is a block expression, we align the dots with
  51 //! the braces.
  52 //! Block:
  53 //!
  54 //! ```ignore
  55 //! let a = foo.bar
  56 //!     .baz()
  57 //!     .qux
  58 //! ```
  59 //!
  60 //! Visual:
  61 //!
  62 //! ```ignore
  63 //! let a = foo.bar
  64 //!            .baz()
  65 //!            .qux
  66 //! ```
  67
  68 use comment::{rewrite_comment, CharClasses, FullCodeCharKind, RichChar};
  69 use config::IndentStyle;
  70 use expr::rewrite_call;
  71 use lists::extract_pre_comment;
  72 use macros::convert_try_mac;
  73 use rewrite::{Rewrite, RewriteContext};
  74 use shape::Shape;
  75 use source_map::SpanUtils;
  76 use utils::{
  77     self, first_line_width, last_line_extendable, last_line_width, mk_sp, rewrite_ident,
  78     trimmed_last_line_width, wrap_str,
  79 };
  80
  81 use std::borrow::Cow;
  82 use std::cmp::min;
  83
  84 use syntax::source_map::{BytePos, Span};
  85 use syntax::{ast, ptr};
  86
  87 pub fn rewrite_chain(expr: &ast::Expr, context: &RewriteContext, shape: Shape) -> Option<String> {
  88     let chain = Chain::from_ast(expr, context);
  89     debug!("rewrite_chain {:?} {:?}", chain, shape);
  90
  91     // If this is just an expression with some `?`s, then format it trivially and
  92     // return early.
  93     if chain.children.is_empty() {
  94         return chain.parent.rewrite(context, shape);
  95     }
  96
  97     chain.rewrite(context, shape)
  98 }
  99
 100 #[derive(Debug)]
 101 enum CommentPosition {
 102     Back,
 103     Top,
 104 }
 105
 106 // An expression plus trailing `?`s to be formatted together.
 107 #[derive(Debug)]
 108 struct ChainItem {
 109     kind: ChainItemKind,
 110     tries: usize,
 111     span: Span,
 112 }
 113
 114 // FIXME: we can't use a reference here because to convert `try!` to `?` we
 115 // synthesise the AST node. However, I think we could use `Cow` and that
 116 // would remove a lot of cloning.
 117 #[derive(Debug)]
 118 enum ChainItemKind {
 119     Parent(ast::Expr),
 120     MethodCall(
 121         ast::PathSegment,
 122         Vec<ast::GenericArg>,
 123         Vec<ptr::P<ast::Expr>>,
 124     ),
 125     StructField(ast::Ident),
 126     TupleField(ast::Ident, bool),
 127     Comment(String, CommentPosition),
 128 }
 129
 130 impl ChainItemKind {
 131     fn is_block_like(&self, context: &RewriteContext, reps: &str) -> bool {
 132         match self {
 133             ChainItemKind::Parent(ref expr) => utils::is_block_expr(context, expr, reps),
 134             ChainItemKind::MethodCall(..)
 135             | ChainItemKind::StructField(..)
 136             | ChainItemKind::TupleField(..)
 137             | ChainItemKind::Comment(..) => false,
 138         }
 139     }
 140
 141     fn is_tup_field_access(expr: &ast::Expr) -> bool {
 142         match expr.node {
 143             ast::ExprKind::Field(_, ref field) => {
 144                 field.name.to_string().chars().all(|c| c.is_digit(10))
 145             }
 146             _ => false,
 147         }
 148     }
 149
 150     fn from_ast(context: &RewriteContext, expr: &ast::Expr) -> (ChainItemKind, Span) {
 151         let (kind, span) = match expr.node {
 152             ast::ExprKind::MethodCall(ref segment, ref expressions) => {
 153                 let types = if let Some(ref generic_args) = segment.args {
 154                     if let ast::GenericArgs::AngleBracketed(ref data) = **generic_args {
 155                         data.args.clone()
 156                     } else {
 157                         vec![]
 158                     }
 159                 } else {
 160                     vec![]
 161                 };
 162                 let span = mk_sp(expressions[0].span.hi(), expr.span.hi());
 163                 let kind = ChainItemKind::MethodCall(segment.clone(), types, expressions.clone());
 164                 (kind, span)
 165             }
 166             ast::ExprKind::Field(ref nested, field) => {
 167                 let kind = if Self::is_tup_field_access(expr) {
 168                     ChainItemKind::TupleField(field, Self::is_tup_field_access(nested))
 169                 } else {
 170                     ChainItemKind::StructField(field)
 171                 };
 172                 let span = mk_sp(nested.span.hi(), field.span.hi());
 173                 (kind, span)
 174             }
 175             _ => return (ChainItemKind::Parent(expr.clone()), expr.span),
 176         };
 177
 178         // Remove comments from the span.
