Check decl nesting for namespaces. (#5910)

Author: csyonghe

source/slang/slang-parser.cpp

@@ -4634,14 +4634,6 @@ static void CompleteDecl(
     ContainerDecl* containerDecl,
     Modifiers modifiers)
 {
-
-    // If this is a namespace and already added, we don't want to add to the parent
-    // Or add any modifiers
-    if (as<NamespaceDecl>(decl) && decl->parentDecl)
-    {
-        return;
-    }
-
     // Add any modifiers we parsed before the declaration to the list
     // of modifiers on the declaration itself.
     //
@@ -4699,6 +4691,13 @@ static void CompleteDecl(
             }
         }
 
+        // If this is a namespace and already added, we don't want to add to the parent
+        // Or add any modifiers
+        if (as<NamespaceDecl>(decl) && decl->parentDecl)
+        {
+            return;
+        }
+
         if (!as<GenericDecl>(containerDecl))
         {
             // Make sure the decl is properly nested inside its lexical parent

tests/diagnostics/invalid-namespace-nesting.slang

@@ -0,0 +1,7 @@
+//DIAGNOSTIC_TEST:SIMPLE(filecheck=CHECK): -target spirv
+
+struct Type
+{
+    // CHECK: ([[# @LINE+1]]): error 30102:
+    namespace ns {}
+}