Rollup merge of #78626 - fusion-engineering-forks:deprecated-trait-impl, r=estebank

Improve errors about #[deprecated] attribute

This change:

1. Turns `#[deprecated]` on a trait impl block into an error, which fixes #78625;
2. Changes these and other errors about `#[deprecated]` to use the span of the attribute instead of the item; and
3. Turns this error into a lint, to make sure it can be capped with `--cap-lints` and doesn't break any existing dependencies.

Can be reviewed per commit.

---
Example:
```rust
struct X;

#[deprecated = "a"]
impl Default for X {
    #[deprecated = "b"]
    fn default() -> Self {
        X
    }
}
```

Before:
```
error: This deprecation annotation is useless
 --> src/main.rs:6:5
  |
6 | /     fn default() -> Self {
7 | |         X
8 | |     }
  | |_____^
```

After:
```
error: this `#[deprecated]' annotation has no effect
 --> src/main.rs:3:1
  |
3 | #[deprecated = "a"]
  | ^^^^^^^^^^^^^^^^^^^ help: try removing the deprecation attribute
  |
  = note: `#[deny(useless_deprecated)]` on by default

error: this `#[deprecated]' annotation has no effect
 --> src/main.rs:5:5
  |
5 |     #[deprecated = "b"]
  |     ^^^^^^^^^^^^^^^^^^^ help: try removing the deprecation attribute
```

4 files changed, 36 insertions, 15 deletions

diff --git a/src/test/ui/deprecation/deprecation-sanity.rs b/src/test/ui/deprecation/deprecation-sanity.rs
index a559908b792..4fc3fddadb9 100644
--- a/src/test/ui/deprecation/deprecation-sanity.rs
+++ b/src/test/ui/deprecation/deprecation-sanity.rs
@@ -24,10 +24,19 @@ mod bogus_attribute_types_1 {
 }
 
 #[deprecated(since = "a", note = "b")]
-#[deprecated(since = "a", note = "b")]
-fn multiple1() { } //~ ERROR multiple deprecated attributes
+#[deprecated(since = "a", note = "b")] //~ ERROR multiple deprecated attributes
+fn multiple1() { }
 
 #[deprecated(since = "a", since = "b", note = "c")] //~ ERROR multiple 'since' items
 fn f1() { }
 
+struct X;
+
+#[deprecated = "hello"] //~ ERROR this `#[deprecated]` annotation has no effect
+impl Default for X {
+    fn default() -> Self {
+        X
+    }
+}
+
 fn main() { }
diff --git a/src/test/ui/deprecation/deprecation-sanity.stderr b/src/test/ui/deprecation/deprecation-sanity.stderr
index 57143d68105..7e70c35eeab 100644
--- a/src/test/ui/deprecation/deprecation-sanity.stderr
+++ b/src/test/ui/deprecation/deprecation-sanity.stderr
@@ -41,10 +41,12 @@ LL |     #[deprecated("test")]
    |                  ^^^^^^
 
 error[E0550]: multiple deprecated attributes
-  --> $DIR/deprecation-sanity.rs:28:1
+  --> $DIR/deprecation-sanity.rs:27:1
    |
-LL | fn multiple1() { }
-   | ^^^^^^^^^^^^^^^^^^
+LL | #[deprecated(since = "a", note = "b")]
+   | -------------------------------------- first deprecation attribute
+LL | #[deprecated(since = "a", note = "b")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ repeated deprecation attribute
 
 error[E0538]: multiple 'since' items
   --> $DIR/deprecation-sanity.rs:30:27
@@ -52,7 +54,15 @@ error[E0538]: multiple 'since' items
 LL | #[deprecated(since = "a", since = "b", note = "c")]
    |                           ^^^^^^^^^^^
 
-error: aborting due to 9 previous errors
+error: this `#[deprecated]` annotation has no effect
+  --> $DIR/deprecation-sanity.rs:35:1
+   |
+LL | #[deprecated = "hello"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^ help: remove the unnecessary deprecation attribute
+   |
+   = note: `#[deny(useless_deprecated)]` on by default
+
+error: aborting due to 10 previous errors
 
 Some errors have detailed explanations: E0538, E0541, E0550, E0551, E0565.
 For more information about an error, try `rustc --explain E0538`.
diff --git a/src/test/ui/stability-attribute/stability-attribute-sanity.rs b/src/test/ui/stability-attribute/stability-attribute-sanity.rs
index 80d7ae6dc63..abd603b356e 100644
--- a/src/test/ui/stability-attribute/stability-attribute-sanity.rs
+++ b/src/test/ui/stability-attribute/stability-attribute-sanity.rs
@@ -59,14 +59,14 @@ fn multiple3() { }
 
 #[stable(feature = "a", since = "b")]
 #[rustc_deprecated(since = "b", reason = "text")]
-#[rustc_deprecated(since = "b", reason = "text")]
+#[rustc_deprecated(since = "b", reason = "text")] //~ ERROR multiple deprecated attributes
 #[rustc_const_unstable(feature = "c", issue = "none")]
 #[rustc_const_unstable(feature = "d", issue = "none")] //~ ERROR multiple stability levels
-pub const fn multiple4() { } //~ ERROR multiple deprecated attributes
+pub const fn multiple4() { }
 //~^ ERROR Invalid stability or deprecation version found
 
 #[rustc_deprecated(since = "a", reason = "text")]
 fn deprecated_without_unstable_or_stable() { }
-//~^ ERROR rustc_deprecated attribute must be paired with either stable or unstable attribute
+//~^^ ERROR rustc_deprecated attribute must be paired with either stable or unstable attribute
 
 fn main() { }
diff --git a/src/test/ui/stability-attribute/stability-attribute-sanity.stderr b/src/test/ui/stability-attribute/stability-attribute-sanity.stderr
index 134c657c620..bf2436a535f 100644
--- a/src/test/ui/stability-attribute/stability-attribute-sanity.stderr
+++ b/src/test/ui/stability-attribute/stability-attribute-sanity.stderr
@@ -83,10 +83,12 @@ LL | #[stable(feature = "a", since = "b")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0550]: multiple deprecated attributes
-  --> $DIR/stability-attribute-sanity.rs:65:1
+  --> $DIR/stability-attribute-sanity.rs:62:1
    |
-LL | pub const fn multiple4() { }
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[rustc_deprecated(since = "b", reason = "text")]
+   | ------------------------------------------------- first deprecation attribute
+LL | #[rustc_deprecated(since = "b", reason = "text")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ repeated deprecation attribute
 
 error[E0544]: multiple stability levels
   --> $DIR/stability-attribute-sanity.rs:64:1
@@ -101,10 +103,10 @@ LL | pub const fn multiple4() { }
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error[E0549]: rustc_deprecated attribute must be paired with either stable or unstable attribute
-  --> $DIR/stability-attribute-sanity.rs:69:1
+  --> $DIR/stability-attribute-sanity.rs:68:1
    |
-LL | fn deprecated_without_unstable_or_stable() { }
-   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | #[rustc_deprecated(since = "a", reason = "text")]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 error: aborting due to 18 previous errors