[clang] [Clang] Fix assertion failure in getASTRecordLayout for invalid declarations (PR #208153)

[Erich Keane via cfe-commits]

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@@ -3384,9 +3384,30 @@ ASTContext::getASTRecordLayout(const RecordDecl *D) const {
   // not a complete definition (which is what isCompleteDefinition() tests)
   // until we *finish* parsing the definition.
   D = D->getDefinition();
-  assert(D && "Cannot get layout of forward declarations!");
-  assert(!D->isInvalidDecl() && "Cannot get layout of invalid decl!");
-  assert(D->isCompleteDefinition() && "Cannot layout type before complete!");
+
+  // Handle invalid declarations gracefully during error recovery
+  // This can happen when there are template specialization errors
+  if (!D || D->isInvalidDecl() || !D->isCompleteDefinition()) {
+    // Check if we already have a cached layout
+    const ASTRecordLayout *Entry = ASTRecordLayouts[D];
+    if (Entry)
+      return *Entry;
+
+    // Create a minimal safe layout for error recovery
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erichkeane wrote:

I THINK this is also wrong, since we check for an entry, what happens if `D` later becomes complete?  

https://github.com/llvm/llvm-project/pull/208153