 179         let lo = context.snippet_provider.span_before(span, ".");
 180         (kind, mk_sp(lo, span.hi()))
 181     }
 182 }
 183
 184 impl Rewrite for ChainItem {
 185     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 186         let shape = shape.sub_width(self.tries)?;
 187         let rewrite = match self.kind {
 188             ChainItemKind::Parent(ref expr) => expr.rewrite(context, shape)?,
 189             ChainItemKind::MethodCall(ref segment, ref types, ref exprs) => {
 190                 Self::rewrite_method_call(segment.ident, types, exprs, self.span, context, shape)?
 191             }
 192             ChainItemKind::StructField(ident) => format!(".{}", rewrite_ident(context, ident)),
 193             ChainItemKind::TupleField(ident, nested) => format!(
 194                 "{}.{}",
 195                 if nested { " " } else { "" },
 196                 rewrite_ident(context, ident)
 197             ),
 198             ChainItemKind::Comment(ref comment, _) => {
 199                 rewrite_comment(comment, false, shape, context.config)?
 200             }
 201         };
 202         Some(format!("{}{}", rewrite, "?".repeat(self.tries)))
 203     }
 204 }
 205
 206 impl ChainItem {
 207     fn new(context: &RewriteContext, expr: &ast::Expr, tries: usize) -> ChainItem {
 208         let (kind, span) = ChainItemKind::from_ast(context, expr);
 209         ChainItem { kind, tries, span }
 210     }
 211
 212     fn comment(span: Span, comment: String, pos: CommentPosition) -> ChainItem {
 213         ChainItem {
 214             kind: ChainItemKind::Comment(comment, pos),
 215             tries: 0,
 216             span,
 217         }
 218     }
 219
 220     fn is_comment(&self) -> bool {
 221         match self.kind {
 222             ChainItemKind::Comment(..) => true,
 223             _ => false,
 224         }
 225     }
 226
 227     fn rewrite_method_call(
 228         method_name: ast::Ident,
 229         types: &[ast::GenericArg],
 230         args: &[ptr::P<ast::Expr>],
 231         span: Span,
 232         context: &RewriteContext,
 233         shape: Shape,
 234     ) -> Option<String> {
 235         let type_str = if types.is_empty() {
 236             String::new()
 237         } else {
 238             let type_list = types
 239                 .iter()
 240                 .map(|ty| ty.rewrite(context, shape))
 241                 .collect::<Option<Vec<_>>>()?;
 242
 243             format!("::<{}>", type_list.join(", "))
 244         };
 245         let callee_str = format!(".{}{}", rewrite_ident(context, method_name), type_str);
 246         rewrite_call(context, &callee_str, &args[1..], span, shape)
 247     }
 248 }
 249
 250 #[derive(Debug)]
 251 struct Chain {
 252     parent: ChainItem,
 253     children: Vec<ChainItem>,
 254 }
 255
 256 impl Chain {
 257     fn from_ast(expr: &ast::Expr, context: &RewriteContext) -> Chain {
 258         let subexpr_list = Self::make_subexpr_list(expr, context);
 259
 260         // Un-parse the expression tree into ChainItems
 261         let mut rev_children = vec![];
 262         let mut sub_tries = 0;
 263         for subexpr in &subexpr_list {
 264             match subexpr.node {
 265                 ast::ExprKind::Try(_) => sub_tries += 1,
 266                 _ => {
 267                     rev_children.push(ChainItem::new(context, subexpr, sub_tries));
 268                     sub_tries = 0;
 269                 }
 270             }
 271         }
 272
 273         fn is_tries(s: &str) -> bool {
 274             s.chars().all(|c| c == '?')
