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 config::IndentStyle;
70 use expr::rewrite_call;
71 use macros::convert_try_mac;
72 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),
124 fn is_block_like(&self, context: &RewriteContext, reps: &str) -> bool {
126 ChainItemKind::Parent(ref expr) => is_block_expr(context, expr, reps),
127 ChainItemKind::MethodCall(..) => reps.contains('\n'),
128 ChainItemKind::StructField(..) | ChainItemKind::TupleField(..) => false,
132 fn is_tup_field_access(expr: &ast::Expr) -> bool {
134 ast::ExprKind::Field(_, ref field) => {
135 field.name.to_string().chars().all(|c| c.is_digit(10))
141 fn from_ast(context: &RewriteContext, expr: &ast::Expr) -> (ChainItemKind, Span) {
142 let (kind, span) = match expr.node {
143 ast::ExprKind::MethodCall(ref segment, ref expressions) => {
144 let types = if let Some(ref generic_args) = segment.args {
145 if let ast::GenericArgs::AngleBracketed(ref data) = **generic_args {
153 let span = mk_sp(expressions[0].span.hi(), expr.span.hi());
154 let kind = ChainItemKind::MethodCall(segment.clone(), types, expressions.clone());
157 ast::ExprKind::Field(ref nested, field) => {
158 let kind = if Self::is_tup_field_access(expr) {
159 ChainItemKind::TupleField(field, Self::is_tup_field_access(nested))
161 ChainItemKind::StructField(field)
163 let span = mk_sp(nested.span.hi(), field.span.hi());
166 _ => return (ChainItemKind::Parent(expr.clone()), expr.span),
169 // Remove comments from the span.
170 let lo = context.snippet_provider.span_before(span, ".");
171 (kind, mk_sp(lo, span.hi()))
175 impl Rewrite for ChainItem {
176 fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
177 let shape = shape.sub_width(self.tries)?;
178 let rewrite = match self.kind {
179 ChainItemKind::Parent(ref expr) => expr.rewrite(context, shape)?,
180 ChainItemKind::MethodCall(ref segment, ref types, ref exprs) => {
181 Self::rewrite_method_call(segment.ident, types, exprs, self.span, context, shape)?
183 ChainItemKind::StructField(ident) => format!(".{}", ident.name),
184 ChainItemKind::TupleField(ident, nested) => {
185 format!("{}.{}", if nested { " " } else { "" }, ident.name)
188 Some(format!("{}{}", rewrite, "?".repeat(self.tries)))
193 fn new(context: &RewriteContext, expr: &ast::Expr, tries: usize) -> ChainItem {
194 let (kind, span) = ChainItemKind::from_ast(context, expr);
195 ChainItem { kind, tries, span }
198 fn rewrite_method_call(
199 method_name: ast::Ident,
200 types: &[ast::GenericArg],
201 args: &[ptr::P<ast::Expr>],
203 context: &RewriteContext,
205 ) -> Option<String> {
206 let type_str = if types.is_empty() {
209 let type_list = types
211 .map(|ty| ty.rewrite(context, shape))
212 .collect::<Option<Vec<_>>>()?;
214 format!("::<{}>", type_list.join(", "))
216 let callee_str = format!(".{}{}", method_name, type_str);
217 rewrite_call(context, &callee_str, &args[1..], span, shape)
224 children: Vec<ChainItem>,
228 fn from_ast(expr: &ast::Expr, context: &RewriteContext) -> Chain {
229 let subexpr_list = Self::make_subexpr_list(expr, context);
231 // Un-parse the expression tree into ChainItems
232 let mut children = vec![];
233 let mut sub_tries = 0;
234 for subexpr in &subexpr_list {
236 ast::ExprKind::Try(_) => sub_tries += 1,
238 children.push(ChainItem::new(context, subexpr, sub_tries));
245 parent: children.pop().unwrap(),
250 // Returns a Vec of the prefixes of the chain.
251 // E.g., for input `a.b.c` we return [`a.b.c`, `a.b`, 'a']
252 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> Vec<ast::Expr> {
253 let mut subexpr_list = vec![expr.clone()];
255 while let Some(subexpr) = Self::pop_expr_chain(subexpr_list.last().unwrap(), context) {
256 subexpr_list.push(subexpr.clone());
262 // Returns the expression's subexpression, if it exists. When the subexpr
263 // is a try! macro, we'll convert it to shorthand when the option is set.
