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 std::borrow::Cow;
  69 use std::cmp::min;
  70
  71 use syntax::source_map::{BytePos, Span};
  72 use syntax::{ast, ptr};
  73
  74 use crate::comment::{rewrite_comment, CharClasses, FullCodeCharKind, RichChar};
  75 use crate::config::IndentStyle;
  76 use crate::expr::rewrite_call;
  77 use crate::lists::extract_pre_comment;
  78 use crate::macros::convert_try_mac;
  79 use crate::rewrite::{Rewrite, RewriteContext};
  80 use crate::shape::Shape;
  81 use crate::source_map::SpanUtils;
  82 use crate::utils::{
  83     self, first_line_width, last_line_extendable, last_line_width, mk_sp, rewrite_ident,
  84     trimmed_last_line_width, wrap_str,
  85 };
  86
  87 pub fn rewrite_chain(
  88     expr: &ast::Expr,
  89     context: &RewriteContext<'_>,
  90     shape: Shape,
  91 ) -> Option<String> {
  92     let chain = Chain::from_ast(expr, context);
  93     debug!("rewrite_chain {:?} {:?}", chain, shape);
  94
  95     // If this is just an expression with some `?`s, then format it trivially and
  96     // return early.
  97     if chain.children.is_empty() {
  98         return chain.parent.rewrite(context, shape);
  99     }
 100
 101     chain.rewrite(context, shape)
 102 }
 103
 104 #[derive(Debug)]
 105 enum CommentPosition {
 106     Back,
 107     Top,
 108 }
 109
 110 // An expression plus trailing `?`s to be formatted together.
 111 #[derive(Debug)]
 112 struct ChainItem {
 113     kind: ChainItemKind,
 114     tries: usize,
 115     span: Span,
 116 }
 117
 118 // FIXME: we can't use a reference here because to convert `try!` to `?` we
 119 // synthesise the AST node. However, I think we could use `Cow` and that
 120 // would remove a lot of cloning.
 121 #[derive(Debug)]
 122 enum ChainItemKind {
 123     Parent(ast::Expr),
 124     MethodCall(
 125         ast::PathSegment,
 126         Vec<ast::GenericArg>,
 127         Vec<ptr::P<ast::Expr>>,
 128     ),
 129     StructField(ast::Ident),
 130     TupleField(ast::Ident, bool),
 131     Comment(String, CommentPosition),
 132 }
 133
 134 impl ChainItemKind {
 135     fn is_block_like(&self, context: &RewriteContext<'_>, reps: &str) -> bool {
 136         match self {
 137             ChainItemKind::Parent(ref expr) => utils::is_block_expr(context, expr, reps),
 138             ChainItemKind::MethodCall(..)
 139             | ChainItemKind::StructField(..)
 140             | ChainItemKind::TupleField(..)
 141             | ChainItemKind::Comment(..) => false,
 142         }
 143     }
 144
 145     fn is_tup_field_access(expr: &ast::Expr) -> bool {
 146         match expr.node {
 147             ast::ExprKind::Field(_, ref field) => {
 148                 field.name.to_string().chars().all(|c| c.is_digit(10))
 149             }
 150             _ => false,
 151         }
 152     }
 153
 154     fn from_ast(context: &RewriteContext<'_>, expr: &ast::Expr) -> (ChainItemKind, Span) {
 155         let (kind, span) = match expr.node {
 156             ast::ExprKind::MethodCall(ref segment, ref expressions) => {
 157                 let types = if let Some(ref generic_args) = segment.args {
 158                     if let ast::GenericArgs::AngleBracketed(ref data) = **generic_args {
 159                         data.args.clone()
 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             _ => return (ChainItemKind::Parent(expr.clone()), expr.span),
 180         };
 181
 182         // Remove comments from the span.
