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 comment::{rewrite_comment, CharClasses, FullCodeCharKind, RichChar};
69 use config::IndentStyle;
70 use expr::rewrite_call;
71 use lists::extract_pre_comment;
72 use macros::convert_try_mac;
73 use rewrite::{Rewrite, RewriteContext};
75 use source_map::SpanUtils;
77 self, first_line_width, last_line_extendable, last_line_width, mk_sp, rewrite_ident,
78 trimmed_last_line_width, wrap_str,
84 use syntax::source_map::{BytePos, 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)
101 enum CommentPosition {
106 // An expression plus trailing `?`s to be formatted together.
114 // FIXME: we can't use a reference here because to convert `try!` to `?` we
115 // synthesise the AST node. However, I think we could use `Cow` and that
116 // would remove a lot of cloning.
122 Vec<ast::GenericArg>,
123 Vec<ptr::P<ast::Expr>>,
125 StructField(ast::Ident),
126 TupleField(ast::Ident, bool),
127 Comment(String, CommentPosition),
131 fn is_block_like(&self, context: &RewriteContext, reps: &str) -> bool {
133 ChainItemKind::Parent(ref expr) => utils::is_block_expr(context, expr, reps),
134 ChainItemKind::MethodCall(..)
135 | ChainItemKind::StructField(..)
136 | ChainItemKind::TupleField(..)
137 | ChainItemKind::Comment(..) => false,
141 fn is_tup_field_access(expr: &ast::Expr) -> bool {
143 ast::ExprKind::Field(_, ref field) => {
144 field.name.to_string().chars().all(|c| c.is_digit(10))
150 fn from_ast(context: &RewriteContext, expr: &ast::Expr) -> (ChainItemKind, Span) {
151 let (kind, span) = match expr.node {
152 ast::ExprKind::MethodCall(ref segment, ref expressions) => {
153 let types = if let Some(ref generic_args) = segment.args {
154 if let ast::GenericArgs::AngleBracketed(ref data) = **generic_args {
162 let span = mk_sp(expressions[0].span.hi(), expr.span.hi());
163 let kind = ChainItemKind::MethodCall(segment.clone(), types, expressions.clone());
166 ast::ExprKind::Field(ref nested, field) => {
167 let kind = if Self::is_tup_field_access(expr) {
168 ChainItemKind::TupleField(field, Self::is_tup_field_access(nested))
170 ChainItemKind::StructField(field)
172 let span = mk_sp(nested.span.hi(), field.span.hi());
175 _ => return (ChainItemKind::Parent(expr.clone()), expr.span),
178 // Remove comments from the span.
179 let lo = context.snippet_provider.span_before(span, ".");
180 (kind, mk_sp(lo, span.hi()))
184 impl Rewrite for ChainItem {
185 fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
186 let shape = shape.sub_width(self.tries)?;
187 let rewrite = match self.kind {
188 ChainItemKind::Parent(ref expr) => expr.rewrite(context, shape)?,
189 ChainItemKind::MethodCall(ref segment, ref types, ref exprs) => {
190 Self::rewrite_method_call(segment.ident, types, exprs, self.span, context, shape)?
192 ChainItemKind::StructField(ident) => format!(".{}", rewrite_ident(context, ident)),
193 ChainItemKind::TupleField(ident, nested) => format!(
195 if nested { " " } else { "" },
196 rewrite_ident(context, ident)
198 ChainItemKind::Comment(ref comment, _) => {
199 rewrite_comment(comment, false, shape, context.config)?
