1 //! Formatting of chained expressions, i.e., expressions that are chained by
2 //! dots: struct and enum field access, method calls, and try shorthand (`?`).
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.
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.
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
15 //! E.g., `let foo = { aaaa; bbb; ccc }.bar.baz();`, we would layout for the
16 //! following values of `chain_indent`:
40 //! If the first item in the chain is a block expression, we align the dots with
61 use rustc_ast::{ast, ptr};
62 use rustc_span::{BytePos, Span};
64 use crate::comment::{rewrite_comment, CharClasses, FullCodeCharKind, RichChar};
65 use crate::config::IndentStyle;
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;
73 self, first_line_width, last_line_extendable, last_line_width, mk_sp, rewrite_ident,
74 trimmed_last_line_width, wrap_str,
77 pub(crate) fn rewrite_chain(
79 context: &RewriteContext<'_>,
82 let chain = Chain::from_ast(expr, context);
83 debug!("rewrite_chain {:?} {:?}", chain, shape);
85 // If this is just an expression with some `?`s, then format it trivially and
87 if chain.children.is_empty() {
88 return chain.parent.rewrite(context, shape);
91 chain.rewrite(context, shape)
95 enum CommentPosition {
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),
122 Comment(String, CommentPosition),
126 fn is_block_like(&self, context: &RewriteContext<'_>, reps: &str) -> bool {
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,
137 fn is_tup_field_access(expr: &ast::Expr) -> bool {
139 ast::ExprKind::Field(_, ref field) => {
140 field.name.to_string().chars().all(|c| c.is_digit(10))
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 {
153 .filter_map(|x| match x {
154 ast::AngleBracketedArg::Arg(ref generic_arg) => {
155 Some(generic_arg.clone())
166 let span = mk_sp(expressions[0].span.hi(), expr.span.hi());
167 let kind = ChainItemKind::MethodCall(segment.clone(), types, expressions.clone());
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))
174 ChainItemKind::StructField(field)
176 let span = mk_sp(nested.span.hi(), field.span.hi());
179 ast::ExprKind::Await(ref nested) => {
180 let span = mk_sp(nested.span.hi(), expr.span.hi());
181 (ChainItemKind::Await, span)
183 _ => return (ChainItemKind::Parent(expr.clone()), expr.span),
186 // Remove comments from the span.
187 let lo = context.snippet_provider.span_before(span, ".");
188 (kind, mk_sp(lo, span.hi()))
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)?
200 ChainItemKind::StructField(ident) => format!(".{}", rewrite_ident(context, ident)),
201 ChainItemKind::TupleField(ident, nested) => format!(
203 if nested { " " } else { "" },
204 rewrite_ident(context, ident)
206 ChainItemKind::Await => ".await".to_owned(),
207 ChainItemKind::Comment(ref comment, _) => {
208 rewrite_comment(comment, false, shape, context.config)?
211 Some(format!("{}{}", rewrite, "?".repeat(self.tries)))
216 fn new(context: &RewriteContext<'_>, expr: &ast::Expr, tries: usize) -> ChainItem {
217 let (kind, span) = ChainItemKind::from_ast(context, expr);
218 ChainItem { kind, tries, span }
221 fn comment(span: Span, comment: String, pos: CommentPosition) -> ChainItem {
223 kind: ChainItemKind::Comment(comment, pos),
229 fn is_comment(&self) -> bool {
231 ChainItemKind::Comment(..) => true,
236 fn rewrite_method_call(
237 method_name: ast::Ident,
238 types: &[ast::GenericArg],
239 args: &[ptr::P<ast::Expr>],
241 context: &RewriteContext<'_>,
243 ) -> Option<String> {
244 let type_str = if types.is_empty() {
247 let type_list = types
249 .map(|ty| ty.rewrite(context, shape))
250 .collect::<Option<Vec<_>>>()?;
252 format!("::<{}>", type_list.join(", "))
254 let callee_str = format!(".{}{}", rewrite_ident(context, method_name), type_str);
255 rewrite_call(context, &callee_str, &args[1..], span, shape)
262 children: Vec<ChainItem>,
266 fn from_ast(expr: &ast::Expr, context: &RewriteContext<'_>) -> Chain {
267 let subexpr_list = Self::make_subexpr_list(expr, context);
269 // Un-parse the expression tree into ChainItems
270 let mut rev_children = vec![];
271 let mut sub_tries = 0;
272 for subexpr in &subexpr_list {
274 ast::ExprKind::Try(_) => sub_tries += 1,
276 rev_children.push(ChainItem::new(context, subexpr, sub_tries));
282 fn is_tries(s: &str) -> bool {
283 s.chars().all(|c| c == '?')
