Commit Graph

25 Commits

Author SHA1 Message Date
Gino Valente
ccb9d0500f
bevy_reflect: Recursive registration (#5781)
# Objective

Resolves #4154

Currently, registration must all be done manually:

```rust
#[derive(Reflect)]
struct Foo(Bar);

#[derive(Reflect)]
struct Bar(Baz);

#[derive(Reflect)]
struct Baz(usize);

fn main() {
  // ...
  app
    .register_type::<Foo>()
    .register_type::<Bar>()
    .register_type::<Baz>()
    // .register_type::<usize>() <- This one is handled by Bevy, thankfully
  // ...
}
```

This can grow really quickly and become very annoying to add, remove,
and update as types change. It would be great if we could help reduce
the number of types that a user must manually implement themselves.

## Solution

As suggested in #4154, this PR adds automatic recursive registration.
Essentially, when a type is registered, it may now also choose to
register additional types along with it using the new
`GetTypeRegistration::register_type_dependencies` trait method.

The `Reflect` derive macro now automatically does this for all fields in
structs, tuple structs, struct variants, and tuple variants. This is
also done for tuples, arrays, `Vec<T>`, `HashMap<K, V>`, and
`Option<T>`.

This allows us to simplify the code above like:

```rust
#[derive(Reflect)]
struct Foo(Bar);

#[derive(Reflect)]
struct Bar(Baz);

#[derive(Reflect)]
struct Baz(usize);

fn main() {
  // ...
  app.register_type::<Foo>()
  // ...
}
```

This automatic registration only occurs if the type has not yet been
registered. If it has been registered, we simply skip it and move to the
next one. This reduces the cost of registration and prevents overwriting
customized registrations.

## Considerations

While this does improve ergonomics on one front, it's important to look
at some of the arguments against adopting a PR like this.

#### Generic Bounds

~~Since we need to be able to register the fields individually, we need
those fields to implement `GetTypeRegistration`. This forces users to
then add this trait as a bound on their generic arguments. This
annoyance could be relieved with something like #5772.~~

This is no longer a major issue as the `Reflect` derive now adds the
`GetTypeRegistration` bound by default. This should technically be okay,
since we already add the `Reflect` bound.

However, this can also be considered a breaking change for manual
implementations that left out a `GetTypeRegistration` impl ~~or for
items that contain dynamic types (e.g. `DynamicStruct`) since those also
do not implement `GetTypeRegistration`~~.

#### Registration Assumptions

By automatically registering fields, users might inadvertently be
relying on certain types to be automatically registered. If `Foo`
auto-registers `Bar`, but `Foo` is later removed from the code, then
anywhere that previously used or relied on `Bar`'s registration would
now fail.

---

## Changelog

- Added recursive type registration to structs, tuple structs, struct
variants, tuple variants, tuples, arrays, `Vec<T>`, `HashMap<K, V>`, and
`Option<T>`
- Added a new trait in the hidden `bevy_reflect::__macro_exports` module
called `RegisterForReflection`
- Added `GetTypeRegistration` impl for
`bevy_render::render_asset::RenderAssetUsages`

## Migration Guide

All types that derive `Reflect` will now automatically add
`GetTypeRegistration` as a bound on all (unignored) fields. This means
that all reflected fields will need to also implement
`GetTypeRegistration`.

If all fields **derive** `Reflect` or are implemented in `bevy_reflect`,
this should not cause any issues. However, manual implementations of
`Reflect` that excluded a `GetTypeRegistration` impl for their type will
need to add one.

```rust
#[derive(Reflect)]
struct Foo<T: FromReflect> {
  data: MyCustomType<T>
}

// OLD
impl<T: FromReflect> Reflect for MyCustomType<T> {/* ... */}

// NEW
impl<T: FromReflect + GetTypeRegistration> Reflect for MyCustomType<T> {/* ... */}
impl<T: FromReflect + GetTypeRegistration> GetTypeRegistration for MyCustomType<T> {/* ... */}
```

---------

Co-authored-by: James Liu <contact@jamessliu.com>
Co-authored-by: radiish <cb.setho@gmail.com>
Co-authored-by: Carter Anderson <mcanders1@gmail.com>
2024-03-04 19:04:10 +00:00
Ame
9d67edc3a6
fix some typos (#12038)
# Objective

Split - containing only the fixed typos

-
https://github.com/bevyengine/bevy/pull/12036#pullrequestreview-1894738751


# Migration Guide
In `crates/bevy_mikktspace/src/generated.rs` 

```rs
// before
pub struct SGroup {
    pub iVertexRepresentitive: i32,
    ..
}

// after
pub struct SGroup {
    pub iVertexRepresentative: i32,
    ..
}
```

In `crates/bevy_core_pipeline/src/core_2d/mod.rs`

```rs
// before
Node2D::ConstrastAdaptiveSharpening

// after
Node2D::ContrastAdaptiveSharpening
```

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: James Liu <contact@jamessliu.com>
Co-authored-by: François <mockersf@gmail.com>
2024-02-22 18:55:22 +00:00
Gino Valente
9e30aa7c92
bevy_reflect_derive: Clean up attribute logic (#11777)
# Objective

The code in `bevy_reflect_derive` could use some cleanup.

## Solution

Took some of the changes in #11659 to create a dedicated PR for cleaning
up the field and container attribute logic.

#### Updated Naming

I renamed `ReflectTraits` and `ReflectFieldAttr` to
`ContainerAttributes` and `FieldAttributes`, respectively. I think these
are clearer.

#### Updated Parsing

##### Readability

The parsing logic wasn't too bad before, but it was getting difficult to
read. There was some duplicated logic between `Meta::List` and
`Meta::Path` attributes. Additionally, all the logic was kept inside a
large method.

To simply things, I replaced the nested meta parsing with `ParseStream`
parsing. In my opinion, this is easier to follow since it breaks up the
large match statement into a small set of single-line if statements,
where each if-block contains a single call to the appropriate attribute
parsing method.

##### Flexibility

On top of the added simplicity, this also makes our attribute parsing
much more flexible. It allows us to more elegantly handle custom where
clauses (i.e. `#[reflect(where T: Foo)]`) and it opens the door for more
non-standard attribute syntax (e.g. #11659).

##### Errors

This also allows us to automatically provide certain errors when
parsing. For example, since we can use `stream.lookahead1()`, we get
errors like the following for free:

```
error: expected one of: `ignore`, `skip_serializing`, `default`
    --> crates/bevy_reflect/src/lib.rs:1988:23
     |
1988 |             #[reflect(foo)]
     |                       ^^^
```

---

## Changelog

> [!note]
> All changes are internal to `bevy_reflect_derive` and should not
affect the public API[^1].

- Renamed `ReflectTraits` to `ContainerAttributes`
  - Renamed `ReflectMeta::traits` to `ReflectMeta::attrs`
- Renamed `ReflectFieldAttr` to `FieldAttributes`
- Updated parsing logic for field/container attribute parsing
  - Now uses a `ParseStream` directly instead of nested meta parsing
- General code cleanup of the field/container attribute modules for
`bevy_reflect_derive`


[^1]: Does not include errors, which may look slightly different.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
2024-02-12 15:16:27 +00:00
Gino Valente
379b9e5cb6
bevy_reflect: Split #[reflect(where)] (#11597)
# Objective

Revert the changes to type parameter bounds introduced in #9046,
improves the `#[reflect(where)]` attribute (also from #9046), and adds
the ability to opt out of field bounds.

This is based on suggestions by @soqb and discussion on
[Discord](https://discord.com/channels/691052431525675048/1002362493634629796/1201227833826103427).

## Solution

Reverts the changes to type parameter bounds when deriving `Reflect`,
introduced in #9046. This was originally done as a means of fixing a
recursion issue (#8965). However, as @soqb pointed out, we could achieve
the same result by simply making an opt-out attribute instead of messing
with the type parameter bounds.

