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 config::IndentStyle;
69 use expr::rewrite_call;
70 use macros::convert_try_mac;
71 use rewrite::{Rewrite, RewriteContext};
73 use utils::{first_line_width, last_line_extendable, last_line_width, mk_sp,
74 trimmed_last_line_width, wrap_str};
80 use syntax::{ast, ptr};
81 use syntax::codemap::Span;
83 pub fn rewrite_chain(expr: &ast::Expr, context: &RewriteContext, shape: Shape) -> Option<String> {
84 debug!("rewrite_chain {:?}", shape);
85 let total_span = expr.span;
86 let (parent, subexpr_list) = make_subexpr_list(expr, context);
88 // Bail out if the chain is just try sugar, i.e., an expression followed by
89 // any number of `?`s.
90 if chain_only_try(&subexpr_list) {
91 return rewrite_try(&parent, subexpr_list.len(), context, shape);
93 let suffix_try_num = subexpr_list.iter().take_while(|e| is_try(e)).count();
94 let prefix_try_num = subexpr_list.iter().rev().take_while(|e| is_try(e)).count();
96 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
97 let parent_shape = if is_block_expr(context, &parent, "\n") {
98 match context.config.indent_style() {
99 IndentStyle::Visual => shape.visual_indent(0),
100 IndentStyle::Block => shape,
105 let parent_rewrite = parent
106 .rewrite(context, parent_shape)
107 .map(|parent_rw| parent_rw + &repeat_try(prefix_try_num))?;
108 let parent_rewrite_contains_newline = parent_rewrite.contains('\n');
109 let is_small_parent = parent_rewrite.len() <= context.config.tab_spaces();
111 // Decide how to layout the rest of the chain. `extend` is true if we can
112 // put the first non-parent item on the same line as the parent.
113 let (nested_shape, extend) = if !parent_rewrite_contains_newline && is_continuable(&parent) {
115 chain_indent(context, shape.add_offset(parent_rewrite.len())),
116 context.config.indent_style() == IndentStyle::Visual || is_small_parent,
118 } else if is_block_expr(context, &parent, &parent_rewrite) {
119 match context.config.indent_style() {
120 // Try to put the first child on the same line with parent's last line
121 IndentStyle::Block => (parent_shape.block_indent(context.config.tab_spaces()), true),
122 // The parent is a block, so align the rest of the chain with the closing
124 IndentStyle::Visual => (parent_shape, false),
128 chain_indent(context, shape.add_offset(parent_rewrite.len())),
133 let other_child_shape = nested_shape.with_max_width(context.config);
135 let first_child_shape = if extend {
136 let overhead = last_line_width(&parent_rewrite);
137 let offset = trimmed_last_line_width(&parent_rewrite) + prefix_try_num;
138 match context.config.indent_style() {
139 IndentStyle::Visual => parent_shape.offset_left(overhead)?,
140 IndentStyle::Block => parent_shape.offset_left(offset)?,
146 "child_shapes {:?} {:?}",
147 first_child_shape, other_child_shape
150 let child_shape_iter = Some(first_child_shape)
152 .chain(iter::repeat(other_child_shape));
153 let subexpr_num = subexpr_list.len();
154 let last_subexpr = &subexpr_list[suffix_try_num];
155 let subexpr_list = &subexpr_list[suffix_try_num..subexpr_num - prefix_try_num];
156 let iter = subexpr_list.iter().skip(1).rev().zip(child_shape_iter);
157 let mut rewrites = iter.map(|(e, shape)| rewrite_chain_subexpr(e, total_span, context, shape))
158 .collect::<Option<Vec<_>>>()?;
160 // Total of all items excluding the last.
161 let extend_last_subexpr = if is_small_parent {
162 rewrites.len() == 1 && last_line_extendable(&rewrites[0])
164 rewrites.is_empty() && last_line_extendable(&parent_rewrite)
166 let almost_total = if extend_last_subexpr {
167 last_line_width(&parent_rewrite)
169 rewrites.iter().fold(0, |a, b| a + b.len()) + parent_rewrite.len()
171 let one_line_budget = if rewrites.is_empty() {
174 min(shape.width, context.config.width_heuristics().chain_width)
176 let all_in_one_line = !parent_rewrite_contains_newline
177 && rewrites.iter().all(|s| !s.contains('\n'))
178 && almost_total < one_line_budget;
179 let last_shape = if rewrites.is_empty() {
183 }.sub_width(shape.rhs_overhead(context.config) + suffix_try_num)?;
185 // Rewrite the last child. The last child of a chain requires special treatment. We need to
186 // know whether 'overflowing' the last child make a better formatting:
188 // A chain with overflowing the last child:
190 // parent.child1.child2.last_child(
197 // A chain without overflowing the last child (in vertical layout):
202 // .last_child(a, b, c)
205 // In particular, overflowing is effective when the last child is a method with a multi-lined
206 // block-like argument (e.g. closure):
208 // parent.child1.child2.last_child(|a, b, c| {
209 // let x = foo(a, b, c);
210 // let y = bar(a, b, c);
218 // `rewrite_last` rewrites the last child on its own line. We use a closure here instead of
219 // directly calling `rewrite_chain_subexpr()` to avoid exponential blowup.