 183         let lo = context.snippet_provider.span_before(span, ".");
 184         (kind, mk_sp(lo, span.hi()))
 185     }
 186 }
 187
 188 impl Rewrite for ChainItem {
 189     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 190         let shape = shape.sub_width(self.tries)?;
 191         let rewrite = match self.kind {
 192             ChainItemKind::Parent(ref expr) => expr.rewrite(context, shape)?,
 193             ChainItemKind::MethodCall(ref segment, ref types, ref exprs) => {
 194                 Self::rewrite_method_call(segment.ident, types, exprs, self.span, context, shape)?
 195             }
 196             ChainItemKind::StructField(ident) => format!(".{}", rewrite_ident(context, ident)),
 197             ChainItemKind::TupleField(ident, nested) => format!(
 198                 "{}.{}",
 199                 if nested { " " } else { "" },
 200                 rewrite_ident(context, ident)
 201             ),
 202             ChainItemKind::Comment(ref comment, _) => {
 203                 rewrite_comment(comment, false, shape, context.config)?
 204             }
 205         };
 206         Some(format!("{}{}", rewrite, "?".repeat(self.tries)))
 207     }
 208 }
 209
 210 impl ChainItem {
 211     fn new(context: &RewriteContext<'_>, expr: &ast::Expr, tries: usize) -> ChainItem {
 212         let (kind, span) = ChainItemKind::from_ast(context, expr);
 213         ChainItem { kind, tries, span }
 214     }
 215
 216     fn comment(span: Span, comment: String, pos: CommentPosition) -> ChainItem {
 217         ChainItem {
 218             kind: ChainItemKind::Comment(comment, pos),
 219             tries: 0,
 220             span,
 221         }
 222     }
 223
 224     fn is_comment(&self) -> bool {
 225         match self.kind {
 226             ChainItemKind::Comment(..) => true,
 227             _ => false,
 228         }
 229     }
 230
 231     fn rewrite_method_call(
 232         method_name: ast::Ident,
 233         types: &[ast::GenericArg],
 234         args: &[ptr::P<ast::Expr>],
 235         span: Span,
 236         context: &RewriteContext<'_>,
 237         shape: Shape,
 238     ) -> Option<String> {
 239         let type_str = if types.is_empty() {
 240             String::new()
 241         } else {
 242             let type_list = types
 243                 .iter()
 244                 .map(|ty| ty.rewrite(context, shape))
 245                 .collect::<Option<Vec<_>>>()?;
 246
 247             format!("::<{}>", type_list.join(", "))
 248         };
 249         let callee_str = format!(".{}{}", rewrite_ident(context, method_name), type_str);
 250         rewrite_call(context, &callee_str, &args[1..], span, shape)
 251     }
 252 }
 253
 254 #[derive(Debug)]
 255 struct Chain {
 256     parent: ChainItem,
 257     children: Vec<ChainItem>,
 258 }
 259
 260 impl Chain {
 261     fn from_ast(expr: &ast::Expr, context: &RewriteContext<'_>) -> Chain {
 262         let subexpr_list = Self::make_subexpr_list(expr, context);
 263
 264         // Un-parse the expression tree into ChainItems
 265         let mut rev_children = vec![];
 266         let mut sub_tries = 0;
 267         for subexpr in &subexpr_list {
 268             match subexpr.node {
 269                 ast::ExprKind::Try(_) => sub_tries += 1,
 270                 _ => {
 271                     rev_children.push(ChainItem::new(context, subexpr, sub_tries));
 272                     sub_tries = 0;
 273                 }
 274             }
 275         }
 276
 277         fn is_tries(s: &str) -> bool {
 278             s.chars().all(|c| c == '?')
 279         }
 280
 281         fn is_post_comment(s: &str) -> bool {
 282             let comment_start_index = s.chars().position(|c| c == '/');
 283             if comment_start_index.is_none() {
 284                 return false;
 285             }
 286
 287             let newline_index = s.chars().position(|c| c == '\n');
 288             if newline_index.is_none() {
 289                 return true;
 290             }
 291
 292             comment_start_index.unwrap() < newline_index.unwrap()
 293         }
 294
 295         fn handle_post_comment(
 296             post_comment_span: Span,
 297             post_comment_snippet: &str,
 298             prev_span_end: &mut BytePos,
 299             children: &mut Vec<ChainItem>,
 300         ) {
 301             let white_spaces: &[_] = &[' ', '\t'];
 302             if post_comment_snippet
 303                 .trim_matches(white_spaces)
 304                 .starts_with('\n')
 305             {
 306                 // No post comment.
