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`:
58 /// If the first item in the chain is a block expression, we align the dots with
80 use config::IndentStyle;
81 use expr::rewrite_call;
82 use macros::convert_try_mac;
83 use rewrite::{Rewrite, RewriteContext};
84 use utils::{first_line_width, last_line_extendable, last_line_width, mk_sp, wrap_str};
88 use syntax::{ast, ptr};
89 use syntax::codemap::Span;
91 pub fn rewrite_chain(expr: &ast::Expr, context: &RewriteContext, shape: Shape) -> Option<String> {
92 debug!("rewrite_chain {:?}", shape);
93 let total_span = expr.span;
94 let (parent, subexpr_list) = make_subexpr_list(expr, context);
96 // Bail out if the chain is just try sugar, i.e., an expression followed by
97 // any number of `?`s.
98 if chain_only_try(&subexpr_list) {
99 return rewrite_try(&parent, subexpr_list.len(), context, shape);
101 let suffix_try_num = subexpr_list.iter().take_while(|e| is_try(e)).count();
102 let prefix_try_num = subexpr_list.iter().rev().take_while(|e| is_try(e)).count();
104 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
105 let parent_shape = if is_block_expr(context, &parent, "\n") {
106 match context.config.chain_indent() {
107 IndentStyle::Visual => shape.visual_indent(0),
108 IndentStyle::Block => shape,
113 let parent_rewrite = try_opt!(
115 .rewrite(context, parent_shape)
116 .map(|parent_rw| parent_rw + &repeat_try(prefix_try_num))
118 let parent_rewrite_contains_newline = parent_rewrite.contains('\n');
119 let is_small_parent = parent_rewrite.len() <= context.config.tab_spaces();
121 // Decide how to layout the rest of the chain. `extend` is true if we can
122 // put the first non-parent item on the same line as the parent.
123 let (nested_shape, extend) = if !parent_rewrite_contains_newline && is_continuable(&parent) {
125 chain_indent(context, shape.add_offset(parent_rewrite.len())),
126 context.config.chain_indent() == IndentStyle::Visual || is_small_parent,
128 } else if is_block_expr(context, &parent, &parent_rewrite) {
129 match context.config.chain_indent() {
130 // Try to put the first child on the same line with parent's last line
131 IndentStyle::Block => (parent_shape.block_indent(context.config.tab_spaces()), true),
132 // The parent is a block, so align the rest of the chain with the closing
134 IndentStyle::Visual => (parent_shape, false),
138 chain_indent(context, shape.add_offset(parent_rewrite.len())),
143 let other_child_shape = nested_shape.with_max_width(context.config);
145 let first_child_shape = if extend {
146 let overhead = last_line_width(&parent_rewrite);
147 let offset = parent_rewrite.lines().rev().next().unwrap().trim().len();
148 match context.config.chain_indent() {
149 IndentStyle::Visual => try_opt!(parent_shape.offset_left(overhead)),
150 IndentStyle::Block => try_opt!(parent_shape.block().offset_left(offset)),
156 "child_shapes {:?} {:?}",
161 let child_shape_iter = Some(first_child_shape)
163 .chain(iter::repeat(other_child_shape));
164 let subexpr_num = subexpr_list.len();
165 let last_subexpr = &subexpr_list[suffix_try_num];
166 let subexpr_list = &subexpr_list[suffix_try_num..subexpr_num - prefix_try_num];
167 let iter = subexpr_list.iter().skip(1).rev().zip(child_shape_iter);
168 let mut rewrites = try_opt!(
169 iter.map(|(e, shape)| {
170 rewrite_chain_subexpr(e, total_span, context, shape)
171 }).collect::<Option<Vec<_>>>()
174 // Total of all items excluding the last.
