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 and method calls.
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_base_indent` is the indent to use for
23 /// blocks in the parent/root/base of the chain.
24 /// E.g., `let foo = { aaaa; bbb; ccc }.bar.baz();`, we would layout for the
25 /// following values of `chain_base_indent`:
57 /// `chain_indent` dictates how the rest of the chain is aligned. This only seems
58 /// to have an effect if the first non-root part of the chain is put on a
59 /// newline, otherwise we align the dots:
64 /// If the first item in the chain is a block expression, we align the dots with
70 /// let a = foo(aaa, bbb)
74 /// Visual seems to be a tab indented from the indent of the whole expression.
77 /// let a = foo(aaa, bbb)
83 /// let a = foo(aaa, bbb)
87 /// `chains_overflow_last` applies only to chains where the last item is a
88 /// method call. Usually, any line break in a chain sub-expression causes the
89 /// whole chain to be split with newlines at each `.`. With `chains_overflow_last`
90 /// true, then we allow the last method call to spill over multiple lines without
91 /// forcing the rest of the chain to be split.
95 use rewrite::{Rewrite, RewriteContext};
96 use utils::{wrap_str, first_line_width};
97 use expr::rewrite_call;
98 use config::BlockIndentStyle;
100 use syntax::{ast, ptr};
101 use syntax::codemap::{mk_sp, Span};
104 pub fn rewrite_chain(expr: &ast::Expr,
105 context: &RewriteContext,
109 let total_span = expr.span;
110 let (parent, subexpr_list) = make_subexpr_list(expr);
112 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
113 let parent_block_indent = chain_base_indent(context, offset);
114 let parent_context = &RewriteContext { block_indent: parent_block_indent, ..*context };
115 let parent_rewrite = try_opt!(parent.rewrite(parent_context, width, offset));
117 // Decide how to layout the rest of the chain. `extend` is true if we can
118 // put the first non-parent item on the same line as the parent.
119 let (indent, extend) = if !parent_rewrite.contains('\n') && is_continuable(parent) ||
120 parent_rewrite.len() <= context.config.tab_spaces {
121 // Try and put at least the first two items on the same line.
122 (chain_indent(context, offset + Indent::new(0, parent_rewrite.len())), true)
123 } else if is_block_expr(parent, &parent_rewrite) {
124 // The parent is a block, so align the rest of the chain with the closing
126 (parent_block_indent, false)
127 } else if parent_rewrite.contains('\n') {
128 (chain_indent(context, parent_block_indent.block_indent(context.config)), false)
130 (hacked_chain_indent(context, offset + Indent::new(0, parent_rewrite.len())), false)
133 let max_width = try_opt!((width + offset.width()).checked_sub(indent.width()));
134 let mut rewrites = try_opt!(subexpr_list.iter()
137 rewrite_chain_subexpr(e,
143 .collect::<Option<Vec<_>>>());
145 // Total of all items excluding the last.
146 let almost_total = rewrites[..rewrites.len() - 1]
148 .fold(0, |a, b| a + first_line_width(b)) + parent_rewrite.len();
149 let total_width = almost_total + first_line_width(rewrites.last().unwrap());
151 let veto_single_line = if context.config.take_source_hints && subexpr_list.len() > 1 {
152 // Look at the source code. Unless all chain elements start on the same
153 // line, we won't consider putting them on a single line either.
154 let last_span = context.snippet(mk_sp(subexpr_list[1].span.hi, total_span.hi));
155 let first_span = context.snippet(subexpr_list[1].span);
156 let last_iter = last_span.chars().take_while(|c| c.is_whitespace());
158 first_span.chars().chain(last_iter).any(|c| c == '\n')
163 let mut fits_single_line = !veto_single_line && total_width <= width;
164 if fits_single_line {
165 let len = rewrites.len();
166 let (init, last) = rewrites.split_at_mut(len - 1);
167 fits_single_line = init.iter().all(|s| !s.contains('\n'));
169 if fits_single_line {
170 fits_single_line = match expr.node {
171 ref e @ ast::ExprKind::MethodCall(..) if context.config.chains_overflow_last => {
172 rewrite_method_call_with_overflow(e,
180 _ => !last[0].contains('\n'),
185 let connector = if fits_single_line && !parent_rewrite.contains('\n') {
186 // Yay, we can put everything on one line.
190 format!("\n{}", indent.to_string(context.config))
193 let first_connector = if extend {
199 wrap_str(format!("{}{}{}",
202 rewrites.join(&connector)),
203 context.config.max_width,
208 // States whether an expression's last line exclusively consists of closing
209 // parens, braces, and brackets in its idiomatic formatting.
