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         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[1..], 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 expressions, _) => {
 404                 Some(Self::convert_try(&expressions[0], context))
 405             }
 406             ast::ExprKind::Field(ref subexpr, _)
 407             | ast::ExprKind::Try(ref subexpr)
 408             | ast::ExprKind::Await(ref subexpr) => Some(Self::convert_try(subexpr, context)),
 409             _ => None,
 410         }
 411     }
 412
 413     fn convert_try(expr: &ast::Expr, context: &RewriteContext<'_>) -> ast::Expr {
 414         match expr.kind {
 415             ast::ExprKind::MacCall(ref mac) if context.config.use_try_shorthand() => {
 416                 if let Some(subexpr) = convert_try_mac(mac, context) {
 417                     subexpr
 418                 } else {
 419                     expr.clone()
 420                 }
 421             }
 422             _ => expr.clone(),
 423         }
 424     }
 425 }
 426
 427 impl Rewrite for Chain {
 428     fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
 429         debug!("rewrite chain {:?} {:?}", self, shape);
 430
 431         let mut formatter = match context.config.indent_style() {
 432             IndentStyle::Block => {
 433                 Box::new(ChainFormatterBlock::new(self)) as Box<dyn ChainFormatter>
 434             }
 435             IndentStyle::Visual => {
 436                 Box::new(ChainFormatterVisual::new(self)) as Box<dyn ChainFormatter>
 437             }
 438         };
 439
 440         formatter.format_root(&self.parent, context, shape)?;
 441         if let Some(result) = formatter.pure_root() {
 442             return wrap_str(result, context.config.max_width(), shape);
 443         }
 444
 445         // Decide how to layout the rest of the chain.
 446         let child_shape = formatter.child_shape(context, shape)?;
 447
 448         formatter.format_children(context, child_shape)?;
 449         formatter.format_last_child(context, shape, child_shape)?;
 450
 451         let result = formatter.join_rewrites(context, child_shape)?;
 452         wrap_str(result, context.config.max_width(), shape)
 453     }
 454 }
 455
 456 // There are a few types for formatting chains. This is because there is a lot
 457 // in common between formatting with block vs visual indent, but they are
 458 // different enough that branching on the indent all over the place gets ugly.
 459 // Anything that can format a chain is a ChainFormatter.
 460 trait ChainFormatter {
 461     // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
 462     // Root is the parent plus any other chain items placed on the first line to
 463     // avoid an orphan. E.g.,
 464     // ```text
 465     // foo.bar
 466     //     .baz()
 467     // ```
 468     // If `bar` were not part of the root, then foo would be orphaned and 'float'.
 469     fn format_root(
 470         &mut self,
 471         parent: &ChainItem,
 472         context: &RewriteContext<'_>,
 473         shape: Shape,
 474     ) -> Option<()>;
 475     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape>;
 476     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()>;
 477     fn format_last_child(
 478         &mut self,
 479         context: &RewriteContext<'_>,
 480         shape: Shape,
 481         child_shape: Shape,
 482     ) -> Option<()>;
 483     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String>;
 484     // Returns `Some` if the chain is only a root, None otherwise.
 485     fn pure_root(&mut self) -> Option<String>;
 486 }
 487
 488 // Data and behaviour that is shared by both chain formatters. The concrete
 489 // formatters can delegate much behaviour to `ChainFormatterShared`.
 490 struct ChainFormatterShared<'a> {
 491     // The current working set of child items.
 492     children: &'a [ChainItem],
 493     // The current rewrites of items (includes trailing `?`s, but not any way to
 494     // connect the rewrites together).
 495     rewrites: Vec<String>,
 496     // Whether the chain can fit on one line.
 497     fits_single_line: bool,
 498     // The number of children in the chain. This is not equal to `self.children.len()`
 499     // because `self.children` will change size as we process the chain.
