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"warning: unnecessary lifetime parameter" unsilenceable lint #96956

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ijackson opened this issue May 11, 2022 · 17 comments · Fixed by #108230, paritytech/parity-common#748 or paritytech/substrate#14096
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"warning: unnecessary lifetime parameter" unsilenceable lint #96956

ijackson opened this issue May 11, 2022 · 17 comments · Fixed by #108230, paritytech/parity-common#748 or paritytech/substrate#14096
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A-diagnostics Area: Messages for errors, warnings, and lints E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. E-help-wanted Call for participation: Help is requested to fix this issue. E-mentor Call for participation: This issue has a mentor. Use #t-compiler/help on Zulip for discussion. P-medium Medium priority regression-untriaged Untriaged performance or correctness regression. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@ijackson
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ijackson commented May 11, 2022 •
edited by rustbot
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Given the following code: 

pub fn thing<'a>(_s: &'a str) where 'a: 'static { }

The current output is:

warning: unnecessary lifetime parameter `'a`
 --> src/lib.rs:2:37
  |
2 | pub fn thing<'a>(_s: &'a str) where 'a: 'static { }
  |                                     ^^
  |
  = help: you can use the `'static` lifetime directly, in place of `'a`

warning: `playground` (lib) generated 1 warning
    Finished dev [unoptimized   debuginfo] target(s) in 1.27s

Ideally the output should also say something like this:

  = note: `#[warn(needless_lifetimes)]` on by default

And of course then #[allow(needless_lifetimes)] ought to work.

Versions affected

rustcargo@zealot:/volatile/rustcargo/Rustup/Game/server$ rustc -vV
rustc 1.62.0-nightly (ecd44958e 2022-05-10)
binary: rustc
commit-hash: ecd44958e0a21110d09862ee080d95a4ca6c52f8
commit-date: 2022-05-10
host: x86_64-unknown-linux-gnu
release: 1.62.0-nightly
LLVM version: 14.0.1
rustcargo@zealot:/volatile/rustcargo/Rustup/Game/server$

The example code is accepted without any complaint by stable and beta, However, in both stable and beta, clippy has the same weird name-less complaint. And saying #![allow(clippy::needless_lifetimes)] doesn't suppress the message.

I searched for "lifetime" in the clippy lints db. Of those that came up, needless_lifetimes and redundant_static_lifetimes seemed like they might be it, but neither of those suppresses the lint on stable's clippy.
@ijackson ijackson added A-diagnostics Area: Messages for errors, warnings, and lints T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels May 11, 2022
@ijackson
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@rustbot modify labels regresson-from-stable-to-nightly

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rustbot commented May 11, 2022

Error: Label regresson-from-stable-to-nightly can only be set by Rust team members

Please let @rust-lang/release know if you're having trouble with this bot.

@ritchie46 ritchie46 mentioned this issue May 18, 2022
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@Alexendoo Alexendoo mentioned this issue May 21, 2022
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@ijackson
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This is not a clippy lint. It is being emitted, here, by rustc:

rustcargo@zealot:~$ cat t.rs
pub fn thing<'a>(_s: &'a str) where 'a: 'static { }
fn main() { thing(""); }
rustcargo@zealot:~$ rustc  nightly t.rs
warning: unnecessary lifetime parameter `'a`
 --> t.rs:1:37
  |
1 | pub fn thing<'a>(_s: &'a str) where 'a: 'static { }
  |                                     ^^
  |
  = help: you can use the `'static` lifetime directly, in place of `'a`

warning: 1 warning emitted

rustcargo@zealot:~$

The situation is confusing because there is (or was?) also a clippy lint for this; I think this may have been promoted into rustc but something was done wrong there.

I have rechecked and:

  • rustc 1.61.0 (fe5b13d68 2022-05-18) (stable) unaffected
  • rustc 1.62.0-beta.2 (daf68b1f7 2022-05-19) affected
  • rustc 1.63.0-nightly (4cbaac699 2022-05-25) affected

@rust-lang/release could you please set the regresson-from-stable-to-beta label for me?

@ijackson ijackson changed the title "warning: unnecessary lifetime parameter" doesn't have (or print?) lint name? "warning: unnecessary lifetime parameter" unsilenceable lint May 26, 2022
@ijackson
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@rustbot ping rust-lang/release

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rustbot commented May 26, 2022

Error: Only Rust team members can ping teams.

