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