src/tools/rustfmt/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::{symbol, BytePos, Span};
  63
  64 use crate::comment::{rewrite_comment, CharClasses, FullCodeCharKind, RichChar};
  65 use crate::config::{IndentStyle, Version};
  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(symbol::Ident),
 120     TupleField(symbol::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 && context.config.version() == Version::One {
 204                     " "
 205                 } else {
 206                     ""
 207                 },
 208                 rewrite_ident(context, ident)
 209             ),
 210             ChainItemKind::Await => ".await".to_owned(),
 211             ChainItemKind::Comment(ref comment, _) => {
 212                 rewrite_comment(comment, false, shape, context.config)?
 213             }
 214         };
 215         Some(format!("{}{}", rewrite, "?".repeat(self.tries)))
 216     }
 217 }
 218
 219 impl ChainItem {
 220     fn new(context: &RewriteContext<'_>, expr: &ast::Expr, tries: usize) -> ChainItem {
 221         let (kind, span) = ChainItemKind::from_ast(context, expr);
 222         ChainItem { kind, tries, span }
 223     }
 224
 225     fn comment(span: Span, comment: String, pos: CommentPosition) -> ChainItem {
 226         ChainItem {
 227             kind: ChainItemKind::Comment(comment, pos),
 228             tries: 0,
 229             span,
 230         }
 231     }
 232
 233     fn is_comment(&self) -> bool {
 234         match self.kind {
 235             ChainItemKind::Comment(..) => true,
 236             _ => false,
 237         }
 238     }
 239
 240     fn rewrite_method_call(
 241         method_name: symbol::Ident,
 242         types: &[ast::GenericArg],
 243         args: &[ptr::P<ast::Expr>],
 244         span: Span,
 245         context: &RewriteContext<'_>,
 246         shape: Shape,
 247     ) -> Option<String> {
 248         let type_str = if types.is_empty() {
 249             String::new()
 250         } else {
 251             let type_list = types
 252                 .iter()
 253                 .map(|ty| ty.rewrite(context, shape))
 254                 .collect::<Option<Vec<_>>>()?;
 255
 256             format!("::<{}>", type_list.join(", "))
 257         };
 258         let callee_str = format!(".{}{}", rewrite_ident(context, method_name), type_str);
 259         rewrite_call(context, &callee_str, &args[1..], span, shape)
 260     }
 261 }
 262
 263 #[derive(Debug)]
 264 struct Chain {
 265     parent: ChainItem,
 266     children: Vec<ChainItem>,
 267 }
 268
 269 impl Chain {
 270     fn from_ast(expr: &ast::Expr, context: &RewriteContext<'_>) -> Chain {
 271         let subexpr_list = Self::make_subexpr_list(expr, context);
 272
 273         // Un-parse the expression tree into ChainItems
 274         let mut rev_children = vec![];
 275         let mut sub_tries = 0;
 276         for subexpr in &subexpr_list {
 277             match subexpr.kind {
 278                 ast::ExprKind::Try(_) => sub_tries += 1,
 279                 _ => {
 280                     rev_children.push(ChainItem::new(context, subexpr, sub_tries));
 281                     sub_tries = 0;
 282                 }
 283             }
 284         }
 285
 286         fn is_tries(s: &str) -> bool {
 287             s.chars().all(|c| c == '?')
 288         }
 289
 290         fn is_post_comment(s: &str) -> bool {
 291             let comment_start_index = s.chars().position(|c| c == '/');
 292             if comment_start_index.is_none() {
 293                 return false;
 294             }
 295
 296             let newline_index = s.chars().position(|c| c == '\n');
 297             if newline_index.is_none() {
 298                 return true;
 299             }
 300
 301             comment_start_index.unwrap() < newline_index.unwrap()
 302         }
 303
 304         fn handle_post_comment(
 305             post_comment_span: Span,
 306             post_comment_snippet: &str,
 307             prev_span_end: &mut BytePos,
 308             children: &mut Vec<ChainItem>,
 309         ) {
 310             let white_spaces: &[_] = &[' ', '\t'];
 311             if post_comment_snippet
 312                 .trim_matches(white_spaces)
 313                 .starts_with('\n')
 314             {
 315                 // No post comment.
