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 lists::{extract_post_comment, extract_pre_comment, get_comment_end};
73 use macros::convert_try_mac;
74 use rewrite::{Rewrite, RewriteContext};
77 first_line_width, last_line_extendable, last_line_width, mk_sp, trimmed_last_line_width,
85 use syntax::codemap::{BytePos, Span};
86 use syntax::{ast, ptr};
88 pub fn rewrite_chain(expr: &ast::Expr, context: &RewriteContext, shape: Shape) -> Option<String> {
89 let chain = Chain::from_ast(expr, context);
90 debug!("rewrite_chain {:?} {:?}", chain, shape);
92 // If this is just an expression with some `?`s, then format it trivially and
94 if chain.children.is_empty() {
95 return chain.parent.rewrite(context, shape);
98 chain.rewrite(context, shape)
102 enum CommentPosition {
107 // An expression plus trailing `?`s to be formatted together.
115 // FIXME: we can't use a reference here because to convert `try!` to `?` we
116 // synthesise the AST node. However, I think we could use `Cow` and that
117 // would remove a lot of cloning.
123 Vec<ast::GenericArg>,
124 Vec<ptr::P<ast::Expr>>,
126 StructField(ast::Ident),
127 TupleField(ast::Ident, bool),
128 Comment(String, CommentPosition),
132 fn is_block_like(&self, context: &RewriteContext, reps: &str) -> bool {
134 ChainItemKind::Parent(ref expr) => is_block_expr(context, expr, reps),
135 ChainItemKind::MethodCall(..) => reps.contains('\n'),
136 ChainItemKind::StructField(..)
137 | ChainItemKind::TupleField(..)
138 | ChainItemKind::Comment(..) => false,
142 fn is_tup_field_access(expr: &ast::Expr) -> bool {
144 ast::ExprKind::Field(_, ref field) => {
145 field.name.to_string().chars().all(|c| c.is_digit(10))
151 fn from_ast(context: &RewriteContext, expr: &ast::Expr) -> (ChainItemKind, Span) {
152 let (kind, span) = match expr.node {
153 ast::ExprKind::MethodCall(ref segment, ref expressions) => {
154 let types = if let Some(ref generic_args) = segment.args {
155 if let ast::GenericArgs::AngleBracketed(ref data) = **generic_args {
163 let span = mk_sp(expressions[0].span.hi(), expr.span.hi());
164 let kind = ChainItemKind::MethodCall(segment.clone(), types, expressions.clone());
167 ast::ExprKind::Field(ref nested, field) => {
168 let kind = if Self::is_tup_field_access(expr) {
169 ChainItemKind::TupleField(field, Self::is_tup_field_access(nested))
171 ChainItemKind::StructField(field)
173 let span = mk_sp(nested.span.hi(), field.span.hi());
176 _ => return (ChainItemKind::Parent(expr.clone()), expr.span),
179 // Remove comments from the span.
180 let lo = context.snippet_provider.span_before(span, ".");
181 (kind, mk_sp(lo, span.hi()))
185 impl Rewrite for ChainItem {
186 fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
187 let shape = shape.sub_width(self.tries)?;
188 let rewrite = match self.kind {
189 ChainItemKind::Parent(ref expr) => expr.rewrite(context, shape)?,
190 ChainItemKind::MethodCall(ref segment, ref types, ref exprs) => {
191 Self::rewrite_method_call(segment.ident, types, exprs, self.span, context, shape)?
193 ChainItemKind::StructField(ident) => format!(".{}", ident.name),
194 ChainItemKind::TupleField(ident, nested) => {
195 format!("{}.{}", if nested { " " } else { "" }, ident.name)
197 ChainItemKind::Comment(ref comment, _) => {
198 rewrite_comment(comment, false, shape, context.config)?
