Rollup merge of #146653 - jdonszelmann:empty-attr-diags, r=nnethercote

improve diagnostics for empty attributes

Adds a note about them not having any effect. This was previously done for `feature` attributes but no other attributes. In [converting the `feature` parser](https://github.com/rust-lang/rust/pull/146652) I removed that note. This PR adds it back in and makes it so all attributes benefit from it.

Not blocked on rust-lang/rust#146652, either can merge first

3 files changed, 21 insertions, 7 deletions

diff --git a/compiler/rustc_attr_parsing/src/context.rs b/compiler/rustc_attr_parsing/src/context.rs
index d7ccf3c7806..e8bb4caa416 100644
--- a/compiler/rustc_attr_parsing/src/context.rs
+++ b/compiler/rustc_attr_parsing/src/context.rs
@@ -597,7 +597,12 @@ impl<'f, 'sess: 'f, S: Stage> AcceptContext<'f, 'sess, S> {
     }
 
     pub(crate) fn warn_empty_attribute(&mut self, span: Span) {
-        self.emit_lint(AttributeLintKind::EmptyAttribute { first_span: span }, span);
+        let attr_path = self.attr_path.clone();
+        let valid_without_list = self.template.word;
+        self.emit_lint(
+            AttributeLintKind::EmptyAttribute { first_span: span, attr_path, valid_without_list },
+            span,
+        );
     }
 }
 
diff --git a/compiler/rustc_attr_parsing/src/lints.rs b/compiler/rustc_attr_parsing/src/lints.rs
index ab8ba0daf1f..3a2a3704669 100644
--- a/compiler/rustc_attr_parsing/src/lints.rs
+++ b/compiler/rustc_attr_parsing/src/lints.rs
@@ -43,12 +43,18 @@ pub fn emit_attribute_lint<L: LintEmitter>(lint: &AttributeLint<L::Id>, lint_emi
                     ),
                 },
             ),
-        AttributeLintKind::EmptyAttribute { first_span } => lint_emitter.emit_node_span_lint(
-            rustc_session::lint::builtin::UNUSED_ATTRIBUTES,
-            *id,
-            *first_span,
-            session_diagnostics::EmptyAttributeList { attr_span: *first_span },
-        ),
+        AttributeLintKind::EmptyAttribute { first_span, attr_path, valid_without_list } => {
+            lint_emitter.emit_node_span_lint(
+                rustc_session::lint::builtin::UNUSED_ATTRIBUTES,
+                *id,
+                *first_span,
+                session_diagnostics::EmptyAttributeList {
+                    attr_span: *first_span,
+                    attr_path: attr_path.clone(),
+                    valid_without_list: *valid_without_list,
+                },
+            )
+        }
         AttributeLintKind::InvalidTarget { name, target, applied, only } => lint_emitter
             .emit_node_span_lint(
                 // This check is here because `deprecated` had its own lint group and removing this would be a breaking change
diff --git a/compiler/rustc_attr_parsing/src/session_diagnostics.rs b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
index 2c2b14c8a68..1194ac5872c 100644
--- a/compiler/rustc_attr_parsing/src/session_diagnostics.rs
+++ b/compiler/rustc_attr_parsing/src/session_diagnostics.rs
@@ -503,9 +503,12 @@ pub(crate) struct EmptyConfusables {
 
 #[derive(LintDiagnostic)]
 #[diag(attr_parsing_empty_attribute)]
+#[note]
 pub(crate) struct EmptyAttributeList {
     #[suggestion(code = "", applicability = "machine-applicable")]
     pub attr_span: Span,
+    pub attr_path: AttrPath,
+    pub valid_without_list: bool,
 }
 
 #[derive(LintDiagnostic)]