1 // Copyright 2017 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.
12 use syntax::codemap::Span;
13 use syntax::parse::classify;
14 use syntax::{ast, ptr};
16 use codemap::SpanUtils;
17 use expr::{block_contains_comment, is_simple_block, is_unsafe_block, rewrite_cond, ToExpr};
18 use items::{span_hi_for_arg, span_lo_for_arg};
19 use lists::{definitive_tactic, itemize_list, write_list, ListFormatting, Separator};
20 use rewrite::{Rewrite, RewriteContext};
22 use utils::{last_line_width, left_most_sub_expr, stmt_expr};
24 // This module is pretty messy because of the rules around closures and blocks:
25 // FIXME - the below is probably no longer true in full.
26 // * if there is a return type, then there must be braces,
27 // * given a closure with braces, whether that is parsed to give an inner block
28 // or not depends on if there is a return type and if there are statements
30 // * if the first expression in the body ends with a block (i.e., is a
31 // statement without needing a semi-colon), then adding or removing braces
32 // can change whether it is treated as an expression or statement.
34 pub fn rewrite_closure(
35 capture: ast::CaptureBy,
36 movability: ast::Movability,
37 fn_decl: &ast::FnDecl,
40 context: &RewriteContext,
43 debug!("rewrite_closure {:?}", body);
45 let (prefix, extra_offset) =
46 rewrite_closure_fn_decl(capture, movability, fn_decl, body, span, context, shape)?;
47 // 1 = space between `|...|` and body.
48 let body_shape = shape.offset_left(extra_offset)?;
50 if let ast::ExprKind::Block(ref block) = body.node {
51 // The body of the closure is an empty block.
52 if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) {
53 return body.rewrite(context, shape)
54 .map(|s| format!("{} {}", prefix, s));
57 let result = match fn_decl.output {
58 ast::FunctionRetTy::Default(_) => {
59 try_rewrite_without_block(body, &prefix, context, shape, body_shape)
65 // Either we require a block, or tried without and failed.
66 rewrite_closure_block(block, &prefix, context, body_shape)
69 rewrite_closure_expr(body, &prefix, context, body_shape).or_else(|| {
70 // The closure originally had a non-block expression, but we can't fit on
71 // one line, so we'll insert a block.
72 rewrite_closure_with_block(body, &prefix, context, body_shape)
77 fn try_rewrite_without_block(
80 context: &RewriteContext,
84 let expr = get_inner_expr(expr, prefix, context);
86 if is_block_closure_forced(context, expr) {
87 rewrite_closure_with_block(expr, prefix, context, shape)
89 rewrite_closure_expr(expr, prefix, context, body_shape)
93 fn get_inner_expr<'a>(
96 context: &RewriteContext,
98 if let ast::ExprKind::Block(ref block) = expr.node {
99 if !needs_block(block, prefix, context) {
100 // block.stmts.len() == 1
101 if let Some(expr) = stmt_expr(&block.stmts[0]) {
102 return get_inner_expr(expr, prefix, context);
110 // Figure out if a block is necessary.
111 fn needs_block(block: &ast::Block, prefix: &str, context: &RewriteContext) -> bool {
112 is_unsafe_block(block) || block.stmts.len() > 1
113 || block_contains_comment(block, context.codemap) || prefix.contains('\n')
116 // Rewrite closure with a single expression wrapping its body with block.
117 fn rewrite_closure_with_block(
120 context: &RewriteContext,
122 ) -> Option<String> {
123 let left_most = left_most_sub_expr(body);
124 let veto_block = left_most != body && !classify::expr_requires_semi_to_be_stmt(left_most);
129 let block = ast::Block {
130 stmts: vec![ast::Stmt {
131 id: ast::NodeId::new(0),
132 node: ast::StmtKind::Expr(ptr::P(body.clone())),
135 id: ast::NodeId::new(0),
136 rules: ast::BlockCheckMode::Default,
140 let block = ::expr::rewrite_block_with_visitor(context, "", &block, None, shape, false)?;
141 Some(format!("{} {}", prefix, block))
144 // Rewrite closure with a single expression without wrapping its body with block.
145 fn rewrite_closure_expr(
148 context: &RewriteContext,
150 ) -> Option<String> {
151 fn allow_multi_line(expr: &ast::Expr) -> bool {
153 ast::ExprKind::Match(..)
154 | ast::ExprKind::Block(..)
155 | ast::ExprKind::Catch(..)
156 | ast::ExprKind::Loop(..)
157 | ast::ExprKind::Struct(..) => true,
159 ast::ExprKind::AddrOf(_, ref expr)
160 | ast::ExprKind::Box(ref expr)
161 | ast::ExprKind::Try(ref expr)
162 | ast::ExprKind::Unary(_, ref expr)
163 | ast::ExprKind::Cast(ref expr, _) => allow_multi_line(expr),
169 // When rewriting closure's body without block, we require it to fit in a single line
170 // unless it is a block-like expression or we are inside macro call.
171 let veto_multiline = (!allow_multi_line(expr) && !context.inside_macro())
172 || context.config.force_multiline_blocks();
173 expr.rewrite(context, shape)
175 if veto_multiline && rw.contains('\n') {
181 .map(|rw| format!("{} {}", prefix, rw))
184 // Rewrite closure whose body is block.
