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`check_preconditions(self, state, host)` is called on a bare `cls()` instance, while the arguments the fact was asked about stay in `fact_kwargs`. A fact that takes parameters therefore cannot use it: it has no way to tell which project, host or pool it is being asked about, which is what a precondition needs in order to check anything. The arguments now go with the call, named as the fact's `command` declares them. `self` is dropped first — `getcallargs` collects it alongside them, and `_make_command` drops it the same way before calling `command`. The signature ends in `*args, **kwargs`, as `requires_command`'s does, so an implementation may declare only what it needs: `(self, state, host)` stays valid, which is what the one existing implementation already writes, and `(self, state, host, pool=None)` becomes possible for a fact that depends on its own parameters. Naming the arguments explicitly would have forced every implementation, present and future, to accept a parameter it ignores. Worth having because the case it serves is a common one: a fact that reads a resource an earlier operation of the same deploy creates — a project, a pool, a namespace. pyinfra gathers facts before it runs any operation, so at that point the resource is not there yet; the fact's command fails, `state.fail_hosts()` drops the host, and the deploy is over before it ran anything. Silencing that during the prepare phase is exactly what `check_preconditions` is for, and it was out of reach for a fact with a parameter.
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check_preconditions(self, state, host)is called on a barecls()instance, while the arguments the fact was asked about stay infact_kwargs. A fact that takes parameters therefore cannot use it: it has no way to tell which project, host or pool it is being asked about, which is what a precondition needs in order to check anything.The arguments now go with the call, named as the fact's
commanddeclares them.selfis dropped first —getcallargscollects it alongside them, and_make_commanddrops it the same way before callingcommand.Nothing changes for a fact whose
commandtakes no parameters: it is called with no keyword arguments, which is whatZfsPools' implementation already expects.Worth having because the case it serves is a common one: a fact that reads a resource an earlier operation of the same deploy creates — a project, a pool, a namespace. pyinfra gathers facts before it runs any operation, so at that point the resource is not there yet; the fact's command fails,
state.fail_hosts()drops the host, and the deploy is over before it ran anything. Silencing that during the prepare phase is exactly whatcheck_preconditionsis for, and it was out of reach for a fact with a parameter.3.xat this time)scripts/dev-test.sh)scripts/dev-lint.sh)conventional commits format