201 Some(format!("{}{}", rewrite, "?".repeat(self.tries)))
206 fn new(context: &RewriteContext, expr: &ast::Expr, tries: usize) -> ChainItem {
207 let (kind, span) = ChainItemKind::from_ast(context, expr);
208 ChainItem { kind, tries, span }
211 fn comment(span: Span, comment: String, pos: CommentPosition) -> ChainItem {
213 kind: ChainItemKind::Comment(comment, pos),
219 fn is_comment(&self) -> bool {
221 ChainItemKind::Comment(..) => true,
226 fn rewrite_method_call(
227 method_name: ast::Ident,
228 types: &[ast::GenericArg],
229 args: &[ptr::P<ast::Expr>],
231 context: &RewriteContext,
233 ) -> Option<String> {
234 let type_str = if types.is_empty() {
237 let type_list = types
239 .map(|ty| ty.rewrite(context, shape))
240 .collect::<Option<Vec<_>>>()?;
242 format!("::<{}>", type_list.join(", "))
244 let callee_str = format!(".{}{}", method_name, type_str);
245 rewrite_call(context, &callee_str, &args[1..], span, shape)
252 children: Vec<ChainItem>,
256 fn from_ast(expr: &ast::Expr, context: &RewriteContext) -> Chain {
257 let subexpr_list = Self::make_subexpr_list(expr, context);
259 // Un-parse the expression tree into ChainItems
260 let mut rev_children = vec![];
261 let mut sub_tries = 0;
262 for subexpr in &subexpr_list {
264 ast::ExprKind::Try(_) => sub_tries += 1,
266 rev_children.push(ChainItem::new(context, subexpr, sub_tries));
272 fn is_tries(s: &str) -> bool {
273 s.chars().all(|c| c == '?')
276 fn handle_post_comment(
277 post_comment_span: Span,
278 post_comment_snippet: &str,
279 prev_span_end: &mut BytePos,
280 children: &mut Vec<ChainItem>,
282 let white_spaces: &[_] = &[' ', '\t'];
283 if post_comment_snippet
284 .trim_matches(white_spaces)
290 // HACK: Treat `?`s as separators.
291 let trimmed_snippet = post_comment_snippet.trim_matches('?');
292 let comment_end = get_comment_end(trimmed_snippet, "?", "", false);
293 let maybe_post_comment = extract_post_comment(trimmed_snippet, comment_end, "?")
294 .and_then(|comment| {
295 if comment.is_empty() {
298 Some((comment, comment_end))
302 if let Some((post_comment, comment_end)) = maybe_post_comment {
303 children.push(ChainItem::comment(
306 CommentPosition::Back,
308 *prev_span_end = *prev_span_end + BytePos(comment_end as u32);
312 let parent = rev_children.pop().unwrap();
313 let mut children = vec![];
314 let mut prev_span_end = parent.span.hi();
315 let mut iter = rev_children.into_iter().rev().peekable();
316 if let Some(first_chain_item) = iter.peek() {
317 let comment_span = mk_sp(prev_span_end, first_chain_item.span.lo());
318 let comment_snippet = context.snippet(comment_span);
319 if !is_tries(comment_snippet.trim()) {
328 while let Some(chain_item) = iter.next() {
329 let comment_snippet = context.snippet(chain_item.span);
330 // FIXME: Figure out the way to get a correct span when converting `try!` to `?`.
332 !(context.config.use_try_shorthand() || is_tries(comment_snippet.trim()));
336 let pre_comment_span = mk_sp(prev_span_end, chain_item.span.lo());
337 let pre_comment_snippet = context.snippet(pre_comment_span);
338 let pre_comment_snippet = pre_comment_snippet.trim().trim_matches('?');
339 let (pre_comment, _) = extract_pre_comment(pre_comment_snippet);
341 Some(ref comment) if !comment.is_empty() => {
342 children.push(ChainItem::comment(
345 CommentPosition::Top,
352 prev_span_end = chain_item.span.hi();
353 children.push(chain_item);
356 if !handle_comment || iter.peek().is_none() {
360 let next_lo = iter.peek().unwrap().span.lo();
361 let post_comment_span = mk_sp(prev_span_end, next_lo);
362 let post_comment_snippet = context.snippet(post_comment_span);
365 post_comment_snippet,
371 Chain { parent, children }
374 // Returns a Vec of the prefixes of the chain.
375 // E.g., for input `a.b.c` we return [`a.b.c`, `a.b`, 'a']
376 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> Vec<ast::Expr> {
377 let mut subexpr_list = vec![expr.clone()];
379 while let Some(subexpr) = Self::pop_expr_chain(subexpr_list.last().unwrap(), context) {
380 subexpr_list.push(subexpr.clone());
386 // Returns the expression's subexpression, if it exists. When the subexpr
387 // is a try! macro, we'll convert it to shorthand when the option is set.
