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`:
47 //! If the first item in the chain is a block expression, we align the dots with
62 use config::IndentStyle;
63 use expr::rewrite_call;
64 use macros::convert_try_mac;
65 use rewrite::{Rewrite, RewriteContext};
67 use utils::{first_line_width, last_line_extendable, last_line_width, mk_sp,
68 trimmed_last_line_width, wrap_str};
74 use syntax::{ast, ptr};
75 use syntax::codemap::Span;
77 pub fn rewrite_chain(expr: &ast::Expr, context: &RewriteContext, shape: Shape) -> Option<String> {
78 debug!("rewrite_chain {:?}", shape);
79 let total_span = expr.span;
80 let (parent, subexpr_list) = make_subexpr_list(expr, context);
82 // Bail out if the chain is just try sugar, i.e., an expression followed by
83 // any number of `?`s.
84 if chain_only_try(&subexpr_list) {
85 return rewrite_try(&parent, subexpr_list.len(), context, shape);
87 let suffix_try_num = subexpr_list.iter().take_while(|e| is_try(e)).count();
88 let prefix_try_num = subexpr_list.iter().rev().take_while(|e| is_try(e)).count();
90 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
91 let parent_shape = if is_block_expr(context, &parent, "\n") {
92 match context.config.indent_style() {
93 IndentStyle::Visual => shape.visual_indent(0),
94 IndentStyle::Block => shape,
99 let parent_rewrite = parent
100 .rewrite(context, parent_shape)
101 .map(|parent_rw| parent_rw + &repeat_try(prefix_try_num))?;
102 let parent_rewrite_contains_newline = parent_rewrite.contains('\n');
103 let is_small_parent = parent_rewrite.len() <= context.config.tab_spaces();
105 // Decide how to layout the rest of the chain. `extend` is true if we can
106 // put the first non-parent item on the same line as the parent.
107 let (nested_shape, extend) = if !parent_rewrite_contains_newline && is_continuable(&parent) {
109 chain_indent(context, shape.add_offset(parent_rewrite.len())),
110 context.config.indent_style() == IndentStyle::Visual || is_small_parent,
112 } else if is_block_expr(context, &parent, &parent_rewrite) {
113 match context.config.indent_style() {
114 // Try to put the first child on the same line with parent's last line
115 IndentStyle::Block => (parent_shape.block_indent(context.config.tab_spaces()), true),
116 // The parent is a block, so align the rest of the chain with the closing
118 IndentStyle::Visual => (parent_shape, false),
122 chain_indent(context, shape.add_offset(parent_rewrite.len())),
127 let other_child_shape = nested_shape.with_max_width(context.config);
129 let first_child_shape = if extend {
130 let overhead = last_line_width(&parent_rewrite);
131 let offset = trimmed_last_line_width(&parent_rewrite) + prefix_try_num;
132 match context.config.indent_style() {
133 IndentStyle::Visual => parent_shape.offset_left(overhead)?,
134 IndentStyle::Block => parent_shape.offset_left(offset)?,
140 "child_shapes {:?} {:?}",
141 first_child_shape, other_child_shape
144 let child_shape_iter = Some(first_child_shape)
146 .chain(iter::repeat(other_child_shape));
147 let subexpr_num = subexpr_list.len();
148 let last_subexpr = &subexpr_list[suffix_try_num];
149 let subexpr_list = &subexpr_list[suffix_try_num..subexpr_num - prefix_try_num];
150 let iter = subexpr_list.iter().skip(1).rev().zip(child_shape_iter);
151 let mut rewrites = iter.map(|(e, shape)| rewrite_chain_subexpr(e, total_span, context, shape))
152 .collect::<Option<Vec<_>>>()?;
154 // Total of all items excluding the last.