185 fn rewrite_closure_block(
188 context: &RewriteContext,
190 ) -> Option<String> {
191 Some(format!("{} {}", prefix, block.rewrite(context, shape)?))
194 // Return type is (prefix, extra_offset)
195 fn rewrite_closure_fn_decl(
196 capture: ast::CaptureBy,
197 movability: ast::Movability,
198 fn_decl: &ast::FnDecl,
201 context: &RewriteContext,
203 ) -> Option<(String, usize)> {
204 let mover = if capture == ast::CaptureBy::Value {
210 let immovable = if movability == ast::Movability::Static {
215 // 4 = "|| {".len(), which is overconservative when the closure consists of
216 // a single expression.
217 let nested_shape = shape
218 .shrink_left(mover.len() + immovable.len())?
222 let argument_offset = nested_shape.indent + 1;
223 let arg_shape = nested_shape.offset_left(1)?.visual_indent(0);
224 let ret_str = fn_decl.output.rewrite(context, arg_shape)?;
226 let arg_items = itemize_list(
227 context.snippet_provider,
228 fn_decl.inputs.iter(),
231 |arg| span_lo_for_arg(arg),
232 |arg| span_hi_for_arg(context, arg),
233 |arg| arg.rewrite(context, arg_shape),
234 context.snippet_provider.span_after(span, "|"),
238 let item_vec = arg_items.collect::<Vec<_>>();
239 // 1 = space between arguments and return type.
240 let horizontal_budget = nested_shape
242 .checked_sub(ret_str.len() + 1)
244 let tactic = definitive_tactic(
246 ListTactic::HorizontalVertical,
250 let arg_shape = match tactic {
251 DefinitiveListTactic::Horizontal => arg_shape.sub_width(ret_str.len() + 1)?,
255 let fmt = ListFormatting {
258 trailing_separator: SeparatorTactic::Never,
259 separator_place: SeparatorPlace::Back,
261 ends_with_newline: false,
262 preserve_newline: true,
263 config: context.config,
265 let list_str = write_list(&item_vec, &fmt)?;
266 let mut prefix = format!("{}{}|{}|", immovable, mover, list_str);
268 if !ret_str.is_empty() {
269 if prefix.contains('\n') {
271 prefix.push_str(&argument_offset.to_string(context.config));
275 prefix.push_str(&ret_str);
277 // 1 = space between `|...|` and body.
278 let extra_offset = last_line_width(&prefix) + 1;
280 Some((prefix, extra_offset))
283 // Rewriting closure which is placed at the end of the function call's arg.
284 // Returns `None` if the reformatted closure 'looks bad'.
285 pub fn rewrite_last_closure(
286 context: &RewriteContext,
289 ) -> Option<String> {
290 if let ast::ExprKind::Closure(capture, movability, ref fn_decl, ref body, _) = expr.node {
291 let body = match body.node {
292 ast::ExprKind::Block(ref block)
293 if !is_unsafe_block(block)
294 && is_simple_block(block, Some(&body.attrs), context.codemap) =>
296 stmt_expr(&block.stmts[0]).unwrap_or(body)
300 let (prefix, extra_offset) = rewrite_closure_fn_decl(
301 capture, movability, fn_decl, body, expr.span, context, shape,
303 // If the closure goes multi line before its body, do not overflow the closure.
304 if prefix.contains('\n') {
308 let body_shape = shape.offset_left(extra_offset)?;
310 // We force to use block for the body of the closure for certain kinds of expressions.
311 if is_block_closure_forced(context, body) {
312 return rewrite_closure_with_block(body, &prefix, context, body_shape).and_then(
314 // If the expression can fit in a single line, we need not force block closure.
315 if body_str.lines().count() <= 7 {
316 match rewrite_closure_expr(body, &prefix, context, shape) {
317 Some(ref single_line_body_str)
318 if !single_line_body_str.contains('\n') =>
320 Some(single_line_body_str.clone())
331 // When overflowing the closure which consists of a single control flow expression,
332 // force to use block if its condition uses multi line.
333 let is_multi_lined_cond = rewrite_cond(context, body, body_shape)
334 .map(|cond| cond.contains('\n') || cond.len() > body_shape.width)
336 if is_multi_lined_cond {
337 return rewrite_closure_with_block(body, &prefix, context, body_shape);
340 // Seems fine, just format the closure in usual manner.
341 return expr.rewrite(context, shape);
346 /// Returns true if the given vector of arguments has more than one `ast::ExprKind::Closure`.
347 pub fn args_have_many_closure<T>(args: &[&T]) -> bool
354 .map(|e| match e.node {
355 ast::ExprKind::Closure(..) => true,
363 fn is_block_closure_forced(context: &RewriteContext, expr: &ast::Expr) -> bool {
364 // If we are inside macro, we do not want to add or remove block from closure body.
365 if context.inside_macro() {
368 is_block_closure_forced_inner(expr)
372 fn is_block_closure_forced_inner(expr: &ast::Expr) -> bool {
374 ast::ExprKind::If(..)
375 | ast::ExprKind::IfLet(..)
376 | ast::ExprKind::While(..)
377 | ast::ExprKind::WhileLet(..)
378 | ast::ExprKind::ForLoop(..) => true,
379 ast::ExprKind::AddrOf(_, ref expr)
380 | ast::ExprKind::Box(ref expr)
381 | ast::ExprKind::Try(ref expr)
382 | ast::ExprKind::Unary(_, ref expr)
383 | ast::ExprKind::Cast(ref expr, _) => is_block_closure_forced_inner(expr),