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missing-const-for-fn when const fn would require unstable features #8864

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clubby789 opened this issue May 21, 2022 · 1 comment · Fixed by #12713
Closed

missing-const-for-fn when const fn would require unstable features #8864

clubby789 opened this issue May 21, 2022 · 1 comment · Fixed by #12713
Labels
C-bug Category: Clippy is not doing the correct thing I-false-positive Issue: The lint was triggered on code it shouldn't have I-suggestion-causes-error Issue: The suggestions provided by this Lint cause an ICE/error when applied L-nursery Lint: Currently in the nursery group

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@clubby789
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clubby789 commented May 21, 2022 •
edited

Summary

missing-const-for-fn warns 'this could be a const fn' on code that cannot be due to the required feature being unstable.

Lint Name

missing-const-for-fn

Reproducer

I tried this code:

pub struct Holder {
    val: *const u8
}
impl Holder {
    pub fn func(self) -> usize {
        unsafe {*self.val as usize}
    }
}

I saw this happen:

> cargo +1.54 clippy -- -W clippy::missing_const_for_fn
    Checking repro v0.1.0 (/tmp/repro)
warning: this could be a `const fn`
 --> src/lib.rs:5:5
  |
5 | /     pub fn func(self) -> usize {
6 | |         unsafe {*self.val as usize}
7 | |     }
  | |_____^
  |
  = note: requested on the command line with `-W clippy::missing-const-for-fn`

When adding the suggested const header:

> cargo +1.54 build
   Compiling repro v0.1.0 (/tmp/repro)
error[E0658]: dereferencing raw pointers in constant functions is unstable
 --> src/lib.rs:6:17
  |
6 |         unsafe {*self.val as usize}
  |                 ^^^^^^^^^
  |
  = note: see issue #51911 <https://github.com/rust-lang/rust/issues/51911> for more information

Version

rustc 1.54.0 (a178d0322 2021-07-26)
binary: rustc
commit-hash: a178d0322ce20e33eac124758e837cbd80a6f633
commit-date: 2021-07-26
host: x86_64-unknown-linux-gnu
release: 1.54.0
LLVM version: 12.0.1

Additional Labels

@rustbot label +I-suggestion-causes-error
@clubby789 clubby789 added C-bug Category: Clippy is not doing the correct thing I-false-positive Issue: The lint was triggered on code it shouldn't have labels May 21, 2022
@rustbot rustbot added the I-suggestion-causes-error Issue: The suggestions provided by this Lint cause an ICE/error when applied label May 21, 2022
@giraffate
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This needs msrv: https://github.com/rust-lang/rust/blob/stable/RELEASES.md#version-1580-2022-01-13

@J-ZhengLi J-ZhengLi added the L-nursery Lint: Currently in the nursery group label Apr 25, 2024
@J-ZhengLi J-ZhengLi mentioned this issue Apr 25, 2024
Merged
@bors bors closed this as completed in caad063 May 15, 2024
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Labels
C-bug Category: Clippy is not doing the correct thing I-false-positive Issue: The lint was triggered on code it shouldn't have I-suggestion-causes-error Issue: The suggestions provided by this Lint cause an ICE/error when applied L-nursery Lint: Currently in the nursery group
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@clubby789 @giraffate @J-ZhengLi @rustbot