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_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.
58 /// If the first item in the chain is a block expression, we align the dots with
78 /// `chains_overflow_last` applies only to chains where the last item is a
79 /// method call. Usually, any line break in a chain sub-expression causes the
80 /// whole chain to be split with newlines at each `.`. With `chains_overflow_last`
81 /// true, then we allow the last method call to spill over multiple lines without
82 /// forcing the rest of the chain to be split.
85 use rewrite::{Rewrite, RewriteContext};
86 use utils::{wrap_str, first_line_width};
87 use expr::rewrite_call;
88 use config::BlockIndentStyle;
89 use macros::convert_try_mac;
92 use syntax::{ast, ptr};
93 use syntax::codemap::{mk_sp, Span};
95 pub fn rewrite_chain(expr: &ast::Expr,
96 context: &RewriteContext,
100 let total_span = expr.span;
101 let (parent, subexpr_list) = make_subexpr_list(expr, context);
103 // Bail out if the chain is just try sugar, i.e., an expression followed by
104 // any number of `?`s.
105 if chain_only_try(&subexpr_list) {
106 return rewrite_try(&parent, subexpr_list.len(), context, width, offset);
109 // Parent is the first item in the chain, e.g., `foo` in `foo.bar.baz()`.
110 let parent_block_indent = chain_base_indent(context, offset);
111 let parent_context = &RewriteContext { block_indent: parent_block_indent, ..*context };
112 let parent_rewrite = try_opt!(parent.rewrite(parent_context, width, offset));
114 // Decide how to layout the rest of the chain. `extend` is true if we can
115 // put the first non-parent item on the same line as the parent.
116 let (indent, extend) = if !parent_rewrite.contains('\n') && is_continuable(&parent) ||
117 parent_rewrite.len() <= context.config.tab_spaces {
119 let indent = if let ast::ExprKind::Try(..) = subexpr_list.last().unwrap().node {
120 parent_block_indent.block_indent(context.config)
122 chain_indent(context, offset + Indent::new(0, parent_rewrite.len()))
125 } else if is_block_expr(&parent, &parent_rewrite) {
126 // The parent is a block, so align the rest of the chain with the closing
128 (parent_block_indent, false)
129 } else if parent_rewrite.contains('\n') {
130 (chain_indent(context, parent_block_indent.block_indent(context.config)), false)
132 (chain_indent_newline(context, offset + Indent::new(0, parent_rewrite.len())), false)
135 let max_width = try_opt!((width + offset.width()).checked_sub(indent.width()));
136 let mut rewrites = try_opt!(subexpr_list.iter()
138 .map(|e| rewrite_chain_subexpr(e, total_span, context, max_width, indent))
139 .collect::<Option<Vec<_>>>());
141 // Total of all items excluding the last.
142 let almost_total = rewrites[..rewrites.len() - 1]
144 .fold(0, |a, b| a + first_line_width(b)) + parent_rewrite.len();
145 let total_width = almost_total + first_line_width(rewrites.last().unwrap());
147 let veto_single_line = if context.config.take_source_hints && subexpr_list.len() > 1 {
148 // Look at the source code. Unless all chain elements start on the same
149 // line, we won't consider putting them on a single line either.
150 let last_span = context.snippet(mk_sp(subexpr_list[1].span.hi, total_span.hi));
151 let first_span = context.snippet(subexpr_list[1].span);
152 let last_iter = last_span.chars().take_while(|c| c.is_whitespace());
154 first_span.chars().chain(last_iter).any(|c| c == '\n')
159 let mut fits_single_line = !veto_single_line && total_width <= width;
160 if fits_single_line {
161 let len = rewrites.len();
162 let (init, last) = rewrites.split_at_mut(len - 1);
163 fits_single_line = init.iter().all(|s| !s.contains('\n'));
165 if fits_single_line {
166 fits_single_line = match expr.node {
167 ref e @ ast::ExprKind::MethodCall(..) if context.config.chains_overflow_last => {
168 rewrite_method_call_with_overflow(e,
176 _ => !last[0].contains('\n'),
181 let connector = if fits_single_line && !parent_rewrite.contains('\n') {
182 // Yay, we can put everything on one line.
186 format!("\n{}", indent.to_string(context.config))
189 let first_connector = if extend || subexpr_list.is_empty() {
191 } else if let ast::ExprKind::Try(_) = subexpr_list[0].node {
197 wrap_str(format!("{}{}{}",
200 join_rewrites(&rewrites, &subexpr_list, &connector)),
201 context.config.max_width,
206 // True if the chain is only `?`s.
207 fn chain_only_try(exprs: &[ast::Expr]) -> bool {
208 exprs.iter().all(|e| if let ast::ExprKind::Try(_) = e.node {
215 pub fn rewrite_try(expr: &ast::Expr,
217 context: &RewriteContext,
221 let sub_expr = try_opt!(expr.rewrite(context, width - try_count, offset));
224 iter::repeat("?").take(try_count).collect::<String>()))
227 fn join_rewrites(rewrites: &[String], subexps: &[ast::Expr], connector: &str) -> String {
228 let mut rewrite_iter = rewrites.iter();
229 let mut result = rewrite_iter.next().unwrap().clone();
230 let mut subexpr_iter = subexps.iter().rev();
233 for (rewrite, expr) in rewrite_iter.zip(subexpr_iter) {
235 ast::ExprKind::Try(_) => (),
236 _ => result.push_str(connector),
238 result.push_str(&rewrite[..]);
244 // States whether an expression's last line exclusively consists of closing
245 // parens, braces, and brackets in its idiomatic formatting.
