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 rewrite::{Rewrite, RewriteContext};
81 use utils::{wrap_str, first_line_width, last_line_width};
82 use expr::rewrite_call;
83 use config::BlockIndentStyle;
84 use macros::convert_try_mac;
87 use syntax::{ast, ptr};
88 use syntax::codemap::{mk_sp, Span};
90 pub fn rewrite_chain(expr: &ast::Expr, context: &RewriteContext, shape: Shape) -> Option<String> {
91 debug!("rewrite_chain {:?}", shape);
92 let total_span = expr.span;
93 let (parent, subexpr_list) = make_subexpr_list(expr, context);
95 // Bail out if the chain is just try sugar, i.e., an expression followed by
96 // any number of `?`s.
97 if chain_only_try(&subexpr_list) {
98 return rewrite_try(&parent, subexpr_list.len(), context, shape);
101 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
102 let mut parent_shape = shape;
103 if is_block_expr(&parent, "\n") {
104 parent_shape = chain_indent(context, shape);
106 let parent_rewrite = try_opt!(parent.rewrite(context, parent_shape));
108 // Decide how to layout the rest of the chain. `extend` is true if we can
109 // put the first non-parent item on the same line as the parent.
110 let (nested_shape, extend) = if !parent_rewrite.contains('\n') && is_continuable(&parent) {
111 let nested_shape = if let ast::ExprKind::Try(..) = subexpr_list.last().unwrap().node {
112 parent_shape.block_indent(context.config.tab_spaces)
114 chain_indent(context, shape.add_offset(parent_rewrite.len()))
117 } else if is_block_expr(&parent, &parent_rewrite) {
118 // The parent is a block, so align the rest of the chain with the closing
120 (parent_shape, false)
121 } else if parent_rewrite.contains('\n') {
122 (chain_indent(context,
123 parent_shape.block_indent(context.config.tab_spaces)),
126 (shape.block_indent(context.config.tab_spaces), false)
129 let max_width = try_opt!((shape.width + shape.indent.width() + shape.offset)
130 .checked_sub(nested_shape.indent.width() +
131 nested_shape.offset));
133 let other_child_shape = Shape { width: max_width, ..nested_shape };
134 let first_child_shape = if extend {
135 let mut shape = try_opt!(parent_shape.shrink_left(last_line_width(&parent_rewrite)));
136 match context.config.chain_indent {
137 BlockIndentStyle::Visual => other_child_shape,
138 BlockIndentStyle::Tabbed => {
139 shape.offset = shape.offset.checked_sub(context.config.tab_spaces).unwrap_or(0);
140 shape.indent.block_indent += context.config.tab_spaces;
147 debug!("child_shapes {:?} {:?}",
151 let child_shape_iter =
152 Some(first_child_shape).into_iter().chain(::std::iter::repeat(other_child_shape)
153 .take(subexpr_list.len() - 1));
154 let iter = subexpr_list.iter().rev().zip(child_shape_iter);
156 try_opt!(iter.map(|(e, shape)| rewrite_chain_subexpr(e, total_span, context, shape))
157 .collect::<Option<Vec<_>>>());
159 // Total of all items excluding the last.
160 let almost_total = rewrites[..rewrites.len() - 1].iter().fold(0, |a, b| {
161 a + first_line_width(b)
162 }) + parent_rewrite.len();
164 let veto_single_line = if subexpr_list.len() > context.config.chain_one_line_max - 1 {
165 // -1 above because subexpr_list does not include the parent.
167 } else if context.config.take_source_hints && subexpr_list.len() > 1 {
168 // Look at the source code. Unless all chain elements start on the same
169 // line, we won't consider putting them on a single line either.
170 let last_span = context.snippet(mk_sp(subexpr_list[1].span.hi, total_span.hi));
171 let first_span = context.snippet(subexpr_list[1].span);
172 let last_iter = last_span.chars().take_while(|c| c.is_whitespace());
174 first_span.chars().chain(last_iter).any(|c| c == '\n')
179 let mut fits_single_line = !veto_single_line && almost_total <= shape.width;
180 if fits_single_line {
181 let len = rewrites.len();
182 let (init, last) = rewrites.split_at_mut(len - 1);
183 fits_single_line = init.iter().all(|s| !s.contains('\n'));
185 if fits_single_line {
186 fits_single_line = match expr.node {
187 ref e @ ast::ExprKind::MethodCall(..) => {
188 rewrite_method_call_with_overflow(e,
195 _ => !last[0].contains('\n'),
200 let connector = if fits_single_line && !parent_rewrite.contains('\n') {
201 // Yay, we can put everything on one line.
205 format!("\n{}", nested_shape.indent.to_string(context.config))
208 let first_connector = if extend || subexpr_list.is_empty() {
210 } else if let ast::ExprKind::Try(_) = subexpr_list[0].node {
216 wrap_str(format!("{}{}{}",
219 join_rewrites(&rewrites, &subexpr_list, &connector)),
220 context.config.max_width,
224 // True if the chain is only `?`s.