This PR has four main changes:
1. Reverts the type parameter bounds from #9046
2. Includes `TypePath` as a default bound for active fields
3. Changes `#reflect(where)]` to be strictly additive
4. Adds `#reflect(no_field_bounds)]` to opt out of field bounds

Change 1 means that, like before, type parameters only receive at most
the `TypePath` bound (if `#[reflect(type_path = false)]` is not present)
and active fields receive the `Reflect` or `FromReflect` bound. And with
Change 2, they will also receive `TypePath` (since it's indirectly
required by `Typed` to construct `NamedField` and `UnnamedField`
instances).

Change 3 was made to make room for Change 4. By splitting out the
responsibility of `#reflect(where)]`, we can use it with or without
`#reflect(no_field_bounds)]` for various use cases.

For example, if we hadn't done this, the following would have failed:

```rust
// Since we're not using `#reflect(no_field_bounds)]`, 
// `T::Assoc` is automatically given the required bounds
// of `FromReflect + TypePath`
#[derive(Reflect)]
#[reflect(where T::Assoc: OtherTrait)]
struct Foo<T: MyTrait> {
  value: T::Assoc,
}
```

This provides more flexibility to the user while still letting them add
or remove most trait bounds.

And to solve the original recursion issue, we can do:

```rust
#[derive(Reflect)]
#[reflect(no_field_bounds)] // <-- Added
struct Foo {
  foo: Vec<Foo>
}
```

#### Bounds

All in all, we now have four sets of trait bounds:
- `Self` gets the bounds `Any + Send + Sync`
- Type parameters get the bound `TypePath`. This can be opted out of
with `#[reflect(type_path = false)]`
- Active fields get the bounds `TypePath` and `FromReflect`/`Reflect`
bounds. This can be opted out of with `#reflect(no_field_bounds)]`
- Custom bounds can be added with `#[reflect(where)]`

---

## Changelog

- Revert some changes #9046
- `#reflect(where)]` is now strictly additive
- Added `#reflect(no_field_bounds)]` attribute to opt out of automatic
field trait bounds when deriving `Reflect`
- Made the `TypePath` requirement on fields when deriving `Reflect` more
explicit

## Migration Guide

> [!important]
> This PR shouldn't be a breaking change relative to the current version
of Bevy (v0.12). And since it removes the breaking parts of #9046, that
PR also won't need a migration guide.
2024-01-29 17:54:17 +00:00
Gino Valente
6e959db134
bevy_reflect: Type parameter bounds (#9046)
# Objective

Fixes #8965.

#### Background

For convenience and to ensure everything is setup properly, we
automatically add certain bounds to the derived types. The current
implementation does this by taking the types from all active fields and
adding them to the where-clause of the generated impls. I believe this
method was chosen because it won't add bounds to types that are
otherwise ignored.

```rust
#[derive(Reflect)]
struct Foo<T, U: SomeTrait, V> {
  t: T,
  u: U::Assoc,
  #[reflect(ignore)]
  v: [V; 2]
}

// Generates something like:
impl<T, U: SomeTrait, V> for Foo<T, U, V>
where
  // Active:
  T: Reflect,
  U::Assoc: Reflect,

  // Ignored:
  [V; 2]: Send + Sync + Any
{
  // ...
}
```

The self-referential type fails because it ends up using _itself_ as a
type bound due to being one of its own active fields.

```rust
#[derive(Reflect)]
struct Foo {
  foo: Vec<Foo>
}

// Foo where Vec<Foo>: Reflect -> Vec<T> where T: Reflect -> Foo where Vec<Foo>: Reflect -> ...
```

## Solution

We can't simply parse all field types for the name of our type. That
would be both complex and prone to errors and false-positives. And even
if it wasn't, what would we replace the bound with?

Instead, I opted to go for a solution that only adds the bounds to what
really needs it: the type parameters. While the bounds on concrete types
make errors a bit cleaner, they aren't strictly necessary. This means we
can change our generated where-clause to only add bounds to generic type
parameters.

Doing this, though, returns us back to the problem of over-bounding
parameters that don't need to be bounded. To solve this, I added a new
container attribute (based on
[this](https://github.com/dtolnay/syn/issues/422#issuecomment-406882925)
comment and @nicopap's
[comment](https://github.com/bevyengine/bevy/pull/9046#issuecomment-1623593780))
that allows us to pass in a custom where clause to modify what bounds
are added to these type parameters.

This allows us to do stuff like:

```rust
trait Trait {
  type Assoc;
}

// We don't need `T` to be reflectable since we only care about `T::Assoc`.
#[derive(Reflect)]
#[reflect(where T::Assoc: FromReflect)]
struct Foo<T: Trait>(T::Assoc);

#[derive(TypePath)]
struct Bar;

impl Trait for Bar {
  type Assoc = usize;
}

#[derive(Reflect)]
struct Baz {
  a: Foo<Bar>,
}
```

> **Note**
> I also
[tried](dc139ea34c)
allowing `#[reflect(ignore)]` to be used on the type parameters
themselves, but that proved problematic since the derive macro does not
consume the attribute. This is why I went with the container attribute
approach.

### Alternatives

One alternative could possibly be to just not add reflection bounds
automatically (i.e. only add required bounds like `Send`, `Sync`, `Any`,
and `TypePath`).

The downside here is we add more friction to using reflection, which
already comes with its own set of considerations. This is a potentially
viable option, but we really need to consider whether or not the
ergonomics hit is worth it.

If we did decide to go the more manual route, we should at least
consider something like #5772 to make it easier for users to add the
right bounds (although, this could still become tricky with
`FromReflect` also being automatically derived).

### Open Questions

1. Should we go with this approach or the manual alternative?
2. ~~Should we add a `skip_params` attribute to avoid the `T: 'static`
trick?~~ ~~Decided to go with `custom_where()` as it's the simplest~~
Scratch that, went with a normal where clause
3. ~~`custom_where` bikeshedding?~~ No longer needed since we are using
a normal where clause

### TODO

- [x] Add compile-fail tests

---

## Changelog

- Fixed issue preventing recursive types from deriving `Reflect`
- Changed how where-clause bounds are generated by the `Reflect` derive
macro
- They are now only applied to the type parameters, not to all active
fields
- Added `#[reflect(where T: Trait, U::Assoc: Trait, ...)]` container
attribute

## Migration Guide

When deriving `Reflect`, generic type params that do not need the
automatic reflection bounds (such as `Reflect`) applied to them will
need to opt-out using a custom where clause like: `#[reflect(where T:
Trait, U::Assoc: Trait, ...)]`.

The attribute can define custom bounds only used by the reflection
impls. To simply opt-out all the type params, we can pass in an empty
where clause: `#[reflect(where)]`.

```rust
// BEFORE:
#[derive(Reflect)]
struct Foo<T>(#[reflect(ignore)] T);

// AFTER:
#[derive(Reflect)]
#[reflect(where)]
struct Foo<T>(#[reflect(ignore)] T);
```

---------

Co-authored-by: Nicola Papale <nicopap@users.noreply.github.com>
2024-01-28 16:24:03 +00:00
Doonv
189ceaf0d3
Replace or document ignored doctests (#11040)
# Objective

There are a lot of doctests that are `ignore`d for no documented reason.
And that should be fixed.

## Solution

I searched the bevy repo with the regex ` ```[a-z,]*ignore ` in order to
find all `ignore`d doctests. For each one of the `ignore`d doctests, I
did the following steps:
1. Attempt to remove the `ignored` attribute while still passing the
test. I did this by adding hidden dummy structs and imports.
2. If step 1 doesn't work, attempt to replace the `ignored` attribute
with the `no_run` attribute while still passing the test.
3. If step 2 doesn't work, keep the `ignored` attribute but add
documentation for why the `ignored` attribute was added.

---------

Co-authored-by: François <mockersf@gmail.com>
2024-01-01 16:50:56 +00:00
radiish
13feac6721
reflect: maximally relax TypePath bounds (#11037)
# Objective

- Provides an alternate solution to the one implemented in #10791
without breaking changes.