202 Some(format!("{}{}", rewrite, "?".repeat(self.tries)))
207 fn new(context: &RewriteContext, expr: &ast::Expr, tries: usize) -> ChainItem {
208 let (kind, span) = ChainItemKind::from_ast(context, expr);
209 ChainItem { kind, tries, span }
212 fn comment(span: Span, comment: String, pos: CommentPosition) -> ChainItem {
214 kind: ChainItemKind::Comment(comment, pos),
220 fn is_comment(&self) -> bool {
222 ChainItemKind::Comment(..) => true,
227 fn rewrite_method_call(
228 method_name: ast::Ident,
229 types: &[ast::GenericArg],
230 args: &[ptr::P<ast::Expr>],
232 context: &RewriteContext,
234 ) -> Option<String> {
235 let type_str = if types.is_empty() {
238 let type_list = types
240 .map(|ty| ty.rewrite(context, shape))
241 .collect::<Option<Vec<_>>>()?;
243 format!("::<{}>", type_list.join(", "))
245 let callee_str = format!(".{}{}", rewrite_ident(context, method_name), type_str);
246 rewrite_call(context, &callee_str, &args[1..], span, shape)
253 children: Vec<ChainItem>,
257 fn from_ast(expr: &ast::Expr, context: &RewriteContext) -> Chain {
258 let subexpr_list = Self::make_subexpr_list(expr, context);
260 // Un-parse the expression tree into ChainItems
261 let mut rev_children = vec![];
262 let mut sub_tries = 0;
263 for subexpr in &subexpr_list {
265 ast::ExprKind::Try(_) => sub_tries += 1,
267 rev_children.push(ChainItem::new(context, subexpr, sub_tries));
273 fn is_tries(s: &str) -> bool {
274 s.chars().all(|c| c == '?')
277 fn is_post_comment(s: &str) -> bool {
278 let comment_start_index = s.chars().position(|c| c == '/');
279 if comment_start_index.is_none() {
283 let newline_index = s.chars().position(|c| c == '\n');
284 if newline_index.is_none() {
288 comment_start_index.unwrap() < newline_index.unwrap()
291 fn handle_post_comment(
292 post_comment_span: Span,
293 post_comment_snippet: &str,
294 prev_span_end: &mut BytePos,
295 children: &mut Vec<ChainItem>,
297 let white_spaces: &[_] = &[' ', '\t'];
298 if post_comment_snippet
299 .trim_matches(white_spaces)
305 let trimmed_snippet = trim_tries(post_comment_snippet);
306 if is_post_comment(&trimmed_snippet) {
307 children.push(ChainItem::comment(
309 trimmed_snippet.trim().to_owned(),
310 CommentPosition::Back,
312 *prev_span_end = post_comment_span.hi();
316 let parent = rev_children.pop().unwrap();
317 let mut children = vec![];
318 let mut prev_span_end = parent.span.hi();
319 let mut iter = rev_children.into_iter().rev().peekable();
320 if let Some(first_chain_item) = iter.peek() {
321 let comment_span = mk_sp(prev_span_end, first_chain_item.span.lo());
322 let comment_snippet = context.snippet(comment_span);
323 if !is_tries(comment_snippet.trim()) {
332 while let Some(chain_item) = iter.next() {
333 let comment_snippet = context.snippet(chain_item.span);
334 // FIXME: Figure out the way to get a correct span when converting `try!` to `?`.
336 !(context.config.use_try_shorthand() || is_tries(comment_snippet.trim()));
340 let pre_comment_span = mk_sp(prev_span_end, chain_item.span.lo());
341 let pre_comment_snippet = trim_tries(context.snippet(pre_comment_span));
342 let (pre_comment, _) = extract_pre_comment(&pre_comment_snippet);
344 Some(ref comment) if !comment.is_empty() => {
345 children.push(ChainItem::comment(
348 CommentPosition::Top,
355 prev_span_end = chain_item.span.hi();
356 children.push(chain_item);
359 if !handle_comment || iter.peek().is_none() {
363 let next_lo = iter.peek().unwrap().span.lo();
364 let post_comment_span = mk_sp(prev_span_end, next_lo);
365 let post_comment_snippet = context.snippet(post_comment_span);
368 post_comment_snippet,
374 Chain { parent, children }
377 // Returns a Vec of the prefixes of the chain.