 316                 return;
 317             }
 318             let trimmed_snippet = trim_tries(post_comment_snippet);
 319             if is_post_comment(&trimmed_snippet) {
 320                 children.push(ChainItem::comment(
 321                     post_comment_span,
 322                     trimmed_snippet.trim().to_owned(),
 323                     CommentPosition::Back,
 324                 ));
 325                 *prev_span_end = post_comment_span.hi();
 326             }
 327         }
 328
 329         let parent = rev_children.pop().unwrap();
 330         let mut children = vec![];
 331         let mut prev_span_end = parent.span.hi();
 332         let mut iter = rev_children.into_iter().rev().peekable();
 333         if let Some(first_chain_item) = iter.peek() {
 334             let comment_span = mk_sp(prev_span_end, first_chain_item.span.lo());
 335             let comment_snippet = context.snippet(comment_span);
 336             if !is_tries(comment_snippet.trim()) {
 337                 handle_post_comment(
 338                     comment_span,
 339                     comment_snippet,
 340                     &mut prev_span_end,
 341                     &mut children,
 342                 );
 343             }
 344         }
 345         while let Some(chain_item) = iter.next() {
 346             let comment_snippet = context.snippet(chain_item.span);
 347             // FIXME: Figure out the way to get a correct span when converting `try!` to `?`.
 348             let handle_comment =
 349                 !(context.config.use_try_shorthand() || is_tries(comment_snippet.trim()));
 350
 351             // Pre-comment
 352             if handle_comment {
 353                 let pre_comment_span = mk_sp(prev_span_end, chain_item.span.lo());
 354                 let pre_comment_snippet = trim_tries(context.snippet(pre_comment_span));
 355                 let (pre_comment, _) = extract_pre_comment(&pre_comment_snippet);
 356                 match pre_comment {
 357                     Some(ref comment) if !comment.is_empty() => {
 358                         children.push(ChainItem::comment(
 359                             pre_comment_span,
 360                             comment.to_owned(),
 361                             CommentPosition::Top,
 362                         ));
 363                     }
 364                     _ => (),
 365                 }
 366             }
 367
 368             prev_span_end = chain_item.span.hi();
 369             children.push(chain_item);
 370
 371             // Post-comment
 372             if !handle_comment || iter.peek().is_none() {
 373                 continue;
 374             }
 375
 376             let next_lo = iter.peek().unwrap().span.lo();
 377             let post_comment_span = mk_sp(prev_span_end, next_lo);
 378             let post_comment_snippet = context.snippet(post_comment_span);
 379             handle_post_comment(
 380                 post_comment_span,
 381                 post_comment_snippet,
 382                 &mut prev_span_end,
 383                 &mut children,
 384             );
 385         }
 386
 387         Chain { parent, children }
 388     }
 389
 390     // Returns a Vec of the prefixes of the chain.
 391     // E.g., for input `a.b.c` we return [`a.b.c`, `a.b`, 'a']
 392     fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext<'_>) -> Vec<ast::Expr> {
 393         let mut subexpr_list = vec![expr.clone()];
 394
 395         while let Some(subexpr) = Self::pop_expr_chain(subexpr_list.last().unwrap(), context) {
 396             subexpr_list.push(subexpr.clone());
 397         }
 398
 399         subexpr_list
 400     }
 401
 402     // Returns the expression's subexpression, if it exists. When the subexpr
 403     // is a try! macro, we'll convert it to shorthand when the option is set.