 307                 return;
 308             }
 309             let trimmed_snippet = trim_tries(post_comment_snippet);
 310             if is_post_comment(&trimmed_snippet) {
 311                 children.push(ChainItem::comment(
 312                     post_comment_span,
 313                     trimmed_snippet.trim().to_owned(),
 314                     CommentPosition::Back,
 315                 ));
 316                 *prev_span_end = post_comment_span.hi();
 317             }
 318         }
 319
 320         let parent = rev_children.pop().unwrap();
 321         let mut children = vec![];
 322         let mut prev_span_end = parent.span.hi();
 323         let mut iter = rev_children.into_iter().rev().peekable();
 324         if let Some(first_chain_item) = iter.peek() {
 325             let comment_span = mk_sp(prev_span_end, first_chain_item.span.lo());
 326             let comment_snippet = context.snippet(comment_span);
 327             if !is_tries(comment_snippet.trim()) {
 328                 handle_post_comment(
 329                     comment_span,
 330                     comment_snippet,
 331                     &mut prev_span_end,
 332                     &mut children,
 333                 );
 334             }
 335         }
 336         while let Some(chain_item) = iter.next() {
 337             let comment_snippet = context.snippet(chain_item.span);
 338             // FIXME: Figure out the way to get a correct span when converting `try!` to `?`.
 339             let handle_comment =
 340                 !(context.config.use_try_shorthand() || is_tries(comment_snippet.trim()));
 341
 342             // Pre-comment
 343             if handle_comment {
 344                 let pre_comment_span = mk_sp(prev_span_end, chain_item.span.lo());
 345                 let pre_comment_snippet = trim_tries(context.snippet(pre_comment_span));
 346                 let (pre_comment, _) = extract_pre_comment(&pre_comment_snippet);
 347                 match pre_comment {
 348                     Some(ref comment) if !comment.is_empty() => {
 349                         children.push(ChainItem::comment(
 350                             pre_comment_span,
 351                             comment.to_owned(),
 352                             CommentPosition::Top,
 353                         ));
 354                     }
 355                     _ => (),
 356                 }
 357             }
 358
 359             prev_span_end = chain_item.span.hi();
 360             children.push(chain_item);
 361
 362             // Post-comment
 363             if !handle_comment || iter.peek().is_none() {
 364                 continue;
 365             }
 366
 367             let next_lo = iter.peek().unwrap().span.lo();
 368             let post_comment_span = mk_sp(prev_span_end, next_lo);
 369             let post_comment_snippet = context.snippet(post_comment_span);
 370             handle_post_comment(
 371                 post_comment_span,
 372                 post_comment_snippet,
 373                 &mut prev_span_end,
 374                 &mut children,
 375             );
 376         }
 377
 378         Chain { parent, children }
 379     }
 380
 381     // Returns a Vec of the prefixes of the chain.
 382     // E.g., for input `a.b.c` we return [`a.b.c`, `a.b`, 'a']
 383     fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext<'_>) -> Vec<ast::Expr> {
 384         let mut subexpr_list = vec![expr.clone()];
 385
 386         while let Some(subexpr) = Self::pop_expr_chain(subexpr_list.last().unwrap(), context) {
 387             subexpr_list.push(subexpr.clone());
 388         }
 389
 390         subexpr_list
 391     }
 392
 393     // Returns the expression's subexpression, if it exists. When the subexpr
 394     // is a try! macro, we'll convert it to shorthand when the option is set.
