[clang] Avoid assert in substqualifier (PR #182707)

[Ayush Kumar Gaur via cfe-commits]

https://github.com/Ayush3941 updated https://github.com/llvm/llvm-project/pull/182707

>From a36f1ac769ac7a770a1eafd160f3f40a1bdf75fd Mon Sep 17 00:00:00 2001
From: Ayush3941 <ayushkgaur1 at gmail.com>
Date: Mon, 16 Mar 2026 11:01:26 -0400
Subject: [PATCH] [Clang][Sema] Propagate invalidity for local static member
 definitions

---
 clang/lib/Sema/SemaDecl.cpp          |  7 ++++++-
 clang/test/SemaTemplate/GH176152.cpp | 12 ++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/SemaTemplate/GH176152.cpp

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 3db91b00f9d80..4fb74827ee01c 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -4702,6 +4702,9 @@ void Sema::MergeVarDecl(VarDecl *New, LookupResult &Previous) {
     return New->setInvalidDecl();
   }
 
+  if (Old->isInvalidDecl())
+    return New->setInvalidDecl();
+
   // If the old declaration was found in an inline namespace and the new
   // declaration was qualified, update the DeclContext to match.
   adjustDeclContextForDeclaratorDecl(New, Old);
@@ -7929,7 +7932,7 @@ NamedDecl *Sema::ActOnVariableDeclarator(
 
     if (CurContext->isRecord()) {
       if (SC == SC_Static) {
-        if (const CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(DC)) {
+        if (CXXRecordDecl *RD = dyn_cast<CXXRecordDecl>(DC)) {
           // Walk up the enclosing DeclContexts to check for any that are
           // incompatible with static data members.
           const DeclContext *FunctionOrMethod = nullptr;
@@ -7951,6 +7954,8 @@ NamedDecl *Sema::ActOnVariableDeclarator(
             Diag(D.getIdentifierLoc(),
                  diag::err_static_data_member_not_allowed_in_local_class)
                 << Name << RD->getDeclName() << RD->getTagKind();
+            Invalid = true;
+            RD->setInvalidDecl();
           } else if (AnonStruct) {
             // C++ [class.static.data]p4: Unnamed classes and classes contained
             // directly or indirectly within unnamed classes shall not contain
diff --git a/clang/test/SemaTemplate/GH176152.cpp b/clang/test/SemaTemplate/GH176152.cpp
new file mode 100644
index 0000000000000..7d61aa292982d
--- /dev/null
+++ b/clang/test/SemaTemplate/GH176152.cpp
@@ -0,0 +1,12 @@
+// RUN: %clang_cc1 -std=c++23 -fsyntax-only -verify %s
+
+template <class T> int f(T) {
+  struct MyClass {
+    static int staticField;
+    // expected-error at -1 {{static data member 'staticField' not allowed in local struct 'MyClass'}}
+  };
+  int MyClass::staticField = 42;
+  return 0;
+}
+
+int x = f(0);