 275         }
 276
 277         fn is_post_comment(s: &str) -> bool {
 278             let comment_start_index = s.chars().position(|c| c == '/');
 279             if comment_start_index.is_none() {
 280                 return false;
 281             }
 282
 283             let newline_index = s.chars().position(|c| c == '\n');
 284             if newline_index.is_none() {
 285                 return true;
 286             }
 287
 288             comment_start_index.unwrap() < newline_index.unwrap()
 289         }
 290
 291         fn handle_post_comment(
 292             post_comment_span: Span,
 293             post_comment_snippet: &str,
 294             prev_span_end: &mut BytePos,
 295             children: &mut Vec<ChainItem>,
 296         ) {
 297             let white_spaces: &[_] = &[' ', '\t'];
 298             if post_comment_snippet
 299                 .trim_matches(white_spaces)
 300                 .starts_with('\n')
 301             {
 302                 // No post comment.
 303                 return;
 304             }
 305             let trimmed_snippet = trim_tries(post_comment_snippet);
 306             if is_post_comment(&trimmed_snippet) {
 307                 children.push(ChainItem::comment(
 308                     post_comment_span,
 309                     trimmed_snippet.trim().to_owned(),
 310                     CommentPosition::Back,
 311                 ));
 312                 *prev_span_end = post_comment_span.hi();
 313             }
 314         }
 315
 316         let parent = rev_children.pop().unwrap();
 317         let mut children = vec![];
 318         let mut prev_span_end = parent.span.hi();
 319         let mut iter = rev_children.into_iter().rev().peekable();
 320         if let Some(first_chain_item) = iter.peek() {
 321             let comment_span = mk_sp(prev_span_end, first_chain_item.span.lo());
 322             let comment_snippet = context.snippet(comment_span);
 323             if !is_tries(comment_snippet.trim()) {
 324                 handle_post_comment(
 325                     comment_span,
 326                     comment_snippet,
 327                     &mut prev_span_end,
 328                     &mut children,
 329                 );
 330             }
 331         }
 332         while let Some(chain_item) = iter.next() {
 333             let comment_snippet = context.snippet(chain_item.span);
 334             // FIXME: Figure out the way to get a correct span when converting `try!` to `?`.
 335             let handle_comment =
 336                 !(context.config.use_try_shorthand() || is_tries(comment_snippet.trim()));
 337
 338             // Pre-comment
 339             if handle_comment {
 340                 let pre_comment_span = mk_sp(prev_span_end, chain_item.span.lo());
 341                 let pre_comment_snippet = trim_tries(context.snippet(pre_comment_span));
 342                 let (pre_comment, _) = extract_pre_comment(&pre_comment_snippet);
 343                 match pre_comment {
 344                     Some(ref comment) if !comment.is_empty() => {
 345                         children.push(ChainItem::comment(
 346                             pre_comment_span,
 347                             comment.to_owned(),
 348                             CommentPosition::Top,
 349                         ));
 350                     }
 351                     _ => (),
 352                 }
 353             }
 354
 355             prev_span_end = chain_item.span.hi();
 356             children.push(chain_item);
 357
 358             // Post-comment
 359             if !handle_comment || iter.peek().is_none() {
 360                 continue;
 361             }
 362
 363             let next_lo = iter.peek().unwrap().span.lo();
 364             let post_comment_span = mk_sp(prev_span_end, next_lo);
 365             let post_comment_snippet = context.snippet(post_comment_span);
 366             handle_post_comment(
 367                 post_comment_span,
 368                 post_comment_snippet,
 369                 &mut prev_span_end,
 370                 &mut children,
 371             );
 372         }
 373
 374         Chain { parent, children }
 375     }
 376
 377     // Returns a Vec of the prefixes of the chain.
 378     // E.g., for input `a.b.c` we return [`a.b.c`, `a.b`, 'a']
 379     fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> Vec<ast::Expr> {
 380         let mut subexpr_list = vec![expr.clone()];
 381
 382         while let Some(subexpr) = Self::pop_expr_chain(subexpr_list.last().unwrap(), context) {
 383             subexpr_list.push(subexpr.clone());
 384         }
 385
 386         subexpr_list
 387     }
 388
 389     // Returns the expression's subexpression, if it exists. When the subexpr
 390     // is a try! macro, we'll convert it to shorthand when the option is set.
