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.
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.
11 //! Formatting of chained expressions, i.e. expressions which are chained by
12 //! dots: struct and enum field access, method calls, and try shorthand (?).
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.
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.
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
25 //! E.g., `let foo = { aaaa; bbb; ccc }.bar.baz();`, we would layout for the
26 //! following values of `chain_indent`:
50 //! If the first item in the chain is a block expression, we align the dots with
68 use codemap::SpanUtils;
69 use comment::rewrite_comment;
70 use config::IndentStyle;
71 use expr::rewrite_call;
72 use macros::convert_try_mac;
73 use rewrite::{Rewrite, RewriteContext};
76 first_line_width, last_line_extendable, last_line_width, mk_sp, trimmed_last_line_width,
84 use syntax::codemap::Span;
85 use syntax::{ast, ptr};
87 pub fn rewrite_chain(expr: &ast::Expr, context: &RewriteContext, shape: Shape) -> Option<String> {
88 let chain = Chain::from_ast(expr, context);
89 debug!("rewrite_chain {:?} {:?}", chain, shape);
91 // If this is just an expression with some `?`s, then format it trivially and
93 if chain.children.is_empty() {
94 return chain.parent.rewrite(context, shape);
97 chain.rewrite(context, shape)
100 // An expression plus trailing `?`s to be formatted together.
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.
116 Vec<ast::GenericArg>,
117 Vec<ptr::P<ast::Expr>>,
119 StructField(ast::Ident),
120 TupleField(ast::Ident, bool),
125 fn is_block_like(&self, context: &RewriteContext, reps: &str) -> bool {
127 ChainItemKind::Parent(ref expr) => is_block_expr(context, expr, reps),
128 ChainItemKind::MethodCall(..) => reps.contains('\n'),
129 ChainItemKind::StructField(..)
130 | ChainItemKind::TupleField(..)
131 | ChainItemKind::Comment => false,
135 fn is_tup_field_access(expr: &ast::Expr) -> bool {
137 ast::ExprKind::Field(_, ref field) => {
138 field.name.to_string().chars().all(|c| c.is_digit(10))
144 fn from_ast(context: &RewriteContext, expr: &ast::Expr) -> (ChainItemKind, Span) {
145 let (kind, span) = match expr.node {
146 ast::ExprKind::MethodCall(ref segment, ref expressions) => {
147 let types = if let Some(ref generic_args) = segment.args {
148 if let ast::GenericArgs::AngleBracketed(ref data) = **generic_args {
156 let span = mk_sp(expressions[0].span.hi(), expr.span.hi());
157 let kind = ChainItemKind::MethodCall(segment.clone(), types, expressions.clone());
160 ast::ExprKind::Field(ref nested, field) => {
161 let kind = if Self::is_tup_field_access(expr) {
162 ChainItemKind::TupleField(field, Self::is_tup_field_access(nested))
164 ChainItemKind::StructField(field)
166 let span = mk_sp(nested.span.hi(), field.span.hi());
169 _ => return (ChainItemKind::Parent(expr.clone()), expr.span),
172 // Remove comments from the span.
173 let lo = context.snippet_provider.span_before(span, ".");
174 (kind, mk_sp(lo, span.hi()))
178 impl Rewrite for ChainItem {
179 fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
180 let shape = shape.sub_width(self.tries)?;
181 let rewrite = match self.kind {
182 ChainItemKind::Parent(ref expr) => expr.rewrite(context, shape)?,
183 ChainItemKind::MethodCall(ref segment, ref types, ref exprs) => {
184 Self::rewrite_method_call(segment.ident, types, exprs, self.span, context, shape)?
186 ChainItemKind::StructField(ident) => format!(".{}", ident.name),
187 ChainItemKind::TupleField(ident, nested) => {
188 format!("{}.{}", if nested { " " } else { "" }, ident.name)
190 ChainItemKind::Comment => {
191 rewrite_comment(context.snippet(self.span).trim(), false, shape, context.config)?
