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bevy/crates/bevy_derive/compile_fail/README.md

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bevy_derive: Add `#[deref]` attribute (#8552) # Objective Bevy code tends to make heavy use of the [newtype]( https://doc.rust-lang.org/rust-by-example/generics/new_types.html) pattern, which is why we have a dedicated derive for [`Deref`](https://doc.rust-lang.org/std/ops/trait.Deref.html) and [`DerefMut`](https://doc.rust-lang.org/std/ops/trait.DerefMut.html). This derive works for any struct with a single field: ```rust #[derive(Component, Deref, DerefMut)] struct MyNewtype(usize); ``` One reason for the single-field limitation is to prevent confusion and footguns related that would arise from allowing multi-field structs: <table align="center"> <tr> <th colspan="2"> Similar structs, different derefs </th> </tr> <tr> <td> ```rust #[derive(Deref, DerefMut)] struct MyStruct { foo: usize, // <- Derefs usize bar: String, } ``` </td> <td> ```rust #[derive(Deref, DerefMut)] struct MyStruct { bar: String, // <- Derefs String foo: usize, } ``` </td> </tr> <tr> <th colspan="2"> Why `.1`? </th> </tr> <tr> <td colspan="2"> ```rust #[derive(Deref, DerefMut)] struct MyStruct(Vec<usize>, Vec<f32>); let mut foo = MyStruct(vec![123], vec![1.23]); // Why can we skip the `.0` here? foo.push(456); // But not here? foo.1.push(4.56); ``` </td> </tr> </table> However, there are certainly cases where it's useful to allow for structs with multiple fields. Such as for structs with one "real" field and one `PhantomData` to allow for generics: ```rust #[derive(Deref, DerefMut)] struct MyStruct<T>( // We want use this field for the `Deref`/`DerefMut` impls String, // But we need this field so that we can make this struct generic PhantomData<T> ); // ERROR: Deref can only be derived for structs with a single field // ERROR: DerefMut can only be derived for structs with a single field ``` Additionally, the possible confusion and footguns are mainly an issue for newer Rust/Bevy users. Those familiar with `Deref` and `DerefMut` understand what adding the derive really means and can anticipate its behavior. ## Solution Allow users to opt into multi-field `Deref`/`DerefMut` derives using a `#[deref]` attribute: ```rust #[derive(Deref, DerefMut)] struct MyStruct<T>( // Use this field for the `Deref`/`DerefMut` impls #[deref] String, // We can freely include any other field without a compile error PhantomData<T> ); ``` This prevents the footgun pointed out in the first issue described in the previous section, but it still leaves the possible confusion surrounding `.0`-vs-`.#`. However, the idea is that by making this behavior explicit with an attribute, users will be more aware of it and can adapt appropriately. --- ## Changelog - Added `#[deref]` attribute to `Deref` and `DerefMut` derives
2023-05-16 18:29:09 +00:00
# Compile fail tests for Bevy macros
This crate is not part of the Bevy workspace in order to not fail `crater` tests for Bevy.
The tests assert on the exact compiler errors and can easily fail for new Rust versions due to updated compiler errors (e.g. changes in spans).
Move compile fail tests (#13196) # Objective - Follow-up of #13184 :) - We use `ui_test` to test compiler errors for our custom macros. - There are four crates related to compile fail tests - `bevy_ecs_compile_fail_tests`, `bevy_macros_compile_fail_tests`, and `bevy_reflect_compile_fail_tests`, which actually test the macros. - [`bevy_compile_test_utils`](https://github.com/bevyengine/bevy/tree/64c1c65783938facc59d9b36cbaa6deba435d84e/crates/bevy_compile_test_utils), which provides helpers and common patterns for these tests. - All of these crates reside within the `crates` directory. - This can be confusing, especially for newcomers. All of the other folders in `crates` are actual published libraries, except for these 4. ## Solution - Move all compile fail tests to a `compile_fail` folder under their corresponding crate. - E.g. `crates/bevy_ecs_compile_fail_tests` would be moved to `crates/bevy_ecs/compile_fail`. - Move `bevy_compile_test_utils` to `tools/compile_fail_utils`. There are a few benefits to this approach: 1. An internal testing detail is less intrusive (and confusing) for those who just want to browse the public Bevy interface. 2. Follows a pre-existing approach of organizing related crates inside a larger crate's folder. - See `bevy_gizmos/macros` for an example. 4. Makes consistent the terms `compile_test`, `compile_fail`, and `compile_fail_test` in code. It's all just `compile_fail` now, because we are specifically testing the error messages on compiler failures. - To be clear it can still be referred to by these terms in comments and speech, just the names of the crates and the CI command are now consistent. ## Testing Run the compile fail CI command: ```shell cargo run -p ci -- compile-fail ``` If it still passes, then my refactor was successful.
2024-05-03 13:35:21 +00:00
The `CI` workflow executes these tests on the stable rust toolchain (see [tools/ci](../../../tools/ci/src/main.rs)).
Switch to ui_test in compile fail tests. (#12810) # Objective Make compile fail tests less likely to break with new Rust versions. Closes #12627 ## Solution Switch from [`trybuild`](https://github.com/dtolnay/trybuild) to [`ui_test`](https://github.com/oli-obk/ui_test). ## TODO - [x] Update `bevy_ecs_compile_fail_tests` - [x] Update `bevy_macros_compile_fail_tests` - [x] Update `bevy_reflect_compile_fail_tests` --------- Co-authored-by: Oli Scherer <github35764891676564198441@oli-obk.de> Co-authored-by: BD103 <59022059+BD103@users.noreply.github.com>
2024-04-27 00:00:57 +00:00
Move compile fail tests (#13196) # Objective - Follow-up of #13184 :) - We use `ui_test` to test compiler errors for our custom macros. - There are four crates related to compile fail tests - `bevy_ecs_compile_fail_tests`, `bevy_macros_compile_fail_tests`, and `bevy_reflect_compile_fail_tests`, which actually test the macros. - [`bevy_compile_test_utils`](https://github.com/bevyengine/bevy/tree/64c1c65783938facc59d9b36cbaa6deba435d84e/crates/bevy_compile_test_utils), which provides helpers and common patterns for these tests. - All of these crates reside within the `crates` directory. - This can be confusing, especially for newcomers. All of the other folders in `crates` are actual published libraries, except for these 4. ## Solution - Move all compile fail tests to a `compile_fail` folder under their corresponding crate. - E.g. `crates/bevy_ecs_compile_fail_tests` would be moved to `crates/bevy_ecs/compile_fail`. - Move `bevy_compile_test_utils` to `tools/compile_fail_utils`. There are a few benefits to this approach: 1. An internal testing detail is less intrusive (and confusing) for those who just want to browse the public Bevy interface. 2. Follows a pre-existing approach of organizing related crates inside a larger crate's folder. - See `bevy_gizmos/macros` for an example. 4. Makes consistent the terms `compile_test`, `compile_fail`, and `compile_fail_test` in code. It's all just `compile_fail` now, because we are specifically testing the error messages on compiler failures. - To be clear it can still be referred to by these terms in comments and speech, just the names of the crates and the CI command are now consistent. ## Testing Run the compile fail CI command: ```shell cargo run -p ci -- compile-fail ``` If it still passes, then my refactor was successful.
2024-05-03 13:35:21 +00:00
For information on writing tests see [compile_fail_utils/README.md](../../../tools/compile_fail_utils/README.md).
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