## Solution

- Changes the bounds of macro-generated `TypePath` implementations to
universally ignore the types of fields, rather than use the same bounds
as other implementations. I think this is a more holistic solution than
#10791 because it totally erases the finicky bounds we currently
generate, helping to untangle the reflection trait system.
2023-12-24 17:45:46 +00:00
Gino Valente
daa8bf20df
Fix nested generics in Reflect derive (#10791)
# Objective

> Issue raised on
[Discord](https://discord.com/channels/691052431525675048/1002362493634629796/1179182488787103776)

Currently the following code fails due to a missing `TypePath` bound:

```rust
#[derive(Reflect)] struct Foo<T>(T);
#[derive(Reflect)] struct Bar<T>(Foo<T>);
#[derive(Reflect)] struct Baz<T>(Bar<Foo<T>>);
```

## Solution

Add `TypePath` to the per-field bounds instead of _just_ the generic
type parameter bounds.

### Related Work

It should be noted that #9046 would help make these kinds of issues
easier to work around and/or avoid entirely.

---

## Changelog

- Fixes missing `TypePath` requirement when deriving `Reflect` on nested
generics
2023-11-29 01:46:09 +00:00
Gino Valente
60773e6787
bevy_reflect: Fix ignored/skipped field order (#7575)
# Objective

Fixes #5101
Alternative to #6511

## Solution

Corrected the behavior for ignored fields in `FromReflect`, which was
previously using the incorrect field indexes.

Similarly, fields marked with `#[reflect(skip_serializing)]` no longer
break when using `FromReflect` after deserialization. This was done by
modifying `SerializationData` to store a function pointer that can later
be used to generate a default instance of the skipped field during
deserialization.

The function pointer points to a function generated by the derive macro
using the behavior designated by `#[reflect(default)]` (or just
`Default` if none provided). The entire output of the macro is now
wrapped in an [unnamed
constant](https://doc.rust-lang.org/stable/reference/items/constant-items.html#unnamed-constant)
which keeps this behavior hygienic.

#### Rationale

The biggest downside to this approach is that it requires fields marked
`#[reflect(skip_serializing)]` to provide the ability to create a
default instance— either via a `Default` impl or by specifying a custom
one. While this isn't great, I think it might be justified by the fact
that we really need to create this value when using `FromReflect` on a
deserialized object. And we need to do this _during_ deserialization
because after that (at least for tuples and tuple structs) we lose
information about which field is which: _"is the value at index 1 in
this `DynamicTupleStruct` the actual value for index 1 or is it really
the value for index 2 since index 1 is skippable...?"_

#### Alternatives

An alternative would be to store `Option<Box<dyn Reflect>>` within
`DynamicTuple` and `DynamicTupleStruct` instead of just `Box<dyn
Reflect>`. This would allow us to insert "empty"/"missing" fields during
deserialization, thus saving the positional information of the skipped
fields. However, this may require changing the API of `Tuple` and
`TupleStruct` such that they can account for their dynamic counterparts
returning `None` for a skipped field. In practice this would probably
mean exposing the `Option`-ness of the dynamics onto implementors via
methods like `Tuple::drain` or `TupleStruct::field`.

Personally, I think requiring `Default` would be better than muddying up
the API to account for these special cases. But I'm open to trying out
this other approach if the community feels that it's better.

---

## Changelog

### Public Changes

#### Fixed

- The behaviors of `#[reflect(ignore)]` and
`#[reflect(skip_serializing)]` are no longer dependent on field order

#### Changed

- Fields marked with `#[reflect(skip_serializing)]` now need to either
implement `Default` or specify a custom default function using
`#[reflect(default = "path::to::some_func")]`
- Deserializing a type with fields marked `#[reflect(skip_serializing)]`
will now include that field initialized to its specified default value
- `SerializationData::new` now takes the new `SkippedField` struct along
with the skipped field index
- Renamed `SerializationData::is_ignored_field` to
`SerializationData::is_field_skipped`

#### Added

- Added `SkippedField` struct
- Added methods `SerializationData::generate_default` and
`SerializationData::iter_skipped`

### Internal Changes

#### Changed

- Replaced `members_to_serialization_denylist` and `BitSet<u32>` with
`SerializationDataDef`
- The `Reflect` derive is more hygienic as it now outputs within an
[unnamed
constant](https://doc.rust-lang.org/stable/reference/items/constant-items.html#unnamed-constant)
- `StructField::index` has been split up into
`StructField::declaration_index` and `StructField::reflection_index`

#### Removed

- Removed `bitset` dependency

## Migration Guide

* Fields marked `#[reflect(skip_serializing)]` now must implement
`Default` or specify a custom default function with `#[reflect(default =
"path::to::some_func")]`
    ```rust
    #[derive(Reflect)]
    struct MyStruct {
      #[reflect(skip_serializing)]
      #[reflect(default = "get_foo_default")]
foo: Foo, // <- `Foo` does not impl `Default` so requires a custom
function
      #[reflect(skip_serializing)]
      bar: Bar, // <- `Bar` impls `Default`
    }
    
    #[derive(Reflect)]
    struct Foo(i32);
    
    #[derive(Reflect, Default)]
    struct Bar(i32);
    
    fn get_foo_default() -> Foo {
      Foo(123)
    }
    ```
* `SerializationData::new` has been changed to expect an iterator of
`(usize, SkippedField)` rather than one of just `usize`
    ```rust
    // BEFORE
    SerializationData::new([0, 3].into_iter());
    
    // AFTER
    SerializationData::new([
      (0, SkippedField::new(field_0_default_fn)),
      (3, SkippedField::new(field_3_default_fn)),
    ].into_iter());
    ```
* `Serialization::is_ignored_field` has been renamed to
`Serialization::is_field_skipped`
* Fields marked `#[reflect(skip_serializing)]` are now included in
deserialization output. This may affect logic that expected those fields
to be absent.
2023-10-22 12:43:31 +00:00
Zachary Harrold
e5dbde86fb
Moved fq_std from bevy_reflect_derive to bevy_macro_utils (#9956)
# Objective

- Fixes #9363

## Solution

Moved `fq_std` from `bevy_reflect_derive` to `bevy_macro_utils`. This
does make the `FQ*` types public where they were previously private,
which is a change to the public-facing API, but I don't believe a
breaking one. Additionally, I've done a basic QA pass over the
`bevy_macro_utils` crate, adding `deny(unsafe)`, `warn(missing_docs)`,
and documentation where required.
2023-10-02 00:22:57 +00:00
Gino Valente
f96cd758cd
bevy_reflect: Opt-out attribute for TypePath (#9140)
# Objective

Fixes #9094

## Solution

Takes a bit from
[this](https://github.com/bevyengine/bevy/issues/9094#issuecomment-1629333851)
comment as well as a
[comment](https://discord.com/channels/691052431525675048/1002362493634629796/1128024873260810271)
from @soqb.

This allows users to opt-out of the `TypePath` implementation that is
automatically generated by the `Reflect` derive macro, allowing custom
`TypePath` implementations.

```rust
#[derive(Reflect)]
#[reflect(type_path = false)]
struct Foo<T> {
    #[reflect(ignore)]
    _marker: PhantomData<T>,
}

struct NotTypePath;

impl<T: 'static> TypePath for Foo<T> {
    fn type_path() -> &'static str {
        std::any::type_name::<Self>()
    }

    fn short_type_path() -> &'static str {
        static CELL: GenericTypePathCell = GenericTypePathCell::new();
        CELL.get_or_insert::<Self, _>(|| {
            bevy_utils::get_short_name(std::any::type_name::<Self>())
        })
    }

    fn crate_name() -> Option<&'static str> {
        Some("my_crate")
    }

    fn module_path() -> Option<&'static str> {
        Some("my_crate::foo")
    }

    fn type_ident() -> Option<&'static str> {
        Some("Foo")
    }
}

// Can use `TypePath`
let _ = <Foo<NotTypePath> as TypePath>::type_path();

// Can register the type
let mut registry = TypeRegistry::default();
registry.register::<Foo<NotTypePath>>();
```

#### Type Path Stability

The stability of type paths mainly come into play during serialization.
If a type is moved between builds, an unstable type path may become
invalid.