194 Some(format!("{}{}", rewrite, "?".repeat(self.tries)))
199 fn new(context: &RewriteContext, expr: &ast::Expr, tries: usize) -> ChainItem {
200 let (kind, span) = ChainItemKind::from_ast(context, expr);
201 ChainItem { kind, tries, span }
204 fn comment(span: Span) -> ChainItem {
206 kind: ChainItemKind::Comment,
212 fn rewrite_method_call(
213 method_name: ast::Ident,
214 types: &[ast::GenericArg],
215 args: &[ptr::P<ast::Expr>],
217 context: &RewriteContext,
219 ) -> Option<String> {
220 let type_str = if types.is_empty() {
223 let type_list = types
225 .map(|ty| ty.rewrite(context, shape))
226 .collect::<Option<Vec<_>>>()?;
228 format!("::<{}>", type_list.join(", "))
230 let callee_str = format!(".{}{}", method_name, type_str);
231 rewrite_call(context, &callee_str, &args[1..], span, shape)
238 children: Vec<ChainItem>,
242 fn from_ast(expr: &ast::Expr, context: &RewriteContext) -> Chain {
243 let subexpr_list = Self::make_subexpr_list(expr, context);
245 // Un-parse the expression tree into ChainItems
246 let mut rev_children = vec![];
247 let mut sub_tries = 0;
248 for subexpr in &subexpr_list {
250 ast::ExprKind::Try(_) => sub_tries += 1,
252 rev_children.push(ChainItem::new(context, subexpr, sub_tries));
258 let parent = rev_children.pop().unwrap();
259 let mut children = vec![];
260 let mut prev_hi = parent.span.hi();
261 for chain_item in rev_children.into_iter().rev() {
262 let comment_span = mk_sp(prev_hi, chain_item.span.lo());
263 let comment_snippet = context.snippet(comment_span);
264 if !comment_snippet.trim().is_empty() {
265 children.push(ChainItem::comment(comment_span));
267 prev_hi = chain_item.span.hi();
268 children.push(chain_item);
271 Chain { parent, children }
274 // Returns a Vec of the prefixes of the chain.
275 // E.g., for input `a.b.c` we return [`a.b.c`, `a.b`, 'a']
276 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> Vec<ast::Expr> {
277 let mut subexpr_list = vec![expr.clone()];
279 while let Some(subexpr) = Self::pop_expr_chain(subexpr_list.last().unwrap(), context) {
280 subexpr_list.push(subexpr.clone());
286 // Returns the expression's subexpression, if it exists. When the subexpr
287 // is a try! macro, we'll convert it to shorthand when the option is set.
288 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
290 ast::ExprKind::MethodCall(_, ref expressions) => {
291 Some(Self::convert_try(&expressions[0], context))
293 ast::ExprKind::Field(ref subexpr, _) | ast::ExprKind::Try(ref subexpr) => {
294 Some(Self::convert_try(subexpr, context))
300 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
302 ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
303 if let Some(subexpr) = convert_try_mac(mac, context) {
314 impl Rewrite for Chain {
315 fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
316 debug!("rewrite chain {:?} {:?}", self, shape);
318 let mut formatter = match context.config.indent_style() {
319 IndentStyle::Block => Box::new(ChainFormatterBlock::new(self)) as Box<ChainFormatter>,
320 IndentStyle::Visual => Box::new(ChainFormatterVisual::new(self)) as Box<ChainFormatter>,
323 formatter.format_root(&self.parent, context, shape)?;
324 if let Some(result) = formatter.pure_root() {
325 return wrap_str(result, context.config.max_width(), shape);
328 // Decide how to layout the rest of the chain.
329 let child_shape = formatter.child_shape(context, shape)?;
331 formatter.format_children(context, child_shape)?;
332 formatter.format_last_child(context, shape, child_shape)?;
334 let result = formatter.join_rewrites(context, child_shape)?;
335 wrap_str(result, context.config.max_width(), shape)
339 // There are a few types for formatting chains. This is because there is a lot
340 // in common between formatting with block vs visual indent, but they are
341 // different enough that branching on the indent all over the place gets ugly.
342 // Anything that can format a chain is a ChainFormatter.
343 trait ChainFormatter {
344 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
345 // Root is the parent plus any other chain items placed on the first line to
346 // avoid an orphan. E.g.,
351 // If `bar` were not part of the root, then foo would be orphaned and 'float'.
355 context: &RewriteContext,
358 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape>;
359 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()>;
360 fn format_last_child(
362 context: &RewriteContext,
366 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String>;
367 // Returns `Some` if the chain is only a root, None otherwise.
368 fn pure_root(&mut self) -> Option<String>;
371 // Data and behaviour that is shared by both chain formatters. The concrete
372 // formatters can delegate much behaviour to `ChainFormatterShared`.
373 struct ChainFormatterShared<'a> {
374 // The current working set of child items.
375 children: &'a [ChainItem],
376 // The current rewrites of items (includes trailing `?`s, but not any way to
377 // connect the rewrites together).
378 rewrites: Vec<String>,
379 // Whether the chain can fit on one line.
380 fits_single_line: bool,
381 // The number of children in the chain. This is not equal to `self.children.len()`
382 // because `self.children` will change size as we process the chain.