 391     fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
 392         match expr.node {
 393             ast::ExprKind::MethodCall(_, ref expressions) => {
 394                 Some(Self::convert_try(&expressions[0], context))
 395             }
 396             ast::ExprKind::Field(ref subexpr, _) | ast::ExprKind::Try(ref subexpr) => {
 397                 Some(Self::convert_try(subexpr, context))
 398             }
 399             _ => None,
 400         }
 401     }
 402
 403     fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
 404         match expr.node {
 405             ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
 406                 if let Some(subexpr) = convert_try_mac(mac, context) {
 407                     subexpr
 408                 } else {
 409                     expr.clone()
 410                 }
 411             }
 412             _ => expr.clone(),
 413         }
 414     }
 415 }
 416
 417 impl Rewrite for Chain {
 418     fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
 419         debug!("rewrite chain {:?} {:?}", self, shape);
 420
 421         let mut formatter = match context.config.indent_style() {
 422             IndentStyle::Block => Box::new(ChainFormatterBlock::new(self)) as Box<ChainFormatter>,
 423             IndentStyle::Visual => Box::new(ChainFormatterVisual::new(self)) as Box<ChainFormatter>,
 424         };
 425
 426         formatter.format_root(&self.parent, context, shape)?;
 427         if let Some(result) = formatter.pure_root() {
 428             return wrap_str(result, context.config.max_width(), shape);
 429         }
 430
 431         // Decide how to layout the rest of the chain.
 432         let child_shape = formatter.child_shape(context, shape)?;
 433
 434         formatter.format_children(context, child_shape)?;
 435         formatter.format_last_child(context, shape, child_shape)?;
 436
 437         let result = formatter.join_rewrites(context, child_shape)?;
 438         wrap_str(result, context.config.max_width(), shape)
 439     }
 440 }
 441
 442 // There are a few types for formatting chains. This is because there is a lot
 443 // in common between formatting with block vs visual indent, but they are
 444 // different enough that branching on the indent all over the place gets ugly.
 445 // Anything that can format a chain is a ChainFormatter.
 446 trait ChainFormatter {
 447     // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
 448     // Root is the parent plus any other chain items placed on the first line to
 449     // avoid an orphan. E.g.,
 450     // ```ignore
 451     // foo.bar
 452     //     .baz()
 453     // ```
 454     // If `bar` were not part of the root, then foo would be orphaned and 'float'.
 455     fn format_root(
 456         &mut self,
 457         parent: &ChainItem,
 458         context: &RewriteContext,
 459         shape: Shape,
 460     ) -> Option<()>;
 461     fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape>;
 462     fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()>;
 463     fn format_last_child(
 464         &mut self,
 465         context: &RewriteContext,
 466         shape: Shape,
 467         child_shape: Shape,
 468     ) -> Option<()>;
 469     fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String>;
 470     // Returns `Some` if the chain is only a root, None otherwise.
 471     fn pure_root(&mut self) -> Option<String>;
 472 }
 473
 474 // Data and behaviour that is shared by both chain formatters. The concrete
 475 // formatters can delegate much behaviour to `ChainFormatterShared`.
 476 struct ChainFormatterShared<'a> {
 477     // The current working set of child items.
 478     children: &'a [ChainItem],
 479     // The current rewrites of items (includes trailing `?`s, but not any way to
 480     // connect the rewrites together).
 481     rewrites: Vec<String>,
 482     // Whether the chain can fit on one line.
 483     fits_single_line: bool,
 484     // The number of children in the chain. This is not equal to `self.children.len()`
 485     // because `self.children` will change size as we process the chain.