286 fn is_post_comment(s: &str) -> bool {
287 let comment_start_index = s.chars().position(|c| c == '/');
288 if comment_start_index.is_none() {
292 let newline_index = s.chars().position(|c| c == '\n');
293 if newline_index.is_none() {
297 comment_start_index.unwrap() < newline_index.unwrap()
300 fn handle_post_comment(
301 post_comment_span: Span,
302 post_comment_snippet: &str,
303 prev_span_end: &mut BytePos,
304 children: &mut Vec<ChainItem>,
306 let white_spaces: &[_] = &[' ', '\t'];
307 if post_comment_snippet
308 .trim_matches(white_spaces)
314 let trimmed_snippet = trim_tries(post_comment_snippet);
315 if is_post_comment(&trimmed_snippet) {
316 children.push(ChainItem::comment(
318 trimmed_snippet.trim().to_owned(),
319 CommentPosition::Back,
321 *prev_span_end = post_comment_span.hi();
325 let parent = rev_children.pop().unwrap();
326 let mut children = vec![];
327 let mut prev_span_end = parent.span.hi();
328 let mut iter = rev_children.into_iter().rev().peekable();
329 if let Some(first_chain_item) = iter.peek() {
330 let comment_span = mk_sp(prev_span_end, first_chain_item.span.lo());
331 let comment_snippet = context.snippet(comment_span);
332 if !is_tries(comment_snippet.trim()) {
341 while let Some(chain_item) = iter.next() {
342 let comment_snippet = context.snippet(chain_item.span);
343 // FIXME: Figure out the way to get a correct span when converting `try!` to `?`.
345 !(context.config.use_try_shorthand() || is_tries(comment_snippet.trim()));
349 let pre_comment_span = mk_sp(prev_span_end, chain_item.span.lo());
350 let pre_comment_snippet = trim_tries(context.snippet(pre_comment_span));
351 let (pre_comment, _) = extract_pre_comment(&pre_comment_snippet);
353 Some(ref comment) if !comment.is_empty() => {
354 children.push(ChainItem::comment(
357 CommentPosition::Top,
364 prev_span_end = chain_item.span.hi();
365 children.push(chain_item);
368 if !handle_comment || iter.peek().is_none() {
372 let next_lo = iter.peek().unwrap().span.lo();
373 let post_comment_span = mk_sp(prev_span_end, next_lo);
374 let post_comment_snippet = context.snippet(post_comment_span);
377 post_comment_snippet,
383 Chain { parent, children }
386 // Returns a Vec of the prefixes of the chain.
387 // E.g., for input `a.b.c` we return [`a.b.c`, `a.b`, 'a']
388 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext<'_>) -> Vec<ast::Expr> {
389 let mut subexpr_list = vec![expr.clone()];
391 while let Some(subexpr) = Self::pop_expr_chain(subexpr_list.last().unwrap(), context) {
392 subexpr_list.push(subexpr.clone());
398 // Returns the expression's subexpression, if it exists. When the subexpr
399 // is a try! macro, we'll convert it to shorthand when the option is set.
400 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext<'_>) -> Option<ast::Expr> {
402 ast::ExprKind::MethodCall(_, ref expressions) => {
403 Some(Self::convert_try(&expressions[0], context))
405 ast::ExprKind::Field(ref subexpr, _)
406 | ast::ExprKind::Try(ref subexpr)
407 | ast::ExprKind::Await(ref subexpr) => Some(Self::convert_try(subexpr, context)),
412 fn convert_try(expr: &ast::Expr, context: &RewriteContext<'_>) -> ast::Expr {
414 ast::ExprKind::MacCall(ref mac) if context.config.use_try_shorthand() => {
415 if let Some(subexpr) = convert_try_mac(mac, context) {
426 impl Rewrite for Chain {
427 fn rewrite(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<String> {
428 debug!("rewrite chain {:?} {:?}", self, shape);
430 let mut formatter = match context.config.indent_style() {
431 IndentStyle::Block => {
432 Box::new(ChainFormatterBlock::new(self)) as Box<dyn ChainFormatter>
434 IndentStyle::Visual => {
435 Box::new(ChainFormatterVisual::new(self)) as Box<dyn ChainFormatter>
439 formatter.format_root(&self.parent, context, shape)?;
440 if let Some(result) = formatter.pure_root() {
441 return wrap_str(result, context.config.max_width(), shape);
444 // Decide how to layout the rest of the chain.