155 let extend_last_subexpr = if is_small_parent {
156 rewrites.len() == 1 && last_line_extendable(&rewrites[0])
158 rewrites.is_empty() && last_line_extendable(&parent_rewrite)
160 let almost_total = if extend_last_subexpr {
161 last_line_width(&parent_rewrite)
163 rewrites.iter().fold(0, |a, b| a + b.len()) + parent_rewrite.len()
165 let one_line_budget = if rewrites.is_empty() {
168 min(shape.width, context.config.width_heuristics().chain_width)
170 let all_in_one_line = !parent_rewrite_contains_newline
171 && rewrites.iter().all(|s| !s.contains('\n'))
172 && almost_total < one_line_budget;
173 let last_shape = if rewrites.is_empty() {
177 }.sub_width(shape.rhs_overhead(context.config) + suffix_try_num)?;
179 // Rewrite the last child. The last child of a chain requires special treatment. We need to
180 // know whether 'overflowing' the last child make a better formatting:
182 // A chain with overflowing the last child:
184 // parent.child1.child2.last_child(
191 // A chain without overflowing the last child (in vertical layout):
196 // .last_child(a, b, c)
199 // In particular, overflowing is effective when the last child is a method with a multi-lined
200 // block-like argument (e.g. closure):
202 // parent.child1.child2.last_child(|a, b, c| {
203 // let x = foo(a, b, c);
204 // let y = bar(a, b, c);
212 // `rewrite_last` rewrites the last child on its own line. We use a closure here instead of
213 // directly calling `rewrite_chain_subexpr()` to avoid exponential blowup.
214 let rewrite_last = || rewrite_chain_subexpr(last_subexpr, total_span, context, last_shape);
215 let (last_subexpr_str, fits_single_line) = if all_in_one_line || extend_last_subexpr {
216 // First we try to 'overflow' the last child and see if it looks better than using
218 parent_shape.offset_left(almost_total).map(|shape| {
219 if let Some(rw) = rewrite_chain_subexpr(last_subexpr, total_span, context, shape) {
220 // We allow overflowing here only if both of the following conditions match:
221 // 1. The entire chain fits in a single line expect the last child.
222 // 2. `last_child_str.lines().count() >= 5`.
223 let line_count = rw.lines().count();
224 let fits_single_line = almost_total + first_line_width(&rw) <= one_line_budget;
225 if fits_single_line && line_count >= 5 {
228 // We could not know whether overflowing is better than using vertical layout,
229 // just by looking at the overflowed rewrite. Now we rewrite the last child
230 // on its own line, and compare two rewrites to choose which is better.
231 match rewrite_last() {
232 Some(ref new_rw) if !fits_single_line => (Some(new_rw.clone()), false),
233 Some(ref new_rw) if new_rw.lines().count() >= line_count => {
234 (Some(rw), fits_single_line)
236 new_rw @ Some(..) => (new_rw, false),
237 _ => (Some(rw), fits_single_line),
241 (rewrite_last(), false)
245 (rewrite_last(), false)
247 rewrites.push(last_subexpr_str?);
249 let connector = if fits_single_line && !parent_rewrite_contains_newline {
250 // Yay, we can put everything on one line.
254 if context.force_one_line_chain {
257 nested_shape.indent.to_string_with_newline(context.config)
260 let first_connector = if is_small_parent || fits_single_line
261 || last_line_extendable(&parent_rewrite)
262 || context.config.indent_style() == IndentStyle::Visual
269 let result = if is_small_parent && rewrites.len() > 1 {
270 let second_connector = if fits_single_line || rewrites[1] == "?"
271 || last_line_extendable(&rewrites[0])
272 || context.config.indent_style() == IndentStyle::Visual
284 join_rewrites(&rewrites[1..], &connector)
291 join_rewrites(&rewrites, &connector)
294 let result = format!("{}{}", result, repeat_try(suffix_try_num));
295 if context.config.indent_style() == IndentStyle::Visual {
296 wrap_str(result, context.config.max_width(), shape)
302 // True if the chain is only `?`s.
303 fn chain_only_try(exprs: &[ast::Expr]) -> bool {
304 exprs.iter().all(|e| {
305 if let ast::ExprKind::Try(_) = e.node {
313 // Try to rewrite and replace the last non-try child. Return `true` if
314 // replacing succeeds.
315 fn repeat_try(try_count: usize) -> String {
316 iter::repeat("?").take(try_count).collect::<String>()
322 context: &RewriteContext,
324 ) -> Option<String> {
325 let sub_expr = expr.rewrite(context, shape.sub_width(try_count)?)?;
326 Some(format!("{}{}", sub_expr, repeat_try(try_count)))
329 fn join_rewrites(rewrites: &[String], connector: &str) -> String {
330 let mut rewrite_iter = rewrites.iter();
331 let mut result = rewrite_iter.next().unwrap().clone();
333 for rewrite in rewrite_iter {
335 result.push_str(connector);
337 result.push_str(&rewrite[..]);
343 // States whether an expression's last line exclusively consists of closing
344 // parens, braces, and brackets in its idiomatic formatting.
