Fix Self substitution for generics

trans/transpiler/phases/typing/expr.py

@@ -104,7 +104,7 @@ class ScoperExprVisitor(ScoperVisitor):
     def visit_Call(self, node: ast.Call) -> BaseType:
         ftype = self.visit(node.func)
         if ftype.typevars:
-            ftype = ftype.gen_sub(ftype, {v.name: TypeVariable(v.name) for v in ftype.typevars})
+            ftype = ftype.gen_sub(None, {v.name: TypeVariable(v.name) for v in ftype.typevars})
         rtype = self.visit_function_call(ftype, [self.visit(arg) for arg in node.args])
         actual = rtype
         node.is_await = False

trans/transpiler/phases/typing/types.py

@@ -345,8 +345,9 @@ class TypeType(TypeOperator):
 
 TY_SELF = TypeOperator.make_type("Self")
 def self_gen_sub(this, typevars, _):
-    assert this is not None
-    return this
+    if this is not None:
+        return this
+    return TY_SELF
 TY_SELF.gen_sub = self_gen_sub
 TY_BOOL = TypeOperator.make_type("bool")
 DEFAULT_EQ = FunctionType([TY_SELF, TY_SELF], TY_BOOL)