388 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
390 ast::ExprKind::MethodCall(_, ref expressions) => {
391 Some(Self::convert_try(&expressions[0], context))
393 ast::ExprKind::Field(ref subexpr, _) | ast::ExprKind::Try(ref subexpr) => {
394 Some(Self::convert_try(subexpr, context))
400 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
402 ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
403 if let Some(subexpr) = convert_try_mac(mac, context) {
414 impl Rewrite for Chain {
415 fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
416 debug!("rewrite chain {:?} {:?}", self, shape);
418 let mut formatter = match context.config.indent_style() {
419 IndentStyle::Block => Box::new(ChainFormatterBlock::new(self)) as Box<ChainFormatter>,
420 IndentStyle::Visual => Box::new(ChainFormatterVisual::new(self)) as Box<ChainFormatter>,
423 formatter.format_root(&self.parent, context, shape)?;
424 if let Some(result) = formatter.pure_root() {
425 return wrap_str(result, context.config.max_width(), shape);
428 // Decide how to layout the rest of the chain.
429 let child_shape = formatter.child_shape(context, shape)?;
431 formatter.format_children(context, child_shape)?;
432 formatter.format_last_child(context, shape, child_shape)?;
434 let result = formatter.join_rewrites(context, child_shape)?;
435 wrap_str(result, context.config.max_width(), shape)
439 // There are a few types for formatting chains. This is because there is a lot
440 // in common between formatting with block vs visual indent, but they are
441 // different enough that branching on the indent all over the place gets ugly.
442 // Anything that can format a chain is a ChainFormatter.
443 trait ChainFormatter {
444 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
445 // Root is the parent plus any other chain items placed on the first line to
446 // avoid an orphan. E.g.,
451 // If `bar` were not part of the root, then foo would be orphaned and 'float'.
455 context: &RewriteContext,
458 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape>;
459 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()>;
460 fn format_last_child(
462 context: &RewriteContext,
466 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String>;
467 // Returns `Some` if the chain is only a root, None otherwise.
468 fn pure_root(&mut self) -> Option<String>;
471 // Data and behaviour that is shared by both chain formatters. The concrete
472 // formatters can delegate much behaviour to `ChainFormatterShared`.
473 struct ChainFormatterShared<'a> {
474 // The current working set of child items.
475 children: &'a [ChainItem],
476 // The current rewrites of items (includes trailing `?`s, but not any way to
477 // connect the rewrites together).
478 rewrites: Vec<String>,
479 // Whether the chain can fit on one line.
480 fits_single_line: bool,
481 // The number of children in the chain. This is not equal to `self.children.len()`
482 // because `self.children` will change size as we process the chain.
486 impl<'a> ChainFormatterShared<'a> {
487 fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
488 ChainFormatterShared {
489 children: &chain.children,
490 rewrites: Vec::with_capacity(chain.children.len() + 1),
491 fits_single_line: false,
492 child_count: chain.children.len(),
496 fn pure_root(&mut self) -> Option<String> {
497 if self.children.is_empty() {
498 assert_eq!(self.rewrites.len(), 1);
499 Some(self.rewrites.pop().unwrap())
505 // Rewrite the last child. The last child of a chain requires special treatment. We need to
506 // know whether 'overflowing' the last child make a better formatting:
508 // A chain with overflowing the last child:
510 // parent.child1.child2.last_child(
517 // A chain without overflowing the last child (in vertical layout):
522 // .last_child(a, b, c)
525 // In particular, overflowing is effective when the last child is a method with a multi-lined
526 // block-like argument (e.g. closure):
528 // parent.child1.child2.last_child(|a, b, c| {
529 // let x = foo(a, b, c);
530 // let y = bar(a, b, c);
537 fn format_last_child(
540 context: &RewriteContext,
544 let last = self.children.last()?;
545 let extendable = may_extend && last_line_extendable(&self.rewrites[0]);
546 let prev_last_line_width = last_line_width(&self.rewrites[0]);
548 // Total of all items excluding the last.