386 impl<'a> ChainFormatterShared<'a> {
387 fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
388 ChainFormatterShared {
389 children: &chain.children,
390 rewrites: Vec::with_capacity(chain.children.len() + 1),
391 fits_single_line: false,
392 child_count: chain.children.len(),
396 fn pure_root(&mut self) -> Option<String> {
397 if self.children.is_empty() {
398 assert_eq!(self.rewrites.len(), 1);
399 Some(self.rewrites.pop().unwrap())
405 // Rewrite the last child. The last child of a chain requires special treatment. We need to
406 // know whether 'overflowing' the last child make a better formatting:
408 // A chain with overflowing the last child:
410 // parent.child1.child2.last_child(
417 // A chain without overflowing the last child (in vertical layout):
422 // .last_child(a, b, c)
425 // In particular, overflowing is effective when the last child is a method with a multi-lined
426 // block-like argument (e.g. closure):
428 // parent.child1.child2.last_child(|a, b, c| {
429 // let x = foo(a, b, c);
430 // let y = bar(a, b, c);
437 fn format_last_child(
440 context: &RewriteContext,
444 let last = self.children.last()?;
445 let extendable = may_extend && last_line_extendable(&self.rewrites[0]);
446 let prev_last_line_width = last_line_width(&self.rewrites[0]);
448 // Total of all items excluding the last.
449 let almost_total = if extendable {
452 self.rewrites.iter().fold(0, |a, b| a + b.len())
454 let one_line_budget = if self.child_count == 1 {
457 min(shape.width, context.config.width_heuristics().chain_width)
458 }.saturating_sub(almost_total);
460 let all_in_one_line =
461 self.rewrites.iter().all(|s| !s.contains('\n')) && one_line_budget > 0;
462 let last_shape = if all_in_one_line {
463 shape.sub_width(last.tries)?
464 } else if extendable {
465 child_shape.sub_width(last.tries)?
467 child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
470 let mut last_subexpr_str = None;
471 if all_in_one_line || extendable {
472 // First we try to 'overflow' the last child and see if it looks better than using
474 if let Some(one_line_shape) = last_shape.offset_left(almost_total) {
475 if let Some(rw) = last.rewrite(context, one_line_shape) {
476 // We allow overflowing here only if both of the following conditions match:
477 // 1. The entire chain fits in a single line except the last child.
478 // 2. `last_child_str.lines().count() >= 5`.
479 let line_count = rw.lines().count();
480 let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
481 if could_fit_single_line && line_count >= 5 {
482 last_subexpr_str = Some(rw);
483 self.fits_single_line = all_in_one_line;
485 // We could not know whether overflowing is better than using vertical
486 // layout, just by looking at the overflowed rewrite. Now we rewrite the
487 // last child on its own line, and compare two rewrites to choose which is
489 let last_shape = child_shape
490 .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
491 match last.rewrite(context, last_shape) {
492 Some(ref new_rw) if !could_fit_single_line => {
493 last_subexpr_str = Some(new_rw.clone());
495 Some(ref new_rw) if new_rw.lines().count() >= line_count => {
496 last_subexpr_str = Some(rw);
497 self.fits_single_line = could_fit_single_line && all_in_one_line;
499 new_rw @ Some(..) => {
500 last_subexpr_str = new_rw;
503 last_subexpr_str = Some(rw);
504 self.fits_single_line = could_fit_single_line && all_in_one_line;
512 last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
513 self.rewrites.push(last_subexpr_str?);
519 context: &RewriteContext,
521 block_like_iter: impl Iterator<Item = bool>,
522 ) -> Option<String> {
523 let connector = if self.fits_single_line {
524 // Yay, we can put everything on one line.
528 if *context.force_one_line_chain.borrow() {
531 child_shape.to_string_with_newline(context.config)
534 let mut rewrite_iter = self.rewrites.iter();
535 let mut result = rewrite_iter.next().unwrap().clone();
537 for (rewrite, prev_is_block_like) in rewrite_iter.zip(block_like_iter) {
538 if !prev_is_block_like {
539 result.push_str(&connector);
541 result.push_str(&rewrite);
548 // Formats a chain using block indent.
549 struct ChainFormatterBlock<'a> {
550 shared: ChainFormatterShared<'a>,
551 // For each rewrite, whether the corresponding item is block-like.