 404     fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext<'_>) -> Option<ast::Expr> {
 405         match expr.kind {
 406             ast::ExprKind::MethodCall(_, ref expressions, _) => {
 407                 Some(Self::convert_try(&expressions[0], context))
 408             }
 409             ast::ExprKind::Field(ref subexpr, _)
 410             | ast::ExprKind::Try(ref subexpr)
 411             | ast::ExprKind::Await(ref subexpr) => Some(Self::convert_try(subexpr, context)),
 412             _ => None,
 413         }
 414     }
 415
 416     fn convert_try(expr: &ast::Expr, context: &RewriteContext<'_>) -> ast::Expr {
 417         match expr.kind {
 418             ast::ExprKind::MacCall(ref mac) if context.config.use_try_shorthand() => {
 419                 if let Some(subexpr) = convert_try_mac(mac, context) {
 420                     subexpr
 421                 } else {
 422                     expr.clone()
 423                 }
 424             }
 425             _ => expr.clone(),
 426         }
 427     }
 428 }
 429
 430 impl Rewrite for Chain {
 431     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 432         debug!("rewrite chain {:?} {:?}", self, shape);
 433
 434         let mut formatter = match context.config.indent_style() {
 435             IndentStyle::Block => {
 436                 Box::new(ChainFormatterBlock::new(self)) as Box<dyn ChainFormatter>
 437             }
 438             IndentStyle::Visual => {
 439                 Box::new(ChainFormatterVisual::new(self)) as Box<dyn ChainFormatter>
 440             }
 441         };
 442
 443         formatter.format_root(&self.parent, context, shape)?;
 444         if let Some(result) = formatter.pure_root() {
 445             return wrap_str(result, context.config.max_width(), shape);
 446         }
 447
 448         // Decide how to layout the rest of the chain.
 449         let child_shape = formatter.child_shape(context, shape)?;
 450
 451         formatter.format_children(context, child_shape)?;
 452         formatter.format_last_child(context, shape, child_shape)?;
 453
 454         let result = formatter.join_rewrites(context, child_shape)?;
 455         wrap_str(result, context.config.max_width(), shape)
 456     }
 457 }
 458
 459 // There are a few types for formatting chains. This is because there is a lot
 460 // in common between formatting with block vs visual indent, but they are
 461 // different enough that branching on the indent all over the place gets ugly.
 462 // Anything that can format a chain is a ChainFormatter.
 463 trait ChainFormatter {
 464     // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
 465     // Root is the parent plus any other chain items placed on the first line to
 466     // avoid an orphan. E.g.,
 467     // ```text
 468     // foo.bar
 469     //     .baz()
 470     // ```
 471     // If `bar` were not part of the root, then foo would be orphaned and 'float'.
 472     fn format_root(
 473         &mut self,
 474         parent: &ChainItem,
 475         context: &RewriteContext<'_>,
 476         shape: Shape,
 477     ) -> Option<()>;
 478     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape>;
 479     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()>;
 480     fn format_last_child(
 481         &mut self,
 482         context: &RewriteContext<'_>,
 483         shape: Shape,
 484         child_shape: Shape,
 485     ) -> Option<()>;
 486     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String>;
 487     // Returns `Some` if the chain is only a root, None otherwise.
 488     fn pure_root(&mut self) -> Option<String>;
 489 }
 490
 491 // Data and behaviour that is shared by both chain formatters. The concrete
 492 // formatters can delegate much behaviour to `ChainFormatterShared`.
 493 struct ChainFormatterShared<'a> {
 494     // The current working set of child items.
 495     children: &'a [ChainItem],
 496     // The current rewrites of items (includes trailing `?`s, but not any way to
 497     // connect the rewrites together).
 498     rewrites: Vec<String>,
 499     // Whether the chain can fit on one line.
 500     fits_single_line: bool,
 501     // The number of children in the chain. This is not equal to `self.children.len()`
 502     // because `self.children` will change size as we process the chain.
