Warning "variant is never used" is confusing when programmer just woke up #44565

nox · 2017-09-14T12:55:56Z

I was changing some code from integer constants to a proper enum and was greeted by the following warning:

   Compiling script v0.0.1 (file:///Users/nox/src/servo/components/script)
warning: variant is never used: `HaveMetadata`
  --> /Users/nox/src/servo/components/script/dom/htmlmediaelement.rs:88:5
   |
88 |     HaveMetadata = HTMLMediaElementConstants::HAVE_METADATA as u8,
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: #[warn(dead_code)] on by default

The warning sounded weird to me because I was pattern-matching on that damn variant in various places of the code; but I was pointed out to the fact that I wasn't actually creating that value.

Maybe the warning should be rewritten to explicitly mention value creation?

Cc @arielb1

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arielb1 · 2017-09-14T12:57:31Z

cc @Manishearth that looks like your thing

ollie27 · 2017-09-14T14:00:25Z

duplicate of #19140

steveklabnik · 2017-09-14T14:21:03Z

Yup! Closing in favor of that.

As reported in rust-lang#19140, rust-lang#44083, and rust-lang#44565, some users were confused when the dead-code lint reported an enum variant to be "unused" when it was matched on (but not constructed). This wording change makes it clearer that the lint is in fact checking for construction. We continue to say "used" for all other items (it's tempting to say "called" for functions and methods, but this turns out not to be correct: functions can be passed as arguments and the dead-code lint isn't special-casing that or anything). Resolves rust-lang#19140.

@pnkfelix

…y_never_constructed_for_variants, r=arielb1 dead code lint to say "never constructed" for variants As reported in rust-lang#19140, rust-lang#44083, and rust-lang#44565, some users were confused when the dead-code lint reported an enum variant to be "unused" when it was matched on (but not constructed). This wording change makes it clearer that the lint is in fact checking for construction. We continue to say "used" for all other items (it's tempting to say "called" for functions and methods, but this turns out not to be correct: functions can be passed as arguments and the dead-code lint isn't special-casing that or anything). Resolves rust-lang#19140. r? @pnkfelix

Respectively. This is a sequel to November 2017's rust-lang#46103 / 1a9dc2e. It had been reported (more than once—at least rust-lang#19140, rust-lang#44083, and rust-lang#44565) that the "never used" language was confusing for enum variants that were "used" as match patterns, so the wording was changed to say never "constructed" specifically for enum variants. More recently, the same issue was raised for structs (rust-lang#52325). It seems consistent to say "constructed" here, too, for the same reasons. While we're here, we can also use more specific word "called" for unused functions and methods. (We declined to do this in rust-lang#46103, but the rationale given in the commit message doesn't actually make sense.) This resolves rust-lang#52325.

…y_2_electric_boogaloo, r=pnkfelix dead-code lint: say "constructed", "called" for structs, functions Respectively. This is a sequel to November 2017's rust-lang#46103 / 1a9dc2e. It had been reported (more than once—at least rust-lang#19140, rust-lang#44083, and rust-lang#44565) that the "never used" language was confusing for enum variants that were "used" as match patterns, so the wording was changed to say never "constructed" specifically for enum variants. More recently, the same issue was raised for structs (rust-lang#52325). It seems consistent to say "constructed" here, too, for the same reasons. While we're here, we can also use more specific word "called" for unused functions and methods. (We declined to do this in rust-lang#46103, but the rationale given in the commit message doesn't actually make sense.) This resolves rust-lang#52325.

This is a sequel to November 2017's rust-lang#46103 / 1a9dc2e. It had been reported (more than once—at least rust-lang#19140, rust-lang#44083, and rust-lang#44565) that the "never used" language was confusing for enum variants that were "used" as match patterns, so the wording was changed to say never "constructed" specifically for enum variants. More recently, the same issue was raised for structs (rust-lang#52325). It seems consistent to say "constructed" here, too, for the same reasons. We considered using more specific word "called" for unused functions and methods (while we declined to do this in rust-lang#46103, the rationale given in the commit message doesn't actually make sense), but it turns out that Cargo's test suite expects the "never used" message, and maybe we don't care enough even to make a Cargo PR over such a petty and subjective wording change. This resolves rust-lang#52325.

…y_2_electric_boogaloo, r=pnkfelix dead-code lint: say "constructed" for structs Respectively. This is a sequel to November 2017's rust-lang#46103 / 1a9dc2e. It had been reported (more than once—at least rust-lang#19140, rust-lang#44083, and rust-lang#44565) that the "never used" language was confusing for enum variants that were "used" as match patterns, so the wording was changed to say never "constructed" specifically for enum variants. More recently, the same issue was raised for structs (rust-lang#52325). It seems consistent to say "constructed" here, too, for the same reasons. ~~While we're here, we can also use more specific word "called" for unused functions and methods. (We declined to do this in rust-lang#46103, but the rationale given in the commit message doesn't actually make sense.)~~ This resolves rust-lang#52325.

…c_boogaloo, r=pnkfelix dead-code lint: say "constructed" for structs Respectively. This is a sequel to November 2017's #46103 / 1a9dc2e. It had been reported (more than once—at least #19140, #44083, and #44565) that the "never used" language was confusing for enum variants that were "used" as match patterns, so the wording was changed to say never "constructed" specifically for enum variants. More recently, the same issue was raised for structs (#52325). It seems consistent to say "constructed" here, too, for the same reasons. ~~While we're here, we can also use more specific word "called" for unused functions and methods. (We declined to do this in #46103, but the rationale given in the commit message doesn't actually make sense.)~~ This resolves #52325.

arielb1 added the A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. label Sep 14, 2017

steveklabnik closed this as completed Sep 14, 2017

zackmdavis mentioned this issue Nov 19, 2017

dead code lint to say "never constructed" for variants #46103

Merged

zackmdavis mentioned this issue Jul 13, 2018

dead-code lint: say "constructed" for structs #52332

Merged

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Warning "variant is never used" is confusing when programmer just woke up #44565

Warning "variant is never used" is confusing when programmer just woke up #44565

nox commented Sep 14, 2017

arielb1 commented Sep 14, 2017

ollie27 commented Sep 14, 2017

steveklabnik commented Sep 14, 2017

Warning "variant is never used" is confusing when programmer just woke up #44565

Warning "variant is never used" is confusing when programmer just woke up #44565

Comments

nox commented Sep 14, 2017

arielb1 commented Sep 14, 2017

ollie27 commented Sep 14, 2017

steveklabnik commented Sep 14, 2017