Auto merge of rust-lang#132038 - kailan:deprecated-use, r=<try>

Add lint rule for `#[deprecated]` on re-exports

As reported in rust-lang#30827 and rust-lang#84584, marking a re-export (`pub use`) with `#[deprecated]` does not produce a warning for consumers. In fact, there are instances of this in the `core` and `std` crates (see past issue rust-lang#82080 where this caused some confusion).

This change modifies the stability annotation visitor to mark `#[deprecated]` annotations on `use` statements with `AnnotationKind::DeprecationProhibited` so that library developers are aware that the annotation is not warning their users as expected.

```rust
#[deprecated]
pub use a_module::ActiveType;
```
```
error: this `#[deprecated]` annotation has no effect
  --> $DIR/deprecated_use.rs:6:1
   |
LL | #[deprecated]
   | ^^^^^^^^^^^^^ help: remove the unnecessary deprecation attribute
   |
   = note: `#[deny(useless_deprecated)]` on by default

error: aborting due to 1 previous error
```

try-job: dist-x86_64-linux

Author: bors

compiler/rustc_passes/src/stability.rs

@@ -411,6 +411,9 @@ impl<'a, 'tcx> Visitor<'tcx> for Annotator<'a, 'tcx> {
                 kind = AnnotationKind::DeprecationProhibited;
                 const_stab_inherit = InheritConstStability::Yes;
             }
+            hir::ItemKind::Use(_, _) => {
+                kind = AnnotationKind::DeprecationProhibited;
+            }
             hir::ItemKind::Struct(ref sd, _) => {
                 if let Some(ctor_def_id) = sd.ctor_def_id() {
                     self.annotate(

library/core/src/alloc/mod.rs

@@ -10,11 +10,6 @@ pub use self::global::GlobalAlloc;
 #[stable(feature = "alloc_layout", since = "1.28.0")]
 pub use self::layout::Layout;
 #[stable(feature = "alloc_layout", since = "1.28.0")]
-#[deprecated(
-    since = "1.52.0",
-    note = "Name does not follow std convention, use LayoutError",
-    suggestion = "LayoutError"
-)]
 #[allow(deprecated, deprecated_in_future)]
 pub use self::layout::LayoutErr;
 #[stable(feature = "alloc_layout_error", since = "1.50.0")]

library/std/src/collections/mod.rs

@@ -433,8 +433,7 @@ pub use self::hash_map::HashMap;
 #[doc(inline)]
 pub use self::hash_set::HashSet;
 #[stable(feature = "rust1", since = "1.0.0")]
-// FIXME(#82080) The deprecation here is only theoretical, and does not actually produce a warning.
-#[deprecated(note = "moved to `std::ops::Bound`", since = "1.26.0")]
+// FIXME(#82080) This has moved but #[deprecated] on `use` is unsupported.
 #[doc(hidden)]
 pub use crate::ops::Bound;
 

tests/ui/deprecation/deprecation-sanity.rs

@@ -39,4 +39,11 @@ impl Default for X {
     }
 }
 
+mod inner {
+    pub struct Y;
+}
+
+#[deprecated] //~ ERROR this `#[deprecated]` annotation has no effect
+pub use inner::Y;
+
 fn main() { }

tests/ui/deprecation/deprecation-sanity.stderr

@@ -68,7 +68,13 @@ LL | #[deprecated = "hello"]
    |
    = note: `#[deny(useless_deprecated)]` on by default
 
-error: aborting due to 10 previous errors
+error: this `#[deprecated]` annotation has no effect
+  --> $DIR/deprecation-sanity.rs:46:1
+   |
+LL | #[deprecated]
+   | ^^^^^^^^^^^^^ help: remove the unnecessary deprecation attribute
+
+error: aborting due to 11 previous errors
 
 Some errors have detailed explanations: E0538, E0539, E0541, E0565.
 For more information about an error, try `rustc --explain E0538`.

tests/ui/imports/unused-import-issue-87973.fixed

@@ -1,5 +1,6 @@
 //@ run-rustfix
 #![deny(unused_imports)]
+#![allow(useless_deprecated)]
 
 // Check that attributes get removed too. See #87973.
 //~^ ERROR unused import

tests/ui/imports/unused-import-issue-87973.rs

@@ -1,5 +1,6 @@
 //@ run-rustfix
 #![deny(unused_imports)]
+#![allow(useless_deprecated)]
 
 // Check that attributes get removed too. See #87973.
 #[deprecated]

tests/ui/imports/unused-import-issue-87973.stderr

@@ -1,5 +1,5 @@
 error: unused import: `std::fs`
-  --> $DIR/unused-import-issue-87973.rs:8:5
+  --> $DIR/unused-import-issue-87973.rs:9:5
    |
 LL | use std::fs;
    |     ^^^^^^^