Users that opt-out of `TypePath` and rely on something like
`std::any::type_name` as in the example above, should be aware that this
solution removes the stability guarantees. Deserialization thus expects
that type to never move. If it does, then the serialized type paths will
need to be updated accordingly.

If a user depends on stability, they will need to implement that
stability logic manually (probably by looking at the expanded output of
a typical `Reflect`/`TypePath` derive). This could be difficult for type
parameters that don't/can't implement `TypePath`, and will need to make
heavy use of string parsing and manipulation to achieve the same effect
(alternatively, they can choose to simply exclude any type parameter
that doesn't implement `TypePath`).

---

## Changelog

- Added the `#[reflect(type_path = false)]` attribute to opt out of the
`TypePath` impl when deriving `Reflect`

---------

Co-authored-by: Carter Anderson <mcanders1@gmail.com>
2023-08-10 00:37:56 +00:00
Gino Valente
aeeb20ec4c
bevy_reflect: FromReflect Ergonomics Implementation (#6056)
# Objective

**This implementation is based on
https://github.com/bevyengine/rfcs/pull/59.**

---

Resolves #4597

Full details and motivation can be found in the RFC, but here's a brief
summary.

`FromReflect` is a very powerful and important trait within the
reflection API. It allows Dynamic types (e.g., `DynamicList`, etc.) to
be formed into Real ones (e.g., `Vec<i32>`, etc.).

This mainly comes into play concerning deserialization, where the
reflection deserializers both return a `Box<dyn Reflect>` that almost
always contain one of these Dynamic representations of a Real type. To
convert this to our Real type, we need to use `FromReflect`.

It also sneaks up in other ways. For example, it's a required bound for
`T` in `Vec<T>` so that `Vec<T>` as a whole can be made `FromReflect`.
It's also required by all fields of an enum as it's used as part of the
`Reflect::apply` implementation.

So in other words, much like `GetTypeRegistration` and `Typed`, it is
very much a core reflection trait.

The problem is that it is not currently treated like a core trait and is
not automatically derived alongside `Reflect`. This makes using it a bit
cumbersome and easy to forget.

## Solution

Automatically derive `FromReflect` when deriving `Reflect`.

Users can then choose to opt-out if needed using the
`#[reflect(from_reflect = false)]` attribute.

```rust
#[derive(Reflect)]
struct Foo;

#[derive(Reflect)]
#[reflect(from_reflect = false)]
struct Bar;

fn test<T: FromReflect>(value: T) {}

test(Foo); // <-- OK
test(Bar); // <-- Panic! Bar does not implement trait `FromReflect`
```

#### `ReflectFromReflect`

This PR also automatically adds the `ReflectFromReflect` (introduced in
#6245) registration to the derived `GetTypeRegistration` impl— if the
type hasn't opted out of `FromReflect` of course.

<details>
<summary><h4>Improved Deserialization</h4></summary>

> **Warning**
> This section includes changes that have since been descoped from this
PR. They will likely be implemented again in a followup PR. I am mainly
leaving these details in for archival purposes, as well as for reference
when implementing this logic again.

And since we can do all the above, we might as well improve
deserialization. We can now choose to deserialize into a Dynamic type or
automatically convert it using `FromReflect` under the hood.

`[Un]TypedReflectDeserializer::new` will now perform the conversion and
return the `Box`'d Real type.

`[Un]TypedReflectDeserializer::new_dynamic` will work like what we have
now and simply return the `Box`'d Dynamic type.

```rust
// Returns the Real type
let reflect_deserializer = UntypedReflectDeserializer::new(&registry);
let mut deserializer = ron:🇩🇪:Deserializer::from_str(input)?;

let output: SomeStruct = reflect_deserializer.deserialize(&mut deserializer)?.take()?;

// Returns the Dynamic type
let reflect_deserializer = UntypedReflectDeserializer::new_dynamic(&registry);
let mut deserializer = ron:🇩🇪:Deserializer::from_str(input)?;

let output: DynamicStruct = reflect_deserializer.deserialize(&mut deserializer)?.take()?;
```

</details>

---

## Changelog

* `FromReflect` is now automatically derived within the `Reflect` derive
macro
* This includes auto-registering `ReflectFromReflect` in the derived
`GetTypeRegistration` impl
* ~~Renamed `TypedReflectDeserializer::new` and
`UntypedReflectDeserializer::new` to
`TypedReflectDeserializer::new_dynamic` and
`UntypedReflectDeserializer::new_dynamic`, respectively~~ **Descoped**
* ~~Changed `TypedReflectDeserializer::new` and
`UntypedReflectDeserializer::new` to automatically convert the
deserialized output using `FromReflect`~~ **Descoped**

## Migration Guide

* `FromReflect` is now automatically derived within the `Reflect` derive
macro. Items with both derives will need to remove the `FromReflect`
one.

  ```rust
  // OLD
  #[derive(Reflect, FromReflect)]
  struct Foo;
  
  // NEW
  #[derive(Reflect)]
  struct Foo;
  ```

If using a manual implementation of `FromReflect` and the `Reflect`
derive, users will need to opt-out of the automatic implementation.

  ```rust
  // OLD
  #[derive(Reflect)]
  struct Foo;
  
  impl FromReflect for Foo {/* ... */}
  
  // NEW
  #[derive(Reflect)]
  #[reflect(from_reflect = false)]
  struct Foo;
  
  impl FromReflect for Foo {/* ... */}
  ```

<details>
<summary><h4>Removed Migrations</h4></summary>

> **Warning**
> This section includes changes that have since been descoped from this
PR. They will likely be implemented again in a followup PR. I am mainly
leaving these details in for archival purposes, as well as for reference
when implementing this logic again.

* The reflect deserializers now perform a `FromReflect` conversion
internally. The expected output of `TypedReflectDeserializer::new` and
`UntypedReflectDeserializer::new` is no longer a Dynamic (e.g.,
`DynamicList`), but its Real counterpart (e.g., `Vec<i32>`).

  ```rust
let reflect_deserializer =
UntypedReflectDeserializer::new_dynamic(&registry);
  let mut deserializer = ron:🇩🇪:Deserializer::from_str(input)?;
  
  // OLD
let output: DynamicStruct = reflect_deserializer.deserialize(&mut
deserializer)?.take()?;
  
  // NEW
let output: SomeStruct = reflect_deserializer.deserialize(&mut
deserializer)?.take()?;
  ```

Alternatively, if this behavior isn't desired, use the
`TypedReflectDeserializer::new_dynamic` and
`UntypedReflectDeserializer::new_dynamic` methods instead:

  ```rust
  // OLD
  let reflect_deserializer = UntypedReflectDeserializer::new(&registry);
  
  // NEW
let reflect_deserializer =
UntypedReflectDeserializer::new_dynamic(&registry);
  ```

</details>

---------

Co-authored-by: Carter Anderson <mcanders1@gmail.com>
2023-06-29 01:31:34 +00:00
Jamie Ridding
1e97c79ec1
bevy_reflect: Disambiguate type bounds in where clauses. (#8761)
# Objective

It was accidentally found that rustc is unable to parse certain
constructs in `where` clauses properly. `bevy_reflect::Reflect`'s habit
of copying and pasting the field types in a type's definition to its
`where` clauses made it very easy to accidentally run into this
behaviour - particularly with the construct
```rust
where
    for<'a> fn(&'a T) -> &'a T: Trait1 + Trait2
```

which was incorrectly parsed as
```rust
where
    for<'a> (fn(&'a T) -> &'a T: Trait1 + Trait2)
            ^                                   ^ incorrect syntax grouping
```

instead of
```rust
where
    (for<'a> fn(&'a T) -> &'a T): Trait1 + Trait2
    ^                          ^ correct syntax grouping
```

Fixes #8759 

## Solution

This commit fixes the issue by inserting explicit parentheses to
disambiguate types from their bound lists.
2023-06-05 22:47:08 +00:00
radiish
1efc762924
reflect: stable type path v2 (#7184)
# Objective

- Introduce a stable alternative to
[`std::any::type_name`](https://doc.rust-lang.org/std/any/fn.type_name.html).
- Rewrite of #5805 with heavy inspiration in design.
- On the path to #5830.
- Part of solving #3327.