 500     child_count: usize,
 501 }
 502
 503 impl<'a> ChainFormatterShared<'a> {
 504     fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
 505         ChainFormatterShared {
 506             children: &chain.children,
 507             rewrites: Vec::with_capacity(chain.children.len() + 1),
 508             fits_single_line: false,
 509             child_count: chain.children.len(),
 510         }
 511     }
 512
 513     fn pure_root(&mut self) -> Option<String> {
 514         if self.children.is_empty() {
 515             assert_eq!(self.rewrites.len(), 1);
 516             Some(self.rewrites.pop().unwrap())
 517         } else {
 518             None
 519         }
 520     }
 521
 522     // Rewrite the last child. The last child of a chain requires special treatment. We need to
 523     // know whether 'overflowing' the last child make a better formatting:
 524     //
 525     // A chain with overflowing the last child:
 526     // ```text
 527     // parent.child1.child2.last_child(
 528     //     a,
 529     //     b,
 530     //     c,
 531     // )
 532     // ```
 533     //
 534     // A chain without overflowing the last child (in vertical layout):
 535     // ```text
 536     // parent
 537     //     .child1
 538     //     .child2
 539     //     .last_child(a, b, c)
 540     // ```
 541     //
 542     // In particular, overflowing is effective when the last child is a method with a multi-lined
 543     // block-like argument (e.g., closure):
 544     // ```text
 545     // parent.child1.child2.last_child(|a, b, c| {
 546     //     let x = foo(a, b, c);
 547     //     let y = bar(a, b, c);
 548     //
 549     //     // ...
 550     //
 551     //     result
 552     // })
 553     // ```
 554     fn format_last_child(
 555         &mut self,
 556         may_extend: bool,
 557         context: &RewriteContext<'_>,
 558         shape: Shape,
 559         child_shape: Shape,
 560     ) -> Option<()> {
 561         let last = self.children.last()?;
 562         let extendable = may_extend && last_line_extendable(&self.rewrites[0]);
 563         let prev_last_line_width = last_line_width(&self.rewrites[0]);
 564
 565         // Total of all items excluding the last.
 566         let almost_total = if extendable {
 567             prev_last_line_width
 568         } else {
 569             self.rewrites
 570                 .iter()
 571                 .map(|rw| utils::unicode_str_width(rw))
 572                 .sum()
 573         } + last.tries;
 574         let one_line_budget = if self.child_count == 1 {
 575             shape.width
 576         } else {
 577             min(shape.width, context.config.chain_width())
 578         }
 579         .saturating_sub(almost_total);
 580
 581         let all_in_one_line = !self.children.iter().any(ChainItem::is_comment)
 582             && self.rewrites.iter().all(|s| !s.contains('\n'))
 583             && one_line_budget > 0;
 584         let last_shape = if all_in_one_line {
 585             shape.sub_width(last.tries)?
 586         } else if extendable {
 587             child_shape.sub_width(last.tries)?
 588         } else {
 589             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 590         };
 591
 592         let mut last_subexpr_str = None;
 593         if all_in_one_line || extendable {
 594             // First we try to 'overflow' the last child and see if it looks better than using
 595             // vertical layout.
 596             let one_line_shape = if context.use_block_indent() {
 597                 last_shape.offset_left(almost_total)
 598             } else {
 599                 last_shape
 600                     .visual_indent(almost_total)
 601                     .sub_width(almost_total)
 602             };
 603
 604             if let Some(one_line_shape) = one_line_shape {
 605                 if let Some(rw) = last.rewrite(context, one_line_shape) {
 606                     // We allow overflowing here only if both of the following conditions match:
 607                     // 1. The entire chain fits in a single line except the last child.
 608                     // 2. `last_child_str.lines().count() >= 5`.
 609                     let line_count = rw.lines().count();
 610                     let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
 611                     if could_fit_single_line && line_count >= 5 {
 612                         last_subexpr_str = Some(rw);
 613                         self.fits_single_line = all_in_one_line;
 614                     } else {
 615                         // We could not know whether overflowing is better than using vertical
 616                         // layout, just by looking at the overflowed rewrite. Now we rewrite the
 617                         // last child on its own line, and compare two rewrites to choose which is
 618                         // better.
