Improve error message for missing events #18683
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alice-i-cecile
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kristoff3r
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alice-i-cecile
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Lovely! @Bleachfuel, would you be able to give me a quick review here? I've really appreciated your macro expertise.
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LGTM! However maybe we should merge #18199 first as it makes this code more reasonable, since we now are doing all kinds of stuff inside one iter()
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# Objective Improve the parameter validation error message for `Event(Reader|Writer|Mutator)`. System parameters defined using `#[derive(SystemParam)]`, including the parameters for events, currently propagate the validation errors from their subparameters. The error includes the type of the failing parameter, so the resulting error includes the type of the failing subparameter instead of the derived parameter. In particular, `EventReader<T>` will report an error from a `Res<Events<T>>`, even though the user has no parameter of that type! This is a follow-up to #18593. ## Solution Have `#[derive]`d system parameters map errors during propagation so that they report the outer parameter type. To continue to provide context, add a field to `SystemParamValidationError` that identifies the subparameter by name, and is empty for non-`#[derive]`d parameters. Allow them to override the failure message for individual parameters. Use this to convert "Resource does not exist" to "Event not initialized" for `Event(Reader|Writer|Mutator)`. ## Showcase The validation error for a `EventReader<SomeEvent>` parameter when `add_event` has not been called changes from: Before: ``` Parameter `Res<Events<SomeEvent>>` failed validation: Resource does not exist ``` After ``` Parameter `EventReader<SomeEvent>::events` failed validation: Event not initialized ```
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Objective
Improve the parameter validation error message for
Event(Reader|Writer|Mutator).System parameters defined using
#[derive(SystemParam)], including the parameters for events, currently propagate the validation errors from their subparameters. The error includes the type of the failing parameter, so the resulting error includes the type of the failing subparameter instead of the derived parameter.In particular,
EventReader<T>will report an error from aRes<Events<T>>, even though the user has no parameter of that type!This is a follow-up to #18593.
Solution
Have
#[derive]d system parameters map errors during propagation so that they report the outer parameter type.To continue to provide context, add a field to
SystemParamValidationErrorthat identifies the subparameter by name, and is empty for non-#[derive]d parameters.Allow them to override the failure message for individual parameters. Use this to convert "Resource does not exist" to "Event not initialized" for
Event(Reader|Writer|Mutator).Showcase
The validation error for a
EventReader<SomeEvent>parameter whenadd_eventhas not been called changes from:Before:
After