246 fn is_block_expr(expr: &ast::Expr, repr: &str) -> bool {
248 ast::ExprKind::Struct(..) |
249 ast::ExprKind::While(..) |
250 ast::ExprKind::WhileLet(..) |
251 ast::ExprKind::If(..) |
252 ast::ExprKind::IfLet(..) |
253 ast::ExprKind::Block(..) |
254 ast::ExprKind::Loop(..) |
255 ast::ExprKind::ForLoop(..) |
256 ast::ExprKind::Match(..) => repr.contains('\n'),
257 ast::ExprKind::Paren(ref expr) |
258 ast::ExprKind::Binary(_, _, ref expr) |
259 ast::ExprKind::Index(_, ref expr) |
260 ast::ExprKind::Unary(_, ref expr) => is_block_expr(expr, repr),
265 // Returns the root of the chain and a Vec of the prefixes of the rest of the chain.
266 // E.g., for input `a.b.c` we return (`a`, [`a.b.c`, `a.b`])
267 fn make_subexpr_list(expr: &ast::Expr, context: &RewriteContext) -> (ast::Expr, Vec<ast::Expr>) {
268 let mut subexpr_list = vec![expr.clone()];
270 while let Some(subexpr) = pop_expr_chain(subexpr_list.last().unwrap(), context) {
271 subexpr_list.push(subexpr.clone());
274 let parent = subexpr_list.pop().unwrap();
275 (parent, subexpr_list)
278 fn chain_base_indent(context: &RewriteContext, offset: Indent) -> Indent {
279 match context.config.chain_base_indent {
280 BlockIndentStyle::Visual => offset,
281 BlockIndentStyle::Inherit => context.block_indent,
282 BlockIndentStyle::Tabbed => context.block_indent.block_indent(context.config),
286 fn chain_indent(context: &RewriteContext, offset: Indent) -> Indent {
287 match context.config.chain_indent {
288 BlockIndentStyle::Visual => offset,
289 BlockIndentStyle::Inherit => context.block_indent,
290 BlockIndentStyle::Tabbed => context.block_indent.block_indent(context.config),
294 // Ignores visual indenting because this function should be called where it is
295 // not possible to use visual indentation because we are starting on a newline.
296 fn chain_indent_newline(context: &RewriteContext, _offset: Indent) -> Indent {
297 match context.config.chain_indent {
298 BlockIndentStyle::Inherit => context.block_indent,
299 BlockIndentStyle::Visual | BlockIndentStyle::Tabbed => {
300 context.block_indent.block_indent(context.config)
305 fn rewrite_method_call_with_overflow(expr_kind: &ast::ExprKind,
310 context: &RewriteContext,
313 if let &ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) = expr_kind {
314 let budget = match width.checked_sub(almost_total) {
316 None => return false,
318 let mut last_rewrite = rewrite_method_call(method_name.node,
324 offset + almost_total);
326 if let Some(ref mut s) = last_rewrite {
327 ::std::mem::swap(s, last);
337 // Returns the expression's subexpression, if it exists. When the subexpr
338 // is a try! macro, we'll convert it to shorthand when the option is set.
339 fn pop_expr_chain(expr: &ast::Expr, context: &RewriteContext) -> Option<ast::Expr> {
341 ast::ExprKind::MethodCall(_, _, ref expressions) => {
342 Some(convert_try(&expressions[0], context))
344 ast::ExprKind::TupField(ref subexpr, _) |
345 ast::ExprKind::Field(ref subexpr, _) |
346 ast::ExprKind::Try(ref subexpr) => Some(convert_try(subexpr, context)),
351 fn convert_try(expr: &ast::Expr, context: &RewriteContext) -> ast::Expr {
353 ast::ExprKind::Mac(ref mac) if context.config.use_try_shorthand => {
354 if let Some(subexpr) = convert_try_mac(mac, context) {
364 // Rewrite the last element in the chain `expr`. E.g., given `a.b.c` we rewrite
366 fn rewrite_chain_subexpr(expr: &ast::Expr,
368 context: &RewriteContext,
373 ast::ExprKind::MethodCall(ref method_name, ref types, ref expressions) => {
374 let inner = &RewriteContext { block_indent: offset, ..*context };
375 rewrite_method_call(method_name.node,
383 ast::ExprKind::Field(_, ref field) => {
384 let s = format!(".{}", field.node);
385 if s.len() <= width { Some(s) } else { None }
387 ast::ExprKind::TupField(_, ref field) => {
388 let s = format!(".{}", field.node);
389 if s.len() <= width { Some(s) } else { None }
391 ast::ExprKind::Try(_) => if width >= 1 { Some("?".into()) } else { None },
396 // Determines if we can continue formatting a given expression on the same line.
397 fn is_continuable(expr: &ast::Expr) -> bool {
399 ast::ExprKind::Path(..) => true,
404 fn rewrite_method_call(method_name: ast::Ident,
405 types: &[ptr::P<ast::Ty>],
406 args: &[ptr::P<ast::Expr>],
408 context: &RewriteContext,
412 let (lo, type_str) = if types.is_empty() {
413 (args[0].span.hi, String::new())
415 let type_list: Vec<_> = try_opt!(types.iter()
416 .map(|ty| ty.rewrite(context, width, offset))
419 (types.last().unwrap().span.hi, format!("::<{}>", type_list.join(", ")))
422 let callee_str = format!(".{}{}", method_name, type_str);
423 let span = mk_sp(lo, span.hi);
425 rewrite_call(context, &callee_str, &args[1..], span, width, offset)