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.

1 files changed, 6 insertions, 1 deletions

diff --git a/tests/language-feature/interfaces/default-construct-conformance.slang b/tests/language-feature/interfaces/default-construct-conformance.slang
index 4a6aed869..b68dc8a4c 100644
--- a/tests/language-feature/interfaces/default-construct-conformance.slang
+++ b/tests/language-feature/interfaces/default-construct-conformance.slang
@@ -33,6 +33,11 @@ struct TestAny : ITest
         value = v;
     }
 
+    __init()
+    {
+        value = 0;
+    }
+
     uint getValue() { return value; }
 }
 
@@ -183,4 +188,4 @@ void testMain(uint3 threadID: SV_DispatchThreadID)
     }
 
     expected[outputIdx++] = uint(-1);
-}
\ No newline at end of file
+}