Properly emit diagnostic for diagnostic::on_move being used without feature gate

Author: mejrs

compiler/rustc_attr_parsing/src/attributes/diagnostic/on_move.rs

@@ -24,6 +24,7 @@ impl OnMoveParser {
         mode: Mode,
     ) {
         if !cx.features().diagnostic_on_move() {
+            // `UnknownDiagnosticAttribute` is emitted in rustc_resolve/macros.rs
             return;
         }
 

compiler/rustc_resolve/src/macros.rs

@@ -715,7 +715,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
         const DIAGNOSTIC_ATTRIBUTES: &[(Symbol, Option<Symbol>)] = &[
             (sym::on_unimplemented, None),
             (sym::do_not_recommend, None),
-            (sym::on_move, None),
+            (sym::on_move, Some(sym::diagnostic_on_move)),
             (sym::on_const, Some(sym::diagnostic_on_const)),
             (sym::on_unknown, Some(sym::diagnostic_on_unknown)),
         ];

tests/ui/feature-gates/feature-gate-diagnostic-on-move.rs

@@ -2,9 +2,8 @@
 //! gate, but the fact that not adding the feature gate will cause the
 //! diagnostic to not emit the custom diagnostic message
 //!
-#[diagnostic::on_move(
-    message = "Foo"
-)]
+#[diagnostic::on_move(message = "Foo")]
+//~^ WARN unknown diagnostic attribute
 #[derive(Debug)]
 struct Foo;
 

tests/ui/feature-gates/feature-gate-diagnostic-on-move.stderr

@@ -1,5 +1,13 @@
+warning: unknown diagnostic attribute
+  --> $DIR/feature-gate-diagnostic-on-move.rs:5:15
+   |
+LL | #[diagnostic::on_move(message = "Foo")]
+   |               ^^^^^^^
+   |
+   = note: `#[warn(unknown_diagnostic_attributes)]` (part of `#[warn(unknown_or_malformed_diagnostic_attributes)]`) on by default
+
 error[E0382]: use of moved value: `foo`
-  --> $DIR/feature-gate-diagnostic-on-move.rs:16:15
+  --> $DIR/feature-gate-diagnostic-on-move.rs:15:15
    |
 LL |     let foo = Foo;
    |         --- move occurs because `foo` has type `Foo`, which does not implement the `Copy` trait
@@ -9,21 +17,21 @@ LL |     let bar = foo;
    |               ^^^ value used here after move
    |
 note: consider changing this parameter type in function `takes_foo` to borrow instead if owning the value isn't necessary
-  --> $DIR/feature-gate-diagnostic-on-move.rs:11:17
+  --> $DIR/feature-gate-diagnostic-on-move.rs:10:17
    |
 LL | fn takes_foo(_: Foo) {}
    |    ---------    ^^^ this parameter takes ownership of the value
    |    |
    |    in this function
 note: if `Foo` implemented `Clone`, you could clone the value
-  --> $DIR/feature-gate-diagnostic-on-move.rs:9:1
+  --> $DIR/feature-gate-diagnostic-on-move.rs:8:1
    |
 LL | struct Foo;
    | ^^^^^^^^^^ consider implementing `Clone` for this type
 ...
 LL |     takes_foo(foo);
    |               --- you could clone this value
 
-error: aborting due to 1 previous error
+error: aborting due to 1 previous error; 1 warning emitted
 
 For more information about this error, try `rustc --explain E0382`.