 395     fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext<'_>) -> Option<ast::Expr> {
 396         match expr.node {
 397             ast::ExprKind::MethodCall(_, ref expressions) => {
 398                 Some(Self::convert_try(&expressions[0], context))
 399             }
 400             ast::ExprKind::Field(ref subexpr, _) | ast::ExprKind::Try(ref subexpr) => {
 401                 Some(Self::convert_try(subexpr, context))
 402             }
 403             _ => None,
 404         }
 405     }
 406
 407     fn convert_try(expr: &ast::Expr, context: &RewriteContext<'_>) -> ast::Expr {
 408         match expr.node {
 409             ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
 410                 if let Some(subexpr) = convert_try_mac(mac, context) {
 411                     subexpr
 412                 } else {
 413                     expr.clone()
 414                 }
 415             }
 416             _ => expr.clone(),
 417         }
 418     }
 419 }
 420
 421 impl Rewrite for Chain {
 422     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 423         debug!("rewrite chain {:?} {:?}", self, shape);
 424
 425         let mut formatter = match context.config.indent_style() {
 426             IndentStyle::Block => {
 427                 Box::new(ChainFormatterBlock::new(self)) as Box<dyn ChainFormatter>
 428             }
 429             IndentStyle::Visual => {
 430                 Box::new(ChainFormatterVisual::new(self)) as Box<dyn ChainFormatter>
 431             }
 432         };
 433
 434         formatter.format_root(&self.parent, context, shape)?;
 435         if let Some(result) = formatter.pure_root() {
 436             return wrap_str(result, context.config.max_width(), shape);
 437         }
 438
 439         // Decide how to layout the rest of the chain.
 440         let child_shape = formatter.child_shape(context, shape)?;
 441
 442         formatter.format_children(context, child_shape)?;
 443         formatter.format_last_child(context, shape, child_shape)?;
 444
 445         let result = formatter.join_rewrites(context, child_shape)?;
 446         wrap_str(result, context.config.max_width(), shape)
 447     }
 448 }
 449
 450 // There are a few types for formatting chains. This is because there is a lot
 451 // in common between formatting with block vs visual indent, but they are
 452 // different enough that branching on the indent all over the place gets ugly.
 453 // Anything that can format a chain is a ChainFormatter.
 454 trait ChainFormatter {
 455     // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
 456     // Root is the parent plus any other chain items placed on the first line to
 457     // avoid an orphan. E.g.,
 458     // ```ignore
 459     // foo.bar
 460     //     .baz()
 461     // ```
 462     // If `bar` were not part of the root, then foo would be orphaned and 'float'.
 463     fn format_root(
 464         &mut self,
 465         parent: &ChainItem,
 466         context: &RewriteContext<'_>,
 467         shape: Shape,
 468     ) -> Option<()>;
 469     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape>;
 470     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()>;
 471     fn format_last_child(
 472         &mut self,
 473         context: &RewriteContext<'_>,
 474         shape: Shape,
 475         child_shape: Shape,
 476     ) -> Option<()>;
 477     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String>;
 478     // Returns `Some` if the chain is only a root, None otherwise.
 479     fn pure_root(&mut self) -> Option<String>;
 480 }
 481
 482 // Data and behaviour that is shared by both chain formatters. The concrete
 483 // formatters can delegate much behaviour to `ChainFormatterShared`.
 484 struct ChainFormatterShared<'a> {
 485     // The current working set of child items.
 486     children: &'a [ChainItem],
 487     // The current rewrites of items (includes trailing `?`s, but not any way to
 488     // connect the rewrites together).
 489     rewrites: Vec<String>,
 490     // Whether the chain can fit on one line.
 491     fits_single_line: bool,
 492     // The number of children in the chain. This is not equal to `self.children.len()`
 493     // because `self.children` will change size as we process the chain.
