# Objective
The current `QueryData` derive panics when it encounters an error.
Additionally, it doesn't provide the clearest error message:
```rust
#[derive(QueryData)]
#[query_data(mut)]
struct Foo {
// ...
}
```
```
error: proc-macro derive panicked
--> src/foo.rs:16:10
|
16 | #[derive(QueryData)]
| ^^^^^^^^^
|
= help: message: Invalid `query_data` attribute format
```
## Solution
Updated the derive logic to not panic and gave a bit more detail in the
error message.
This is makes the error message just a bit clearer and maintains the
correct span:
```
error: invalid attribute, expected `mutable` or `derive`
--> src/foo.rs:17:14
|
17 | #[query_data(mut)]
| ^^^
```
## Testing
You can test locally by running the following in
`crates/bevy_ecs/compile_fail`:
```
cargo test --target-dir ../../../target
```
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