feature request: Check that templates exist on route creation

[JacobHayes]

Hi, thanks for the cool library! One thing I've been wanting is eager validation that the referenced templates exist when the route is defined, rather than when run. Simple name references would check that the path exists; ComponentHeader would iterate over the templates and check as above; arbitrary RequestComponentSelector may just be a no-op (or add an optional method to run some validation).

I otherwise use a Path for my templates dir and was previously referencing templates with templates_path / "template.html" and would check for .exists().

[volfpeter]

Hi,

Yeah, it's quite common with Jinja to for example mistype the template name, because the lack of IDE support and static analysis. This is why for new projects I actually recommend (and use) htmy instead.

Note that you can also mistype template names in your Jinja templates (imports, includes, extends), which can not be validated without rendering the templates, so a pre-flight check like you described may in fact give you a false sense of security.

Nevertheless, I see some utility in this request, so I think it is something that could be added to the library if others need it as well.

[volfpeter]

@JacobHayes I've been going over the issues, and while reading the description of this one, it came to my mind that this feature doesn't really require any change in the library, because the logic can be placed inside a RequestComponentSelector implementation.

Here is the (partially typed) pseudo-code for such a component selector:

@dataclass
class EagerJinjaComponentSelector:
    templates: dict[str, str]

    def __post_init__(self):
        for key, path in template.items():
            # TODO: check if template exists and raise ValueError if it doesn't
            ...

    def get_component(self, request: Request, error: Exception | None) -> str:
        template_path = ""  # TODO
        return template_template_path

Please let me know what you think about such a solution. A more generic implementation would wrap a component selector to make it easy to combine eager validation with any template selection logic.

As the library seems to support this use-case, I'd convert this issue to a discussion, so others can find it more easily. Would that be okay for you?