 494     child_count: usize,
 495 }
 496
 497 impl<'a> ChainFormatterShared<'a> {
 498     fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
 499         ChainFormatterShared {
 500             children: &chain.children,
 501             rewrites: Vec::with_capacity(chain.children.len() + 1),
 502             fits_single_line: false,
 503             child_count: chain.children.len(),
 504         }
 505     }
 506
 507     fn pure_root(&mut self) -> Option<String> {
 508         if self.children.is_empty() {
 509             assert_eq!(self.rewrites.len(), 1);
 510             Some(self.rewrites.pop().unwrap())
 511         } else {
 512             None
 513         }
 514     }
 515
 516     // Rewrite the last child. The last child of a chain requires special treatment. We need to
 517     // know whether 'overflowing' the last child make a better formatting:
 518     //
 519     // A chain with overflowing the last child:
 520     // ```ignore
 521     // parent.child1.child2.last_child(
 522     //     a,
 523     //     b,
 524     //     c,
 525     // )
 526     // ```
 527     //
 528     // A chain without overflowing the last child (in vertical layout):
 529     // ```ignore
 530     // parent
 531     //     .child1
 532     //     .child2
 533     //     .last_child(a, b, c)
 534     // ```
 535     //
 536     // In particular, overflowing is effective when the last child is a method with a multi-lined
 537     // block-like argument (e.g. closure):
 538     // ```ignore
 539     // parent.child1.child2.last_child(|a, b, c| {
 540     //     let x = foo(a, b, c);
 541     //     let y = bar(a, b, c);
 542     //
 543     //     // ...
 544     //
 545     //     result
 546     // })
 547     // ```
 548     fn format_last_child(
 549         &mut self,
 550         may_extend: bool,
 551         context: &RewriteContext<'_>,
 552         shape: Shape,
 553         child_shape: Shape,
 554     ) -> Option<()> {
 555         let last = self.children.last()?;
 556         let extendable = may_extend && last_line_extendable(&self.rewrites[0]);
 557         let prev_last_line_width = last_line_width(&self.rewrites[0]);
 558
 559         // Total of all items excluding the last.
 560         let almost_total = if extendable {
 561             prev_last_line_width
 562         } else {
 563             self.rewrites.iter().fold(0, |a, b| a + b.len())
 564         } + last.tries;
 565         let one_line_budget = if self.child_count == 1 {
 566             shape.width
 567         } else {
 568             min(shape.width, context.config.width_heuristics().chain_width)
 569         }
 570         .saturating_sub(almost_total);
 571
 572         let all_in_one_line = !self.children.iter().any(ChainItem::is_comment)
 573             && self.rewrites.iter().all(|s| !s.contains('\n'))
 574             && one_line_budget > 0;
 575         let last_shape = if all_in_one_line {
 576             shape.sub_width(last.tries)?
 577         } else if extendable {
 578             child_shape.sub_width(last.tries)?
 579         } else {
 580             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 581         };
 582
 583         let mut last_subexpr_str = None;
 584         if all_in_one_line || extendable {
 585             // First we try to 'overflow' the last child and see if it looks better than using
 586             // vertical layout.
 587             let one_line_shape = if context.use_block_indent() {
 588                 last_shape.offset_left(almost_total)
 589             } else {
 590                 last_shape
 591                     .visual_indent(almost_total)
 592                     .sub_width(almost_total)
 593             };
 594
 595             if let Some(one_line_shape) = one_line_shape {
 596                 if let Some(rw) = last.rewrite(context, one_line_shape) {
 597                     // We allow overflowing here only if both of the following conditions match:
 598                     // 1. The entire chain fits in a single line except the last child.
 599                     // 2. `last_child_str.lines().count() >= 5`.
 600                     let line_count = rw.lines().count();
 601                     let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
 602                     if could_fit_single_line && line_count >= 5 {
 603                         last_subexpr_str = Some(rw);
 604                         self.fits_single_line = all_in_one_line;
 605                     } else {
 606                         // We could not know whether overflowing is better than using vertical
 607                         // layout, just by looking at the overflowed rewrite. Now we rewrite the
 608                         // last child on its own line, and compare two rewrites to choose which is
 609                         // better.
