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Add unit test for case that didn't seem to be covered in existing UI …
…tests (since I made this mistake at first but the tests didn't catch it): we should not suggest adding `mut` to a reassigned `ref` or `ref mut` binding. (The Rust language, since at least 1.0, does not have `mut ref mut` or `ref mut mut` etc.)
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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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// Tests how we behave when the user attempts to mutate an immutable | ||
// binding that was introduced by either `ref` or `ref mut` | ||
// patterns. | ||
// | ||
// Such bindings cannot be made mutable via the mere addition of the | ||
// `mut` keyword, and thus we want to check that the compiler does not | ||
// suggest doing so. | ||
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fn main() { | ||
let (mut one_two, mut three_four) = ((1, 2), (3, 4)); | ||
let &mut (ref a, ref mut b) = &mut one_two; | ||
a = &three_four.0; | ||
//~^ ERROR cannot assign twice to immutable variable `a` [E0384] | ||
b = &mut three_four.1; | ||
//~^ ERROR cannot assign twice to immutable variable `b` [E0384] | ||
} |
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error[E0384]: cannot assign twice to immutable variable `a` | ||
--> $DIR/reassign-ref-mut.rs:22:5 | ||
| | ||
LL | let &mut (ref a, ref mut b) = &mut one_two; | ||
| ----- first assignment to `a` | ||
LL | a = &three_four.0; | ||
| ^^^^^^^^^^^^^^^^^ cannot assign twice to immutable variable | ||
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error[E0384]: cannot assign twice to immutable variable `b` | ||
--> $DIR/reassign-ref-mut.rs:24:5 | ||
| | ||
LL | let &mut (ref a, ref mut b) = &mut one_two; | ||
| --------- first assignment to `b` | ||
... | ||
LL | b = &mut three_four.1; | ||
| ^^^^^^^^^^^^^^^^^^^^^ cannot assign twice to immutable variable | ||
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error: aborting due to 2 previous errors | ||
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For more information about this error, try `rustc --explain E0384`. |