[Clang][Sema] set declaration invalid earlier to prevent crash in calculating record layout

clang/docs/ReleaseNotes.rst

@@ -536,6 +536,8 @@ Bug Fixes to C++ Support
   Fixes (#GH70604), (#GH79754), (#GH84163), (#GH84425), (#GH86054), (#GH86398), and (#GH86399).
 - Fix a crash when deducing ``auto`` from an invalid dereference (#GH88329).
 - Fix a crash in requires expression with templated base class member function. Fixes (#GH84020).
+- Fix a crash caused by defined struct in a type alias template when the structure
+  has fields with dependent type. Fixes (#GH75221).
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/include/clang/Sema/Scope.h

@@ -156,6 +156,9 @@ class Scope {
     /// This is the scope of an OpenACC Compute Construct, which restricts
     /// jumping into/out of it.
     OpenACCComputeConstructScope = 0x10000000,
+
+    /// This is a scope of type alias declaration.
+    TypeAliasScope = 0x20000000,
   };
 
 private:
@@ -580,6 +583,9 @@ class Scope {
   /// if/switch/while/for statement.
   bool isControlScope() const { return getFlags() & Scope::ControlScope; }
 
+  /// Determine whether this scope is a type alias scope.
+  bool isTypeAliasScope() const { return getFlags() & Scope::TypeAliasScope; }
+
   /// Returns if rhs has a higher scope depth than this.
   ///
   /// The caller is responsible for calling this only if one of the two scopes

clang/lib/Parse/ParseDeclCXX.cpp

@@ -799,6 +799,11 @@ Parser::DeclGroupPtrTy Parser::ParseUsingDeclaration(
     ProhibitAttributes(PrefixAttrs);
 
     Decl *DeclFromDeclSpec = nullptr;
+    Scope *CurScope = getCurScope();
+    if (CurScope)
+      CurScope->setFlags(Scope::ScopeFlags::TypeAliasScope |
+                         CurScope->getFlags());
+
     Decl *AD = ParseAliasDeclarationAfterDeclarator(
         TemplateInfo, UsingLoc, D, DeclEnd, AS, Attrs, &DeclFromDeclSpec);
     return Actions.ConvertDeclToDeclGroup(AD, DeclFromDeclSpec);

clang/lib/Sema/SemaDecl.cpp

@@ -19529,6 +19529,13 @@ void Sema::ActOnFields(Scope *S, SourceLocation RecLoc, Decl *EnclosingDecl,
   // Okay, we successfully defined 'Record'.
   if (Record) {
     bool Completed = false;
+    if (S) {
+      Scope *Parent = S->getParent();
+      if (Parent && Parent->isTypeAliasScope() &&
+          Parent->isTemplateParamScope())
+        Record->setInvalidDecl();
+    }
+
     if (CXXRecord) {
       if (!CXXRecord->isInvalidDecl()) {
         // Set access bits correctly on the directly-declared conversions.

clang/test/SemaCXX/PR75221.cpp

@@ -0,0 +1,6 @@
+// RUN: %clang_cc1 -verify -std=c++11 -fsyntax-only %s
+
+template <class T> using foo = struct foo { // expected-error {{'foo' cannot be defined in a type alias template}}
+  T size = 0;
+};
+foo a;