Prompt self-templating

[yajo]

We need to go from:

# copier.yml
smtp_host: example.com
smtp_user: [email protected]

To:

# copier.yml
smtp_host: example.com
smtp_user: postmaster@[[smtp_host]]

[pykong]

Makes total sense to have it. This feature would make a nice addtion to copier.
I would accept a PR for it. ;-)

[pykong]

With:

smtp_user: "[[smtp_user]]@example.com"

I get the following prompt:

  smtp_user? Format: yaml
🎤 [[[smtp_user]]@example.com]: 

@yajo So, this is already implemented and we can close this issue now?

[yajo]

No, this is missing still. I noticed the description was misleading so I updated the example. It makes sense now 🤣

[yajo]

I moved this to next milestone, v3 seems ready to go for me.

[pawamoy]

I'd like to work on this, could you give me hints?

I guess the default value must be rendered using the previous answers in query_user_data, and that I should use code similar to Renderer.string method:

default = answers_data.get(question, details.get("default"))
tmpl = env.from_string(default)  # how do I get 'env'?
default = tmpl.render(**results)
answer = default

Question is: how do I get access to the Jinja env from within this function?

[yajo]

I bet you'd have to create a new env for each loop, because the values would differ as the user keeps answering.

In any case, you have to at least create a new temporary env, because the normal env is not created until we have all answers in place, and at this point we still don't have them.

Also you shouldn't just render default but all values in the question dict: default, help and maybe even choices (key and value in this case, if it's a dict).

One thing you have to think is that there could be templating errors if one answer is not yet given while asking the previous one.

You can take a look at #161 also, which depends on this one and shouldn't be very hard to implement once this is fixed.

🤔 This is trickier than it seems, but your help will be very appreciated! 😊 🙌

[pawamoy]

I bet you'd have to create a new env for each loop, because the values would differ as the user keeps answering.

I don't think so. You don't need a new env when the context changes. The env just contains the filters, some configuration, and templates loader (and in this case templates are strings). At each iteration, new values are added to results and these values are used as context to render the values for the next iteration.

In any case, you have to at least create a new temporary env, because the normal env is not created until we have all answers in place, and at this point we still don't have them.

OK!

Also you shouldn't just render default but all values in the question dict: default, help and maybe even choices (key and value in this case, if it's a dict).

Makes sense, I will try 🙂

One thing you have to think is that there could be templating errors if one answer is not yet given while asking the previous one.

I guess it's the user responsibility to write their copier.yml fields in the right order. We could indeed print a warning if the value is templated but was not rendered. Not sure if there's a Jinja method allowing to tell if a string is "templated" or not.

[yajo]

I guess it's the user responsibility to write their copier.yml fields in the right order.

I agree.

We could indeed print a warning if the value is templated but was not rendered. Not sure if there's a Jinja method allowing to tell if a string is "templated" or not.

That'd be nice. Gotta see if Jinja allows that. Otherwise, an exception would be acceptable for what you said before.

[pawamoy]

Otherwise, an exception would be acceptable for what you said before.

Oh silly me. In strict mode, if the string cannot be rendered (due to variables not being defined or else), it will trigger an exception. That's how we'll know. For some reason when writing this I was thinking that, if the string couldn't be rendered, it would be returned as-is, but it's not true. Instead it would be returned empty (or partially empty), and that would be hard to detect.

Strict mode it is! And catch the exception to abort and print a readable warning?

[yajo]

And catch the exception to abort and print a readable warning?

Just reraise it as copier.config.objects.UserMessageError and it should be enough.