264 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
266 ast::ExprKind::MethodCall(_, ref expressions) => {
267 Some(Self::convert_try(&expressions[0], context))
269 ast::ExprKind::Field(ref subexpr, _) | ast::ExprKind::Try(ref subexpr) => {
270 Some(Self::convert_try(subexpr, context))
276 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
278 ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
279 if let Some(subexpr) = convert_try_mac(mac, context) {
290 impl Rewrite for Chain {
291 fn rewrite(&self, context: &RewriteContext, shape: Shape) -> Option<String> {
292 debug!("rewrite chain {:?} {:?}", self, shape);
294 let mut formatter = match context.config.indent_style() {
295 IndentStyle::Block => Box::new(ChainFormatterBlock::new(self)) as Box<ChainFormatter>,
296 IndentStyle::Visual => Box::new(ChainFormatterVisual::new(self)) as Box<ChainFormatter>,
299 formatter.format_root(&self.parent, context, shape)?;
300 if let Some(result) = formatter.pure_root() {
301 return wrap_str(result, context.config.max_width(), shape);
304 // Decide how to layout the rest of the chain.
305 let child_shape = formatter.child_shape(context, shape)?;
307 formatter.format_children(context, child_shape)?;
308 formatter.format_last_child(context, shape, child_shape)?;
310 let result = formatter.join_rewrites(context, child_shape)?;
311 wrap_str(result, context.config.max_width(), shape)
315 // There are a few types for formatting chains. This is because there is a lot
316 // in common between formatting with block vs visual indent, but they are
317 // different enough that branching on the indent all over the place gets ugly.
318 // Anything that can format a chain is a ChainFormatter.
319 trait ChainFormatter {
320 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
321 // Root is the parent plus any other chain items placed on the first line to
322 // avoid an orphan. E.g.,
327 // If `bar` were not part of the root, then foo would be orphaned and 'float'.
331 context: &RewriteContext,
334 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape>;
335 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()>;
336 fn format_last_child(
338 context: &RewriteContext,
342 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String>;
343 // Returns `Some` if the chain is only a root, None otherwise.
344 fn pure_root(&mut self) -> Option<String>;
347 // Data and behaviour that is shared by both chain formatters. The concrete
348 // formatters can delegate much behaviour to `ChainFormatterShared`.
349 struct ChainFormatterShared<'a> {
350 // The current working set of child items.
351 children: &'a [ChainItem],
352 // The current rewrites of items (includes trailing `?`s, but not any way to
353 // connect the rewrites together).
354 rewrites: Vec<String>,
355 // Whether the chain can fit on one line.
356 fits_single_line: bool,
357 // The number of children in the chain. This is not equal to `self.children.len()`
358 // because `self.children` will change size as we process the chain.
362 impl<'a> ChainFormatterShared<'a> {
363 fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
364 ChainFormatterShared {
365 children: &chain.children,
366 rewrites: Vec::with_capacity(chain.children.len() + 1),
367 fits_single_line: false,
368 child_count: chain.children.len(),
372 fn pure_root(&mut self) -> Option<String> {
373 if self.children.is_empty() {
374 assert_eq!(self.rewrites.len(), 1);
375 Some(self.rewrites.pop().unwrap())
381 // Rewrite the last child. The last child of a chain requires special treatment. We need to
382 // know whether 'overflowing' the last child make a better formatting:
384 // A chain with overflowing the last child:
386 // parent.child1.child2.last_child(
393 // A chain without overflowing the last child (in vertical layout):
398 // .last_child(a, b, c)
401 // In particular, overflowing is effective when the last child is a method with a multi-lined
402 // block-like argument (e.g. closure):
404 // parent.child1.child2.last_child(|a, b, c| {
405 // let x = foo(a, b, c);
406 // let y = bar(a, b, c);
413 fn format_last_child(
416 context: &RewriteContext,
420 let last = &self.children[0];
422 may_extend && last_line_extendable(&self.rewrites[self.rewrites.len() - 1]);
423 let prev_last_line_width = last_line_width(&self.rewrites[self.rewrites.len() - 1]);
425 // Total of all items excluding the last.
