Enhancement - Simplify creation of configuration object about copier HOT 5 CLOSED

@jpscaletti Can you see this issue I described and would be open to a PR which will give us a simpler more robust code? (Still passing all tests of course ;-) )

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Memo:

I really like how pydantic offers both validation and providing default values at the same time.
We could use this to first merge args provided by command line, configuration files and potentially environment variables and then validate against a defined scheme which will at the same time fill out all None values with defaults. Very powerful. Very elegant.

https://github.com/samuelcolvin/pydantic#a-simple-example

This is all done using the modern type hint syntax. Unfortunately, this means we will not be able to use pydantic for copier as we still support py 3.5.

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I agree, this definetely could improve. As you said, here is too much code duplication.

About pydantic and validation, I don't think it is generally applicable enough to justify it.

from copier.

I agree, this definetely could improve. As you said, here is too much code duplication.

Great. I am working on a PR right now.

About pydantic and validation, I don't think it is generally applicable enough to justify it.

I am referring to our own variables, not any arbitrary setting a user might define.
For example we might check that extra_paths is actually a list of (valid) paths and quiet is a bool.
I consider it best practice to validate user input at a single place before feeding it into the deeper strata of a program. (It makes error handling easier and allows for easier way to provide feedback to the user.

As we are stuck with python 3.5 I need to find an alternative lib to pydantic or implement an own validation routine.

Do you concur that we should perform a basic validation of the user input at least?

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