 503     child_count: usize,
 504 }
 505
 506 impl<'a> ChainFormatterShared<'a> {
 507     fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
 508         ChainFormatterShared {
 509             children: &chain.children,
 510             rewrites: Vec::with_capacity(chain.children.len() + 1),
 511             fits_single_line: false,
 512             child_count: chain.children.len(),
 513         }
 514     }
 515
 516     fn pure_root(&mut self) -> Option<String> {
 517         if self.children.is_empty() {
 518             assert_eq!(self.rewrites.len(), 1);
 519             Some(self.rewrites.pop().unwrap())
 520         } else {
 521             None
 522         }
 523     }
 524
 525     // Rewrite the last child. The last child of a chain requires special treatment. We need to
 526     // know whether 'overflowing' the last child make a better formatting:
 527     //
 528     // A chain with overflowing the last child:
 529     // ```text
 530     // parent.child1.child2.last_child(
 531     //     a,
 532     //     b,
 533     //     c,
 534     // )
 535     // ```
 536     //
 537     // A chain without overflowing the last child (in vertical layout):
 538     // ```text
 539     // parent
 540     //     .child1
 541     //     .child2
 542     //     .last_child(a, b, c)
 543     // ```
 544     //
 545     // In particular, overflowing is effective when the last child is a method with a multi-lined
 546     // block-like argument (e.g., closure):
 547     // ```text
 548     // parent.child1.child2.last_child(|a, b, c| {
 549     //     let x = foo(a, b, c);
 550     //     let y = bar(a, b, c);
 551     //
 552     //     // ...
 553     //
 554     //     result
 555     // })
 556     // ```
 557     fn format_last_child(
 558         &mut self,
 559         may_extend: bool,
 560         context: &RewriteContext<'_>,
 561         shape: Shape,
 562         child_shape: Shape,
 563     ) -> Option<()> {
 564         let last = self.children.last()?;
 565         let extendable = may_extend && last_line_extendable(&self.rewrites[0]);
 566         let prev_last_line_width = last_line_width(&self.rewrites[0]);
 567
 568         // Total of all items excluding the last.
 569         let almost_total = if extendable {
 570             prev_last_line_width
 571         } else {
 572             self.rewrites
 573                 .iter()
 574                 .map(|rw| utils::unicode_str_width(&rw))
 575                 .sum()
 576         } + last.tries;
 577         let one_line_budget = if self.child_count == 1 {
 578             shape.width
 579         } else {
 580             min(shape.width, context.config.chain_width())
 581         }
 582         .saturating_sub(almost_total);
 583
 584         let all_in_one_line = !self.children.iter().any(ChainItem::is_comment)
 585             && self.rewrites.iter().all(|s| !s.contains('\n'))
 586             && one_line_budget > 0;
 587         let last_shape = if all_in_one_line {
 588             shape.sub_width(last.tries)?
 589         } else if extendable {
 590             child_shape.sub_width(last.tries)?
 591         } else {
 592             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 593         };
 594
 595         let mut last_subexpr_str = None;
 596         if all_in_one_line || extendable {
 597             // First we try to 'overflow' the last child and see if it looks better than using
 598             // vertical layout.
 599             let one_line_shape = if context.use_block_indent() {
 600                 last_shape.offset_left(almost_total)
 601             } else {
 602                 last_shape
 603                     .visual_indent(almost_total)
 604                     .sub_width(almost_total)
 605             };
 606
 607             if let Some(one_line_shape) = one_line_shape {
 608                 if let Some(rw) = last.rewrite(context, one_line_shape) {
 609                     // We allow overflowing here only if both of the following conditions match:
 610                     // 1. The entire chain fits in a single line except the last child.
 611                     // 2. `last_child_str.lines().count() >= 5`.
 612                     let line_count = rw.lines().count();
 613                     let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
 614                     if could_fit_single_line && line_count >= 5 {
 615                         last_subexpr_str = Some(rw);
 616                         self.fits_single_line = all_in_one_line;
 617                     } else {
 618                         // We could not know whether overflowing is better than using vertical
 619                         // layout, just by looking at the overflowed rewrite. Now we rewrite the
 620                         // last child on its own line, and compare two rewrites to choose which is
 621                         // better.