 486     child_count: usize,
 487 }
 488
 489 impl<'a> ChainFormatterShared<'a> {
 490     fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
 491         ChainFormatterShared {
 492             children: &chain.children,
 493             rewrites: Vec::with_capacity(chain.children.len() + 1),
 494             fits_single_line: false,
 495             child_count: chain.children.len(),
 496         }
 497     }
 498
 499     fn pure_root(&mut self) -> Option<String> {
 500         if self.children.is_empty() {
 501             assert_eq!(self.rewrites.len(), 1);
 502             Some(self.rewrites.pop().unwrap())
 503         } else {
 504             None
 505         }
 506     }
 507
 508     // Rewrite the last child. The last child of a chain requires special treatment. We need to
 509     // know whether 'overflowing' the last child make a better formatting:
 510     //
 511     // A chain with overflowing the last child:
 512     // ```ignore
 513     // parent.child1.child2.last_child(
 514     //     a,
 515     //     b,
 516     //     c,
 517     // )
 518     // ```
 519     //
 520     // A chain without overflowing the last child (in vertical layout):
 521     // ```ignore
 522     // parent
 523     //     .child1
 524     //     .child2
 525     //     .last_child(a, b, c)
 526     // ```
 527     //
 528     // In particular, overflowing is effective when the last child is a method with a multi-lined
 529     // block-like argument (e.g. closure):
 530     // ```ignore
 531     // parent.child1.child2.last_child(|a, b, c| {
 532     //     let x = foo(a, b, c);
 533     //     let y = bar(a, b, c);
 534     //
 535     //     // ...
 536     //
 537     //     result
 538     // })
 539     // ```
 540     fn format_last_child(
 541         &mut self,
 542         may_extend: bool,
 543         context: &RewriteContext,
 544         shape: Shape,
 545         child_shape: Shape,
 546     ) -> Option<()> {
 547         let last = self.children.last()?;
 548         let extendable = may_extend && last_line_extendable(&self.rewrites[0]);
 549         let prev_last_line_width = last_line_width(&self.rewrites[0]);
 550
 551         // Total of all items excluding the last.
 552         let almost_total = if extendable {
 553             prev_last_line_width
 554         } else {
 555             self.rewrites.iter().fold(0, |a, b| a + b.len())
 556         } + last.tries;
 557         let one_line_budget = if self.child_count == 1 {
 558             shape.width
 559         } else {
 560             min(shape.width, context.config.width_heuristics().chain_width)
 561         }
 562         .saturating_sub(almost_total);
 563
 564         let all_in_one_line = !self.children.iter().any(ChainItem::is_comment)
 565             && self.rewrites.iter().all(|s| !s.contains('\n'))
 566             && one_line_budget > 0;
 567         let last_shape = if all_in_one_line {
 568             shape.sub_width(last.tries)?
 569         } else if extendable {
 570             child_shape.sub_width(last.tries)?
 571         } else {
 572             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 573         };
 574
 575         let mut last_subexpr_str = None;
 576         if all_in_one_line || extendable {
 577             // First we try to 'overflow' the last child and see if it looks better than using
 578             // vertical layout.
 579             let one_line_shape = if context.use_block_indent() {
 580                 last_shape.offset_left(almost_total)
 581             } else {
 582                 last_shape
 583                     .visual_indent(almost_total)
 584                     .sub_width(almost_total)
 585             };
 586
 587             if let Some(one_line_shape) = one_line_shape {
 588                 if let Some(rw) = last.rewrite(context, one_line_shape) {
 589                     // We allow overflowing here only if both of the following conditions match:
 590                     // 1. The entire chain fits in a single line except the last child.
 591                     // 2. `last_child_str.lines().count() >= 5`.
 592                     let line_count = rw.lines().count();
 593                     let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
 594                     if could_fit_single_line && line_count >= 5 {
 595                         last_subexpr_str = Some(rw);
 596                         self.fits_single_line = all_in_one_line;
 597                     } else {
 598                         // We could not know whether overflowing is better than using vertical
 599                         // layout, just by looking at the overflowed rewrite. Now we rewrite the
 600                         // last child on its own line, and compare two rewrites to choose which is
 601                         // better.
