Add --validator-class option for passing a validator class #327
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This adds the necessary pieces for passing a custom validator class to check-jsonschema. `--fill-defaults` help text contains a hint that it may conflict (depending on the validator), to help warn of the potential for surprising interplay between a custom validator class and optional check-jsonschema behaviors. This commit only adds the interface pieces for passing the validator class to the CLI in a well-specified format, and handles the import/load of that value. No implementation in terms of threading the resulting value down to the validator(s) is included yet.
Implement the underlying arg-passing to set the `--validator-class` from CLI arguments when creating a SchemaLoader (the class used when `--schemafile` is used).
In order to better guarantee that `--validator-class` provides the name of a `jsonschema.protocols.Validator` class, require that the value passed is a type and not an alternative function. This requirement does not lose significant expressive power and allows us to more safely assume that the validator really is an implementation of the protocol which can be extended with `--fill-defaults` and other validator-related hooks. There is no real way to guarantee the safety of using the user's Validator. After all -- it could always raise an error at any time -- but this matches check-jsonschema's expectations about the argument better. This change can always be reverted in the future if there is significant demand for a function-as-a-validator-class option.
Using the mock_module fixture (lifted to top-level conftest), setup a custom validator which does some "real" validation work.
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--validator-classThe basics are all here, and this should resolve #262
For users seeing this, and for comparison with the old
jsonschemaCLIfeature, I have a few notes on the interface and some related topics:
--validator-classis the option name (there is no short opt)The syntax for specifying this is slightly different from
--validatorinthe old CLI -- you must separate your module name from your class name with
a colon, as in
foopkg.barmodule:MyValidator.This could be loosened to the purely dotted notation if there's a strong
argument for doing so, but the interface is simpler and cleaner with this
syntax, so please think critically about whether or not it's important
before asking for it to change.
As an example usage,
--validator-class 'jsonschema.validators.Draft3Validator'.There is no special case for the
jsonschemabuiltin validatorscheck-jsonschemahas a few features which expect the validator class tobe built only using the documented
jsonschemainterfaces. In particular:--fill-defaultsuses theextendAPI to modify the validator classreferencingregistry is used (rather thanRefResolver) and is passedon init
FORMAT_CHECKERon the--validator-classvalueUsages may change over time as
jsonschemaandcheck-jsonschemacontinueto evolve. Barring major issues, I do not intend to treat incompatibility
between a custom validator class and
check-jsonschemabehaviors as a bug.The above stated, if
check-jsonschemais doing something outside of thejsonschemaAPI contract and it causes issues with a custom validator, thatis a bug; please report any of those and we can get them fixed. :)
Within the scope of this change, no change is being made to the dependency
bounds being applied by
check-jsonschema. There will probably be somemeasure of change to make it easier to control dependency versions used, but
check-jsonschemaalso has pre-commit hook usage to consider, with its ownimplications about appropriate dependency specification
check-jsonschemacurrently will not callcheck_schemawhen using a customvalidator class (please open an issue if you would like this to change; it is
a point of flexibility based on user demand)
The CLI validation currently requires that the value be a
type, meaning ittypically has to be a proper python
class. The possibility of some callbackor alternative extension point is open if a well-reasoned proposal for some
secondary behavior can be made.
All of the decisions being made here about the interface, implicit API
contract, and expectations are subject to change if there's a good reason.
After all, this is an advanced feature for "power users".