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Merged
merged 3 commits into from
Mar 30, 2025
Merged

Improve error message for missing resources #18593

merged 3 commits into from
Mar 30, 2025

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chescock
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Objective

Fixes #18515

After the recent changes to system param validation, the panic message for a missing resource is currently:

Encountered an error in system `missing_resource_error::res_system`: SystemParamValidationError { skipped: false }

Add the parameter type name and a descriptive message, improving the panic message to:

Encountered an error in system `missing_resource_error::res_system`: SystemParamValidationError { skipped: false, message: "Resource does not exist", param: "bevy_ecs::change_detection::Res<missing_resource_error::MissingResource>" }

Solution

Add fields to SystemParamValidationError for error context. Include the type_name of the param and a message.

Store them as Cow<'static, str> and only format them into a friendly string in the Display impl. This lets us create errors using a &'static str with no allocation or formatting, while still supporting runtime String values if necessary.

Add a unit test that verifies the panic message.

Future Work

If we change the default error handling to use Display instead of Debug, and to use ShortName for the system name, the panic message could be further improved to:

Encountered an error in system `res_system`: Parameter `Res<MissingResource>` failed validation: Resource does not exist

However, BevyError currently includes the backtrace in Debug but not Display, and I didn't want to try to change that in this PR.

@chescock chescock added A-ECS Entities, components, systems, and events C-Usability A targeted quality-of-life change that makes Bevy easier to use S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels Mar 28, 2025
@chescock chescock added this to the 0.16 milestone Mar 28, 2025
alice-i-cecile
alice-i-cecile approved these changes Mar 30, 2025
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Thanks for polishing this up: this is important follow-up that I deliberately punted on :) I think I agree that it would be irresponsible to ship without this.

@alice-i-cecile alice-i-cecile added S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it and removed S-Needs-Review Needs reviewer attention (from anyone!) to move forward labels Mar 30, 2025
@alice-i-cecile alice-i-cecile added this pull request to the merge queue Mar 30, 2025
Merged via the queue into bevyengine:main with commit 30ee5ff Mar 30, 2025
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mockersf pushed a commit that referenced this pull request Mar 30, 2025
@chescock @mockersf
Improve error message for missing resources (#18593)
ac04ec0 
# Objective

Fixes #18515 

After the recent changes to system param validation, the panic message
for a missing resource is currently:

```
Encountered an error in system `missing_resource_error::res_system`: SystemParamValidationError { skipped: false }
```

Add the parameter type name and a descriptive message, improving the
panic message to:

```
Encountered an error in system `missing_resource_error::res_system`: SystemParamValidationError { skipped: false, message: "Resource does not exist", param: "bevy_ecs::change_detection::Res<missing_resource_error::MissingResource>" }
```

## Solution

Add fields to `SystemParamValidationError` for error context. Include
the `type_name` of the param and a message.

Store them as `Cow<'static, str>` and only format them into a friendly
string in the `Display` impl. This lets us create errors using a
`&'static str` with no allocation or formatting, while still supporting
runtime `String` values if necessary.

Add a unit test that verifies the panic message.

## Future Work

If we change the default error handling to use `Display` instead of
`Debug`, and to use `ShortName` for the system name, the panic message
could be further improved to:

```
Encountered an error in system `res_system`: Parameter `Res<MissingResource>` failed validation: Resource does not exist
```

However, `BevyError` currently includes the backtrace in `Debug` but not
`Display`, and I didn't want to try to change that in this PR.
@chescock chescock mentioned this pull request Mar 30, 2025
Merged
github-merge-queue bot pushed a commit that referenced this pull request Mar 31, 2025
@chescock
Use Display instead of Debug in the default error handler (#18629)
b4614da 
# Objective

Improve error messages for missing resources.  

The default error handler currently prints the `Debug` representation of
the error type instead of `Display`. Most error types use
`#[derive(Debug)]`, resulting in a dump of the structure, but will have
a user-friendly message for `Display`.

Follow-up to #18593

## Solution

Change the default error handler to use `Display` instead of `Debug`.  

Change `BevyError` to include the backtrace in the `Display` format in
addition to `Debug` so that it is still included.

## Showcase

Before: 

```
Encountered an error in system `system_name`: SystemParamValidationError { skipped: false, message: "Resource does not exist", param: "bevy_ecs::change_detection::Res<app_name::ResourceType>" }

Encountered an error in system `other_system_name`: "String message with\nmultiple lines."
```

After

```
Encountered an error in system `system_name`: Parameter `Res<ResourceType>` failed validation: Resource does not exist

Encountered an error in system `other_system_name`: String message with
multiple lines.
```
mockersf pushed a commit that referenced this pull request Mar 31, 2025
@chescock @mockersf
Use Display instead of Debug in the default error handler (#18629)
d5c5de2 
# Objective

Improve error messages for missing resources.  

The default error handler currently prints the `Debug` representation of
the error type instead of `Display`. Most error types use
`#[derive(Debug)]`, resulting in a dump of the structure, but will have
a user-friendly message for `Display`.

Follow-up to #18593

## Solution

Change the default error handler to use `Display` instead of `Debug`.  

Change `BevyError` to include the backtrace in the `Display` format in
addition to `Debug` so that it is still included.

## Showcase

Before: 

```
Encountered an error in system `system_name`: SystemParamValidationError { skipped: false, message: "Resource does not exist", param: "bevy_ecs::change_detection::Res<app_name::ResourceType>" }

Encountered an error in system `other_system_name`: "String message with\nmultiple lines."
```

After

```
Encountered an error in system `system_name`: Parameter `Res<ResourceType>` failed validation: Resource does not exist

Encountered an error in system `other_system_name`: String message with
multiple lines.
```
@chescock chescock mentioned this pull request Apr 2, 2025
Merged
github-merge-queue bot pushed a commit that referenced this pull request Apr 2, 2025
@chescock
Improve error message for missing events (#18683)
9e240ee 
# 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
```
mockersf pushed a commit that referenced this pull request Apr 3, 2025
@chescock @mockersf
Improve error message for missing events (#18683)
ed28b5c 
# 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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A-ECS Entities, components, systems, and events C-Usability A targeted quality-of-life change that makes Bevy easier to use S-Ready-For-Final-Review This PR has been approved by the community. It's ready for a maintainer to consider merging it
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Return the failed system parameter(s) in SystemParamValidationError
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