175 let extend_last_subexr = last_line_extendable(&parent_rewrite) && rewrites.is_empty();
176 let almost_total = if extend_last_subexr {
177 last_line_width(&parent_rewrite)
179 rewrites.iter().fold(0, |a, b| a + b.len()) + parent_rewrite.len()
181 let one_line_budget = if rewrites.is_empty() && !context.config.chain_split_single_child() {
184 min(shape.width, context.config.chain_one_line_max())
186 let all_in_one_line = !parent_rewrite_contains_newline &&
187 rewrites.iter().all(|s| !s.contains('\n')) &&
188 almost_total < one_line_budget;
189 let rewrite_last = || rewrite_chain_subexpr(last_subexpr, total_span, context, nested_shape);
190 let (last_subexpr_str, fits_single_line) = try_opt!(if all_in_one_line || extend_last_subexr {
191 parent_shape.offset_left(almost_total).map(|shape| {
192 if let Some(rw) = rewrite_chain_subexpr(last_subexpr, total_span, context, shape) {
193 let line_count = rw.lines().count();
194 let fits_single_line = almost_total + first_line_width(&rw) <= one_line_budget;
195 if (line_count >= 5 && fits_single_line) || extend_last_subexr {
198 match rewrite_last() {
199 Some(ref new_rw) if !fits_single_line => (Some(new_rw.clone()), false),
200 Some(ref new_rw) if new_rw.lines().count() >= line_count => {
201 (Some(rw), fits_single_line)
203 new_rw @ Some(..) => (new_rw, false),
204 _ => (Some(rw), fits_single_line),
208 (rewrite_last(), false)
212 Some((rewrite_last(), false))
214 rewrites.push(try_opt!(last_subexpr_str));
216 let connector = if fits_single_line && !parent_rewrite_contains_newline {
217 // Yay, we can put everything on one line.
221 if context.force_one_line_chain {
224 format!("\n{}", nested_shape.indent.to_string(context.config))
227 let first_connector = if is_small_parent || fits_single_line ||
228 last_line_extendable(&parent_rewrite) ||
229 context.config.chain_indent() == IndentStyle::Visual
236 let subexpr_num = subexpr_list.len();
237 let result = if is_small_parent && rewrites.len() > 1 {
238 let second_connector = choose_first_connector(
243 &subexpr_list[..subexpr_num - 1],
252 join_rewrites(&rewrites[1..], &subexpr_list[..subexpr_num - 1], &connector)
259 join_rewrites(&rewrites, subexpr_list, &connector)
262 let result = format!("{}{}", result, repeat_try(suffix_try_num));
263 wrap_str(result, context.config.max_width(), shape)
266 fn is_extendable_parent(context: &RewriteContext, parent_str: &str) -> bool {
267 context.config.chain_indent() == IndentStyle::Block && last_line_extendable(parent_str)
270 // True if the chain is only `?`s.
271 fn chain_only_try(exprs: &[ast::Expr]) -> bool {
272 exprs.iter().all(|e| if let ast::ExprKind::Try(_) = e.node {
279 // Try to rewrite and replace the last non-try child. Return `true` if
280 // replacing succeeds.
281 fn repeat_try(try_count: usize) -> String {
282 iter::repeat("?").take(try_count).collect::<String>()
288 context: &RewriteContext,
290 ) -> Option<String> {
291 let sub_expr = try_opt!(expr.rewrite(context, try_opt!(shape.sub_width(try_count))));
292 Some(format!("{}{}", sub_expr, repeat_try(try_count)))
295 fn join_rewrites(rewrites: &[String], subexps: &[ast::Expr], connector: &str) -> String {
296 let mut rewrite_iter = rewrites.iter();
297 let mut result = rewrite_iter.next().unwrap().clone();
298 let mut subexpr_iter = subexps.iter().rev();
301 for (rewrite, expr) in rewrite_iter.zip(subexpr_iter) {
303 ast::ExprKind::Try(_) => (),
304 _ => result.push_str(connector),
306 result.push_str(&rewrite[..]);
312 // States whether an expression's last line exclusively consists of closing
313 // parens, braces, and brackets in its idiomatic formatting.
314 fn is_block_expr(context: &RewriteContext, expr: &ast::Expr, repr: &str) -> bool {
316 ast::ExprKind::Mac(..) | ast::ExprKind::Call(..) => {
317 context.use_block_indent() && repr.contains('\n')
319 ast::ExprKind::Struct(..) |
320 ast::ExprKind::While(..) |
321 ast::ExprKind::WhileLet(..) |
322 ast::ExprKind::If(..) |
323 ast::ExprKind::IfLet(..) |
324 ast::ExprKind::Block(..) |
325 ast::ExprKind::Loop(..) |
326 ast::ExprKind::ForLoop(..) |
327 ast::ExprKind::Match(..) => repr.contains('\n'),
328 ast::ExprKind::Paren(ref expr) |
329 ast::ExprKind::Binary(_, _, ref expr) |
330 ast::ExprKind::Index(_, ref expr) |
331 ast::ExprKind::Unary(_, ref expr) => is_block_expr(context, expr, repr),
336 // Returns the root of the chain and a Vec of the prefixes of the rest of the chain.
