Please point me to an "old" model that was able to do something similar to my example, and was general enough to do that not only for any custom schema, but for basically all often used languages as well (both natural languages as input, and programming languages as output).
It's possible to start with tests and then generate the code, using tests to ensure it is correct. Humans iterate many times on a piece of code - write, execute, compare with your desired output, AI should work step by step with executions and feedback too.