378 // E.g., for input `a.b.c` we return [`a.b.c`, `a.b`, 'a']
379 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> Vec<ast::Expr> {
380 let mut subexpr_list = vec![expr.clone()];
382 while let Some(subexpr) = Self::pop_expr_chain(subexpr_list.last().unwrap(), context) {
383 subexpr_list.push(subexpr.clone());
389 // Returns the expression's subexpression, if it exists. When the subexpr
390 // is a try! macro, we'll convert it to shorthand when the option is set.
391 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
393 ast::ExprKind::MethodCall(_, ref expressions) => {
394 Some(Self::convert_try(&expressions[0], context))
396 ast::ExprKind::Field(ref subexpr, _) | ast::ExprKind::Try(ref subexpr) => {
397 Some(Self::convert_try(subexpr, context))
403 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
405 ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
406 if let Some(subexpr) = convert_try_mac(mac, context) {
417 impl Rewrite for Chain {
418 fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
419 debug!("rewrite chain {:?} {:?}", self, shape);
421 let mut formatter = match context.config.indent_style() {
422 IndentStyle::Block => Box::new(ChainFormatterBlock::new(self)) as Box<ChainFormatter>,
423 IndentStyle::Visual => Box::new(ChainFormatterVisual::new(self)) as Box<ChainFormatter>,
426 formatter.format_root(&self.parent, context, shape)?;
427 if let Some(result) = formatter.pure_root() {
428 return wrap_str(result, context.config.max_width(), shape);
431 // Decide how to layout the rest of the chain.
432 let child_shape = formatter.child_shape(context, shape)?;
434 formatter.format_children(context, child_shape)?;
435 formatter.format_last_child(context, shape, child_shape)?;
437 let result = formatter.join_rewrites(context, child_shape)?;
438 wrap_str(result, context.config.max_width(), shape)
442 // There are a few types for formatting chains. This is because there is a lot
443 // in common between formatting with block vs visual indent, but they are
444 // different enough that branching on the indent all over the place gets ugly.
445 // Anything that can format a chain is a ChainFormatter.
446 trait ChainFormatter {
447 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
448 // Root is the parent plus any other chain items placed on the first line to
449 // avoid an orphan. E.g.,
454 // If `bar` were not part of the root, then foo would be orphaned and 'float'.
458 context: &RewriteContext,
461 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape>;
462 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()>;
463 fn format_last_child(
465 context: &RewriteContext,
469 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String>;
470 // Returns `Some` if the chain is only a root, None otherwise.
471 fn pure_root(&mut self) -> Option<String>;
474 // Data and behaviour that is shared by both chain formatters. The concrete
475 // formatters can delegate much behaviour to `ChainFormatterShared`.
476 struct ChainFormatterShared<'a> {
477 // The current working set of child items.
478 children: &'a [ChainItem],
479 // The current rewrites of items (includes trailing `?`s, but not any way to
480 // connect the rewrites together).
481 rewrites: Vec<String>,
482 // Whether the chain can fit on one line.
483 fits_single_line: bool,
484 // The number of children in the chain. This is not equal to `self.children.len()`
485 // because `self.children` will change size as we process the chain.
489 impl<'a> ChainFormatterShared<'a> {
490 fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
491 ChainFormatterShared {
492 children: &chain.children,
493 rewrites: Vec::with_capacity(chain.children.len() + 1),
494 fits_single_line: false,
495 child_count: chain.children.len(),
499 fn pure_root(&mut self) -> Option<String> {
500 if self.children.is_empty() {
501 assert_eq!(self.rewrites.len(), 1);
502 Some(self.rewrites.pop().unwrap())
508 // Rewrite the last child. The last child of a chain requires special treatment. We need to
509 // know whether 'overflowing' the last child make a better formatting:
511 // A chain with overflowing the last child:
513 // parent.child1.child2.last_child(
520 // A chain without overflowing the last child (in vertical layout):
525 // .last_child(a, b, c)
528 // In particular, overflowing is effective when the last child is a method with a multi-lined
529 // block-like argument (e.g. closure):
531 // parent.child1.child2.last_child(|a, b, c| {
532 // let x = foo(a, b, c);
533 // let y = bar(a, b, c);
540 fn format_last_child(
543 context: &RewriteContext,
547 let last = self.children.last()?;
548 let extendable = may_extend && last_line_extendable(&self.rewrites[0]);
549 let prev_last_line_width = last_line_width(&self.rewrites[0]);
551 // Total of all items excluding the last.