445 let child_shape = formatter.child_shape(context, shape)?;
447 formatter.format_children(context, child_shape)?;
448 formatter.format_last_child(context, shape, child_shape)?;
450 let result = formatter.join_rewrites(context, child_shape)?;
451 wrap_str(result, context.config.max_width(), shape)
455 // There are a few types for formatting chains. This is because there is a lot
456 // in common between formatting with block vs visual indent, but they are
457 // different enough that branching on the indent all over the place gets ugly.
458 // Anything that can format a chain is a ChainFormatter.
459 trait ChainFormatter {
460 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
461 // Root is the parent plus any other chain items placed on the first line to
462 // avoid an orphan. E.g.,
467 // If `bar` were not part of the root, then foo would be orphaned and 'float'.
471 context: &RewriteContext<'_>,
474 fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape>;
475 fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()>;
476 fn format_last_child(
478 context: &RewriteContext<'_>,
482 fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String>;
483 // Returns `Some` if the chain is only a root, None otherwise.
484 fn pure_root(&mut self) -> Option<String>;
487 // Data and behaviour that is shared by both chain formatters. The concrete
488 // formatters can delegate much behaviour to `ChainFormatterShared`.
489 struct ChainFormatterShared<'a> {
490 // The current working set of child items.
491 children: &'a [ChainItem],
492 // The current rewrites of items (includes trailing `?`s, but not any way to
493 // connect the rewrites together).
494 rewrites: Vec<String>,
495 // Whether the chain can fit on one line.
496 fits_single_line: bool,
497 // The number of children in the chain. This is not equal to `self.children.len()`
498 // because `self.children` will change size as we process the chain.
502 impl<'a> ChainFormatterShared<'a> {
503 fn new(chain: &'a Chain) -> ChainFormatterShared<'a> {
504 ChainFormatterShared {
505 children: &chain.children,
506 rewrites: Vec::with_capacity(chain.children.len() + 1),
507 fits_single_line: false,
508 child_count: chain.children.len(),
512 fn pure_root(&mut self) -> Option<String> {
513 if self.children.is_empty() {
514 assert_eq!(self.rewrites.len(), 1);
515 Some(self.rewrites.pop().unwrap())
521 // Rewrite the last child. The last child of a chain requires special treatment. We need to
522 // know whether 'overflowing' the last child make a better formatting:
524 // A chain with overflowing the last child:
526 // parent.child1.child2.last_child(
533 // A chain without overflowing the last child (in vertical layout):
538 // .last_child(a, b, c)
541 // In particular, overflowing is effective when the last child is a method with a multi-lined
542 // block-like argument (e.g., closure):
544 // parent.child1.child2.last_child(|a, b, c| {
545 // let x = foo(a, b, c);
546 // let y = bar(a, b, c);
553 fn format_last_child(
556 context: &RewriteContext<'_>,
560 let last = self.children.last()?;
561 let extendable = may_extend && last_line_extendable(&self.rewrites[0]);
562 let prev_last_line_width = last_line_width(&self.rewrites[0]);
564 // Total of all items excluding the last.
565 let almost_total = if extendable {
570 .map(|rw| utils::unicode_str_width(&rw))
573 let one_line_budget = if self.child_count == 1 {
576 min(shape.width, context.config.width_heuristics().chain_width)
578 .saturating_sub(almost_total);
580 let all_in_one_line = !self.children.iter().any(ChainItem::is_comment)
581 && self.rewrites.iter().all(|s| !s.contains('\n'))
582 && one_line_budget > 0;
583 let last_shape = if all_in_one_line {
584 shape.sub_width(last.tries)?