## Solution

- Add a `TypePath` trait for static stable type path/name information.
- Add a `TypePath` derive macro.
- Add a `impl_type_path` macro for implementing internal and foreign
types in `bevy_reflect`.

---

## Changelog

- Added `TypePath` trait.
- Added `DynamicTypePath` trait and `get_type_path` method to `Reflect`.
- Added a `TypePath` derive macro.
- Added a `bevy_reflect::impl_type_path` for implementing `TypePath` on
internal and foreign types in `bevy_reflect`.
- Changed `bevy_reflect::utility::(Non)GenericTypeInfoCell` to
`(Non)GenericTypedCell<T>` which allows us to be generic over both
`TypeInfo` and `TypePath`.
- `TypePath` is now a supertrait of `Asset`, `Material` and
`Material2d`.
- `impl_reflect_struct` needs a `#[type_path = "..."]` attribute to be
specified.
- `impl_reflect_value` needs to either specify path starting with a
double colon (`::core::option::Option`) or an `in my_crate::foo`
declaration.
- Added `bevy_reflect_derive::ReflectTypePath`.
- Most uses of `Ident` in `bevy_reflect_derive` changed to use
`ReflectTypePath`.

## Migration Guide

- Implementors of `Asset`, `Material` and `Material2d` now also need to
derive `TypePath`.
- Manual implementors of `Reflect` will need to implement the new
`get_type_path` method.

## Open Questions
- [x] ~This PR currently does not migrate any usages of
`std::any::type_name` to use `bevy_reflect::TypePath` to ease the review
process. Should it?~ Migration will be left to a follow-up PR.
- [ ] This PR adds a lot of `#[derive(TypePath)]` and `T: TypePath` to
satisfy new bounds, mostly when deriving `TypeUuid`. Should we make
`TypePath` a supertrait of `TypeUuid`? [Should we remove `TypeUuid` in
favour of
`TypePath`?](2afbd85532 (r961067892))
2023-06-05 20:31:20 +00:00
Wybe Westra
abf12f3b3b
Fixed several missing links in docs. (#8117)
Links in the api docs are nice. I noticed that there were several places
where structs / functions and other things were referenced in the docs,
but weren't linked. I added the links where possible / logical.

---------

Co-authored-by: Alice Cecile <alice.i.cecile@gmail.com>
Co-authored-by: François <mockersf@gmail.com>
2023-04-23 17:28:36 +00:00
Mikkel Rasmussen
e9312254d8
Non-breaking change* from UK spellings to US (#8291)
Fixes issue mentioned in PR #8285.

_Note: By mistake, this is currently dependent on #8285_
# Objective

Ensure consistency in the spelling of the documentation.

Exceptions:
`crates/bevy_mikktspace/src/generated.rs` - Has not been changed from
licence to license as it is part of a licensing agreement.

Maybe for further consistency,
https://github.com/bevyengine/bevy-website should also be given a look.

## Solution

### Changed the spelling of the current words (UK/CN/AU -> US) :
cancelled -> canceled (Breaking API changes in #8285)
behaviour -> behavior (Breaking API changes in #8285)
neighbour -> neighbor
grey -> gray
recognise -> recognize
centre -> center
metres -> meters
colour -> color

### ~~Update [`engine_style_guide.md`]~~ Moved to #8324 

---

## Changelog

Changed UK spellings in documentation to US

## Migration Guide

Non-breaking changes*

\* If merged after #8285
2023-04-08 16:22:46 +00:00
Gino Valente
5e5a305d43
bevy_reflect: Fix trailing comma breaking derives (#8014)
# Objective

Fixes #7989

Based on #7991 by @CoffeeVampir3

## Solution

There were three parts to this issue:
1. `extend_where_clause` did not account for the optionality of a where
clause's trailing comma
    ```rust
    // OKAY
    struct Foo<T> where T: Asset, {/* ... */}
    // ERROR
    struct Foo<T> where T: Asset {/* ... */}
    ```
2. `FromReflect` derive logic was not actively using
`extend_where_clause` which led to some inconsistencies (enums weren't
adding _any_ additional bounds even)
3. Using `extend_where_clause` in the `FromReflect` derive logic meant
we had to optionally add `Default` bounds to ignored fields iff the
entire item itself was not already `Default` (otherwise the definition
for `Handle<T>` wouldn't compile since `HandleType` doesn't impl
`Default` but `Handle<T>` itself does)

---

## Changelog

- Fixed issue where a missing trailing comma could break the reflection
derives
2023-03-27 21:47:33 +00:00
Ikko Eltociear Ashimine
e22572d9a3
Fix typo in utility.rs (#7997) 2023-03-09 09:20:45 +00:00
MinerSebas
e5b522064c Follow up on Todo in bevy_reflect_derive (#7461)
# Objective

Follow up on Todo in bevy_reflect_derive

## Solution

- Replaced all Instances that do the same as `ident_or_index` with a call to it.
- Only the following Line wasn't replaced, as it only wants the index, and not the ident:
[69fc8c6b70/crates/bevy_reflect/bevy_reflect_derive/src/impls/tuple_structs.rs (L18))
2023-02-02 04:37:32 +00:00
Charles Bournhonesque
cbb4c26cad Enable deriving Reflect on structs with generic types (#7364)
# Objective

I recently had an issue, where I have a struct:
```
struct Property {
   inner: T
}
```
that I use as a wrapper for internal purposes.
I don't want to update my struct definition to 
```
struct Property<T: Reflect>{
   inner: T
}
```
because I still want to be able to build `Property<T>` for types `T` that are not `Reflect`. (and also because I don't want to update my whole code base with `<T: Reflect>` bounds)

I still wanted to have reflection on it (for `bevy_inspector_egui`), but adding `derive(Reflect)` fails with the error:
`T cannot be sent between threads safely. T needs to implement Sync.`

I believe that `bevy_reflect` should adopt the model of other derives in the case of generics, which is to add the `Reflect` implementation only if the generics also implement `Reflect`. (That is the behaviour of other macros such as `derive(Clone)` or `derive(Debug)`.

It's also the current behavior of `derive(FromReflect)`.

Basically doing something like:
```
impl<T> Reflect for Foo<T>
where T: Reflect
```


## Solution

- I updated the derive macros for `Structs` and `TupleStructs` to add extra `where` bounds.
   -  Every type that is reflected will need a `T: Reflect` bound
   -  Ignored types will need a `T: 'static + Send + Sync` bound. Here's the reason. For cases like this:
```
#[derive(Reflect)]
struct Foo<T, U>{
   a: T
   #[reflect(ignore)]
   b: U
}
```
I had to add the bound `'static + Send + Sync` to ignored generics like `U`.
The reason is that we want `Foo<T, U>` to be `Reflect: 'static + Send + Sync`, so `Foo<T, U>` must be able to implement those auto-traits. `Foo<T, U>` will only implement those auto-traits if every generic type implements them, including ignored types.
This means that the previously compile-fail case now compiles:
```
#[derive(Reflect)]
struct Foo<'a> {
    #[reflect(ignore)]
    value: &'a str,
}
```
But `Foo<'a>` will only be useable in the cases where `'a: 'static` and panic if we don't have `'a: 'static`, which is what we want (nice bonus from this PR ;) )



---

## Changelog

> This section is optional. If this was a trivial fix, or has no externally-visible impact, you can delete this section.

### Added
Possibility to add `derive(Reflect)` to structs and enums that contain generic types, like so:
```
#[derive(Reflect)]
struct Foo<T>{
   a: T
}
```
Reflection will only be available if the generic type T also implements `Reflect`.
(previously, this would just return a compiler error)
2023-01-28 00:12:06 +00:00
Jakob Hellermann
e71c4d2802 fix nightly clippy warnings (#6395)
# Objective

- fix new clippy lints before they get stable and break CI

## Solution

- run `clippy --fix` to auto-fix machine-applicable lints
- silence `clippy::should_implement_trait` for `fn HandleId::default<T: Asset>`

## Changes
- always prefer `format!("{inline}")` over `format!("{}", not_inline)`
- prefer `Box::default` (or `Box::<T>::default` if necessary) over `Box::new(T::default())`
2022-10-28 21:03:01 +00:00
Gino Valente
d30d3e752a bevy_reflect: Improve serialization format even more (#5723)
> Note: This is rebased off #4561 and can be viewed as a competitor to that PR. See `Comparison with #4561` section for details.

