#[deprecated] on re-exported items does not work (original) (raw)

Problem

Given the following code: https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=ac1e0d070ba838247ac3587ca23bbaed

#[derive(PartialEq, Eq)] struct New;

#[deprecated(note = "bang")] use New as DeprecatedAlias;

#[deprecated(note = "bang")] type ConstAndTy = New; //

#[deprecated(note = "bang")] #[allow(nonstandard_style)] const ConstAndTy: New = New;

fn main () { // 😭 (does not warn) let self::DeprecatedAlias: DeprecatedAlias = DeprecatedAlias; let _ = DeprecatedAlias {};

// OK (does warn)
let self::ConstAndTy: ConstAndTy = ConstAndTy;
let _ = ConstAndTy {};

}

The current output is:

• deprecated warnings for all four usages of ConstAndTy (constant value, type, constant pattern, literal struct constructor).
• No warnings whatsoever for any of the four usages of DeprecatedAlias. Details

warning: use of deprecated constant `ConstAndTy`: bang
  --> src/main.rs:21:40
   |
21 |     let self::ConstAndTy: ConstAndTy = ConstAndTy;
   |                                        ^^^^^^^^^^
   |
   = note: `#[warn(deprecated)]` on by default

warning: use of deprecated constant `ConstAndTy`: bang
  --> src/main.rs:21:9
   |
21 |     let self::ConstAndTy: ConstAndTy = ConstAndTy;
   |         ^^^^^^^^^^^^^^^^

warning: use of deprecated type alias `ConstAndTy`: bang
  --> src/main.rs:21:27
   |
21 |     let self::ConstAndTy: ConstAndTy = ConstAndTy;
   |                           ^^^^^^^^^^

warning: use of deprecated type alias `ConstAndTy`: bang
  --> src/main.rs:22:13
   |
22 |     let _ = ConstAndTy {};
   |             ^^^^^^^^^^

Moreover, even if it were to lint about the use-reexported deprecated item, I suspect there would be no mention of the item at the origin of the re-export, even when visible and not deprecated itself.

Suggested improvement

Ideally:

• the output should warn about DeprecatedAlias too:

warning: use of deprecated constant `DeprecatedAlias`: bang  
  --> src/main.rs:17:50  
   |  
17 |     let self::DeprecatedAlias: DeprecatedAlias = DeprecatedAlias;  
   |                                                  ^^^^^^^^^^^^^^^  
   |  
   = note: `#[warn(deprecated)]` on by default  
warning: use of deprecated constant `DeprecatedAlias`: bang  
  --> src/main.rs:17:9  
   |  
17 |     let self::DeprecatedAlias: DeprecatedAlias = DeprecatedAlias;  
   |         ^^^^^^^^^^^^^^^^^^^^^  
warning: use of deprecated type alias `DeprecatedAlias`: bang  
  --> src/main.rs:17:32  
   |  
17 |     let self::DeprecatedAlias: DeprecatedAlias = DeprecatedAlias;  
   |                                ^^^^^^^^^^^^^^^  
warning: use of deprecated type alias `DeprecatedAlias`: bang  
  --> src/main.rs🔞13  
   |  
18 |     let _ = DeprecatedAlias {};  
   |             ^^^^^^^^^^^^^^^  

• And when the source of the re-export is visible to the scope where the deprecated alias is used, it should also suggest using that path instead:
  warning: use of deprecated constant DeprecatedAlias: bang
  --> src/main.rs:17:50
  |
  17 | let self::DeprecatedAlias: DeprecatedAlias = DeprecatedAlias;
  | ^^^^^^^^^^^^^^^

• | help: use the non-deprecated path: New
  |
  = note: #[warn(deprecated)] on by default

warning: use of deprecated constant DeprecatedAlias: bang
--> src/main.rs:17:9
|
17 | let self::DeprecatedAlias: DeprecatedAlias = DeprecatedAlias;
| ^^^^^^^^^^^^^^^^^^^^^

• | help: use the non-deprecated path: self::New

warning: use of deprecated type alias DeprecatedAlias: bang
--> src/main.rs:17:32
|
17 | let self::DeprecatedAlias: DeprecatedAlias = DeprecatedAlias;
| ^^^^^^^^^^^^^^^

• | help: use the non-deprecated path: New

warning: use of deprecated type alias DeprecatedAlias: bang
--> src/main.rs🔞13
|
18 | let _ = DeprecatedAlias {};
| ^^^^^^^^^^^^^^^

• | help: use the non-deprecated path: New

Rationale and further discussion

c.f. https://rust-lang.zulipchat.com/#narrow/stream/122651-general/topic/Updating.20reverse.20dependencies.20using.20code.20modification

• cc @shepmaster @jyn514 @thomcc