Trigger unused_doc_comments on macros at once

compiler/rustc_expand/src/expand.rs

@@ -1060,13 +1060,23 @@ impl<'a, 'b> InvocationCollector<'a, 'b> {
     // since they will not be detected after macro expansion.
     fn check_attributes(&mut self, attrs: &[ast::Attribute]) {
         let features = self.cx.ecfg.features.unwrap();
-        for attr in attrs.iter() {
+        let mut attrs = attrs.iter().peekable();
+        let mut span: Option<Span> = None;
+        while let Some(attr) = attrs.next() {
             rustc_ast_passes::feature_gate::check_attribute(attr, self.cx.sess, features);
             validate_attr::check_meta(&self.cx.sess.parse_sess, attr);
+
+            let current_span = if let Some(sp) = span { sp.to(attr.span) } else { attr.span };
+            span = Some(current_span);
+
+            if attrs.peek().map_or(false, |next_attr| next_attr.doc_str().is_some()) {
+                continue;
+            }
+
             if attr.doc_str().is_some() {
                 self.cx.sess.parse_sess.buffer_lint_with_diagnostic(
                     &UNUSED_DOC_COMMENTS,
-                    attr.span,
+                    current_span,
                     ast::CRATE_NODE_ID,
                     "unused doc comment",
                     BuiltinLintDiagnostics::UnusedDocComment(attr.span),

compiler/rustc_lint/src/builtin.rs

@@ -989,7 +989,7 @@ fn warn_if_doc(cx: &EarlyContext<'_>, node_span: Span, node_kind: &str, attrs: &
                 Some(sugared_span.map_or(attr.span, |span| span.with_hi(attr.span.hi())));
         }
 
-        if attrs.peek().map(|next_attr| next_attr.is_doc_comment()).unwrap_or_default() {
+        if attrs.peek().map_or(false, |next_attr| next_attr.is_doc_comment()) {
             continue;
         }
 

src/test/ui/unused/unused-doc-comments-for-macros.rs

@@ -0,0 +1,17 @@
+#![deny(unused_doc_comments)]
+#![feature(rustc_attrs)]
+
+macro_rules! foo { () => {}; }
+
+fn main() {
+    /// line1 //~ ERROR: unused doc comment
+    /// line2
+    /// line3
+    foo!();
+
+    // Ensure we still detect another doc-comment block.
+    /// line1 //~ ERROR: unused doc comment
+    /// line2
+    /// line3
+    foo!();
+}

src/test/ui/unused/unused-doc-comments-for-macros.stderr

@@ -0,0 +1,31 @@
+error: unused doc comment
+  --> $DIR/unused-doc-comments-for-macros.rs:7:5
+   |
+LL | /     /// line1
+LL | |     /// line2
+LL | |     /// line3
+   | |_____--------^
+   |       |
+   |       rustdoc does not generate documentation for macro invocations
+   |
+note: the lint level is defined here
+  --> $DIR/unused-doc-comments-for-macros.rs:1:9
+   |
+LL | #![deny(unused_doc_comments)]
+   |         ^^^^^^^^^^^^^^^^^^^
+   = help: to document an item produced by a macro, the macro must produce the documentation as part of its expansion
+
+error: unused doc comment
+  --> $DIR/unused-doc-comments-for-macros.rs:13:5
+   |
+LL | /     /// line1
+LL | |     /// line2
+LL | |     /// line3
+   | |_____--------^
+   |       |
+   |       rustdoc does not generate documentation for macro invocations
+   |
+   = help: to document an item produced by a macro, the macro must produce the documentation as part of its expansion
+
+error: aborting due to 2 previous errors
+