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#[deprecated] incorrectly warns in the same crate if derives are involved #55417

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gnzlbg opened this issue Oct 27, 2018 · 4 comments · Fixed by #65310
Closed

#[deprecated] incorrectly warns in the same crate if derives are involved #55417

gnzlbg opened this issue Oct 27, 2018 · 4 comments · Fixed by #65310
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A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..) C-bug Category: This is a bug.

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@gnzlbg
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gnzlbg commented Oct 27, 2018 

#[derive(Debug)]
#[deprecated(since = "0.1.1", note = "oh noes")]
pub struct A;

#[derive(PartialOrd)]
#[deprecated(since = "0.1.1", note = "oh noes")]
pub struct B;

fn main() {}

(Playground)

Errors:

   Compiling playground v0.0.1 (/playground)
warning: use of deprecated item 'A': oh noes
  |
  = note: #[warn(deprecated)] on by default

warning: use of deprecated item 'B': oh noes

error[E0277]: can't compare `B` with `B`
 --> src/main.rs:6:10
  |
6 | #[derive(PartialOrd)]
  |          ^^^^^^^^^^ no implementation for `B == B`
  |
  = help: the trait `std::cmp::PartialEq` is not implemented for `B`

error: aborting due to previous error

An easy fix might be to #[allow(deprecated)] in the custom derive implementations provided by Rust. Right now one has to manually #[allow(deprecated)] on all deprecated structs with derives, which is a pain, and also on all their impls...
@jonas-schievink jonas-schievink added A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..) C-bug Category: This is a bug. labels Mar 23, 2019
@joshlf
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joshlf commented Oct 5, 2019

Same as #38832?

da-x added a commit to da-x/rust that referenced this issue Oct 11, 2019
@da-x
deriving: avoid dummy Span on an artificial type_ident path
a32aec0 
The dummy Span pointed to the beginning of the source file instead to
where the `#[derive]` is located. Later, it tripped the
`in_derive_expansion(span)` check at `src/librustc/middle/stability.rs`,
causing a span-less deprecation warning to be emitted.

Fixes rust-lang#56195, rust-lang#55417.
@da-x da-x mentioned this issue Oct 11, 2019
Merged
@bors bors closed this as completed in c8e3c51 Oct 12, 2019
@joshlf
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joshlf commented Oct 12, 2019

Should this really have been closed? The fix makes the error message better, but doesn't actually address the issue with the deprecation warning being emitted on the generated impl.

@petrochenkov
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#65310 should indeed address the issue and remove the deprecation warning.
Perhaps it's not in nightly yet?

@joshlf
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joshlf commented Oct 12, 2019

Ah you're probably right. I'll check again tomorrow.

@fmease fmease added A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. and removed A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. labels Dec 21, 2024
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A-lints Area: Lints (warnings about flaws in source code) such as unused_mut. A-macros Area: All kinds of macros (custom derive, macro_rules!, proc macros, ..) C-bug Category: This is a bug.
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deriving: avoid dummy Span on an artificial type_ident path da-x/rust
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@gnzlbg @joshlf @jonas-schievink @petrochenkov @fmease