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Auto merge of rust-lang#42634 - Zoxc:for-desugar2, r=nikomatsakis
Change the for-loop desugar so the `break` does not affect type inference. Fixes rust-lang#42618 Rewrite the `for` loop desugaring to avoid contaminating the inference results. Under the older desugaring, `for x in vec![] { .. }` would erroneously type-check, even though the type of `vec![]` is unconstrained. (written by @nikomatsakis)
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19 changes: 19 additions & 0 deletions
19
src/test/compile-fail/for-loop-unconstrained-element-type.rs
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| // Copyright 2017 The Rust Project Developers. See the COPYRIGHT | ||
| // file at the top-level directory of this distribution and at | ||
| // http://rust-lang.org/COPYRIGHT. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
| // option. This file may not be copied, modified, or distributed | ||
| // except according to those terms. | ||
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| // Test that `for` loops don't introduce artificial | ||
| // constraints on the type of the binding (`i`). | ||
| // Subtle changes in the desugaring can cause the | ||
| // type of elements in the vector to (incorrectly) | ||
| // fallback to `!` or `()`. | ||
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| fn main() { | ||
| for i in Vec::new() { } //~ ERROR type annotations needed | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
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| // Copyright 2017 The Rust Project Developers. See the COPYRIGHT | ||
| // file at the top-level directory of this distribution and at | ||
| // http://rust-lang.org/COPYRIGHT. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
| // option. This file may not be copied, modified, or distributed | ||
| // except according to those terms. | ||
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| // Test when destructors run in a for loop. The intention is | ||
| // that the value for each iteration is dropped *after* the loop | ||
| // body has executed. This is true even when the value is assigned | ||
| // to a `_` pattern (and hence ignored). | ||
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| use std::cell::Cell; | ||
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| struct Flag<'a>(&'a Cell<bool>); | ||
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| impl<'a> Drop for Flag<'a> { | ||
| fn drop(&mut self) { | ||
| self.0.set(false) | ||
| } | ||
| } | ||
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| fn main() { | ||
| let alive2 = Cell::new(true); | ||
| for _i in std::iter::once(Flag(&alive2)) { | ||
| // The Flag value should be alive in the for loop body | ||
| assert_eq!(alive2.get(), true); | ||
| } | ||
| // The Flag value should be dead outside of the loop | ||
| assert_eq!(alive2.get(), false); | ||
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| let alive = Cell::new(true); | ||
| for _ in std::iter::once(Flag(&alive)) { | ||
| // The Flag value should be alive in the for loop body even if it wasn't | ||
| // bound by the for loop | ||
| assert_eq!(alive.get(), true); | ||
| } | ||
| // The Flag value should be dead outside of the loop | ||
| assert_eq!(alive.get(), false); | ||
| } |
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,15 @@ | ||
| // Copyright 2014 The Rust Project Developers. See the COPYRIGHT | ||
| // file at the top-level directory of this distribution and at | ||
| // http://rust-lang.org/COPYRIGHT. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
| // option. This file may not be copied, modified, or distributed | ||
| // except according to those terms. | ||
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| // Tests that for loops can bind elements as mutable references | ||
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| fn main() { | ||
| for ref mut _a in std::iter::once(true) {} | ||
| } |
20 changes: 20 additions & 0 deletions
20
src/test/run-pass/for-loop-unconstrained-element-type-i32-fallback.rs
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| @@ -0,0 +1,20 @@ | ||
| // Copyright 2017 The Rust Project Developers. See the COPYRIGHT | ||
| // file at the top-level directory of this distribution and at | ||
| // http://rust-lang.org/COPYRIGHT. | ||
| // | ||
| // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or | ||
| // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license | ||
| // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your | ||
| // option. This file may not be copied, modified, or distributed | ||
| // except according to those terms. | ||
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| // Test that the type of `sum` falls back to `i32` here, | ||
| // and that the for loop desugaring doesn't inferfere with | ||
| // that. | ||
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| fn main() { | ||
| let mut sum = 0; | ||
| for i in Vec::new() { | ||
| sum += i; | ||
| } | ||
| } |