426 let almost_total = if extendable {
429 self.rewrites.iter().fold(0, |a, b| a + b.len())
431 let one_line_budget = if self.child_count == 1 {
434 min(shape.width, context.config.width_heuristics().chain_width)
435 }.saturating_sub(almost_total);
437 let all_in_one_line =
438 self.rewrites.iter().all(|s| !s.contains('\n')) && one_line_budget > 0;
439 let last_shape = if all_in_one_line {
440 shape.sub_width(last.tries)?
441 } else if extendable {
442 child_shape.sub_width(last.tries)?
444 child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
447 let mut last_subexpr_str = None;
448 if all_in_one_line || extendable {
449 // First we try to 'overflow' the last child and see if it looks better than using
451 if let Some(one_line_shape) = last_shape.offset_left(almost_total) {
452 if let Some(rw) = last.rewrite(context, one_line_shape) {
453 // We allow overflowing here only if both of the following conditions match:
454 // 1. The entire chain fits in a single line except the last child.
455 // 2. `last_child_str.lines().count() >= 5`.
456 let line_count = rw.lines().count();
457 let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
458 if could_fit_single_line && line_count >= 5 {
459 last_subexpr_str = Some(rw);
460 self.fits_single_line = all_in_one_line;
462 // We could not know whether overflowing is better than using vertical
463 // layout, just by looking at the overflowed rewrite. Now we rewrite the
464 // last child on its own line, and compare two rewrites to choose which is
466 let last_shape = child_shape
467 .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
468 match last.rewrite(context, last_shape) {
469 Some(ref new_rw) if !could_fit_single_line => {
470 last_subexpr_str = Some(new_rw.clone());
472 Some(ref new_rw) if new_rw.lines().count() >= line_count => {
473 last_subexpr_str = Some(rw);
474 self.fits_single_line = could_fit_single_line && all_in_one_line;
476 new_rw @ Some(..) => {
477 last_subexpr_str = new_rw;
480 last_subexpr_str = Some(rw);
481 self.fits_single_line = could_fit_single_line && all_in_one_line;
489 last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
490 self.rewrites.push(last_subexpr_str?);
496 context: &RewriteContext,
498 block_like_iter: impl Iterator<Item = bool>,
499 ) -> Option<String> {
500 let connector = if self.fits_single_line {
501 // Yay, we can put everything on one line.
505 if *context.force_one_line_chain.borrow() {
508 child_shape.to_string_with_newline(context.config)
511 let mut rewrite_iter = self.rewrites.iter();
512 let mut result = rewrite_iter.next().unwrap().clone();
514 for (rewrite, prev_is_block_like) in rewrite_iter.zip(block_like_iter) {
515 if !prev_is_block_like {
516 result.push_str(&connector);
518 result.push_str(&rewrite);
525 // Formats a chain using block indent.
526 struct ChainFormatterBlock<'a> {
527 shared: ChainFormatterShared<'a>,
528 // For each rewrite, whether the corresponding item is block-like.
529 is_block_like: Vec<bool>,
532 impl<'a> ChainFormatterBlock<'a> {
533 fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
534 ChainFormatterBlock {
535 shared: ChainFormatterShared::new(chain),
536 is_block_like: Vec::with_capacity(chain.children.len() + 1),
541 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
545 context: &RewriteContext,
548 let mut root_rewrite: String = parent.rewrite(context, shape)?;
550 let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
551 let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
553 while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
554 let item = &self.shared.children[self.shared.children.len() - 1];
555 let shape = shape.offset_left(root_rewrite.len())?;
556 match &item.rewrite(context, shape) {
557 Some(rewrite) => root_rewrite.push_str(rewrite),
561 root_ends_with_block = item.kind.is_block_like(context, &root_rewrite);
563 self.shared.children = &self.shared.children[..self.shared.children.len() - 1];
564 if self.shared.children.is_empty() {
568 self.is_block_like.push(root_ends_with_block);
569 self.shared.rewrites.push(root_rewrite);
573 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape> {
575 if self.is_block_like[0] {
576 shape.block_indent(0)
578 shape.block_indent(context.config.tab_spaces())
579 }.with_max_width(context.config),
583 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()> {
584 for item in self.shared.children[1..].iter().rev() {
585 let rewrite = item.rewrite(context, child_shape)?;
587 .push(item.kind.is_block_like(context, &rewrite));
588 self.shared.rewrites.push(rewrite);
593 fn format_last_child(
595 context: &RewriteContext,
600 .format_last_child(true, context, shape, child_shape)
603 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
605 .join_rewrites(context, child_shape, self.is_block_like.iter().cloned())
608 fn pure_root(&mut self) -> Option<String> {
609 self.shared.pure_root()
613 // Format a chain using visual indent.