345 fn is_block_expr(context: &RewriteContext, expr: &ast::Expr, repr: &str) -> bool {
347 ast::ExprKind::Mac(..) | ast::ExprKind::Call(..) => {
348 context.use_block_indent() && repr.contains('\n')
350 ast::ExprKind::Struct(..)
351 | ast::ExprKind::While(..)
352 | ast::ExprKind::WhileLet(..)
353 | ast::ExprKind::If(..)
354 | ast::ExprKind::IfLet(..)
355 | ast::ExprKind::Block(..)
356 | ast::ExprKind::Loop(..)
357 | ast::ExprKind::ForLoop(..)
358 | ast::ExprKind::Match(..) => repr.contains('\n'),
359 ast::ExprKind::Paren(ref expr)
360 | ast::ExprKind::Binary(_, _, ref expr)
361 | ast::ExprKind::Index(_, ref expr)
362 | ast::ExprKind::Unary(_, ref expr) => is_block_expr(context, expr, repr),
367 // Returns the root of the chain and a Vec of the prefixes of the rest of the chain.
368 // E.g., for input `a.b.c` we return (`a`, [`a.b.c`, `a.b`])
369 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> (ast::Expr, Vec<ast::Expr>) {
370 let mut subexpr_list = vec![expr.clone()];
372 while let Some(subexpr) = pop_expr_chain(subexpr_list.last().unwrap(), context) {
373 subexpr_list.push(subexpr.clone());
376 let parent = subexpr_list.pop().unwrap();
377 (parent, subexpr_list)
380 fn chain_indent(context: &RewriteContext, shape: Shape) -> Shape {
381 match context.config.indent_style() {
382 IndentStyle::Visual => shape.visual_indent(0),
383 IndentStyle::Block => shape
384 .block_indent(context.config.tab_spaces())
385 .with_max_width(context.config),
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(convert_try(&expressions[0], context))
396 ast::ExprKind::TupField(ref subexpr, _)
397 | ast::ExprKind::Field(ref subexpr, _)
398 | ast::ExprKind::Try(ref subexpr) => Some(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) {
416 // Rewrite the last element in the chain `expr`. E.g., given `a.b.c` we rewrite
418 fn rewrite_chain_subexpr(
421 context: &RewriteContext,
423 ) -> Option<String> {
424 let rewrite_element = |expr_str: String| {
425 if expr_str.len() <= shape.width {
433 ast::ExprKind::MethodCall(ref segment, ref expressions) => {
434 let types = match segment.parameters {
435 Some(ref params) => match **params {
436 ast::PathParameters::AngleBracketed(ref data) => &data.types[..],
441 rewrite_method_call(segment.identifier, types, expressions, span, context, shape)
443 ast::ExprKind::Field(_, ref field) => rewrite_element(format!(".{}", field.node)),
444 ast::ExprKind::TupField(ref expr, ref field) => {
445 let space = match expr.node {
446 ast::ExprKind::TupField(..) => " ",
449 rewrite_element(format!("{}.{}", space, field.node))
451 ast::ExprKind::Try(_) => rewrite_element(String::from("?")),
456 // Determines if we can continue formatting a given expression on the same line.
457 fn is_continuable(expr: &ast::Expr) -> bool {
459 ast::ExprKind::Path(..) => true,
464 fn is_try(expr: &ast::Expr) -> bool {
466 ast::ExprKind::Try(..) => true,
471 fn rewrite_method_call(
472 method_name: ast::Ident,
473 types: &[ptr::P<ast::Ty>],
474 args: &[ptr::P<ast::Expr>],
476 context: &RewriteContext,
478 ) -> Option<String> {
479 let (lo, type_str) = if types.is_empty() {
480 (args[0].span.hi(), String::new())
482 let type_list = types
484 .map(|ty| ty.rewrite(context, shape))
485 .collect::<Option<Vec<_>>>()?;
488 if context.config.spaces_within_parens_and_brackets() && !type_list.is_empty() {
489 format!("::< {} >", type_list.join(", "))
491 format!("::<{}>", type_list.join(", "))
494 (types.last().unwrap().span.hi(), type_str)
497 let callee_str = format!(".{}{}", method_name, type_str);
498 let span = mk_sp(lo, span.hi());
500 rewrite_call(context, &callee_str, &args[1..], span, shape)