Fix a bug in default ctor synthesizing (#6527)

* Fix a bug in default ctor synthesizing

- This is fix for the implementation bug, when a struct has explicit ctor
  we should not synthesize the default ctor anymore.

- When invoke the synthesized ctor converted from initializer list, we should
  check if the struct is a c-style type if it struct has no synthesized ctor. In this
  case we should report error because it's invalid to use initializer list here.

- The only exception is the unsized array, we still have to fall back to use the
  legacy initializer list logic to initialize the unsized array until we formalize a
  proper solution.

- update test.

2 files changed, 26 insertions, 5 deletions

diff --git a/source/slang/slang-check-conversion.cpp b/source/slang/slang-check-conversion.cpp
index c5cf192ee..1c8846e66 100644
--- a/source/slang/slang-check-conversion.cpp
+++ b/source/slang/slang-check-conversion.cpp
@@ -396,14 +396,35 @@ bool SemanticsVisitor::createInvokeExprForSynthesizedCtor(
 {
     StructDecl* structDecl = isDeclRefTypeOf<StructDecl>(toType).getDecl();
 
-    if (!structDecl || !_getSynthesizedConstructor(
-                           structDecl,
-                           ConstructorDecl::ConstructorFlavor::SynthesizedDefault))
+    if (!structDecl)
         return false;
 
     HashSet<Type*> isVisit;
-    bool isCStyle = isCStyleType(toType, isVisit);
+    bool isCStyle = false;
+    if (!_getSynthesizedConstructor(
+            structDecl,
+            ConstructorDecl::ConstructorFlavor::SynthesizedDefault))
+    {
+        // When a struct has no constructor and it's not a C-style type, the initializer list is
+        // invalid.
+        isCStyle = isCStyleType(toType, isVisit);
+
+        // WAR: We currently still has to allow legacy initializer list for array type until we have
+        // more proper solution for array initialization, so if the right hand side is an array
+        // type, we will not report error and fall-back to legacy initializer list logic.
+        bool isArrayType = as<ArrayExpressionType>(toType) != nullptr;
+        if (!isCStyle && !isArrayType)
+        {
+            getSink()->diagnose(
+                fromInitializerListExpr->loc,
+                Diagnostics::cannotUseInitializerListForType,
+                toType);
+        }
+
+        return false;
+    }
 
+    isCStyle = isCStyleType(toType, isVisit);
     // TODO: This is just a special case for a backwards-compatibility feature
     // for HLSL, this flag will imply that the initializer list is synthesized
     // for a type cast from a literal zero to a 'struct'. In this case, we will fall
diff --git a/source/slang/slang-check-decl.cpp b/source/slang/slang-check-decl.cpp
index 5ee8ba3ef..34143ad75 100644
--- a/source/slang/slang-check-decl.cpp
+++ b/source/slang/slang-check-decl.cpp
@@ -12412,7 +12412,7 @@ bool SemanticsDeclAttributesVisitor::_synthesizeCtorSignature(StructDecl* struct
     // any constructors. see:
     // https://github.com/shader-slang/slang/blob/master/docs/proposals/004-initialization.md#inheritance-initialization
     if (_hasExplicitConstructor(structDecl, true))
-        return false;
+        return true;
 
     // synthesize the signature first.
     // The constructor's visibility level is the same as the struct itself.