614 struct ChainFormatterVisual<'a> {
615 shared: ChainFormatterShared<'a>,
616 // The extra offset from the chain's shape to the position of the `.`
620 impl<'a> ChainFormatterVisual<'a> {
621 fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
622 ChainFormatterVisual {
623 shared: ChainFormatterShared::new(chain),
629 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
633 context: &RewriteContext,
636 let parent_shape = shape.visual_indent(0);
637 let mut root_rewrite = parent.rewrite(context, parent_shape)?;
638 let multiline = root_rewrite.contains('\n');
639 self.offset = if multiline {
640 last_line_width(&root_rewrite).saturating_sub(shape.used_width())
642 trimmed_last_line_width(&root_rewrite)
645 if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
646 let item = &self.shared.children[self.shared.children.len() - 1];
647 let child_shape = parent_shape
648 .visual_indent(self.offset)
649 .sub_width(self.offset)?;
650 let rewrite = item.rewrite(context, child_shape)?;
651 match wrap_str(rewrite, context.config.max_width(), shape) {
652 Some(rewrite) => root_rewrite.push_str(&rewrite),
654 // We couldn't fit in at the visual indent, try the last
656 let rewrite = item.rewrite(context, parent_shape)?;
657 root_rewrite.push_str(&rewrite);
662 self.shared.children = &self.shared.children[..self.shared.children.len() - 1];
665 self.shared.rewrites.push(root_rewrite);
669 fn child_shape(&self, context: &RewriteContext, shape: Shape) -> Option<Shape> {
671 .with_max_width(context.config)
672 .offset_left(self.offset)
673 .map(|s| s.visual_indent(0))
676 fn format_children(&mut self, context: &RewriteContext, child_shape: Shape) -> Option<()> {
677 for item in self.shared.children[1..].iter().rev() {
678 let rewrite = item.rewrite(context, child_shape)?;
679 self.shared.rewrites.push(rewrite);
684 fn format_last_child(
686 context: &RewriteContext,
691 .format_last_child(false, context, shape, child_shape)
694 fn join_rewrites(&self, context: &RewriteContext, child_shape: Shape) -> Option<String> {
696 .join_rewrites(context, child_shape, iter::repeat(false))
699 fn pure_root(&mut self) -> Option<String> {
700 self.shared.pure_root()
704 // States whether an expression's last line exclusively consists of closing
705 // parens, braces, and brackets in its idiomatic formatting.
706 fn is_block_expr(context: &RewriteContext, expr: &ast::Expr, repr: &str) -> bool {
708 ast::ExprKind::Mac(..)
709 | ast::ExprKind::Call(..)
710 | ast::ExprKind::MethodCall(..)
711 | ast::ExprKind::Struct(..)
712 | ast::ExprKind::While(..)
713 | ast::ExprKind::WhileLet(..)
714 | ast::ExprKind::If(..)
715 | ast::ExprKind::IfLet(..)
716 | ast::ExprKind::Block(..)
717 | ast::ExprKind::Loop(..)
718 | ast::ExprKind::ForLoop(..)
719 | ast::ExprKind::Match(..) => repr.contains('\n'),
720 ast::ExprKind::Paren(ref expr)
721 | ast::ExprKind::Binary(_, _, ref expr)
722 | ast::ExprKind::Index(_, ref expr)
723 | ast::ExprKind::Unary(_, ref expr)
724 | ast::ExprKind::Closure(_, _, _, _, ref expr, _)
725 | ast::ExprKind::Try(ref expr)
726 | ast::ExprKind::Yield(Some(ref expr)) => is_block_expr(context, expr, repr),
727 // This can only be a string lit
728 ast::ExprKind::Lit(_) => {
729 repr.contains('\n') && trimmed_last_line_width(repr) <= context.config.tab_spaces()