552 let almost_total = if extendable {
555 self.rewrites.iter().fold(0, |a, b| a + b.len())
557 let one_line_budget = if self.child_count == 1 {
560 min(shape.width, context.config.width_heuristics().chain_width)
562 .saturating_sub(almost_total);
564 let all_in_one_line = !self.children.iter().any(ChainItem::is_comment)
565 && self.rewrites.iter().all(|s| !s.contains('\n'))
566 && one_line_budget > 0;
567 let last_shape = if all_in_one_line {
568 shape.sub_width(last.tries)?
569 } else if extendable {
570 child_shape.sub_width(last.tries)?
572 child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
575 let mut last_subexpr_str = None;
576 if all_in_one_line || extendable {
577 // First we try to 'overflow' the last child and see if it looks better than using
579 let one_line_shape = if context.use_block_indent() {
580 last_shape.offset_left(almost_total)
583 .visual_indent(almost_total)
584 .sub_width(almost_total)
587 if let Some(one_line_shape) = one_line_shape {
588 if let Some(rw) = last.rewrite(context, one_line_shape) {
589 // We allow overflowing here only if both of the following conditions match:
590 // 1. The entire chain fits in a single line except the last child.
591 // 2. `last_child_str.lines().count() >= 5`.
592 let line_count = rw.lines().count();
593 let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
594 if could_fit_single_line && line_count >= 5 {
595 last_subexpr_str = Some(rw);
596 self.fits_single_line = all_in_one_line;
598 // We could not know whether overflowing is better than using vertical
599 // layout, just by looking at the overflowed rewrite. Now we rewrite the
600 // last child on its own line, and compare two rewrites to choose which is
602 let last_shape = child_shape
603 .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
604 match last.rewrite(context, last_shape) {
605 Some(ref new_rw) if !could_fit_single_line => {
606 last_subexpr_str = Some(new_rw.clone());
608 Some(ref new_rw) if new_rw.lines().count() >= line_count => {
609 last_subexpr_str = Some(rw);
610 self.fits_single_line = could_fit_single_line && all_in_one_line;
612 new_rw @ Some(..) => {
613 last_subexpr_str = new_rw;
616 last_subexpr_str = Some(rw);
617 self.fits_single_line = could_fit_single_line && all_in_one_line;
625 let last_shape = if context.use_block_indent() {
628 child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
631 last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
632 self.rewrites.push(last_subexpr_str?);
636 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
637 let connector = if self.fits_single_line {
638 // Yay, we can put everything on one line.
642 if *context.force_one_line_chain.borrow() {
645 child_shape.to_string_with_newline(context.config)
648 let mut rewrite_iter = self.rewrites.iter();
649 let mut result = rewrite_iter.next().unwrap().clone();
650 let children_iter = self.children.iter();
651 let iter = rewrite_iter.zip(children_iter);
653 for (rewrite, chain_item) in iter {
654 match chain_item.kind {
655 ChainItemKind::Comment(_, CommentPosition::Back) => result.push(' '),
656 ChainItemKind::Comment(_, CommentPosition::Top) => result.push_str(&connector),
657 _ => result.push_str(&connector),
659 result.push_str(&rewrite);
666 // Formats a chain using block indent.
