fix(lints): Improve ill_formed_attribute_input with better help message for the cases where it matches the usage of #![allow]

Author: JayanAXHF

compiler/rustc_attr_parsing/src/attributes/doc.rs

@@ -665,7 +665,11 @@ impl DocParser {
                 let span = cx.attr_span;
                 cx.emit_lint(
                     rustc_session::lint::builtin::INVALID_DOC_ATTRIBUTES,
-                    AttributeLintKind::IllFormedAttributeInput { suggestions, docs: None },
+                    AttributeLintKind::IllFormedAttributeInput {
+                        suggestions,
+                        docs: None,
+                        help: None,
+                    },
                     span,
                 );
             }

compiler/rustc_attr_parsing/src/attributes/test_attrs.rs

@@ -27,8 +27,12 @@ impl<S: Stage> SingleAttributeParser<S> for IgnoreParser {
                     };
                     Some(str_value)
                 }
-                ArgParser::List(_) => {
-                    cx.warn_ill_formed_attribute_input(ILL_FORMED_ATTRIBUTE_INPUT);
+                ArgParser::List(list) => {
+                    let help = list.single().and_then(|item| item.meta_item()).and_then(|item| {
+                        item.args().no_args().ok()?;
+                        Some(item.path().to_string())
+                    });
+                    cx.warn_ill_formed_attribute_input_with_help(ILL_FORMED_ATTRIBUTE_INPUT, help);
                     return None;
                 }
             },

compiler/rustc_attr_parsing/src/context.rs

@@ -669,11 +669,19 @@ impl<'f, 'sess: 'f, S: Stage> AcceptContext<'f, 'sess, S> {
     }
 
     pub(crate) fn warn_ill_formed_attribute_input(&mut self, lint: &'static Lint) {
+        self.warn_ill_formed_attribute_input_with_help(lint, None);
+    }
+
+    pub(crate) fn warn_ill_formed_attribute_input_with_help(
+        &mut self,
+        lint: &'static Lint,
+        help: Option<String>,
+    ) {
         let suggestions = self.suggestions();
         let span = self.attr_span;
         self.emit_lint(
             lint,
-            AttributeLintKind::IllFormedAttributeInput { suggestions, docs: None },
+            AttributeLintKind::IllFormedAttributeInput { suggestions, docs: None, help },
             span,
         );
     }

compiler/rustc_attr_parsing/src/validate_attr.rs

@@ -211,6 +211,7 @@ fn emit_malformed_attribute(
             BuiltinLintDiag::AttributeLint(AttributeLintKind::IllFormedAttributeInput {
                 suggestions: suggestions.clone(),
                 docs: template.docs,
+                help: None,
             }),
         );
     } else {

compiler/rustc_lint/src/early/diagnostics.rs

@@ -175,14 +175,15 @@ impl<'a> Diagnostic<'a, ()> for DecorateAttrLint<'_, '_, '_> {
             &AttributeLintKind::UnusedDuplicate { this, other, warning } => {
                 lints::UnusedDuplicate { this, other, warning }.into_diag(dcx, level)
             }
-            AttributeLintKind::IllFormedAttributeInput { suggestions, docs } => {
+            AttributeLintKind::IllFormedAttributeInput { suggestions, docs, help } => {
                 lints::IllFormedAttributeInput {
                     num_suggestions: suggestions.len(),
                     suggestions: DiagArgValue::StrListSepByAnd(
                         suggestions.into_iter().map(|s| format!("`{s}`").into()).collect(),
                     ),
                     has_docs: docs.is_some(),
                     docs: docs.unwrap_or(""),
+                    help: help.clone().map(|h| lints::IllFormedAttributeInputHelp { lint: h }),
                 }
                 .into_diag(dcx, level)
             }

compiler/rustc_lint/src/lints.rs

@@ -3009,6 +3009,16 @@ pub(crate) struct IllFormedAttributeInput {
     #[note("for more information, visit <{$docs}>")]
     pub has_docs: bool,
     pub docs: &'static str,
+    #[subdiagnostic]
+    pub help: Option<IllFormedAttributeInputHelp>,
+}
+
+#[derive(Subdiagnostic)]
+#[help(
+    "if you meant to silence a warning, consider using #![allow({$lint})] or #![expect({$lint})]"
+)]
+pub(crate) struct IllFormedAttributeInputHelp {
+    pub lint: String,
 }
 
 #[derive(Diagnostic)]

compiler/rustc_lint_defs/src/lib.rs

@@ -703,6 +703,7 @@ pub enum AttributeLintKind {
     IllFormedAttributeInput {
         suggestions: Vec<String>,
         docs: Option<&'static str>,
+        help: Option<String>,
     },
     EmptyAttribute {
         first_span: Span,