 622                         let last_shape = child_shape
 623                             .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
 624                         match last.rewrite(context, last_shape) {
 625                             Some(ref new_rw) if !could_fit_single_line => {
 626                                 last_subexpr_str = Some(new_rw.clone());
 627                             }
 628                             Some(ref new_rw) if new_rw.lines().count() >= line_count => {
 629                                 last_subexpr_str = Some(rw);
 630                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 631                             }
 632                             new_rw @ Some(..) => {
 633                                 last_subexpr_str = new_rw;
 634                             }
 635                             _ => {
 636                                 last_subexpr_str = Some(rw);
 637                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 638                             }
 639                         }
 640                     }
 641                 }
 642             }
 643         }
 644
 645         let last_shape = if context.use_block_indent() {
 646             last_shape
 647         } else {
 648             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 649         };
 650
 651         last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
 652         self.rewrites.push(last_subexpr_str?);
 653         Some(())
 654     }
 655
 656     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 657         let connector = if self.fits_single_line {
 658             // Yay, we can put everything on one line.
 659             Cow::from("")
 660         } else {
 661             // Use new lines.
 662             if context.force_one_line_chain.get() {
 663                 return None;
 664             }
 665             child_shape.to_string_with_newline(context.config)
 666         };
 667
 668         let mut rewrite_iter = self.rewrites.iter();
 669         let mut result = rewrite_iter.next().unwrap().clone();
 670         let children_iter = self.children.iter();
 671         let iter = rewrite_iter.zip(children_iter);
 672
 673         for (rewrite, chain_item) in iter {
 674             match chain_item.kind {
 675                 ChainItemKind::Comment(_, CommentPosition::Back) => result.push(' '),
 676                 ChainItemKind::Comment(_, CommentPosition::Top) => result.push_str(&connector),
 677                 _ => result.push_str(&connector),
 678             }
 679             result.push_str(&rewrite);
 680         }
 681
 682         Some(result)
 683     }
 684 }
 685
 686 // Formats a chain using block indent.
 687 struct ChainFormatterBlock<'a> {
 688     shared: ChainFormatterShared<'a>,
 689     root_ends_with_block: bool,
 690 }
 691
 692 impl<'a> ChainFormatterBlock<'a> {
 693     fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
 694         ChainFormatterBlock {
 695             shared: ChainFormatterShared::new(chain),
 696             root_ends_with_block: false,
 697         }
 698     }
 699 }
 700
 701 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
 702     fn format_root(
 703         &mut self,
 704         parent: &ChainItem,
 705         context: &RewriteContext<'_>,
 706         shape: Shape,
 707     ) -> Option<()> {
 708         let mut root_rewrite: String = parent.rewrite(context, shape)?;
 709
 710         let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
 711         let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
 712
 713         while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
 714             let item = &self.shared.children[0];
 715             if let ChainItemKind::Comment(..) = item.kind {
 716                 break;
 717             }
 718             let shape = shape.offset_left(root_rewrite.len())?;
 719             match &item.rewrite(context, shape) {
 720                 Some(rewrite) => root_rewrite.push_str(rewrite),
 721                 None => break,
 722             }
 723
 724             root_ends_with_block = last_line_extendable(&root_rewrite);
 725
 726             self.shared.children = &self.shared.children[1..];
 727             if self.shared.children.is_empty() {
 728                 break;
 729             }
 730         }
 731         self.shared.rewrites.push(root_rewrite);
 732         self.root_ends_with_block = root_ends_with_block;
 733         Some(())
 734     }
 735
 736     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
 737         Some(
 738             if self.root_ends_with_block {
 739                 shape.block_indent(0)
 740             } else {
 741                 shape.block_indent(context.config.tab_spaces())
 742             }
 743             .with_max_width(context.config),
 744         )
 745     }
 746
 747     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
 748         for item in &self.shared.children[..self.shared.children.len() - 1] {
 749             let rewrite = item.rewrite(context, child_shape)?;
 750             self.shared.rewrites.push(rewrite);
 751         }
 752         Some(())
 753     }
 754
 755     fn format_last_child(
 756         &mut self,
 757         context: &RewriteContext<'_>,
 758         shape: Shape,
 759         child_shape: Shape,
 760     ) -> Option<()> {
 761         self.shared
 762             .format_last_child(true, context, shape, child_shape)
 763     }
 764
 765     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 766         self.shared.join_rewrites(context, child_shape)
 767     }
 768
 769     fn pure_root(&mut self) -> Option<String> {
 770         self.shared.pure_root()
 771     }
 772 }
 773
 774 // Format a chain using visual indent.