552 is_block_like: Vec<bool>,
555 impl<'a> ChainFormatterBlock<'a> {
556 fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
557 ChainFormatterBlock {
558 shared: ChainFormatterShared::new(chain),
559 is_block_like: Vec::with_capacity(chain.children.len() + 1),
564 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
568 context: &RewriteContext,
571 let mut root_rewrite: String = parent.rewrite(context, shape)?;
573 let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
574 let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
576 while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
577 let item = &self.shared.children[0];
578 if let ChainItemKind::Comment = item.kind {
581 let shape = shape.offset_left(root_rewrite.len())?;
582 match &item.rewrite(context, shape) {
583 Some(rewrite) => root_rewrite.push_str(rewrite),
587 root_ends_with_block = item.kind.is_block_like(context, &root_rewrite);
589 self.shared.children = &self.shared.children[1..];
590 if self.shared.children.is_empty() {
594 self.is_block_like.push(root_ends_with_block);
595 self.shared.rewrites.push(root_rewrite);
599 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape> {
601 if self.is_block_like[0] {
602 shape.block_indent(0)
604 shape.block_indent(context.config.tab_spaces())
605 }.with_max_width(context.config),
609 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()> {
610 for item in &self.shared.children[..self.shared.children.len() - 1] {
611 let rewrite = item.rewrite(context, child_shape)?;
613 .push(item.kind.is_block_like(context, &rewrite));
614 self.shared.rewrites.push(rewrite);
619 fn format_last_child(
621 context: &RewriteContext,
626 .format_last_child(true, context, shape, child_shape)
629 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
631 .join_rewrites(context, child_shape, self.is_block_like.iter().cloned())
634 fn pure_root(&mut self) -> Option<String> {
635 self.shared.pure_root()
639 // Format a chain using visual indent.
640 struct ChainFormatterVisual<'a> {
641 shared: ChainFormatterShared<'a>,
642 // The extra offset from the chain's shape to the position of the `.`
646 impl<'a> ChainFormatterVisual<'a> {
647 fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
648 ChainFormatterVisual {
649 shared: ChainFormatterShared::new(chain),
655 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
659 context: &RewriteContext,
662 let parent_shape = shape.visual_indent(0);
663 let mut root_rewrite = parent.rewrite(context, parent_shape)?;
664 let multiline = root_rewrite.contains('\n');
665 self.offset = if multiline {
666 last_line_width(&root_rewrite).saturating_sub(shape.used_width())
668 trimmed_last_line_width(&root_rewrite)
671 if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
672 let item = &self.shared.children[0];
673 if let ChainItemKind::Comment = item.kind {
674 self.shared.rewrites.push(root_rewrite);
677 let child_shape = parent_shape
678 .visual_indent(self.offset)
679 .sub_width(self.offset)?;
680 let rewrite = item.rewrite(context, child_shape)?;
681 match wrap_str(rewrite, context.config.max_width(), shape) {
682 Some(rewrite) => root_rewrite.push_str(&rewrite),
684 // We couldn't fit in at the visual indent, try the last
686 let rewrite = item.rewrite(context, parent_shape)?;
687 root_rewrite.push_str(&rewrite);
692 self.shared.children = &self.shared.children[1..];
695 self.shared.rewrites.push(root_rewrite);
699 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape> {
701 .with_max_width(context.config)
702 .offset_left(self.offset)
703 .map(|s| s.visual_indent(0))
706 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()> {
707 for item in &self.shared.children[..self.shared.children.len() - 1] {
708 let rewrite = item.rewrite(context, child_shape)?;
709 self.shared.rewrites.push(rewrite);
714 fn format_last_child(
716 context: &RewriteContext,
721 .format_last_child(false, context, shape, child_shape)
724 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
726 .join_rewrites(context, child_shape, iter::repeat(false))
729 fn pure_root(&mut self) -> Option<String> {
730 self.shared.pure_root()
734 // States whether an expression's last line exclusively consists of closing
735 // parens, braces, and brackets in its idiomatic formatting.
736 fn is_block_expr(context: &RewriteContext, expr: &ast::Expr, repr: &str) -> bool {
738 ast::ExprKind::Mac(..)
739 | ast::ExprKind::Call(..)
740 | ast::ExprKind::MethodCall(..)
741 | ast::ExprKind::Struct(..)
742 | ast::ExprKind::While(..)
743 | ast::ExprKind::WhileLet(..)
744 | ast::ExprKind::If(..)
745 | ast::ExprKind::IfLet(..)
746 | ast::ExprKind::Block(..)
747 | ast::ExprKind::Loop(..)
748 | ast::ExprKind::ForLoop(..)
749 | ast::ExprKind::Match(..) => repr.contains('\n'),
750 ast::ExprKind::Paren(ref expr)
751 | ast::ExprKind::Binary(_, _, ref expr)
752 | ast::ExprKind::Index(_, ref expr)
753 | ast::ExprKind::Unary(_, ref expr)
754 | ast::ExprKind::Closure(_, _, _, _, ref expr, _)
755 | ast::ExprKind::Try(ref expr)
756 | ast::ExprKind::Yield(Some(ref expr)) => is_block_expr(context, expr, repr),
757 // This can only be a string lit
758 ast::ExprKind::Lit(_) => {
759 repr.contains('\n') && trimmed_last_line_width(repr) <= context.config.tab_spaces()