220 let rewrite_last = || rewrite_chain_subexpr(last_subexpr, total_span, context, last_shape);
221 let (last_subexpr_str, fits_single_line) = if all_in_one_line || extend_last_subexpr {
222 // First we try to 'overflow' the last child and see if it looks better than using
224 parent_shape.offset_left(almost_total).map(|shape| {
225 if let Some(rw) = rewrite_chain_subexpr(last_subexpr, total_span, context, shape) {
226 // We allow overflowing here only if both of the following conditions match:
227 // 1. The entire chain fits in a single line expect the last child.
228 // 2. `last_child_str.lines().count() >= 5`.
229 let line_count = rw.lines().count();
230 let fits_single_line = almost_total + first_line_width(&rw) <= one_line_budget;
231 if fits_single_line && line_count >= 5 {
234 // We could not know whether overflowing is better than using vertical layout,
235 // just by looking at the overflowed rewrite. Now we rewrite the last child
236 // on its own line, and compare two rewrites to choose which is better.
237 match rewrite_last() {
238 Some(ref new_rw) if !fits_single_line => (Some(new_rw.clone()), false),
239 Some(ref new_rw) if new_rw.lines().count() >= line_count => {
240 (Some(rw), fits_single_line)
242 new_rw @ Some(..) => (new_rw, false),
243 _ => (Some(rw), fits_single_line),
247 (rewrite_last(), false)
251 (rewrite_last(), false)
253 rewrites.push(last_subexpr_str?);
255 let connector = if fits_single_line && !parent_rewrite_contains_newline {
256 // Yay, we can put everything on one line.
260 if context.force_one_line_chain {
263 nested_shape.indent.to_string_with_newline(context.config)
266 let first_connector = if is_small_parent || fits_single_line
267 || last_line_extendable(&parent_rewrite)
268 || context.config.indent_style() == IndentStyle::Visual
275 let result = if is_small_parent && rewrites.len() > 1 {
276 let second_connector = if fits_single_line || rewrites[1] == "?"
277 || last_line_extendable(&rewrites[0])
278 || context.config.indent_style() == IndentStyle::Visual
290 join_rewrites(&rewrites[1..], &connector)
297 join_rewrites(&rewrites, &connector)
300 let result = format!("{}{}", result, repeat_try(suffix_try_num));
301 if context.config.indent_style() == IndentStyle::Visual {
302 wrap_str(result, context.config.max_width(), shape)
308 // True if the chain is only `?`s.
309 fn chain_only_try(exprs: &[ast::Expr]) -> bool {
310 exprs.iter().all(|e| {
311 if let ast::ExprKind::Try(_) = e.node {
319 // Try to rewrite and replace the last non-try child. Return `true` if
320 // replacing succeeds.
321 fn repeat_try(try_count: usize) -> String {
322 iter::repeat("?").take(try_count).collect::<String>()
328 context: &RewriteContext,
330 ) -> Option<String> {
331 let sub_expr = expr.rewrite(context, shape.sub_width(try_count)?)?;
332 Some(format!("{}{}", sub_expr, repeat_try(try_count)))
335 fn join_rewrites(rewrites: &[String], connector: &str) -> String {
336 let mut rewrite_iter = rewrites.iter();
337 let mut result = rewrite_iter.next().unwrap().clone();
339 for rewrite in rewrite_iter {
341 result.push_str(connector);
343 result.push_str(&rewrite[..]);
349 // States whether an expression's last line exclusively consists of closing
350 // parens, braces, and brackets in its idiomatic formatting.
351 fn is_block_expr(context: &RewriteContext, expr: &ast::Expr, repr: &str) -> bool {
353 ast::ExprKind::Mac(..) | ast::ExprKind::Call(..) => {
354 context.use_block_indent() && repr.contains('\n')
356 ast::ExprKind::Struct(..)
