feature gate doc(primitive)

src/test/rustdoc-ui/coverage/exotic.rs

@@ -2,6 +2,7 @@
 // check-pass
 
 #![feature(doc_keyword)]
+#![feature(doc_primitive)]
 
 //! the features only used in std also have entries in the table, so make sure those get pulled out
 //! properly as well

src/test/ui/rustdoc/feature-gate-doc_primitive.rs

@@ -0,0 +1,8 @@
+// check-pass
+#[doc(primitive = "usize")]
+//~^ WARNING `doc(primitive)` should never have been stable
+//~| WARNING hard error in a future release
+/// Some docs
+mod usize {}
+
+fn main() {}

src/test/ui/rustdoc/feature-gate-doc_primitive.stderr

@@ -0,0 +1,12 @@
+warning: `doc(primitive)` should never have been stable
+  --> $DIR/feature-gate-doc_primitive.rs:2:7
+   |
+LL | #[doc(primitive = "usize")]
+   |       ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: `#[warn(invalid_doc_attributes)]` on by default
+   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
+   = note: for more information, see issue #82730 <https://github.com/rust-lang/rust/issues/82730>
+
+warning: 1 warning emitted
+