 610                         let last_shape = child_shape
 611                             .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
 612                         match last.rewrite(context, last_shape) {
 613                             Some(ref new_rw) if !could_fit_single_line => {
 614                                 last_subexpr_str = Some(new_rw.clone());
 615                             }
 616                             Some(ref new_rw) if new_rw.lines().count() >= line_count => {
 617                                 last_subexpr_str = Some(rw);
 618                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 619                             }
 620                             new_rw @ Some(..) => {
 621                                 last_subexpr_str = new_rw;
 622                             }
 623                             _ => {
 624                                 last_subexpr_str = Some(rw);
 625                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 626                             }
 627                         }
 628                     }
 629                 }
 630             }
 631         }
 632
 633         let last_shape = if context.use_block_indent() {
 634             last_shape
 635         } else {
 636             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 637         };
 638
 639         last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
 640         self.rewrites.push(last_subexpr_str?);
 641         Some(())
 642     }
 643
 644     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 645         let connector = if self.fits_single_line {
 646             // Yay, we can put everything on one line.
 647             Cow::from("")
 648         } else {
 649             // Use new lines.
 650             if *context.force_one_line_chain.borrow() {
 651                 return None;
 652             }
 653             child_shape.to_string_with_newline(context.config)
 654         };
 655
 656         let mut rewrite_iter = self.rewrites.iter();
 657         let mut result = rewrite_iter.next().unwrap().clone();
 658         let children_iter = self.children.iter();
 659         let iter = rewrite_iter.zip(children_iter);
 660
 661         for (rewrite, chain_item) in iter {
 662             match chain_item.kind {
 663                 ChainItemKind::Comment(_, CommentPosition::Back) => result.push(' '),
 664                 ChainItemKind::Comment(_, CommentPosition::Top) => result.push_str(&connector),
 665                 _ => result.push_str(&connector),
 666             }
 667             result.push_str(&rewrite);
 668         }
 669
 670         Some(result)
 671     }
 672 }
 673
 674 // Formats a chain using block indent.
 675 struct ChainFormatterBlock<'a> {
 676     shared: ChainFormatterShared<'a>,
 677     root_ends_with_block: bool,
 678 }
 679
 680 impl<'a> ChainFormatterBlock<'a> {
 681     fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
 682         ChainFormatterBlock {
 683             shared: ChainFormatterShared::new(chain),
 684             root_ends_with_block: false,
 685         }
 686     }
 687 }
 688
 689 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
 690     fn format_root(
 691         &mut self,
 692         parent: &ChainItem,
 693         context: &RewriteContext<'_>,
 694         shape: Shape,
 695     ) -> Option<()> {
 696         let mut root_rewrite: String = parent.rewrite(context, shape)?;
 697
 698         let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
 699         let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
 700
 701         while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
 702             let item = &self.shared.children[0];
 703             if let ChainItemKind::Comment(..) = item.kind {
 704                 break;
 705             }
 706             let shape = shape.offset_left(root_rewrite.len())?;
 707             match &item.rewrite(context, shape) {
 708                 Some(rewrite) => root_rewrite.push_str(rewrite),
 709                 None => break,
 710             }
 711
 712             root_ends_with_block = last_line_extendable(&root_rewrite);
 713
 714             self.shared.children = &self.shared.children[1..];
 715             if self.shared.children.is_empty() {
 716                 break;
 717             }
 718         }
 719         self.shared.rewrites.push(root_rewrite);
 720         self.root_ends_with_block = root_ends_with_block;
 721         Some(())
 722     }
 723
 724     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
 725         Some(
 726             if self.root_ends_with_block {
 727                 shape.block_indent(0)
 728             } else {
 729                 shape.block_indent(context.config.tab_spaces())
 730             }
 731             .with_max_width(context.config),
 732         )
 733     }
 734
 735     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
 736         for item in &self.shared.children[..self.shared.children.len() - 1] {
 737             let rewrite = item.rewrite(context, child_shape)?;
 738             self.shared.rewrites.push(rewrite);
 739         }
 740         Some(())
 741     }
 742
 743     fn format_last_child(
 744         &mut self,
 745         context: &RewriteContext<'_>,
 746         shape: Shape,
 747         child_shape: Shape,
 748     ) -> Option<()> {
 749         self.shared
 750             .format_last_child(true, context, shape, child_shape)
 751     }
 752
 753     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 754         self.shared.join_rewrites(context, child_shape)
 755     }
 756
 757     fn pure_root(&mut self) -> Option<String> {
 758         self.shared.pure_root()
 759     }
 760 }
 761
 762 // Format a chain using visual indent.