 619                         let last_shape = child_shape
 620                             .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
 621                         match last.rewrite(context, last_shape) {
 622                             Some(ref new_rw) if !could_fit_single_line => {
 623                                 last_subexpr_str = Some(new_rw.clone());
 624                             }
 625                             Some(ref new_rw) if new_rw.lines().count() >= line_count => {
 626                                 last_subexpr_str = Some(rw);
 627                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 628                             }
 629                             new_rw @ Some(..) => {
 630                                 last_subexpr_str = new_rw;
 631                             }
 632                             _ => {
 633                                 last_subexpr_str = Some(rw);
 634                                 self.fits_single_line = could_fit_single_line && all_in_one_line;
 635                             }
 636                         }
 637                     }
 638                 }
 639             }
 640         }
 641
 642         let last_shape = if context.use_block_indent() {
 643             last_shape
 644         } else {
 645             child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
 646         };
 647
 648         last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
 649         self.rewrites.push(last_subexpr_str?);
 650         Some(())
 651     }
 652
 653     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 654         let connector = if self.fits_single_line {
 655             // Yay, we can put everything on one line.
 656             Cow::from("")
 657         } else {
 658             // Use new lines.
 659             if context.force_one_line_chain.get() {
 660                 return None;
 661             }
 662             child_shape.to_string_with_newline(context.config)
 663         };
 664
 665         let mut rewrite_iter = self.rewrites.iter();
 666         let mut result = rewrite_iter.next().unwrap().clone();
 667         let children_iter = self.children.iter();
 668         let iter = rewrite_iter.zip(children_iter);
 669
 670         for (rewrite, chain_item) in iter {
 671             match chain_item.kind {
 672                 ChainItemKind::Comment(_, CommentPosition::Back) => result.push(' '),
 673                 ChainItemKind::Comment(_, CommentPosition::Top) => result.push_str(&connector),
 674                 _ => result.push_str(&connector),
 675             }
 676             result.push_str(rewrite);
 677         }
 678
 679         Some(result)
 680     }
 681 }
 682
 683 // Formats a chain using block indent.
 684 struct ChainFormatterBlock<'a> {
 685     shared: ChainFormatterShared<'a>,
 686     root_ends_with_block: bool,
 687 }
 688
 689 impl<'a> ChainFormatterBlock<'a> {
 690     fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
 691         ChainFormatterBlock {
 692             shared: ChainFormatterShared::new(chain),
 693             root_ends_with_block: false,
 694         }
 695     }
 696 }
 697
 698 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
 699     fn format_root(
 700         &mut self,
 701         parent: &ChainItem,
 702         context: &RewriteContext<'_>,
 703         shape: Shape,
 704     ) -> Option<()> {
 705         let mut root_rewrite: String = parent.rewrite(context, shape)?;
 706
 707         let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
 708         let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
 709
 710         while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
 711             let item = &self.shared.children[0];
 712             if let ChainItemKind::Comment(..) = item.kind {
 713                 break;
 714             }
 715             let shape = shape.offset_left(root_rewrite.len())?;
 716             match &item.rewrite(context, shape) {
 717                 Some(rewrite) => root_rewrite.push_str(rewrite),
 718                 None => break,
 719             }
 720
 721             root_ends_with_block = last_line_extendable(&root_rewrite);
 722
 723             self.shared.children = &self.shared.children[1..];
 724             if self.shared.children.is_empty() {
 725                 break;
 726             }
 727         }
 728         self.shared.rewrites.push(root_rewrite);
 729         self.root_ends_with_block = root_ends_with_block;
 730         Some(())
 731     }
 732
 733     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
 734         Some(
 735             if self.root_ends_with_block {
 736                 shape.block_indent(0)
 737             } else {
 738                 shape.block_indent(context.config.tab_spaces())
 739             }
 740             .with_max_width(context.config),
 741         )
 742     }
 743
 744     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
 745         for item in &self.shared.children[..self.shared.children.len() - 1] {
 746             let rewrite = item.rewrite(context, child_shape)?;
 747             self.shared.rewrites.push(rewrite);
 748         }
 749         Some(())
 750     }
 751
 752     fn format_last_child(
 753         &mut self,
 754         context: &RewriteContext<'_>,
 755         shape: Shape,
 756         child_shape: Shape,
 757     ) -> Option<()> {
 758         self.shared
 759             .format_last_child(true, context, shape, child_shape)
 760     }
 761
 762     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 763         self.shared.join_rewrites(context, child_shape)
 764     }
 765
 766     fn pure_root(&mut self) -> Option<String> {
 767         self.shared.pure_root()
 768     }
 769 }
 770
 771 // Format a chain using visual indent.