357 | ast::ExprKind::While(..)
358 | ast::ExprKind::WhileLet(..)
359 | ast::ExprKind::If(..)
360 | ast::ExprKind::IfLet(..)
361 | ast::ExprKind::Block(..)
362 | ast::ExprKind::Loop(..)
363 | ast::ExprKind::ForLoop(..)
364 | ast::ExprKind::Match(..) => repr.contains('\n'),
365 ast::ExprKind::Paren(ref expr)
366 | ast::ExprKind::Binary(_, _, ref expr)
367 | ast::ExprKind::Index(_, ref expr)
368 | ast::ExprKind::Unary(_, ref expr) => is_block_expr(context, expr, repr),
373 // Returns the root of the chain and a Vec of the prefixes of the rest of the chain.
374 // E.g., for input `a.b.c` we return (`a`, [`a.b.c`, `a.b`])
375 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> (ast::Expr, Vec<ast::Expr>) {
376 let mut subexpr_list = vec![expr.clone()];
378 while let Some(subexpr) = pop_expr_chain(subexpr_list.last().unwrap(), context) {
379 subexpr_list.push(subexpr.clone());
382 let parent = subexpr_list.pop().unwrap();
383 (parent, subexpr_list)
386 fn chain_indent(context: &RewriteContext, shape: Shape) -> Shape {
387 match context.config.indent_style() {
388 IndentStyle::Visual => shape.visual_indent(0),
389 IndentStyle::Block => shape
390 .block_indent(context.config.tab_spaces())
391 .with_max_width(context.config),
395 // Returns the expression's subexpression, if it exists. When the subexpr
396 // is a try! macro, we'll convert it to shorthand when the option is set.
397 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
399 ast::ExprKind::MethodCall(_, ref expressions) => {
400 Some(convert_try(&expressions[0], context))
402 ast::ExprKind::TupField(ref subexpr, _)
403 | ast::ExprKind::Field(ref subexpr, _)
404 | ast::ExprKind::Try(ref subexpr) => Some(convert_try(subexpr, context)),
409 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
411 ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
412 if let Some(subexpr) = convert_try_mac(mac, context) {
422 // Rewrite the last element in the chain `expr`. E.g., given `a.b.c` we rewrite
424 fn rewrite_chain_subexpr(
427 context: &RewriteContext,
429 ) -> Option<String> {
430 let rewrite_element = |expr_str: String| {
431 if expr_str.len() <= shape.width {
439 ast::ExprKind::MethodCall(ref segment, ref expressions) => {
440 let types = match segment.parameters {
441 Some(ref params) => match **params {
442 ast::PathParameters::AngleBracketed(ref data) => &data.types[..],
447 rewrite_method_call(segment.identifier, types, expressions, span, context, shape)
449 ast::ExprKind::Field(_, ref field) => rewrite_element(format!(".{}", field.node)),
450 ast::ExprKind::TupField(ref expr, ref field) => {
451 let space = match expr.node {
452 ast::ExprKind::TupField(..) => " ",
455 rewrite_element(format!("{}.{}", space, field.node))
457 ast::ExprKind::Try(_) => rewrite_element(String::from("?")),
462 // Determines if we can continue formatting a given expression on the same line.
463 fn is_continuable(expr: &ast::Expr) -> bool {
465 ast::ExprKind::Path(..) => true,
470 fn is_try(expr: &ast::Expr) -> bool {
472 ast::ExprKind::Try(..) => true,
477 fn rewrite_method_call(
478 method_name: ast::Ident,
479 types: &[ptr::P<ast::Ty>],
480 args: &[ptr::P<ast::Expr>],
482 context: &RewriteContext,
484 ) -> Option<String> {
485 let (lo, type_str) = if types.is_empty() {
486 (args[0].span.hi(), String::new())
488 let type_list = types
490 .map(|ty| ty.rewrite(context, shape))
491 .collect::<Option<Vec<_>>>()?;
494 if context.config.spaces_within_parens_and_brackets() && !type_list.is_empty() {
495 format!("::< {} >", type_list.join(", "))
497 format!("::<{}>", type_list.join(", "))
500 (types.last().unwrap().span.hi(), type_str)
503 let callee_str = format!(".{}{}", method_name, type_str);
504 let span = mk_sp(lo, span.hi());
506 rewrite_call(context, &callee_str, &args[1..], span, shape)