[clang] [HLSL] Disable implicit constructors for user-defined structs/classes (PR #194989)

[Joshua Batista via cfe-commits]

================
@@ -759,19 +759,40 @@ class CXXRecordDecl : public RecordDecl {
            needsImplicitDefaultConstructor();
   }
 
+  // Used by HLSL to determine if a record is a built-in implicit HLSL
+  // struct/class or a user-defined one. User-defined HLSL records cannot
+  // have ctors, dtors, or overloaded operators, while implicit built-in
+  // HLSL records such as resource classes can. It would be nice to use the
+  // isImplicit() methods to determine that, but this flag is not propagated
+  // to template-instanticated classes.
+  //
+  /// Determines whether this class has any user provided special members.
+  bool hasUserProvidedSpecialMembers() const {
+    return data().UserDeclaredSpecialMembers &
+               (SMF_MoveConstructor | SMF_MoveAssignment | SMF_Destructor |
+                SMF_CopyAssignment | SMF_CopyConstructor) ||
+           data().UserDeclaredConstructor ||
+           data().UserProvidedDefaultConstructor;
+  }
+
   /// Determine if we need to declare a default constructor for
   /// this class.
   ///
   /// This value is used for lazy creation of default constructors.
   bool needsImplicitDefaultConstructor() const {
-    return (!data().UserDeclaredConstructor &&
-            !(data().DeclaredSpecialMembers & SMF_DefaultConstructor) &&
-            (!isLambda() || lambdaIsDefaultConstructibleAndAssignable())) ||
-           // FIXME: Proposed fix to core wording issue: if a class inherits
-           // a default constructor and doesn't explicitly declare one, one
-           // is declared implicitly.
-           (data().HasInheritedDefaultConstructor &&
-            !(data().DeclaredSpecialMembers & SMF_DefaultConstructor));
+    return ((!data().UserDeclaredConstructor &&
+             !(data().DeclaredSpecialMembers & SMF_DefaultConstructor) &&
+             (!isLambda() || lambdaIsDefaultConstructibleAndAssignable())) ||
+            // FIXME: Proposed fix to core wording issue: if a class inherits
+            // a default constructor and doesn't explicitly declare one, one
+            // is declared implicitly.
+            (data().HasInheritedDefaultConstructor &&
+             !(data().DeclaredSpecialMembers & SMF_DefaultConstructor))) &&
+           // In HLSL, only built-in records like resources classes can have
+           // constructors.
+           (!getLangOpts().HLSL ||
+            (isLambda() && lambdaIsDefaultConstructibleAndAssignable()) ||
----------------
bob80905 wrote:

Can you explain in the comment above why this line is necessary?
Also, given that you are concerned about lambdas, would we need to change the `lambdaIsDefaultConstructibleAndAssignable` function? So that instead of return `getASTContext().getLangOpts().CPlusPlus20;`, it also checks for the HLSL language?

https://github.com/llvm/llvm-project/pull/194989