585 } else if extendable {
586 child_shape.sub_width(last.tries)?
588 child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
591 let mut last_subexpr_str = None;
592 if all_in_one_line || extendable {
593 // First we try to 'overflow' the last child and see if it looks better than using
595 let one_line_shape = if context.use_block_indent() {
596 last_shape.offset_left(almost_total)
599 .visual_indent(almost_total)
600 .sub_width(almost_total)
603 if let Some(one_line_shape) = one_line_shape {
604 if let Some(rw) = last.rewrite(context, one_line_shape) {
605 // We allow overflowing here only if both of the following conditions match:
606 // 1. The entire chain fits in a single line except the last child.
607 // 2. `last_child_str.lines().count() >= 5`.
608 let line_count = rw.lines().count();
609 let could_fit_single_line = first_line_width(&rw) <= one_line_budget;
610 if could_fit_single_line && line_count >= 5 {
611 last_subexpr_str = Some(rw);
612 self.fits_single_line = all_in_one_line;
614 // We could not know whether overflowing is better than using vertical
615 // layout, just by looking at the overflowed rewrite. Now we rewrite the
616 // last child on its own line, and compare two rewrites to choose which is
618 let last_shape = child_shape
619 .sub_width(shape.rhs_overhead(context.config) + last.tries)?;
620 match last.rewrite(context, last_shape) {
621 Some(ref new_rw) if !could_fit_single_line => {
622 last_subexpr_str = Some(new_rw.clone());
624 Some(ref new_rw) if new_rw.lines().count() >= line_count => {
625 last_subexpr_str = Some(rw);
626 self.fits_single_line = could_fit_single_line && all_in_one_line;
628 new_rw @ Some(..) => {
629 last_subexpr_str = new_rw;
632 last_subexpr_str = Some(rw);
633 self.fits_single_line = could_fit_single_line && all_in_one_line;
641 let last_shape = if context.use_block_indent() {
644 child_shape.sub_width(shape.rhs_overhead(context.config) + last.tries)?
647 last_subexpr_str = last_subexpr_str.or_else(|| last.rewrite(context, last_shape));
648 self.rewrites.push(last_subexpr_str?);
652 fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
653 let connector = if self.fits_single_line {
654 // Yay, we can put everything on one line.
658 if context.force_one_line_chain.get() {
661 child_shape.to_string_with_newline(context.config)
664 let mut rewrite_iter = self.rewrites.iter();
665 let mut result = rewrite_iter.next().unwrap().clone();
666 let children_iter = self.children.iter();
667 let iter = rewrite_iter.zip(children_iter);
669 for (rewrite, chain_item) in iter {
670 match chain_item.kind {
671 ChainItemKind::Comment(_, CommentPosition::Back) => result.push(' '),
672 ChainItemKind::Comment(_, CommentPosition::Top) => result.push_str(&connector),
673 _ => result.push_str(&connector),
675 result.push_str(&rewrite);
682 // Formats a chain using block indent.
683 struct ChainFormatterBlock<'a> {
684 shared: ChainFormatterShared<'a>,
685 root_ends_with_block: bool,
688 impl<'a> ChainFormatterBlock<'a> {
689 fn new(chain: &'a Chain) -> ChainFormatterBlock<'a> {
690 ChainFormatterBlock {
691 shared: ChainFormatterShared::new(chain),
692 root_ends_with_block: false,
697 impl<'a> ChainFormatter for ChainFormatterBlock<'a> {
701 context: &RewriteContext<'_>,
704 let mut root_rewrite: String = parent.rewrite(context, shape)?;
706 let mut root_ends_with_block = parent.kind.is_block_like(context, &root_rewrite);
707 let tab_width = context.config.tab_spaces().saturating_sub(shape.offset);
709 while root_rewrite.len() <= tab_width && !root_rewrite.contains('\n') {
710 let item = &self.shared.children[0];
711 if let ChainItemKind::Comment(..) = item.kind {
714 let shape = shape.offset_left(root_rewrite.len())?;
715 match &item.rewrite(context, shape) {
716 Some(rewrite) => root_rewrite.push_str(rewrite),
720 root_ends_with_block = last_line_extendable(&root_rewrite);
722 self.shared.children = &self.shared.children[1..];
723 if self.shared.children.is_empty() {
727 self.shared.rewrites.push(root_rewrite);
728 self.root_ends_with_block = root_ends_with_block;
732 fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
734 if self.root_ends_with_block {
735 shape.block_indent(0)
737 shape.block_indent(context.config.tab_spaces())
739 .with_max_width(context.config),
743 fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
744 for item in &self.shared.children[..self.shared.children.len() - 1] {
745 let rewrite = item.rewrite(context, child_shape)?;
746 self.shared.rewrites.push(rewrite);
751 fn format_last_child(
753 context: &RewriteContext<'_>,
758 .format_last_child(true, context, shape, child_shape)
761 fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
762 self.shared.join_rewrites(context, child_shape)
765 fn pure_root(&mut self) -> Option<String> {
766 self.shared.pure_root()
770 // Format a chain using visual indent.
