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Poor help error message for unused variable on struct enum match #50303

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Poor help error message for unused variable on struct enum match#50303
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A-diagnosticsArea: Messages for errors, warnings, and lints

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@dandc87
dandc87
opened on Apr 28, 2018

Suppose I've written code like:

enum Foo {
    Bar { bar: u32 },
    Baz,
}

fn is_bar(foo: &Foo) -> bool {
    match foo {
        &Foo::Bar { bar } => true,
        &Foo::Baz => false,
    }
}

The bar variable is unused, and the error message I get looks like:

warning: unused variable: `bar`
  --> src/main.rs:37:21
   |
37 |         &Foo::Bar { bar } => true,
   |                     ^^^ help: consider using `_bar` instead
   |
   = note: #[warn(unused_variables)] on by default

The help is incorrect; _bar is invalid. It should suggest replacing bar with bar: _

Activity

  1. zackmdavis commented on Apr 28, 2018

    @zackmdavis
    zackmdavis
    on Apr 28, 2018
    Contributor

    This bad suggestion was fixed in most cases by #47922, but this case would seem to have evaded it. (Notice that on Nightly you can omit the ampersands from the match guards (due to the stabilization of the match-default-bindings ergonomic) and receive the correct suggestion!)

  2. sfackler
    added
    A-diagnosticsArea: Messages for errors, warnings, and lints
    on Apr 28, 2018
  3. kennytm
    added a commit that references this issue on Apr 30, 2018

    Rollup merge of rust-lang#50327 - varkor:match-unused-struct-field, r…

    cbbdf99
  4. bors
    closed this as completedin #50327on Apr 30, 2018
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