# Objective

The current serialization format used by `bevy_reflect` is both verbose and error-prone. Taking the following structs[^1] for example:

```rust
// -- src/inventory.rs

#[derive(Reflect)]
struct Inventory {
  id: String,
  max_storage: usize,
  items: Vec<Item>
}

#[derive(Reflect)]
struct Item {
  name: String
}
```

Given an inventory of a single item, this would serialize to something like:

```rust
// -- assets/inventory.ron

{
  "type": "my_game::inventory::Inventory",
  "struct": {
    "id": {
      "type": "alloc::string::String",
      "value": "inv001",
    },
    "max_storage": {
      "type": "usize",
      "value": 10
    },
    "items": {
      "type": "alloc::vec::Vec<alloc::string::String>",
      "list": [
        {
          "type": "my_game::inventory::Item",
          "struct": {
            "name": {
              "type": "alloc::string::String",
              "value": "Pickaxe"
            },
          },
        },
      ],
    },
  },
}
```

Aside from being really long and difficult to read, it also has a few "gotchas" that users need to be aware of if they want to edit the file manually. A major one is the requirement that you use the proper keys for a given type. For structs, you need `"struct"`. For lists, `"list"`. For tuple structs, `"tuple_struct"`. And so on.

It also ***requires*** that the `"type"` entry come before the actual data. Despite being a map— which in programming is almost always orderless by default— the entries need to be in a particular order. Failure to follow the ordering convention results in a failure to deserialize the data.

This makes it very prone to errors and annoyances.


## Solution

Using #4042, we can remove a lot of the boilerplate and metadata needed by this older system. Since we now have static access to type information, we can simplify our serialized data to look like:

```rust
// -- assets/inventory.ron

{
  "my_game::inventory::Inventory": (
    id: "inv001",
    max_storage: 10,
    items: [
      (
        name: "Pickaxe"
      ),
    ],
  ),
}
```

This is much more digestible and a lot less error-prone (no more key requirements and no more extra type names).

Additionally, it is a lot more familiar to users as it follows conventional serde mechanics. For example, the struct is represented with `(...)` when serialized to RON.

#### Custom Serialization

Additionally, this PR adds the opt-in ability to specify a custom serde implementation to be used rather than the one created via reflection. For example[^1]:

```rust
// -- src/inventory.rs

#[derive(Reflect, Serialize)]
#[reflect(Serialize)]
struct Item {
  #[serde(alias = "id")]
  name: String
}
```

```rust
// -- assets/inventory.ron

{
  "my_game::inventory::Inventory": (
    id: "inv001",
    max_storage: 10,
    items: [
      (
        id: "Pickaxe"
      ),
    ],
  ),
},
```

By allowing users to define their own serialization methods, we do two things:

1. We give more control over how data is serialized/deserialized to the end user
2. We avoid having to re-define serde's attributes and forcing users to apply both (e.g. we don't need a `#[reflect(alias)]` attribute).

### Improved Formats

One of the improvements this PR provides is the ability to represent data in ways that are more conventional and/or familiar to users. Many users are familiar with RON so here are some of the ways we can now represent data in RON:

###### Structs

```js
{
  "my_crate::Foo": (
    bar: 123
  )
}
// OR
{
  "my_crate::Foo": Foo(
    bar: 123
  )
}
```

<details>
<summary>Old Format</summary>

```js
{
  "type": "my_crate::Foo",
  "struct": {
    "bar": {
      "type": "usize",
      "value": 123
    }
  }
}
```

</details>

###### Tuples

```js
{
  "(f32, f32)": (1.0, 2.0)
}
```

<details>
<summary>Old Format</summary>

```js
{
  "type": "(f32, f32)",
  "tuple": [
    {
      "type": "f32",
      "value": 1.0
    },
    {
      "type": "f32",
      "value": 2.0
    }
  ]
}
```

</details>

###### Tuple Structs

```js
{
  "my_crate::Bar": ("Hello World!")
}
// OR
{
  "my_crate::Bar": Bar("Hello World!")
}
```

<details>
<summary>Old Format</summary>

```js
{
  "type": "my_crate::Bar",
  "tuple_struct": [
    {
      "type": "alloc::string::String",
      "value": "Hello World!"
    }
  ]
}
```

</details>

###### Arrays

It may be a bit surprising to some, but arrays now also use the tuple format. This is because they essentially _are_ tuples (a sequence of values with a fixed size), but only allow for homogenous types. Additionally, this is how RON handles them and is probably a result of the 32-capacity limit imposed on them (both by [serde](https://docs.rs/serde/latest/serde/trait.Serialize.html#impl-Serialize-for-%5BT%3B%2032%5D) and by [bevy_reflect](https://docs.rs/bevy/latest/bevy/reflect/trait.GetTypeRegistration.html#impl-GetTypeRegistration-for-%5BT%3B%2032%5D)).

```js
{
  "[i32; 3]": (1, 2, 3)
}
```

<details>
<summary>Old Format</summary>

```js
{
  "type": "[i32; 3]",
  "array": [
    {
      "type": "i32",
      "value": 1
    },
    {
      "type": "i32",
      "value": 2
    },
    {
      "type": "i32",
      "value": 3
    }
  ]
}
```

</details>

###### Enums

To make things simple, I'll just put a struct variant here, but the style applies to all variant types:

```js
{
  "my_crate::ItemType": Consumable(
    name: "Healing potion"
  )
}
```

<details>
<summary>Old Format</summary>

```js
{
  "type": "my_crate::ItemType",
  "enum": {
    "variant": "Consumable",
    "struct": {
      "name": {
        "type": "alloc::string::String",
        "value": "Healing potion"
      }
    }
  }
}
```

</details>

### Comparison with #4561

This PR is a rebased version of #4561. The reason for the split between the two is because this PR creates a _very_ different scene format. You may notice that the PR descriptions for either PR are pretty similar. This was done to better convey the changes depending on which (if any) gets merged first. If #4561 makes it in first, I will update this PR description accordingly.

---

## Changelog

* Re-worked serialization/deserialization for reflected types
* Added `TypedReflectDeserializer` for deserializing data with known `TypeInfo`
* Renamed `ReflectDeserializer` to `UntypedReflectDeserializer` 
* ~~Replaced usages of `deserialize_any` with `deserialize_map` for non-self-describing formats~~ Reverted this change since there are still some issues that need to be sorted out (in a separate PR). By reverting this, crates like `bincode` can throw an error when attempting to deserialize non-self-describing formats (`bincode` results in `DeserializeAnyNotSupported`)
* Structs, tuples, tuple structs, arrays, and enums are now all de/serialized using conventional serde methods

## Migration Guide

* This PR reduces the verbosity of the scene format. Scenes will need to be updated accordingly:

```js
// Old format
{
  "type": "my_game::item::Item",
  "struct": {
    "id": {
      "type": "alloc::string::String",
      "value": "bevycraft:stone",
    },
    "tags": {
      "type": "alloc::vec::Vec<alloc::string::String>",
      "list": [
        {
          "type": "alloc::string::String",
          "value": "material"
        },
      ],
    },
}

// New format
{
  "my_game::item::Item": (
    id: "bevycraft:stone",
    tags: ["material"]
  )
}
```

[^1]: Some derives omitted for brevity.
2022-09-20 19:38:18 +00:00
Maksymilian Mozolewski
ac1aebed5e Add reflect(skip_serializing) which retains reflection but disables automatic serialization (#5250)
# Objective

- To address problems outlined in https://github.com/bevyengine/bevy/issues/5245

## Solution

- Introduce `reflect(skip_serializing)` on top of `reflect(ignore)` which disables automatic serialisation to scenes, but does not disable reflection of the field.