549 let almost_total = if extendable {
552 self.rewrites.iter().fold(0, |a, b| a + b.len())
554 let one_line_budget = if self.child_count == 1 {
557 min(shape.width, context.config.width_heuristics().chain_width)
558 }.saturating_sub(almost_total);
560 let all_in_one_line = !self.children.iter().any(ChainItem::is_comment)
561 && self.rewrites.iter().all(|s| !s.contains('\n'))
562 && one_line_budget > 0;
563 let last_shape = if all_in_one_line {
564 shape.sub_width(last.tries)?
565 } else if extendable {
566 child_shape.sub_width(last.tries)?
568 child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
571 let mut last_subexpr_str = None;
572 if all_in_one_line || extendable {
573 // First we try to 'overflow' the last child and see if it looks better than using
575 if let Some(one_line_shape) = last_shape.offset_left(almost_total) {
576 if let Some(rw) = last.rewrite(context, one_line_shape) {
577 // We allow overflowing here only if both of the following conditions match:
578 // 1. The entire chain fits in a single line except the last child.
579 // 2. `last_child_str.lines().count() >= 5`.
580 let line_count = rw.lines().count();
581 let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
582 if could_fit_single_line && line_count >= 5 {
583 last_subexpr_str = Some(rw);
584 self.fits_single_line = all_in_one_line;
586 // We could not know whether overflowing is better than using vertical
587 // layout, just by looking at the overflowed rewrite. Now we rewrite the
588 // last child on its own line, and compare two rewrites to choose which is
590 let last_shape = child_shape
591 .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
592 match last.rewrite(context, last_shape) {
593 Some(ref new_rw) if !could_fit_single_line => {
594 last_subexpr_str = Some(new_rw.clone());
596 Some(ref new_rw) if new_rw.lines().count() >= line_count => {
597 last_subexpr_str = Some(rw);
598 self.fits_single_line = could_fit_single_line && all_in_one_line;
600 new_rw @ Some(..) => {
601 last_subexpr_str = new_rw;
604 last_subexpr_str = Some(rw);
605 self.fits_single_line = could_fit_single_line && all_in_one_line;
613 last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
614 self.rewrites.push(last_subexpr_str?);
620 context: &RewriteContext,
622 block_like_iter: impl Iterator<Item = bool>,
623 ) -> Option<String> {
624 let connector = if self.fits_single_line {
625 // Yay, we can put everything on one line.
629 if *context.force_one_line_chain.borrow() {
632 child_shape.to_string_with_newline(context.config)
635 let mut rewrite_iter = self.rewrites.iter();
636 let mut result = rewrite_iter.next().unwrap().clone();
637 let children_iter = self.children.iter();
638 let iter = rewrite_iter.zip(block_like_iter).zip(children_iter);
640 for ((rewrite, prev_is_block_like), chain_item) in iter {
641 match chain_item.kind {
642 ChainItemKind::Comment(_, CommentPosition::Back) => result.push(' '),
643 ChainItemKind::Comment(_, CommentPosition::Top) => result.push_str(&connector),
645 if !prev_is_block_like {
646 result.push_str(&connector);
650 result.push_str(&rewrite);
657 // Formats a chain using block indent.
658 struct ChainFormatterBlock<'a> {
659 shared: ChainFormatterShared<'a>,
660 // For each rewrite, whether the corresponding item is block-like.
661 is_block_like: Vec<bool>,
664 impl<'a> ChainFormatterBlock<'a> {
665 fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
666 ChainFormatterBlock {
667 shared: ChainFormatterShared::new(chain),
668 is_block_like: Vec::with_capacity(chain.children.len() + 1),
673 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
677 context: &RewriteContext,
680 let mut root_rewrite: String = parent.rewrite(context, shape)?;
682 let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
683 let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
685 while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
686 let item = &self.shared.children[0];
687 if let ChainItemKind::Comment(..) = item.kind {
690 let shape = shape.offset_left(root_rewrite.len())?;
691 match &item.rewrite(context, shape) {
692 Some(rewrite) => root_rewrite.push_str(rewrite),
696 root_ends_with_block = item.kind.is_block_like(context, &root_rewrite);
698 self.shared.children = &self.shared.children[1..];
699 if self.shared.children.is_empty() {
703 self.is_block_like.push(root_ends_with_block);
704 self.shared.rewrites.push(root_rewrite);
708 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape> {
710 if self.is_block_like[0] {
711 shape.block_indent(0)
713 shape.block_indent(context.config.tab_spaces())
714 }.with_max_width(context.config),
718 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()> {
719 for item in &self.shared.children[..self.shared.children.len() - 1] {
720 let rewrite = item.rewrite(context, child_shape)?;
722 .push(item.kind.is_block_like(context, &rewrite));
723 self.shared.rewrites.push(rewrite);
728 fn format_last_child(
730 context: &RewriteContext,
735 .format_last_child(true, context, shape, child_shape)
738 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
740 .join_rewrites(context, child_shape, self.is_block_like.iter().cloned())
743 fn pure_root(&mut self) -> Option<String> {
744 self.shared.pure_root()
748 // Format a chain using visual indent.
