[clang] [HLSL] Implement HLSL intialization list support (PR #123141)

[Justin Bogner via cfe-commits]

================
@@ -1462,6 +1462,14 @@ void CXXRecordDecl::addedMember(Decl *D) {
     if (Using->getDeclName().getCXXOverloadedOperator() == OO_Equal)
       data().HasInheritedAssignment = true;
   }
+
+  // HLSL: All user-defined data types are aggregates and use aggregate
+  // initialization. This _needs_ to change in the future. There are two
+  // relevant HLSL feature proposals that will depend on this changing:
+  // * 0005-strict-initializer-lists.md
+  // * https://github.com/microsoft/hlsl-specs/pull/325
+  if (getLangOpts().HLSL)
+    data().Aggregate = data().UserDeclaredSpecialMembers == 0;
----------------
bogner wrote:

Does this comment match what this is doing? If I'm reading this correctly we're using the fact that there are no user declared constructors/destructors/assignment operators to decide that this is an aggregate - I guess that's because users aren't allowed to write those in HLSL so we can use it as a proxy?

https://github.com/llvm/llvm-project/pull/123141