Marking hookspec as requiring at least one implementation

[MrGreenTea]

Marking hookspec as requiring at least one implementation

[nicoddemus]

I don't think there's support for that currently, but one workaround might for your plugin to implement the hook and return some sentinel object. When you call the hook implementation, you then might check if the call returned only [sentinel] which means only your call was implemented and treat that accordingly.

[MrGreenTea]

I implemented that functionality, but am unsure how to name the parameter.
requireimplementation=True is very long and not as readable as I would like, require_implementation=True is inconsistent with the other parameter firstresult.
I named it requireimpl for now, because of HookImplMarker and it often being assigned to hookimpl.

What do you/others think?

[nicoddemus]

How about required=True?

[hoefling]

@nicoddemus:

When you call the hook implementation, you then might check if the call returned only [sentinel] which means only your call was implemented and treat that accordingly.

This means that it's not possible to validate plugin availability without their implicit execution?

[MrGreenTea]

required=True sounds good, but I feel is not telling enough what exactly is required.

@hoefling Do you mean hook implementations? There is a has_plugin method for checking plugin availability.

[nicoddemus]

IMHO:

@hookspec(required=True)
def my_hook():

Is clear enough, but that's just me. requireimpl sounds fine as well, although I like my suggestion better. 😁

[MrGreenTea]

I would love to hear another opinion on this, though I agree with you that required looks nicer :)

[hoefling]

@MrGreenTea:

Do you mean hook implementations?

Sure, my bad.

[hpk42]

I am with hoefling on that required=True does not convey much meaning.

Moreover, i am skeptical of putting this into the hookspec. I'd rather like to have another runtime-API like my_hook.has_implementations() returning True or False. In several projects using pluggy i've never had the need for asserting that a hook must have implementations FWIW.

[MrGreenTea]

I believe having it in the actual hook definition makes it easier to see what hooks require an implementation. Having to find the places where the hook is called and checking if their is a check for my_hook.has_implementation() sounds unnecessary when developing plugins. It also adheres to the principle of EAFP.

We plan on using pluggy to allow easy interchangability of parts of the system, also for some "core functionality" of the whole system. That's where I believe an explicit error will help in development and testing.

[RonnyPfannschmidt]

why is it a problem to begin with if certain hooks have no implementation at all?

@MrGreenTea do you have a minimal example that illustrates this, both @hpk42 and me have a very different perspective on the issue/usage and may be completely missing your point without a painfully oblivious illustration

[hpk42]

I am closing this as i don't see enough rationale yet for adding something to hookspec. I'd like to keep pluggy minimal especially wrt to hookspec. I hold that something like assert hook.has_implementations() would be sufficient and simpler to understand directly at the calling site of the hook. @MrGreenTea feel free to add a PR along those lines and thanks for your efforts so far!