---

## Changelog
- Adds: 
  - `bevy_reflect::serde::type_data` module
  - `SerializationData` structure for describing which fields are to be/not to be ignored, automatically registers as type_data for struct-based types
  - the `skip_serialization` flag for `#[reflect(...)]`
 - Removes:
   - ability to ignore Enum variants in serialization, since that didn't work anyway   
 

## Migration Guide
- Change `#[reflect(ignore)]` to `#[reflect(skip_serializing)]` where disabling reflection is not the intended effect.
- Remove ignore/skip attributes from enum variants as these won't do anything anymore
2022-09-19 16:12:10 +00:00
Gino Valente
15826d6019 bevy_reflect: Reflect enums (#4761)
# Objective

> This is a revival of #1347. Credit for the original PR should go to @Davier.

Currently, enums are treated as `ReflectRef::Value` types by `bevy_reflect`. Obviously, there needs to be better a better representation for enums using the reflection API.

## Solution

Based on prior work from @Davier, an `Enum` trait has been added as well as the ability to automatically implement it via the `Reflect` derive macro. This allows enums to be expressed dynamically:

```rust
#[derive(Reflect)]
enum Foo {
  A,
  B(usize),
  C { value: f32 },
}

let mut foo = Foo::B(123);
assert_eq!("B", foo.variant_name());
assert_eq!(1, foo.field_len());

let new_value = DynamicEnum::from(Foo::C { value: 1.23 });
foo.apply(&new_value);
assert_eq!(Foo::C{value: 1.23}, foo);
```

### Features

#### Derive Macro

Use the `#[derive(Reflect)]` macro to automatically implement the `Enum` trait for enum definitions. Optionally, you can use `#[reflect(ignore)]` with both variants and variant fields, just like you can with structs. These ignored items will not be considered as part of the reflection and cannot be accessed via reflection.

```rust
#[derive(Reflect)]
enum TestEnum {
  A,
  // Uncomment to ignore all of `B`
  // #[reflect(ignore)]
  B(usize),
  C {
    // Uncomment to ignore only field `foo` of `C`
    // #[reflect(ignore)]
    foo: f32,
    bar: bool,
  },
}
```

#### Dynamic Enums

Enums may be created/represented dynamically via the `DynamicEnum` struct. The main purpose of this struct is to allow enums to be deserialized into a partial state and to allow dynamic patching. In order to ensure conversion from a `DynamicEnum` to a concrete enum type goes smoothly, be sure to add `FromReflect` to your derive macro.

```rust
let mut value = TestEnum::A;

// Create from a concrete instance
let dyn_enum = DynamicEnum::from(TestEnum::B(123));

value.apply(&dyn_enum);
assert_eq!(TestEnum::B(123), value);

// Create a purely dynamic instance
let dyn_enum = DynamicEnum::new("TestEnum", "A", ());

value.apply(&dyn_enum);
assert_eq!(TestEnum::A, value);
```

#### Variants

An enum value is always represented as one of its variants— never the enum in its entirety.

```rust
let value = TestEnum::A;
assert_eq!("A", value.variant_name());

// Since we are using the `A` variant, we cannot also be the `B` variant
assert_ne!("B", value.variant_name());
```

All variant types are representable within the `Enum` trait: unit, struct, and tuple.

You can get the current type like:

```rust
match value.variant_type() {
  VariantType::Unit => println!("A unit variant!"),
  VariantType::Struct => println!("A struct variant!"),
  VariantType::Tuple => println!("A tuple variant!"),
}
```

> Notice that they don't contain any values representing the fields. These are purely tags.

If a variant has them, you can access the fields as well:

```rust
let mut value = TestEnum::C {
  foo: 1.23,
  bar: false
};

// Read/write specific fields
*value.field_mut("bar").unwrap() = true;

// Iterate over the entire collection of fields
for field in value.iter_fields() {
  println!("{} = {:?}", field.name(), field.value());
}
```

#### Variant Swapping

It might seem odd to group all variant types under a single trait (why allow `iter_fields` on a unit variant?), but the reason this was done ~~is to easily allow *variant swapping*.~~ As I was recently drafting up the **Design Decisions** section, I discovered that other solutions could have been made to work with variant swapping. So while there are reasons to keep the all-in-one approach, variant swapping is _not_ one of them.

```rust
let mut value: Box<dyn Enum> = Box::new(TestEnum::A);
value.set(Box::new(TestEnum::B(123))).unwrap();
```

#### Serialization

Enums can be serialized and deserialized via reflection without needing to implement `Serialize` or `Deserialize` themselves (which can save thousands of lines of generated code). Below are the ways an enum can be serialized.

> Note, like the rest of reflection-based serialization, the order of the keys in these representations is important!

##### Unit

```json
{
  "type": "my_crate::TestEnum",
  "enum": {
    "variant": "A"
  }
}
```

##### Tuple

```json
{
  "type": "my_crate::TestEnum",
  "enum": {
    "variant": "B",
    "tuple": [
      {
        "type": "usize",
        "value": 123
      }
    ]
  }
}
```

<details>
<summary>Effects on Option</summary>

This ends up making `Option` look a little ugly:

```json
{
  "type": "core::option::Option<usize>",
  "enum": {
    "variant": "Some",
    "tuple": [
      {
        "type": "usize",
        "value": 123
      }
    ]
  }
}
```


</details>

##### Struct

```json
{
  "type": "my_crate::TestEnum",
  "enum": {
    "variant": "C",
    "struct": {
      "foo": {
        "type": "f32",
        "value": 1.23
      },
      "bar": {
        "type": "bool",
        "value": false
      }
    }
  }
}
```

## Design Decisions

<details>
<summary><strong>View Section</strong></summary>

This section is here to provide some context for why certain decisions were made for this PR, alternatives that could have been used instead, and what could be improved upon in the future.

### Variant Representation

One of the biggest decisions was to decide on how to represent variants. The current design uses a "all-in-one" design where unit, tuple, and struct variants are all simultaneously represented by the `Enum` trait. This is not the only way it could have been done, though.

#### Alternatives

##### 1. Variant Traits

One way of representing variants would be to define traits for each variant, implementing them whenever an enum featured at least one instance of them. This would allow us to define variants like:

```rust
pub trait Enum: Reflect {
  fn variant(&self) -> Variant;
}

pub enum Variant<'a> {
    Unit,
    Tuple(&'a dyn TupleVariant),
    Struct(&'a dyn StructVariant),
}

pub trait TupleVariant {
  fn field_len(&self) -> usize;
  // ...
}
```

And then do things like:

```rust
fn get_tuple_len(foo: &dyn Enum) -> usize {
  match foo.variant() {
    Variant::Tuple(tuple) => tuple.field_len(),
    _ => panic!("not a tuple variant!")
  }
}
```

The reason this PR does not go with this approach is because of the fact that variants are not separate types. In other words, we cannot implement traits on specific variants— these cover the *entire* enum. This means we offer an easy footgun:

```rust
let foo: Option<i32> = None;
let my_enum = Box::new(foo) as Box<dyn TupleVariant>;
```

Here, `my_enum` contains `foo`, which is a unit variant. However, since we need to implement `TupleVariant` for `Option` as a whole, it's possible to perform such a cast. This is obviously wrong, but could easily go unnoticed. So unfortunately, this makes it not a good candidate for representing variants.

##### 2. Variant Structs

To get around the issue of traits necessarily needing to apply to both the enum and its variants, we could instead use structs that are created on a per-variant basis. This was also considered but was ultimately [[removed](71d27ab3c6) due to concerns about allocations.

 Each variant struct would probably look something like:

```rust
pub trait Enum: Reflect {
  fn variant_mut(&self) -> VariantMut;
}

pub enum VariantMut<'a> {
    Unit,
    Tuple(TupleVariantMut),
    Struct(StructVariantMut),
}

struct StructVariantMut<'a> {
  fields: Vec<&'a mut dyn Reflect>,
  field_indices: HashMap<Cow<'static, str>, usize>
}
```

This allows us to isolate struct variants into their own defined struct and define methods specifically for their use. It also prevents users from casting to it since it's not a trait. However, this is not an optimal solution. Both `field_indices` and `fields` will require an allocation (remember, a `Box<[T]>` still requires a `Vec<T>` in order to be constructed). This *might* be a problem if called frequently enough.