667 struct ChainFormatterBlock<'a> {
668 shared: ChainFormatterShared<'a>,
669 root_ends_with_block: bool,
672 impl<'a> ChainFormatterBlock<'a> {
673 fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
674 ChainFormatterBlock {
675 shared: ChainFormatterShared::new(chain),
676 root_ends_with_block: false,
681 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
685 context: &RewriteContext,
688 let mut root_rewrite: String = parent.rewrite(context, shape)?;
690 let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
691 let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
693 while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
694 let item = &self.shared.children[0];
695 if let ChainItemKind::Comment(..) = item.kind {
698 let shape = shape.offset_left(root_rewrite.len())?;
699 match &item.rewrite(context, shape) {
700 Some(rewrite) => root_rewrite.push_str(rewrite),
704 root_ends_with_block = last_line_extendable(&root_rewrite);
706 self.shared.children = &self.shared.children[1..];
707 if self.shared.children.is_empty() {
711 self.shared.rewrites.push(root_rewrite);
712 self.root_ends_with_block = root_ends_with_block;
716 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape> {
718 if self.root_ends_with_block {
719 shape.block_indent(0)
721 shape.block_indent(context.config.tab_spaces())
723 .with_max_width(context.config),
727 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()> {
728 for item in &self.shared.children[..self.shared.children.len() - 1] {
729 let rewrite = item.rewrite(context, child_shape)?;
730 self.shared.rewrites.push(rewrite);
735 fn format_last_child(
737 context: &RewriteContext,
742 .format_last_child(true, context, shape, child_shape)
745 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
746 self.shared.join_rewrites(context, child_shape)
749 fn pure_root(&mut self) -> Option<String> {
750 self.shared.pure_root()
754 // Format a chain using visual indent.
755 struct ChainFormatterVisual<'a> {
756 shared: ChainFormatterShared<'a>,
757 // The extra offset from the chain's shape to the position of the `.`
761 impl<'a> ChainFormatterVisual<'a> {
762 fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
763 ChainFormatterVisual {
764 shared: ChainFormatterShared::new(chain),
770 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
774 context: &RewriteContext,
777 let parent_shape = shape.visual_indent(0);
778 let mut root_rewrite = parent.rewrite(context, parent_shape)?;
779 let multiline = root_rewrite.contains('\n');
780 self.offset = if multiline {
781 last_line_width(&root_rewrite).saturating_sub(shape.used_width())
783 trimmed_last_line_width(&root_rewrite)
786 if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
787 let item = &self.shared.children[0];
788 if let ChainItemKind::Comment(..) = item.kind {
789 self.shared.rewrites.push(root_rewrite);
792 let child_shape = parent_shape
793 .visual_indent(self.offset)
794 .sub_width(self.offset)?;
795 let rewrite = item.rewrite(context, child_shape)?;
796 match wrap_str(rewrite, context.config.max_width(), shape) {
797 Some(rewrite) => root_rewrite.push_str(&rewrite),
799 // We couldn't fit in at the visual indent, try the last
801 let rewrite = item.rewrite(context, parent_shape)?;
802 root_rewrite.push_str(&rewrite);
807 self.shared.children = &self.shared.children[1..];
810 self.shared.rewrites.push(root_rewrite);
814 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape> {
816 .with_max_width(context.config)
817 .offset_left(self.offset)
818 .map(|s| s.visual_indent(0))
821 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()> {
822 for item in &self.shared.children[..self.shared.children.len() - 1] {
823 let rewrite = item.rewrite(context, child_shape)?;
824 self.shared.rewrites.push(rewrite);
829 fn format_last_child(
831 context: &RewriteContext,
836 .format_last_child(false, context, shape, child_shape)
839 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
840 self.shared.join_rewrites(context, child_shape)
843 fn pure_root(&mut self) -> Option<String> {
844 self.shared.pure_root()
848 /// Remove try operators (`?`s) that appear in the given string. If removing
849 /// them leaves an empty line, remove that line as well unless it is the first
850 /// line (we need the first newline for detecting pre/post comment).
851 fn trim_tries(s: &str) -> String {
852 let mut result = String::with_capacity(s.len());
853 let mut line_buffer = String::with_capacity(s.len());
854 for (kind, rich_char) in CharClasses::new(s.chars()) {
855 match rich_char.get_char() {
857 if result.is_empty() || !line_buffer.trim().is_empty() {
858 result.push_str(&line_buffer);
863 '?' if kind == FullCodeCharKind::Normal => continue,
864 c => line_buffer.push(c),
867 if !line_buffer.trim().is_empty() {
868 result.push_str(&line_buffer);