Please let @rust-lang/release know if you're having trouble with this bot.

@ijackson ijackson mentioned this issue May 26, 2022
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@ijackson
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@rustbot modify labels regression-untriaged

@rustbot rustbot added regression-untriaged Untriaged performance or correctness regression. I-prioritize Issue: Indicates that prioritization has been requested for this issue. labels May 26, 2022
@ijackson
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Ah! Looking at the "Regression" bug template gave me a hint.

@gimbling-away
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Ahh, I see. I was testing on stable, my bad.

@shawntabrizi shawntabrizi mentioned this issue Jun 6, 2022
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@apiraino
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apiraino commented Jun 7, 2022

bisected the regression (with cargo-bisect) points to pr #93803 (cc @cjgillot )

searched nightlies: from nightly-2022-02-01 to nightly-2022-06-07
regressed nightly: nightly-2022-05-01
searched commit range: a707f40...7c4b476
regressed commit: d201c81

bisected with cargo-bisect-rustc v0.6.1

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --start=2022-02-01 --script=./test.sh

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apiraino commented Jun 7, 2022

Assigning priority as discussed in the Zulip thread of the Prioritization Working Group.

@rustbot label -I-prioritize P-medium

@rustbot rustbot added P-medium Medium priority and removed I-prioritize Issue: Indicates that prioritization has been requested for this issue. labels Jun 7, 2022
@cjgillot
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cjgillot commented Jun 7, 2022

#93803 made this warning more precise, so it triggers more often.
This is a hard-warning. Fixing it requires to turn it into a lint.

Steps:

  • declare the lint in rustc_lint_defs::builtin and write a proper explanation;
  • in rustc_resolve::late::lifetimes, replace the call to struct_span_warn by struct_span_lint_hir, the reference HirId is the bounded lifetime's one;
  • (option) move the lint to rustc_typeck::collect, to where RegionPredicate is processed.

@cjgillot cjgillot added E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. E-mentor Call for participation: This issue has a mentor. Use #t-compiler/help on Zulip for discussion. E-help-wanted Call for participation: Help is requested to fix this issue. labels Jun 7, 2022
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@rustbot claim

@gimbling-away gimbling-away removed their assignment Jun 13, 2022
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I really apologize for this, I'm mostly busy with life and can't really find the time for working on this, feel free to pick it 💜

@jeremydavis519
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@jeremydavis519 jeremydavis519 mentioned this issue Jun 14, 2022
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@mkatychev mkatychev mentioned this issue Jul 12, 2022
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@skunert skunert mentioned this issue Jul 26, 2022
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@bblum bblum mentioned this issue Aug 8, 2022
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@jsdw jsdw mentioned this issue Sep 12, 2022
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@Noratrieb
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PR was closed due to inactivity, feel free to claim it again. @rustbot release-assignment

@LittleFall
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@LittleFall LittleFall mentioned this issue Feb 19, 2023
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compiler-errors added a commit to compiler-errors/rust that referenced this issue Feb 21, 2023
@compiler-errors
Rollup merge of rust-lang#108230 - LittleFall:enhance/warning, r=este…
f9d71d2 
…bank

Convert a hard-warning about named static lifetimes into lint "unused_lifetimes"

Fixes rust-lang#96956.

Some changes are ported from rust-lang#98079, thanks to jeremydavis519.

r? `@estebank` `@petrochenkov`

Any feedback is appreciated!

## Actions
- [x] resolve conflicts
- [x] fix build
- [x] address review comments in last pr
- [x] update tests
@bors bors closed this as completed in a32c500 Feb 22, 2023
This was referenced May 8, 2023
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A-diagnostics Area: Messages for errors, warnings, and lints E-easy Call for participation: Easy difficulty. Experience needed to fix: Not much. Good first issue. E-help-wanted Call for participation: Help is requested to fix this issue. E-mentor Call for participation: This issue has a mentor. Use #t-compiler/help on Zulip for discussion. P-medium Medium priority regression-untriaged Untriaged performance or correctness regression. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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@cjgillot @ijackson @apiraino @jeremydavis519 @LittleFall @rustbot @Noratrieb @gimbling-away