template arg opt-in

[amitu]

From Discord chat:

One problem with our template design is that we can not retroactively add more arguments to the template function 😦

If you need dynamic argument like first-name you are out of luck, if we did not include it in first version, we can not include it in future.

We will have to make our template feature accept unknown keywords and ignore them, we should only allow interpolation for declared variables, to get type safety. This would be enough for future compatibility, this also allows us to have 100s of dynamic variables, but not force template authors to list each of them down, only the ones they care to use should be listed.

Basically when we are calling a template, we can pass more arguments than what template accepts, extra arguments will be ignored, no error will be raised. If any of those arguments are to be used, the template must define them. Further our module interface checker, which verifies if given template is compatible with the interface template, will ensure that the arguments to a provided template match with and are a subset of the original template.