2 files changed, 68 insertions, 4 deletions

diff --git a/source/core/exception.h b/source/core/exception.h
index 6739c6778..dc674de7f 100644
--- a/source/core/exception.h
+++ b/source/core/exception.h
@@ -110,6 +110,13 @@ namespace Slang
 		{
 		}
 	};
+
+    #define SLANG_UNEXPECTED(reason) \
+        throw Slang::Exception("unexpected: " reason)
+
+    #define SLANG_UNIMPLEMENTED_X(what) \
+        throw Slang::NotImplementedException("unimplemented: " what)
+
 }
 
 #endif
\ No newline at end of file
diff --git a/source/slang/lower.cpp b/source/slang/lower.cpp
index e03fd878b..8a732467c 100644
--- a/source/slang/lower.cpp
+++ b/source/slang/lower.cpp
@@ -826,11 +826,68 @@ struct LoweringVisitor
     }
 
     // Catch-all
-    RefPtr<Decl> visit(
-        Decl* decl)
+
+    RefPtr<Decl> visit(ModifierDecl*)
     {
-        assert(!"unimplemented");
-        return decl;
+        // should not occur in user code
+        SLANG_UNEXPECTED("modifiers shouldn't occur in user code");
+    }
+
+    RefPtr<Decl> visit(GenericValueParamDecl*)
+    {
+        SLANG_UNEXPECTED("generics should be lowered to specialized decls");
+    }
+
+    RefPtr<Decl> visit(GenericTypeParamDecl*)
+    {
+        SLANG_UNEXPECTED("generics should be lowered to specialized decls");
+    }
+
+    RefPtr<Decl> visit(GenericTypeConstraintDecl*)
+    {
+        SLANG_UNEXPECTED("generics should be lowered to specialized decls");
+    }
+
+    RefPtr<Decl> visit(GenericDecl*)
+    {
+        SLANG_UNEXPECTED("generics should be lowered to specialized decls");
+    }
+
+    RefPtr<Decl> visit(ProgramSyntaxNode*)
+    {
+        SLANG_UNEXPECTED("module decls should be lowered explicitly");
+    }
+
+    RefPtr<Decl> visit(SubscriptDecl*)
+    {
+        // We don't expect to find direct references to a subscript
+        // declaration, but rather to the underlying accessors
+        return nullptr;
+    }
+
+    RefPtr<Decl> visit(InheritanceDecl*)
+    {
+        // We should deal with these explicitly, as part of lowering
+        // the type that contains them.
+        return nullptr;
+    }
+
+    RefPtr<Decl> visit(ExtensionDecl*)
+    {
+        // Extensions won't exist in the lowered code: their members
+        // will turn into ordinary functions that get called explicitly
+        return nullptr;
+    }
+
+    RefPtr<Decl> visit(TypeDefDecl* decl)
+    {
+        RefPtr<TypeDefDecl> loweredDecl = new TypeDefDecl();
+        lowerDeclCommon(loweredDecl, decl);
+
+        loweredDecl->Type = lowerType(decl->Type);
+
+        addMember(shared->loweredProgram, loweredDecl);
+        return loweredDecl;
     }
 
     RefPtr<ImportDecl> visit(ImportDecl* decl)