771 struct ChainFormatterVisual<'a> {
772 shared: ChainFormatterShared<'a>,
773 // The extra offset from the chain's shape to the position of the `.`
777 impl<'a> ChainFormatterVisual<'a> {
778 fn new(chain: &'a Chain) -> ChainFormatterVisual<'a> {
779 ChainFormatterVisual {
780 shared: ChainFormatterShared::new(chain),
786 impl<'a> ChainFormatter for ChainFormatterVisual<'a> {
790 context: &RewriteContext<'_>,
793 let parent_shape = shape.visual_indent(0);
794 let mut root_rewrite = parent.rewrite(context, parent_shape)?;
795 let multiline = root_rewrite.contains('\n');
796 self.offset = if multiline {
797 last_line_width(&root_rewrite).saturating_sub(shape.used_width())
799 trimmed_last_line_width(&root_rewrite)
802 if !multiline || parent.kind.is_block_like(context, &root_rewrite) {
803 let item = &self.shared.children[0];
804 if let ChainItemKind::Comment(..) = item.kind {
805 self.shared.rewrites.push(root_rewrite);
808 let child_shape = parent_shape
809 .visual_indent(self.offset)
810 .sub_width(self.offset)?;
811 let rewrite = item.rewrite(context, child_shape)?;
812 match wrap_str(rewrite, context.config.max_width(), shape) {
813 Some(rewrite) => root_rewrite.push_str(&rewrite),
815 // We couldn't fit in at the visual indent, try the last
817 let rewrite = item.rewrite(context, parent_shape)?;
818 root_rewrite.push_str(&rewrite);
823 self.shared.children = &self.shared.children[1..];
826 self.shared.rewrites.push(root_rewrite);
830 fn child_shape(&self, context: &RewriteContext<'_>, shape: Shape) -> Option<Shape> {
832 .with_max_width(context.config)
833 .offset_left(self.offset)
834 .map(|s| s.visual_indent(0))
837 fn format_children(&mut self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<()> {
838 for item in &self.shared.children[..self.shared.children.len() - 1] {
839 let rewrite = item.rewrite(context, child_shape)?;
840 self.shared.rewrites.push(rewrite);
845 fn format_last_child(
847 context: &RewriteContext<'_>,
852 .format_last_child(false, context, shape, child_shape)
855 fn join_rewrites(&self, context: &RewriteContext<'_>, child_shape: Shape) -> Option<String> {
856 self.shared.join_rewrites(context, child_shape)
859 fn pure_root(&mut self) -> Option<String> {
860 self.shared.pure_root()
864 /// Removes try operators (`?`s) that appear in the given string. If removing
865 /// them leaves an empty line, remove that line as well unless it is the first
866 /// line (we need the first newline for detecting pre/post comment).
867 fn trim_tries(s: &str) -> String {
868 let mut result = String::with_capacity(s.len());
869 let mut line_buffer = String::with_capacity(s.len());
870 for (kind, rich_char) in CharClasses::new(s.chars()) {
871 match rich_char.get_char() {
873 if result.is_empty() || !line_buffer.trim().is_empty() {
874 result.push_str(&line_buffer);
879 '?' if kind == FullCodeCharKind::Normal => continue,
880 c => line_buffer.push(c),
883 if !line_buffer.trim().is_empty() {
884 result.push_str(&line_buffer);