225 fn chain_only_try(exprs: &[ast::Expr]) -> bool {
226 exprs.iter().all(|e| if let ast::ExprKind::Try(_) = e.node {
233 pub fn rewrite_try(expr: &ast::Expr,
235 context: &RewriteContext,
238 let sub_expr = try_opt!(expr.rewrite(context, try_opt!(shape.sub_width(try_count))));
241 iter::repeat("?").take(try_count).collect::<String>()))
244 fn join_rewrites(rewrites: &[String], subexps: &[ast::Expr], connector: &str) -> String {
245 let mut rewrite_iter = rewrites.iter();
246 let mut result = rewrite_iter.next().unwrap().clone();
247 let mut subexpr_iter = subexps.iter().rev();
250 for (rewrite, expr) in rewrite_iter.zip(subexpr_iter) {
252 ast::ExprKind::Try(_) => (),
253 _ => result.push_str(connector),
255 result.push_str(&rewrite[..]);
261 // States whether an expression's last line exclusively consists of closing
262 // parens, braces, and brackets in its idiomatic formatting.
263 fn is_block_expr(expr: &ast::Expr, repr: &str) -> bool {
265 ast::ExprKind::Struct(..) |
266 ast::ExprKind::While(..) |
267 ast::ExprKind::WhileLet(..) |
268 ast::ExprKind::If(..) |
269 ast::ExprKind::IfLet(..) |
270 ast::ExprKind::Block(..) |
271 ast::ExprKind::Loop(..) |
272 ast::ExprKind::ForLoop(..) |
273 ast::ExprKind::Match(..) => repr.contains('\n'),
274 ast::ExprKind::Paren(ref expr) |
275 ast::ExprKind::Binary(_, _, ref expr) |
276 ast::ExprKind::Index(_, ref expr) |
277 ast::ExprKind::Unary(_, ref expr) => is_block_expr(expr, repr),
282 // Returns the root of the chain and a Vec of the prefixes of the rest of the chain.
283 // E.g., for input `a.b.c` we return (`a`, [`a.b.c`, `a.b`])
284 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> (ast::Expr, Vec<ast::Expr>) {
285 let mut subexpr_list = vec![expr.clone()];
287 while let Some(subexpr) = pop_expr_chain(subexpr_list.last().unwrap(), context) {
288 subexpr_list.push(subexpr.clone());
291 let parent = subexpr_list.pop().unwrap();
292 (parent, subexpr_list)
295 fn chain_indent(context: &RewriteContext, shape: Shape) -> Shape {
296 match context.config.chain_indent {
297 BlockIndentStyle::Visual => shape.visual_indent(0),
298 BlockIndentStyle::Tabbed => shape.block_indent(context.config.tab_spaces),
302 fn rewrite_method_call_with_overflow(expr_kind: &ast::ExprKind,
306 context: &RewriteContext,
309 if let &ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) = expr_kind {
310 let shape = match shape.shrink_left(almost_total) {
312 None => return false,
314 let mut last_rewrite = rewrite_method_call(method_name.node,
321 if let Some(ref mut s) = last_rewrite {
322 ::std::mem::swap(s, last);
332 // Returns the expression's subexpression, if it exists. When the subexpr
333 // is a try! macro, we'll convert it to shorthand when the option is set.
334 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
336 ast::ExprKind::MethodCall(_, _, ref expressions) => {
337 Some(convert_try(&expressions[0], context))
339 ast::ExprKind::TupField(ref subexpr, _) |
340 ast::ExprKind::Field(ref subexpr, _) |
341 ast::ExprKind::Try(ref subexpr) => Some(convert_try(subexpr, context)),
346 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
348 ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand => {
349 if let Some(subexpr) = convert_try_mac(mac, context) {
359 // Rewrite the last element in the chain `expr`. E.g., given `a.b.c` we rewrite
361 fn rewrite_chain_subexpr(expr: &ast::Expr,
363 context: &RewriteContext,
367 ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) => {
368 rewrite_method_call(method_name.node, types, expressions, span, context, shape)
370 ast::ExprKind::Field(_, ref field) => {
371 let s = format!(".{}", field.node);
372 if s.len() <= shape.width {
378 ast::ExprKind::TupField(_, ref field) => {
379 let s = format!(".{}", field.node);
380 if s.len() <= shape.width {
386 ast::ExprKind::Try(_) => {
387 if shape.width >= 1 {
397 // Determines if we can continue formatting a given expression on the same line.
398 fn is_continuable(expr: &ast::Expr) -> bool {
400 ast::ExprKind::Path(..) => true,
405 fn rewrite_method_call(method_name: ast::Ident,
406 types: &[ptr::P<ast::Ty>],
407 args: &[ptr::P<ast::Expr>],
409 context: &RewriteContext,
412 let (lo, type_str) = if types.is_empty() {
413 (args[0].span.hi, String::new())
415 let type_list: Vec<_> =
416 try_opt!(types.iter().map(|ty| ty.rewrite(context, shape)).collect());
418 let type_str = if context.config.spaces_within_angle_brackets && type_list.len() > 0 {
419 format!("::< {} >", type_list.join(", "))
421 format!("::<{}>", type_list.join(", "))
431 let callee_str = format!(".{}{}", method_name, type_str);
432 let span = mk_sp(lo, span.hi);
434 rewrite_call(context, &callee_str, &args[1..], span, shape)