749 struct ChainFormatterVisual<'a> {
750 shared: ChainFormatterShared<'a>,
751 // The extra offset from the chain's shape to the position of the `.`
755 impl<'a> ChainFormatterVisual<'a> {
756 fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
757 ChainFormatterVisual {
758 shared: ChainFormatterShared::new(chain),
764 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
768 context: &RewriteContext,
771 let parent_shape = shape.visual_indent(0);
772 let mut root_rewrite = parent.rewrite(context, parent_shape)?;
773 let multiline = root_rewrite.contains('\n');
774 self.offset = if multiline {
775 last_line_width(&root_rewrite).saturating_sub(shape.used_width())
777 trimmed_last_line_width(&root_rewrite)
780 if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
781 let item = &self.shared.children[0];
782 if let ChainItemKind::Comment(..) = item.kind {
783 self.shared.rewrites.push(root_rewrite);
786 let child_shape = parent_shape
787 .visual_indent(self.offset)
788 .sub_width(self.offset)?;
789 let rewrite = item.rewrite(context, child_shape)?;
790 match wrap_str(rewrite, context.config.max_width(), shape) {
791 Some(rewrite) => root_rewrite.push_str(&rewrite),
793 // We couldn't fit in at the visual indent, try the last
795 let rewrite = item.rewrite(context, parent_shape)?;
796 root_rewrite.push_str(&rewrite);
801 self.shared.children = &self.shared.children[1..];
804 self.shared.rewrites.push(root_rewrite);
808 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape> {
810 .with_max_width(context.config)
811 .offset_left(self.offset)
812 .map(|s| s.visual_indent(0))
815 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()> {
816 for item in &self.shared.children[..self.shared.children.len() - 1] {
817 let rewrite = item.rewrite(context, child_shape)?;
818 self.shared.rewrites.push(rewrite);
823 fn format_last_child(
825 context: &RewriteContext,
830 .format_last_child(false, context, shape, child_shape)
833 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
835 .join_rewrites(context, child_shape, iter::repeat(false))
838 fn pure_root(&mut self) -> Option<String> {
839 self.shared.pure_root()
843 // States whether an expression's last line exclusively consists of closing
844 // parens, braces, and brackets in its idiomatic formatting.
845 fn is_block_expr(context: &RewriteContext, expr: &ast::Expr, repr: &str) -> bool {
847 ast::ExprKind::Mac(..)
848 | ast::ExprKind::Call(..)
849 | ast::ExprKind::MethodCall(..)
850 | ast::ExprKind::Struct(..)
851 | ast::ExprKind::While(..)
852 | ast::ExprKind::WhileLet(..)
853 | ast::ExprKind::If(..)
854 | ast::ExprKind::IfLet(..)
855 | ast::ExprKind::Block(..)
856 | ast::ExprKind::Loop(..)
857 | ast::ExprKind::ForLoop(..)
858 | ast::ExprKind::Match(..) => repr.contains('\n'),
859 ast::ExprKind::Paren(ref expr)
860 | ast::ExprKind::Binary(_, _, ref expr)
861 | ast::ExprKind::Index(_, ref expr)
862 | ast::ExprKind::Unary(_, ref expr)
863 | ast::ExprKind::Closure(_, _, _, _, ref expr, _)
864 | ast::ExprKind::Try(ref expr)
865 | ast::ExprKind::Yield(Some(ref expr)) => is_block_expr(context, expr, repr),
866 // This can only be a string lit
867 ast::ExprKind::Lit(_) => {
868 repr.contains('\n') && trimmed_last_line_width(repr) <= context.config.tab_spaces()