Fix ICE when using #[doc(keyword = "...")] on non-items

src/test/ui/rustdoc/issue-83512.rs

@@ -0,0 +1,10 @@
+// Regression test for the ICE described in #83512.
+
+#![feature(doc_keyword)]
+#![crate_type="lib"]
+
+trait Foo {
+    #[doc(keyword = "match")]
+    //~^ ERROR: `#[doc(keyword = "...")]` can only be used on modules
+    fn quux() {}
+}

src/test/ui/rustdoc/issue-83512.stderr

@@ -0,0 +1,8 @@
+error: `#[doc(keyword = "...")]` can only be used on modules
+  --> $DIR/issue-83512.rs:7:11
+   |
+LL |     #[doc(keyword = "match")]
+   |           ^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+