feat: added the ability to provide another Compiler

[PhilipGarnero]

Hi !

I've simply moved _Compiler to another module and renamed it to Compiler as it's now public.
I've also added a compiler parameter to XMLTemplate that default to Compiler.

The behavior is unchanged by default but now, devs can inherit from Compiler to add features and new nodes.

I'm already using this fork in production so i'll appreciate if that's merged soon.

Thanks !

[amol-]

Personally I think it would be helpful to understand the use case. I'm not arguing against the PR, but there might be a better API to achieve the needs that we are trying to solve compared to making public a previously internal class (as internal classes aren't exactly designed with the idea of being used or subclasses usually)

[PhilipGarnero]

The usecase is pretty simple : I want to be able to extend kajiki's core functionalities.

In our case, we've developed a library of components that we want to be able to use like html tags.
The components are pydantic models (to validate their inputs) that point to a kajiki fragment.
We are calling them like so directly inside our templates :

<MyComponent attr="cool" />
<MyComponent>This is some content</MyComponent>

This will call the MyComponent model with the correct argument which will do some logic and then we render it using its fragment.

With this extensibility feature, we can add pretty much what we want to kajiki without polluting the library with our personal uses.

Of course, things we'd think would be useful to the community would come as a PR 😉

[jackrosenthal]

I will try and complete this code review by the end of the week, I apologize for the delay.

[amol-]

I think we should design a public API for extending the Compiler, allow adding custom tags by registering a function that handles them. Making an internal implementation class that wasn't designed to be public doesn't seem the best course of action. Also in general subclassing isn't a very flexible extension mechanism (imagine you have multiple custom tags coming from different Python packages, you wouldn't be able to easily add them all to the Compiler)