 763 struct ChainFormatterVisual<'a> {
 764     shared: ChainFormatterShared<'a>,
 765     // The extra offset from the chain's shape to the position of the `.`
 766     offset: usize,
 767 }
 768
 769 impl<'a> ChainFormatterVisual<'a> {
 770     fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
 771         ChainFormatterVisual {
 772             shared: ChainFormatterShared::new(chain),
 773             offset: 0,
 774         }
 775     }
 776 }
 777
 778 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
 779     fn format_root(
 780         &mut self,
 781         parent: &ChainItem,
 782         context: &RewriteContext<'_>,
 783         shape: Shape,
 784     ) -> Option<()> {
 785         let parent_shape = shape.visual_indent(0);
 786         let mut root_rewrite = parent.rewrite(context, parent_shape)?;
 787         let multiline = root_rewrite.contains('\n');
 788         self.offset = if multiline {
 789             last_line_width(&root_rewrite).saturating_sub(shape.used_width())
 790         } else {
 791             trimmed_last_line_width(&root_rewrite)
 792         };
 793
 794         if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
 795             let item = &self.shared.children[0];
 796             if let ChainItemKind::Comment(..) = item.kind {
 797                 self.shared.rewrites.push(root_rewrite);
 798                 return Some(());
 799             }
 800             let child_shape = parent_shape
 801                 .visual_indent(self.offset)
 802                 .sub_width(self.offset)?;
 803             let rewrite = item.rewrite(context, child_shape)?;
 804             match wrap_str(rewrite, context.config.max_width(), shape) {
 805                 Some(rewrite) => root_rewrite.push_str(&rewrite),
 806                 None => {
 807                     // We couldn't fit in at the visual indent, try the last
 808                     // indent.
 809                     let rewrite = item.rewrite(context, parent_shape)?;
 810                     root_rewrite.push_str(&rewrite);
 811                     self.offset = 0;
 812                 }
 813             }
 814
 815             self.shared.children = &self.shared.children[1..];
 816         }
 817
 818         self.shared.rewrites.push(root_rewrite);
 819         Some(())
 820     }
 821
 822     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
 823         shape
 824             .with_max_width(context.config)
 825             .offset_left(self.offset)
 826             .map(|s| s.visual_indent(0))
 827     }
 828
 829     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
 830         for item in &self.shared.children[..self.shared.children.len() - 1] {
 831             let rewrite = item.rewrite(context, child_shape)?;
 832             self.shared.rewrites.push(rewrite);
 833         }
 834         Some(())
 835     }
 836
 837     fn format_last_child(
 838         &mut self,
 839         context: &RewriteContext<'_>,
 840         shape: Shape,
 841         child_shape: Shape,
 842     ) -> Option<()> {
 843         self.shared
 844             .format_last_child(false, context, shape, child_shape)
 845     }
 846
 847     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 848         self.shared.join_rewrites(context, child_shape)
 849     }
 850
 851     fn pure_root(&mut self) -> Option<String> {
 852         self.shared.pure_root()
 853     }
 854 }
 855
 856 /// Remove try operators (`?`s) that appear in the given string. If removing
 857 /// them leaves an empty line, remove that line as well unless it is the first
 858 /// line (we need the first newline for detecting pre/post comment).
 859 fn trim_tries(s: &str) -> String {
 860     let mut result = String::with_capacity(s.len());
 861     let mut line_buffer = String::with_capacity(s.len());
 862     for (kind, rich_char) in CharClasses::new(s.chars()) {
 863         match rich_char.get_char() {
 864             '\n' => {
 865                 if result.is_empty() || !line_buffer.trim().is_empty() {
 866                     result.push_str(&line_buffer);
 867                     result.push('\n')
 868                 }
 869                 line_buffer.clear();
 870             }
 871             '?' if kind == FullCodeCharKind::Normal => continue,
 872             c => line_buffer.push(c),
 873         }
 874     }
 875     if !line_buffer.trim().is_empty() {
 876         result.push_str(&line_buffer);
 877     }
 878     result
 879 }