 602                         let last_shape = child_shape
 603                             .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
 604                         match last.rewrite(context, last_shape) {
 605                             Some(ref new_rw) if !could_fit_single_line => {
 606                                 last_subexpr_str = Some(new_rw.clone());
 607                             }
 608                             Some(ref new_rw) if new_rw.lines().count() >= line_count => {
 609                                 last_subexpr_str = Some(rw);
 610                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 611                             }
 612                             new_rw @ Some(..) => {
 613                                 last_subexpr_str = new_rw;
 614                             }
 615                             _ => {
 616                                 last_subexpr_str = Some(rw);
 617                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 618                             }
 619                         }
 620                     }
 621                 }
 622             }
 623         }
 624
 625         let last_shape = if context.use_block_indent() {
 626             last_shape
 627         } else {
 628             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 629         };
 630
 631         last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
 632         self.rewrites.push(last_subexpr_str?);
 633         Some(())
 634     }
 635
 636     fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
 637         let connector = if self.fits_single_line {
 638             // Yay, we can put everything on one line.
 639             Cow::from("")
 640         } else {
 641             // Use new lines.
 642             if *context.force_one_line_chain.borrow() {
 643                 return None;
 644             }
 645             child_shape.to_string_with_newline(context.config)
 646         };
 647
 648         let mut rewrite_iter = self.rewrites.iter();
 649         let mut result = rewrite_iter.next().unwrap().clone();
 650         let children_iter = self.children.iter();
 651         let iter = rewrite_iter.zip(children_iter);
 652
 653         for (rewrite, chain_item) in iter {
 654             match chain_item.kind {
 655                 ChainItemKind::Comment(_, CommentPosition::Back) => result.push(' '),
 656                 ChainItemKind::Comment(_, CommentPosition::Top) => result.push_str(&connector),
 657                 _ => result.push_str(&connector),
 658             }
 659             result.push_str(&rewrite);
 660         }
 661
 662         Some(result)
 663     }
 664 }
 665
 666 // Formats a chain using block indent.
 667 struct ChainFormatterBlock<'a> {
 668     shared: ChainFormatterShared<'a>,
 669     root_ends_with_block: bool,
 670 }
 671
 672 impl<'a> ChainFormatterBlock<'a> {
 673     fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
 674         ChainFormatterBlock {
 675             shared: ChainFormatterShared::new(chain),
 676             root_ends_with_block: false,
 677         }
 678     }
 679 }
 680
 681 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
 682     fn format_root(
 683         &mut self,
 684         parent: &ChainItem,
 685         context: &RewriteContext,
 686         shape: Shape,
 687     ) -> Option<()> {
 688         let mut root_rewrite: String = parent.rewrite(context, shape)?;
 689
 690         let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
 691         let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
 692
 693         while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
 694             let item = &self.shared.children[0];
 695             if let ChainItemKind::Comment(..) = item.kind {
 696                 break;
 697             }
 698             let shape = shape.offset_left(root_rewrite.len())?;
 699             match &item.rewrite(context, shape) {
 700                 Some(rewrite) => root_rewrite.push_str(rewrite),
 701                 None => break,
 702             }
 703
 704             root_ends_with_block = last_line_extendable(&root_rewrite);
 705
 706             self.shared.children = &self.shared.children[1..];
 707             if self.shared.children.is_empty() {
 708                 break;
 709             }
 710         }
 711         self.shared.rewrites.push(root_rewrite);
 712         self.root_ends_with_block = root_ends_with_block;
 713         Some(())
 714     }
 715
 716     fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape> {
 717         Some(
 718             if self.root_ends_with_block {
 719                 shape.block_indent(0)
 720             } else {
 721                 shape.block_indent(context.config.tab_spaces())
 722             }
 723             .with_max_width(context.config),
 724         )
 725     }
 726
 727     fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()> {
 728         for item in &self.shared.children[..self.shared.children.len() - 1] {
 729             let rewrite = item.rewrite(context, child_shape)?;
 730             self.shared.rewrites.push(rewrite);
 731         }
 732         Some(())
 733     }
 734
 735     fn format_last_child(
 736         &mut self,
 737         context: &RewriteContext,
 738         shape: Shape,
 739         child_shape: Shape,
 740     ) -> Option<()> {
 741         self.shared
 742             .format_last_child(true, context, shape, child_shape)
 743     }
 744
 745     fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
 746         self.shared.join_rewrites(context, child_shape)
 747     }
 748
 749     fn pure_root(&mut self) -> Option<String> {
 750         self.shared.pure_root()
 751     }
 752 }
 753
 754 // Format a chain using visual indent.