210 fn is_block_expr(expr: &ast::Expr, repr: &str) -> bool {
212 ast::ExprKind::Struct(..) |
213 ast::ExprKind::While(..) |
214 ast::ExprKind::WhileLet(..) |
215 ast::ExprKind::If(..) |
216 ast::ExprKind::IfLet(..) |
217 ast::ExprKind::Block(..) |
218 ast::ExprKind::Loop(..) |
219 ast::ExprKind::ForLoop(..) |
220 ast::ExprKind::Match(..) => repr.contains('\n'),
221 ast::ExprKind::Paren(ref expr) |
222 ast::ExprKind::Binary(_, _, ref expr) |
223 ast::ExprKind::Index(_, ref expr) |
224 ast::ExprKind::Unary(_, ref expr) => is_block_expr(expr, repr),
229 // Returns the root of the chain and a Vec of the prefixes of the rest of the chain.
230 // E.g., for input `a.b.c` we return (`a`, [`a.b.c`, `a.b`])
231 fn make_subexpr_list(mut expr: &ast::Expr) -> (&ast::Expr, Vec<&ast::Expr>) {
232 fn pop_expr_chain(expr: &ast::Expr) -> Option<&ast::Expr> {
234 ast::ExprKind::MethodCall(_, _, ref expressions) => Some(&expressions[0]),
235 ast::ExprKind::TupField(ref subexpr, _) |
236 ast::ExprKind::Field(ref subexpr, _) => Some(subexpr),
241 let mut subexpr_list = vec![expr];
243 while let Some(subexpr) = pop_expr_chain(expr) {
244 subexpr_list.push(subexpr);
248 let parent = subexpr_list.pop().unwrap();
249 (parent, subexpr_list)
252 fn chain_base_indent(context: &RewriteContext, offset: Indent) -> Indent {
253 match context.config.chain_base_indent {
254 BlockIndentStyle::Visual => offset,
255 BlockIndentStyle::Inherit => context.block_indent,
256 BlockIndentStyle::Tabbed => context.block_indent.block_indent(context.config),
260 fn chain_indent(context: &RewriteContext, offset: Indent) -> Indent {
261 match context.config.chain_indent {
262 BlockIndentStyle::Visual => offset,
263 BlockIndentStyle::Inherit => context.block_indent,
264 BlockIndentStyle::Tabbed => context.block_indent.block_indent(context.config),
268 // Temporary hack - ignores visual indenting because this function should be
269 // called where it is not possible to use visual indentation.
270 fn hacked_chain_indent(context: &RewriteContext, _offset: Indent) -> Indent {
271 match context.config.chain_indent {
272 BlockIndentStyle::Inherit => context.block_indent,
273 BlockIndentStyle::Visual | BlockIndentStyle::Tabbed => {
274 context.block_indent.block_indent(context.config)
279 fn rewrite_method_call_with_overflow(expr_kind: &ast::ExprKind,
284 context: &RewriteContext,
287 if let &ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) = expr_kind {
288 let budget = match width.checked_sub(almost_total) {
290 None => return false,
292 let mut last_rewrite = rewrite_method_call(method_name.node,
298 offset + almost_total);
300 if let Some(ref mut s) = last_rewrite {
301 ::std::mem::swap(s, last);
311 // Rewrite the last element in the chain `expr`. E.g., given `a.b.c` we rewrite
313 fn rewrite_chain_subexpr(expr: &ast::Expr,
315 context: &RewriteContext,
320 ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) => {
321 let inner = &RewriteContext { block_indent: offset, ..*context };
322 rewrite_method_call(method_name.node,
330 ast::ExprKind::Field(_, ref field) => {
331 let s = format!(".{}", field.node);
332 if s.len() <= width {
338 ast::ExprKind::TupField(_, ref field) => {
339 let s = format!(".{}", field.node);
340 if s.len() <= width {
350 // Determines if we can continue formatting a given expression on the same line.
351 fn is_continuable(expr: &ast::Expr) -> bool {
353 ast::ExprKind::Path(..) => true,
358 fn rewrite_method_call(method_name: ast::Ident,
359 types: &[ptr::P<ast::Ty>],
360 args: &[ptr::P<ast::Expr>],
362 context: &RewriteContext,
366 let (lo, type_str) = if types.is_empty() {
367 (args[0].span.hi, String::new())
369 let type_list: Vec<_> = try_opt!(types.iter()
370 .map(|ty| ty.rewrite(context, width, offset))
373 (types.last().unwrap().span.hi, format!("::<{}>", type_list.join(", ")))
376 let callee_str = format!(".{}{}", method_name, type_str);
377 let span = mk_sp(lo, span.hi);
379 rewrite_call(context, &callee_str, &args[1..], span, width, offset)