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 asyncness: ast::IsAsync,
37 movability: ast::Movability,
38 fn_decl: &ast::FnDecl,
41 context: &RewriteContext,
44 debug!("rewrite_closure {:?}", body);
46 let (prefix, extra_offset) = rewrite_closure_fn_decl(
47 capture, asyncness, movability, fn_decl, body, span, context, shape,
49 // 1 = space between `|...|` and body.
50 let body_shape = shape.offset_left(extra_offset)?;
52 if let ast::ExprKind::Block(ref block, _) = body.node {
53 // The body of the closure is an empty block.
54 if block.stmts.is_empty() && !block_contains_comment(block, context.codemap) {
56 .rewrite(context, shape)
57 .map(|s| format!("{} {}", prefix, s));
60 let result = match fn_decl.output {
61 ast::FunctionRetTy::Default(_) => {
62 try_rewrite_without_block(body, &prefix, context, shape, body_shape)
68 // Either we require a block, or tried without and failed.
69 rewrite_closure_block(block, &prefix, context, body_shape)
72 rewrite_closure_expr(body, &prefix, context, body_shape).or_else(|| {
73 // The closure originally had a non-block expression, but we can't fit on
74 // one line, so we'll insert a block.
75 rewrite_closure_with_block(body, &prefix, context, body_shape)
80 fn try_rewrite_without_block(
83 context: &RewriteContext,
87 let expr = get_inner_expr(expr, prefix, context);
89 if is_block_closure_forced(context, expr) {
90 rewrite_closure_with_block(expr, prefix, context, shape)
92 rewrite_closure_expr(expr, prefix, context, body_shape)
96 fn get_inner_expr<'a>(
99 context: &RewriteContext,
101 if let ast::ExprKind::Block(ref block, _) = expr.node {
102 if !needs_block(block, prefix, context) {
103 // block.stmts.len() == 1
104 if let Some(expr) = stmt_expr(&block.stmts[0]) {
105 return get_inner_expr(expr, prefix, context);
113 // Figure out if a block is necessary.
114 fn needs_block(block: &ast::Block, prefix: &str, context: &RewriteContext) -> bool {
115 is_unsafe_block(block)
116 || block.stmts.len() > 1
117 || block_contains_comment(block, context.codemap)
118 || prefix.contains('\n')
121 fn veto_block(e: &ast::Expr) -> bool {
123 ast::ExprKind::Call(..)
124 | ast::ExprKind::Binary(..)
125 | ast::ExprKind::Cast(..)
126 | ast::ExprKind::Type(..)
127 | ast::ExprKind::Assign(..)
128 | ast::ExprKind::AssignOp(..)
129 | ast::ExprKind::Field(..)
130 | ast::ExprKind::Index(..)
131 | ast::ExprKind::Range(..)
132 | ast::ExprKind::Try(..) => true,
137 // Rewrite closure with a single expression wrapping its body with block.
138 fn rewrite_closure_with_block(
141 context: &RewriteContext,
143 ) -> Option<String> {
144 let left_most = left_most_sub_expr(body);
145 let veto_block = veto_block(body) && !classify::expr_requires_semi_to_be_stmt(left_most);
150 let block = ast::Block {
151 stmts: vec![ast::Stmt {
152 id: ast::NodeId::new(0),
153 node: ast::StmtKind::Expr(ptr::P(body.clone())),
156 id: ast::NodeId::new(0),
157 rules: ast::BlockCheckMode::Default,
161 let block = ::expr::rewrite_block_with_visitor(context, "", &block, None, None, shape, false)?;
162 Some(format!("{} {}", prefix, block))
165 // Rewrite closure with a single expression without wrapping its body with block.
166 fn rewrite_closure_expr(
169 context: &RewriteContext,
171 ) -> Option<String> {
172 fn allow_multi_line(expr: &ast::Expr) -> bool {
174 ast::ExprKind::Match(..)
175 | ast::ExprKind::Block(..)
176 | ast::ExprKind::Catch(..)
177 | ast::ExprKind::Loop(..)
178 | ast::ExprKind::Struct(..) => true,
180 ast::ExprKind::AddrOf(_, ref expr)
181 | ast::ExprKind::Box(ref expr)
182 | ast::ExprKind::Try(ref expr)
183 | ast::ExprKind::Unary(_, ref expr)
184 | ast::ExprKind::Cast(ref expr, _) => allow_multi_line(expr),
190 // When rewriting closure's body without block, we require it to fit in a single line
191 // unless it is a block-like expression or we are inside macro call.
192 let veto_multiline = (!allow_multi_line(expr) && !context.inside_macro())
193 || context.config.force_multiline_blocks();
194 expr.rewrite(context, shape)
196 if veto_multiline && rw.contains('\n') {
201 }).map(|rw| format!("{} {}", prefix, rw))
204 // Rewrite closure whose body is block.
205 fn rewrite_closure_block(
208 context: &RewriteContext,
210 ) -> Option<String> {
211 Some(format!("{} {}", prefix, block.rewrite(context, shape)?))
214 // Return type is (prefix, extra_offset)
215 fn rewrite_closure_fn_decl(
216 capture: ast::CaptureBy,
217 asyncness: ast::IsAsync,
218 movability: ast::Movability,
219 fn_decl: &ast::FnDecl,
222 context: &RewriteContext,
224 ) -> Option<(String, usize)> {
225 let is_async = if asyncness.is_async() { "async " } else { "" };
226 let mover = if capture == ast::CaptureBy::Value {
231 let immovable = if movability == ast::Movability::Static {
236 // 4 = "|| {".len(), which is overconservative when the closure consists of
237 // a single expression.
