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kazcw opened this issue Jun 26, 2018 · 2 comments · Fixed by #51964
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nll: incorrect unused_mut with move closure #51801

kazcw opened this issue Jun 26, 2018 · 2 comments · Fixed by #51964
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A-NLL Area: Non-lexical lifetimes (NLL) C-enhancement Category: An issue proposing an enhancement or a PR with one. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@kazcw
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kazcw commented Jun 26, 2018 •
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With the nll feature enabled, a "variable does not need to be mutable" warning is emitted incorrectly when a variable is mutated from inside a move closure.

#![feature(nll)]

fn main() {
    let mut baz = 4; // "warning: variable does not need to be mutable"
    move || { baz = 6 };
}
@kazcw kazcw changed the title feature(nll): incorrect unused_mut warning nll: incorrect unused_mut with move closure Jun 26, 2018
@leonardo-m
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Related to #50897 ?

@matthewjasper matthewjasper added A-NLL Area: Non-lexical lifetimes (NLL) WG-compiler-nll NLL-diagnostics Working towards the "diagnostic parity" goal labels Jun 26, 2018
@jkordish jkordish added C-enhancement Category: An issue proposing an enhancement or a PR with one. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Jun 26, 2018
This was referenced Jun 29, 2018
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@nikomatsakis nikomatsakis mentioned this issue Jun 29, 2018
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@nikomatsakis
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Tagging as NLL-deferred because #51918 has precedence

@nikomatsakis nikomatsakis removed the NLL-diagnostics Working towards the "diagnostic parity" goal label Jun 29, 2018
@matthewjasper matthewjasper mentioned this issue Jul 1, 2018
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bors added a commit that referenced this issue Jul 5, 2018
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Auto merge of #51964 - matthewjasper:unused-mut-mir-generation, r=nik…
b51ca20 
…omatsakis

[NLL] Fix various unused mut errors

Closes #51801
Closes #50897
Closes #51830
Closes #51904
cc #51918 - keeping this one open in case there are any more issues

This PR contains multiple changes. List of changes with examples of what they fix:

* Change mir generation so that the parameter variable doesn't get a name when a `ref` pattern is used as an argument
```rust
fn f(ref y: i32) {} // doesn't trigger lint
```
* Change mir generation so that by-move closure captures don't get first moved into a temporary.
```rust
let mut x = 0; // doesn't trigger lint
move || {
    x = 1;
};
```
* Treat generator upvars the same as closure upvars
```rust
let mut x = 0; // This mut is now necessary and is not linted against.
move || {
    x = 1;
    yield;
};
```

r? @nikomatsakis
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A-NLL Area: Non-lexical lifetimes (NLL) C-enhancement Category: An issue proposing an enhancement or a PR with one. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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[NLL] Fix various unused mut errors matthewjasper/rust
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@jkordish @nikomatsakis @kazcw @matthewjasper @leonardo-m