 775 struct ChainFormatterVisual<'a> {
 776     shared: ChainFormatterShared<'a>,
 777     // The extra offset from the chain's shape to the position of the `.`
 778     offset: usize,
 779 }
 780
 781 impl<'a> ChainFormatterVisual<'a> {
 782     fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
 783         ChainFormatterVisual {
 784             shared: ChainFormatterShared::new(chain),
 785             offset: 0,
 786         }
 787     }
 788 }
 789
 790 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
 791     fn format_root(
 792         &mut self,
 793         parent: &ChainItem,
 794         context: &RewriteContext<'_>,
 795         shape: Shape,
 796     ) -> Option<()> {
 797         let parent_shape = shape.visual_indent(0);
 798         let mut root_rewrite = parent.rewrite(context, parent_shape)?;
 799         let multiline = root_rewrite.contains('\n');
 800         self.offset = if multiline {
 801             last_line_width(&root_rewrite).saturating_sub(shape.used_width())
 802         } else {
 803             trimmed_last_line_width(&root_rewrite)
 804         };
 805
 806         if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
 807             let item = &self.shared.children[0];
 808             if let ChainItemKind::Comment(..) = item.kind {
 809                 self.shared.rewrites.push(root_rewrite);
 810                 return Some(());
 811             }
 812             let child_shape = parent_shape
 813                 .visual_indent(self.offset)
 814                 .sub_width(self.offset)?;
 815             let rewrite = item.rewrite(context, child_shape)?;
 816             match wrap_str(rewrite, context.config.max_width(), shape) {
 817                 Some(rewrite) => root_rewrite.push_str(&rewrite),
 818                 None => {
 819                     // We couldn't fit in at the visual indent, try the last
 820                     // indent.
 821                     let rewrite = item.rewrite(context, parent_shape)?;
 822                     root_rewrite.push_str(&rewrite);
 823                     self.offset = 0;
 824                 }
 825             }
 826
 827             self.shared.children = &self.shared.children[1..];
 828         }
 829
 830         self.shared.rewrites.push(root_rewrite);
 831         Some(())
 832     }
 833
 834     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
 835         shape
 836             .with_max_width(context.config)
 837             .offset_left(self.offset)
 838             .map(|s| s.visual_indent(0))
 839     }
 840
 841     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
 842         for item in &self.shared.children[..self.shared.children.len() - 1] {
 843             let rewrite = item.rewrite(context, child_shape)?;
 844             self.shared.rewrites.push(rewrite);
 845         }
 846         Some(())
 847     }
 848
 849     fn format_last_child(
 850         &mut self,
 851         context: &RewriteContext<'_>,
 852         shape: Shape,
 853         child_shape: Shape,
 854     ) -> Option<()> {
 855         self.shared
 856             .format_last_child(false, context, shape, child_shape)
 857     }
 858
 859     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 860         self.shared.join_rewrites(context, child_shape)
 861     }
 862
 863     fn pure_root(&mut self) -> Option<String> {
 864         self.shared.pure_root()
 865     }
 866 }
 867
 868 /// Removes try operators (`?`s) that appear in the given string. If removing
 869 /// them leaves an empty line, remove that line as well unless it is the first
 870 /// line (we need the first newline for detecting pre/post comment).
 871 fn trim_tries(s: &str) -> String {
 872     let mut result = String::with_capacity(s.len());
 873     let mut line_buffer = String::with_capacity(s.len());
 874     for (kind, rich_char) in CharClasses::new(s.chars()) {
 875         match rich_char.get_char() {
 876             '\n' => {
 877                 if result.is_empty() || !line_buffer.trim().is_empty() {
 878                     result.push_str(&line_buffer);
 879                     result.push('\n')
 880                 }
 881                 line_buffer.clear();
 882             }
 883             '?' if kind == FullCodeCharKind::Normal => continue,
 884             c => line_buffer.push(c),
 885         }
 886     }
 887     if !line_buffer.trim().is_empty() {
 888         result.push_str(&line_buffer);
 889     }
 890     result
 891 }