Emit some additional `unused_doc_comments` lints outside of the main pass

src/librustc_expand/expand.rs

@@ -14,6 +14,7 @@ use rustc_parse::configure;
 use rustc_parse::parser::Parser;
 use rustc_parse::validate_attr;
 use rustc_parse::DirectoryOwnership;
+use rustc_session::lint::builtin::UNUSED_DOC_COMMENTS;
 use rustc_session::parse::{feature_err, ParseSess};
 use rustc_span::source_map::respan;
 use rustc_span::symbol::{sym, Symbol};
@@ -1090,6 +1091,10 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
                     .note("this may become a hard error in a future release")
                     .emit();
             }
+
+            if attr.doc_str().is_some() {
+                self.cx.parse_sess.buffer_lint(&UNUSED_DOC_COMMENTS, attr.span, ast::CRATE_NODE_ID, "yep, it's unused");
+            }
         }
     }
 }

src/librustc_lint/builtin.rs

@@ -738,15 +738,18 @@ impl EarlyLintPass for DeprecatedAttr {
     }
 }
 
-declare_lint! {
-    pub UNUSED_DOC_COMMENTS,
-    Warn,
-    "detects doc comments that aren't used by rustdoc"
+trait UnusedDocCommentExt {
+    fn warn_if_doc(
+        &self,
+        cx: &EarlyContext<'_>,
+        node_span: Span,
+        node_kind: &str,
+        is_macro_expansion: bool,
+        attrs: &[ast::Attribute],
+    );
 }
 
-declare_lint_pass!(UnusedDocComment => [UNUSED_DOC_COMMENTS]);
-
-impl UnusedDocComment {
+impl UnusedDocCommentExt for UnusedDocComment {
     fn warn_if_doc(
         &self,
         cx: &EarlyContext<'_>,

src/librustc_session/lint/builtin.rs

@@ -557,3 +557,11 @@ declare_lint_pass! {
         INLINE_NO_SANITIZE,
     ]
 }
+
+declare_lint! {
+    pub UNUSED_DOC_COMMENTS,
+    Warn,
+    "detects doc comments that aren't used by rustdoc"
+}
+
+declare_lint_pass!(UnusedDocComment => [UNUSED_DOC_COMMENTS]);

src/test/ui/useless-comment.rs

@@ -6,7 +6,7 @@ macro_rules! mac {
     () => {}
 }
 
-/// foo //FIXME ERROR unused doc comment
+/// foo //~ ERROR yep, it's unused
 mac!();
 
 fn foo() {
@@ -29,7 +29,7 @@ fn foo() {
     #[doc = "bar"] //~ ERROR unused doc comment
     3;
 
-    /// bar //FIXME ERROR unused doc comment
+    /// bar //~ ERROR yep, it's unused
     mac!();
 
     let x = /** comment */ 47; //~ ERROR unused doc comment

src/test/ui/useless-comment.stderr

@@ -1,3 +1,21 @@
+error: yep, it's unused
+  --> $DIR/useless-comment.rs:9:1
+   |
+LL | /// foo
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: the lint level is defined here
+  --> $DIR/useless-comment.rs:3:9
+   |
+LL | #![deny(unused_doc_comments)]
+   |         ^^^^^^^^^^^^^^^^^^^
+
+error: yep, it's unused
+  --> $DIR/useless-comment.rs:32:5
+   |
+LL |     /// bar
+   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
 error: unused doc comment
   --> $DIR/useless-comment.rs:13:5
    |
@@ -5,12 +23,6 @@ LL |     /// a
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 LL |     let x = 12;
    |     ----------- rustdoc does not generate documentation for statements
-   |
-note: the lint level is defined here
-  --> $DIR/useless-comment.rs:3:9
-   |
-LL | #![deny(unused_doc_comments)]
-   |         ^^^^^^^^^^^^^^^^^^^
 
 error: unused doc comment
   --> $DIR/useless-comment.rs:16:5
@@ -75,5 +87,5 @@ LL | |
 LL | |     }
    | |_____- rustdoc does not generate documentation for expressions
 
-error: aborting due to 8 previous errors
+error: aborting due to 10 previous errors