337 // E.g., for input `a.b.c` we return (`a`, [`a.b.c`, `a.b`])
338 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> (ast::Expr, Vec<ast::Expr>) {
339 let mut subexpr_list = vec![expr.clone()];
341 while let Some(subexpr) = pop_expr_chain(subexpr_list.last().unwrap(), context) {
342 subexpr_list.push(subexpr.clone());
345 let parent = subexpr_list.pop().unwrap();
346 (parent, subexpr_list)
349 fn chain_indent(context: &RewriteContext, shape: Shape) -> Shape {
350 match context.config.chain_indent() {
351 IndentStyle::Visual => shape.visual_indent(0),
352 IndentStyle::Block => shape
353 .block_indent(context.config.tab_spaces())
354 .with_max_width(context.config),
358 // Returns the expression's subexpression, if it exists. When the subexpr
359 // is a try! macro, we'll convert it to shorthand when the option is set.
360 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
362 ast::ExprKind::MethodCall(_, ref expressions) => {
363 Some(convert_try(&expressions[0], context))
365 ast::ExprKind::TupField(ref subexpr, _) |
366 ast::ExprKind::Field(ref subexpr, _) |
367 ast::ExprKind::Try(ref subexpr) => Some(convert_try(subexpr, context)),
372 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
374 ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand() => {
375 if let Some(subexpr) = convert_try_mac(mac, context) {
385 // Rewrite the last element in the chain `expr`. E.g., given `a.b.c` we rewrite
387 fn rewrite_chain_subexpr(
390 context: &RewriteContext,
392 ) -> Option<String> {
393 let rewrite_element = |expr_str: String| if expr_str.len() <= shape.width {
400 ast::ExprKind::MethodCall(ref segment, ref expressions) => {
401 let types = match segment.parameters {
402 Some(ref params) => match **params {
403 ast::PathParameters::AngleBracketed(ref data) => &data.types[..],
408 rewrite_method_call(segment.identifier, types, expressions, span, context, shape)
410 ast::ExprKind::Field(_, ref field) => rewrite_element(format!(".{}", field.node)),
411 ast::ExprKind::TupField(ref expr, ref field) => {
412 let space = match expr.node {
413 ast::ExprKind::TupField(..) => " ",
416 rewrite_element(format!("{}.{}", space, field.node))
418 ast::ExprKind::Try(_) => rewrite_element(String::from("?")),
423 // Determines if we can continue formatting a given expression on the same line.
424 fn is_continuable(expr: &ast::Expr) -> bool {
426 ast::ExprKind::Path(..) => true,
431 fn is_try(expr: &ast::Expr) -> bool {
433 ast::ExprKind::Try(..) => true,
438 fn choose_first_connector<'a>(
439 context: &RewriteContext,
441 first_child_str: &str,
443 subexpr_list: &[ast::Expr],
446 if subexpr_list.is_empty() {
448 } else if extend || subexpr_list.last().map_or(false, is_try) ||
449 is_extendable_parent(context, parent_str)
451 // 1 = ";", being conservative here.
452 if last_line_width(parent_str) + first_line_width(first_child_str) + 1 <=
453 context.config.max_width()
464 fn rewrite_method_call(
465 method_name: ast::Ident,
466 types: &[ptr::P<ast::Ty>],
467 args: &[ptr::P<ast::Expr>],
469 context: &RewriteContext,
471 ) -> Option<String> {
472 let (lo, type_str) = if types.is_empty() {
473 (args[0].span.hi(), String::new())
475 let type_list: Vec<_> =
476 try_opt!(types.iter().map(|ty| ty.rewrite(context, shape)).collect());
478 let type_str = if context.config.spaces_within_angle_brackets() && !type_list.is_empty() {
479 format!("::< {} >", type_list.join(", "))
481 format!("::<{}>", type_list.join(", "))
484 (types.last().unwrap().span.hi(), type_str)
487 let callee_str = format!(".{}{}", method_name, type_str);
488 let span = mk_sp(lo, span.hi());
490 rewrite_call(context, &callee_str, &args[1..], span, shape)