 755 struct ChainFormatterVisual<'a> {
 756     shared: ChainFormatterShared<'a>,
 757     // The extra offset from the chain's shape to the position of the `.`
 758     offset: usize,
 759 }
 760
 761 impl<'a> ChainFormatterVisual<'a> {
 762     fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
 763         ChainFormatterVisual {
 764             shared: ChainFormatterShared::new(chain),
 765             offset: 0,
 766         }
 767     }
 768 }
 769
 770 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
 771     fn format_root(
 772         &mut self,
 773         parent: &ChainItem,
 774         context: &RewriteContext,
 775         shape: Shape,
 776     ) -> Option<()> {
 777         let parent_shape = shape.visual_indent(0);
 778         let mut root_rewrite = parent.rewrite(context, parent_shape)?;
 779         let multiline = root_rewrite.contains('\n');
 780         self.offset = if multiline {
 781             last_line_width(&root_rewrite).saturating_sub(shape.used_width())
 782         } else {
 783             trimmed_last_line_width(&root_rewrite)
 784         };
 785
 786         if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
 787             let item = &self.shared.children[0];
 788             if let ChainItemKind::Comment(..) = item.kind {
 789                 self.shared.rewrites.push(root_rewrite);
 790                 return Some(());
 791             }
 792             let child_shape = parent_shape
 793                 .visual_indent(self.offset)
 794                 .sub_width(self.offset)?;
 795             let rewrite = item.rewrite(context, child_shape)?;
 796             match wrap_str(rewrite, context.config.max_width(), shape) {
 797                 Some(rewrite) => root_rewrite.push_str(&rewrite),
 798                 None => {
 799                     // We couldn't fit in at the visual indent, try the last
 800                     // indent.
 801                     let rewrite = item.rewrite(context, parent_shape)?;
 802                     root_rewrite.push_str(&rewrite);
 803                     self.offset = 0;
 804                 }
 805             }
 806
 807             self.shared.children = &self.shared.children[1..];
 808         }
 809
 810         self.shared.rewrites.push(root_rewrite);
 811         Some(())
 812     }
 813
 814     fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape> {
 815         shape
 816             .with_max_width(context.config)
 817             .offset_left(self.offset)
 818             .map(|s| s.visual_indent(0))
 819     }
 820
 821     fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()> {
 822         for item in &self.shared.children[..self.shared.children.len() - 1] {
 823             let rewrite = item.rewrite(context, child_shape)?;
 824             self.shared.rewrites.push(rewrite);
 825         }
 826         Some(())
 827     }
 828
 829     fn format_last_child(
 830         &mut self,
 831         context: &RewriteContext,
 832         shape: Shape,
 833         child_shape: Shape,
 834     ) -> Option<()> {
 835         self.shared
 836             .format_last_child(false, context, shape, child_shape)
 837     }
 838
 839     fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
 840         self.shared.join_rewrites(context, child_shape)
 841     }
 842
 843     fn pure_root(&mut self) -> Option<String> {
 844         self.shared.pure_root()
 845     }
 846 }
 847
 848 /// Remove try operators (`?`s) that appear in the given string. If removing
 849 /// them leaves an empty line, remove that line as well unless it is the first
 850 /// line (we need the first newline for detecting pre/post comment).
 851 fn trim_tries(s: &str) -> String {
 852     let mut result = String::with_capacity(s.len());
 853     let mut line_buffer = String::with_capacity(s.len());
 854     for (kind, rich_char) in CharClasses::new(s.chars()) {
 855         match rich_char.get_char() {
 856             '\n' => {
 857                 if result.is_empty() || !line_buffer.trim().is_empty() {
 858                     result.push_str(&line_buffer);
 859                     result.push('\n')
 860                 }
 861                 line_buffer.clear();
 862             }
 863             '?' if kind == FullCodeCharKind::Normal => continue,
 864             c => line_buffer.push(c),
 865         }
 866     }
 867     if !line_buffer.trim().is_empty() {
 868         result.push_str(&line_buffer);
 869     }
 870     result
 871 }