Resolving issue #119101

[rkmaxhero]

CLANG parser previously allowed for invalid C/C++ auto classes declaration due to a lack of logic addressing this case. Logic comparing with a valid case was added to the ParseDeclarationOrFunctionDefinition() function to account for this. Test cases where added to address possible scenarios of auto class declaration. the parser diagnostic file will now detect invalid auto class definitions and output appropriately.

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[llvmbot]

@llvm/pr-subscribers-clang

Author: Rounaq Khan (rkmaxhero)

Changes

CLANG parser previously allowed for invalid C/C++ auto classes declaration due to a lack of logic addressing this case. Logic comparing with a valid case was added to the ParseDeclarationOrFunctionDefinition() function to account for this. Test cases where added to address possible scenarios of auto class declaration. the parser diagnostic file will now detect invalid auto class definitions and output appropriately.

---

Full diff: https://github.com/llvm/llvm-project/pull/119143.diff

3 Files Affected:

• (modified) clang/include/clang/Basic/DiagnosticParseKinds.td (+2)
• (modified) clang/lib/Parse/Parser.cpp (+12)
• (added) clang/test/SemaCXX/invalid-storage-class.cpp (+7)

diff --git a/clang/include/clang/Basic/DiagnosticParseKinds.td b/clang/include/clang/Basic/DiagnosticParseKinds.td
index 0da509280068ad..99d698f57982fc 100644
--- a/clang/include/clang/Basic/DiagnosticParseKinds.td
+++ b/clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -449,6 +449,8 @@ def err_typename_invalid_constexpr : Error<
   "to be specified">;
 def err_typename_identifiers_only : Error<
   "typename is allowed for identifiers only">;
+def err_storage_class_before_class_decl : Error<
+  "'%0' is not allowed before a class declaration">;
 
 def err_friend_invalid_in_context : Error<
   "'friend' used outside of class">;
diff --git a/clang/lib/Parse/Parser.cpp b/clang/lib/Parse/Parser.cpp
index 04c2f1d380bc48..2145f78f4b2749 100644
--- a/clang/lib/Parse/Parser.cpp
+++ b/clang/lib/Parse/Parser.cpp
@@ -1254,6 +1254,18 @@ Parser::DeclGroupPtrTy Parser::ParseDeclarationOrFunctionDefinition(
         Actions.getASTContext().getSourceManager());
   });
 
+  if (DS->getStorageClassSpec() != DeclSpec::SCS_unspecified) {
+  // Check if the next token starts a class/struct/union/enum declaration
+    if (Tok.isOneOf(tok::kw_class, tok::kw_struct, tok::kw_union, tok::kw_enum)) {
+      // Emit an error: storage class specifiers are not allowed before class declarations
+      Diag(DS->getStorageClassSpecLoc(), diag::err_storage_class_before_class_decl)
+          << DeclSpec::getSpecifierName(DS->getStorageClassSpec());
+
+      // Optionally, consume the storage class specifier to continue parsing
+      DS->ClearStorageClassSpecs();
+    }
+  }
+
   if (DS) {
     return ParseDeclOrFunctionDefInternal(Attrs, DeclSpecAttrs, *DS, AS);
   } else {
diff --git a/clang/test/SemaCXX/invalid-storage-class.cpp b/clang/test/SemaCXX/invalid-storage-class.cpp
new file mode 100644
index 00000000000000..ce0dee3711ac03
--- /dev/null
+++ b/clang/test/SemaCXX/invalid-storage-class.cpp
@@ -0,0 +1,7 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+
+auto class X1 {}; // expected-error {{'auto' is not allowed before a class declaration}}
+
+static struct X2 {}; // expected-error {{'static' is not allowed before a class declaration}}
+
+register union X3 {}; // expected-error {{'register' is not allowed before a class declaration}}
\ No newline at end of file

[zygoloid]

Did you mean a different issue than #119101? It's not clear to me what connection this PR has to that issue.

It's not clear to me that there's an issue to be solved here. Under -pedantic-errors, clang already produces an error on examples like the ones here, and by default clang produces a warning on such cases, so we are already diagnosing this. And we need to continue to accept things like static struct A {} a;, which are valid but would be rejected by this change.