238 let nested_shape = shape
239 .shrink_left(is_async.len() + mover.len() + immovable.len())?
243 let argument_offset = nested_shape.indent + 1;
244 let arg_shape = nested_shape.offset_left(1)?.visual_indent(0);
245 let ret_str = fn_decl.output.rewrite(context, arg_shape)?;
247 let arg_items = itemize_list(
248 context.snippet_provider,
249 fn_decl.inputs.iter(),
252 |arg| span_lo_for_arg(arg),
253 |arg| span_hi_for_arg(context, arg),
254 |arg| arg.rewrite(context, arg_shape),
255 context.snippet_provider.span_after(span, "|"),
259 let item_vec = arg_items.collect::<Vec<_>>();
260 // 1 = space between arguments and return type.
261 let horizontal_budget = nested_shape.width.saturating_sub(ret_str.len() + 1);
262 let tactic = definitive_tactic(
264 ListTactic::HorizontalVertical,
268 let arg_shape = match tactic {
269 DefinitiveListTactic::Horizontal => arg_shape.sub_width(ret_str.len() + 1)?,
273 let fmt = ListFormatting {
276 trailing_separator: SeparatorTactic::Never,
277 separator_place: SeparatorPlace::Back,
279 ends_with_newline: false,
280 preserve_newline: true,
282 config: context.config,
284 let list_str = write_list(&item_vec, &fmt)?;
285 let mut prefix = format!("{}{}{}|{}|", is_async, immovable, mover, list_str);
287 if !ret_str.is_empty() {
288 if prefix.contains('\n') {
290 prefix.push_str(&argument_offset.to_string(context.config));
294 prefix.push_str(&ret_str);
296 // 1 = space between `|...|` and body.
297 let extra_offset = last_line_width(&prefix) + 1;
299 Some((prefix, extra_offset))
302 // Rewriting closure which is placed at the end of the function call's arg.
303 // Returns `None` if the reformatted closure 'looks bad'.
304 pub fn rewrite_last_closure(
305 context: &RewriteContext,
308 ) -> Option<String> {
309 if let ast::ExprKind::Closure(capture, asyncness, movability, ref fn_decl, ref body, _) =
312 let body = match body.node {
313 ast::ExprKind::Block(ref block, _)
314 if !is_unsafe_block(block)
315 && is_simple_block(block, Some(&body.attrs), context.codemap) =>
317 stmt_expr(&block.stmts[0]).unwrap_or(body)
321 let (prefix, extra_offset) = rewrite_closure_fn_decl(
322 capture, asyncness, movability, fn_decl, body, expr.span, context, shape,
324 // If the closure goes multi line before its body, do not overflow the closure.
325 if prefix.contains('\n') {
329 let body_shape = shape.offset_left(extra_offset)?;
331 // We force to use block for the body of the closure for certain kinds of expressions.
332 if is_block_closure_forced(context, body) {
333 return rewrite_closure_with_block(body, &prefix, context, body_shape).and_then(
335 // If the expression can fit in a single line, we need not force block closure.
336 if body_str.lines().count() <= 7 {
337 match rewrite_closure_expr(body, &prefix, context, shape) {
338 Some(ref single_line_body_str)
339 if !single_line_body_str.contains('\n') =>
341 Some(single_line_body_str.clone())
352 // When overflowing the closure which consists of a single control flow expression,
353 // force to use block if its condition uses multi line.
354 let is_multi_lined_cond = rewrite_cond(context, body, body_shape)
355 .map(|cond| cond.contains('\n') || cond.len() > body_shape.width)
357 if is_multi_lined_cond {
358 return rewrite_closure_with_block(body, &prefix, context, body_shape);
361 // Seems fine, just format the closure in usual manner.
362 return expr.rewrite(context, shape);
367 /// Returns true if the given vector of arguments has more than one `ast::ExprKind::Closure`.
368 pub fn args_have_many_closure<T>(args: &[&T]) -> bool
375 .map(|e| match e.node {
376 ast::ExprKind::Closure(..) => true,
382 fn is_block_closure_forced(context: &RewriteContext, expr: &ast::Expr) -> bool {
383 // If we are inside macro, we do not want to add or remove block from closure body.
384 if context.inside_macro() {
387 is_block_closure_forced_inner(expr)
391 fn is_block_closure_forced_inner(expr: &ast::Expr) -> bool {
393 ast::ExprKind::If(..)
394 | ast::ExprKind::IfLet(..)
395 | ast::ExprKind::While(..)
396 | ast::ExprKind::WhileLet(..)
397 | ast::ExprKind::ForLoop(..) => true,
398 ast::ExprKind::AddrOf(_, ref expr)
399 | ast::ExprKind::Box(ref expr)
400 | ast::ExprKind::Try(ref expr)
401 | ast::ExprKind::Unary(_, ref expr)
402 | ast::ExprKind::Cast(ref expr, _) => is_block_closure_forced_inner(expr),