 772 struct ChainFormatterVisual<'a> {
 773     shared: ChainFormatterShared<'a>,
 774     // The extra offset from the chain's shape to the position of the `.`
 775     offset: usize,
 776 }
 777
 778 impl<'a> ChainFormatterVisual<'a> {
 779     fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
 780         ChainFormatterVisual {
 781             shared: ChainFormatterShared::new(chain),
 782             offset: 0,
 783         }
 784     }
 785 }
 786
 787 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
 788     fn format_root(
 789         &mut self,
 790         parent: &ChainItem,
 791         context: &RewriteContext<'_>,
 792         shape: Shape,
 793     ) -> Option<()> {
 794         let parent_shape = shape.visual_indent(0);
 795         let mut root_rewrite = parent.rewrite(context, parent_shape)?;
 796         let multiline = root_rewrite.contains('\n');
 797         self.offset = if multiline {
 798             last_line_width(&root_rewrite).saturating_sub(shape.used_width())
 799         } else {
 800             trimmed_last_line_width(&root_rewrite)
 801         };
 802
 803         if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
 804             let item = &self.shared.children[0];
 805             if let ChainItemKind::Comment(..) = item.kind {
 806                 self.shared.rewrites.push(root_rewrite);
 807                 return Some(());
 808             }
 809             let child_shape = parent_shape
 810                 .visual_indent(self.offset)
 811                 .sub_width(self.offset)?;
 812             let rewrite = item.rewrite(context, child_shape)?;
 813             match wrap_str(rewrite, context.config.max_width(), shape) {
 814                 Some(rewrite) => root_rewrite.push_str(&rewrite),
 815                 None => {
 816                     // We couldn't fit in at the visual indent, try the last
 817                     // indent.
 818                     let rewrite = item.rewrite(context, parent_shape)?;
 819                     root_rewrite.push_str(&rewrite);
 820                     self.offset = 0;
 821                 }
 822             }
 823
 824             self.shared.children = &self.shared.children[1..];
 825         }
 826
 827         self.shared.rewrites.push(root_rewrite);
 828         Some(())
 829     }
 830
 831     fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
 832         shape
 833             .with_max_width(context.config)
 834             .offset_left(self.offset)
 835             .map(|s| s.visual_indent(0))
 836     }
 837
 838     fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
 839         for item in &self.shared.children[..self.shared.children.len() - 1] {
 840             let rewrite = item.rewrite(context, child_shape)?;
 841             self.shared.rewrites.push(rewrite);
 842         }
 843         Some(())
 844     }
 845
 846     fn format_last_child(
 847         &mut self,
 848         context: &RewriteContext<'_>,
 849         shape: Shape,
 850         child_shape: Shape,
 851     ) -> Option<()> {
 852         self.shared
 853             .format_last_child(false, context, shape, child_shape)
 854     }
 855
 856     fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
 857         self.shared.join_rewrites(context, child_shape)
 858     }
 859
 860     fn pure_root(&mut self) -> Option<String> {
 861         self.shared.pure_root()
 862     }
 863 }
 864
 865 /// Removes try operators (`?`s) that appear in the given string. If removing
 866 /// them leaves an empty line, remove that line as well unless it is the first
 867 /// line (we need the first newline for detecting pre/post comment).
 868 fn trim_tries(s: &str) -> String {
 869     let mut result = String::with_capacity(s.len());
 870     let mut line_buffer = String::with_capacity(s.len());
 871     for (kind, rich_char) in CharClasses::new(s.chars()) {
 872         match rich_char.get_char() {
 873             '\n' => {
 874                 if result.is_empty() || !line_buffer.trim().is_empty() {
 875                     result.push_str(&line_buffer);
 876                     result.push('\n')
 877                 }
 878                 line_buffer.clear();
 879             }
 880             '?' if kind == FullCodeCharKind::Normal => continue,
 881             c => line_buffer.push(c),
 882         }
 883     }
 884     if !line_buffer.trim().is_empty() {
 885         result.push_str(&line_buffer);
 886     }
 887     result
 888 }