##### 3. Generated Structs

The original design, implemented by @Davier, instead generates structs specific for each variant. So if we had a variant path like `Foo::Bar`, we'd generate a struct named `FooBarWrapper`. This would be newtyped around the original enum and forward tuple or struct methods to the enum with the chosen variant.

Because it involved using the `Tuple` and `Struct` traits (which are also both bound on `Reflect`), this meant a bit more code had to be generated. For a single struct variant with one field, the generated code amounted to ~110LoC. However, each new field added to that variant only added ~6 more LoC.

In order to work properly, the enum had to be transmuted to the generated struct:

```rust
fn variant(&self) -> crate::EnumVariant<'_> {
  match self {
    Foo::Bar {value: i32} => {
      let wrapper_ref = unsafe { 
        std::mem::transmute::<&Self, &FooBarWrapper>(self) 
      };
      crate::EnumVariant::Struct(wrapper_ref as &dyn crate::Struct)
    }
  }
}
```

This works because `FooBarWrapper` is defined as `repr(transparent)`.

Out of all the alternatives, this would probably be the one most likely to be used again in the future. The reasons for why this PR did not continue to use it was because:

* To reduce generated code (which would hopefully speed up compile times)
* To avoid cluttering the code with generated structs not visible to the user
* To keep bevy_reflect simple and extensible (these generated structs act as proxies and might not play well with current or future systems)
* To avoid additional unsafe blocks
* My own misunderstanding of @Davier's code

That last point is obviously on me. I misjudged the code to be too unsafe and unable to handle variant swapping (which it probably could) when I was rebasing it. Looking over it again when writing up this whole section, I see that it was actually a pretty clever way of handling variant representation.

#### Benefits of All-in-One

As stated before, the current implementation uses an all-in-one approach. All variants are capable of containing fields as far as `Enum` is concerned. This provides a few benefits that the alternatives do not (reduced indirection, safer code, etc.).

The biggest benefit, though, is direct field access. Rather than forcing users to have to go through pattern matching, we grant direct access to the fields contained by the current variant. The reason we can do this is because all of the pattern matching happens internally. Getting the field at index `2` will automatically return `Some(...)` for the current variant if it has a field at that index or `None` if it doesn't (or can't).

This could be useful for scenarios where the variant has already been verified or just set/swapped (or even where the type of variant doesn't matter):

```rust
let dyn_enum: &mut dyn Enum = &mut Foo::Bar {value: 123};
// We know it's the `Bar` variant
let field = dyn_enum.field("value").unwrap();
```

Reflection is not a type-safe abstraction— almost every return value is wrapped in `Option<...>`. There are plenty of places to check and recheck that a value is what Reflect says it is. Forcing users to have to go through `match` each time they want to access a field might just be an extra step among dozens of other verification processes.

 Some might disagree, but ultimately, my view is that the benefit here is an improvement to the ergonomics and usability of reflected enums.

</details>

---

## Changelog

### Added

* Added `Enum` trait
* Added `Enum` impl to `Reflect` derive macro
* Added `DynamicEnum` struct
  * Added `DynamicVariant`
* Added `EnumInfo`
  * Added `VariantInfo`
    * Added `StructVariantInfo`
    * Added `TupleVariantInfo`
    * Added `UnitVariantInfo`
* Added serializtion/deserialization support for enums
  * Added `EnumSerializer`

* Added `VariantType`
* Added `VariantFieldIter`
* Added `VariantField`
* Added `enum_partial_eq(...)`
* Added `enum_hash(...)`

### Changed

* `Option<T>` now implements `Enum`
* `bevy_window` now depends on `bevy_reflect`
  * Implemented `Reflect` and `FromReflect` for `WindowId`
* Derive `FromReflect` on `PerspectiveProjection`
* Derive `FromReflect` on `OrthographicProjection`
* Derive `FromReflect` on `WindowOrigin`
* Derive `FromReflect` on `ScalingMode`
* Derive `FromReflect` on `DepthCalculation`


## Migration Guide

* Enums no longer need to be treated as values and usages of `#[reflect_value(...)]` can be removed or replaced by `#[reflect(...)]`
* Enums (including `Option<T>`) now take a different format when serializing. The format is described above, but this may cause issues for existing scenes that make use of enums. 

---

Also shout out to @nicopap for helping clean up some of the code here! It's a big feature so help like this is really appreciated!

Co-authored-by: Gino Valente <gino.valente.code@gmail.com>
2022-08-02 22:14:41 +00:00
MrGVSV
3d8d922566 bevy_reflect_derive: Tidying up the code (#4712)
# Objective

The `bevy_reflect_derive` crate is not the cleanest or easiest to follow/maintain. The `lib.rs` file is especially difficult with over 1000 lines of code written in a confusing order. This is just a result of growth within the crate and it would be nice to clean it up for future work.

## Solution

Split `bevy_reflect_derive` into many more submodules. The submodules include:

* `container_attributes` - Code relating to container attributes
* `derive_data` - Code relating to reflection-based derive metadata
* `field_attributes` - Code relating to field attributes
* `impls` - Code containing actual reflection implementations
* `reflect_value` - Code relating to reflection-based value metadata
* `registration` - Code relating to type registration
* `utility` - General-purpose utility functions

This leaves the `lib.rs` file to contain only the public macros, making it much easier to digest (and fewer than 200 lines).

By breaking up the code into smaller modules, we make it easier for future contributors to find the code they're looking for or identify which module best fits their own additions.

### Metadata Structs

This cleanup also adds two big metadata structs: `ReflectFieldAttr` and `ReflectDeriveData`. The former is used to store all attributes for a struct field (if any). The latter is used to store all metadata for struct-based derive inputs.

Both significantly reduce code duplication and make editing these macros much simpler. The tradeoff is that we may collect more metadata than needed. However, this is usually a small thing (such as checking for attributes when they're not really needed or creating a `ReflectFieldAttr` for every field regardless of whether they actually have an attribute).

We could try to remove these tradeoffs and squeeze some more performance out, but doing so might come at the cost of developer experience. Personally, I think it's much nicer to create a `ReflectFieldAttr` for every field since it means I don't have to do two `Option` checks. Others may disagree, though, and so we can discuss changing this either in this PR or in a future one.

### Out of Scope

_Some_ documentation has been added or improved, but ultimately good docs are probably best saved for a dedicated PR.

## 🔍 Focus Points (for reviewers)

I know it's a lot to sift through, so here is a list of **key points for reviewers**:

- The following files contain code that was mostly just relocated:
  - `reflect_value.rs`
  - `registration.rs`
- `container_attributes.rs` was also mostly moved but features some general cleanup (reducing nesting, removing hardcoded strings, etc.) and lots of doc comments
- Most impl logic was moved from `lib.rs` to `impls.rs`, but they have been significantly modified to use the new `ReflectDeriveData` metadata struct in order to reduce duplication.
- `derive_data.rs` and `field_attributes.rs` contain almost entirely new code and should probably be given the most attention.
- Likewise, `from_reflect.rs` saw major changes using `ReflectDeriveData` so it should also be given focus.
- There was no change to the `lib.rs` exports so the end-user API should be the same.

## Prior Work

This task was initially tackled by @NathanSWard in #2377 (which was closed in favor of this PR), so hats off to them for beating me to the punch by nearly a year!

---

## Changelog

* **[INTERNAL]** Split `bevy_reflect_derive` into smaller submodules
* **[INTERNAL]** Add `ReflectFieldAttr`
* **[INTERNAL]** Add `ReflectDeriveData`
* Add `BevyManifest::get_path_direct()` method (`bevy_macro_utils`)


Co-authored-by: MrGVSV <49806985+MrGVSV@users.noreply.github.com>
2022-05-12 19:43:23 +00:00