Mark Metal protocols as IsRetainable

This may technically be a breaking change if the user implemented these
protocols themselves on a `Mutable` class, but that'd be unsound anyhow,
so I'll consider this a correctness fix.

This is useful for wgpu, see gfx-rs/wgpu#5641,
and the hack will become unnecessary after
#563.

crates/header-translator/src/stmt.rs

@@ -2018,6 +2018,22 @@ impl Stmt {
                         }
                         write!(f, "IsMainThreadOnly")?;
                     }
+                    // HACK: Make all Metal protocols retainable (i.e. allow
+                    // using `.retain()` on `&ProtocolObject<dyn MTLDevice>`).
+                    //
+                    // This is a problem generally, but especially useful in
+                    // Metal, as most of the functionality is only exposed
+                    // through protocols (instead of concrete classes).
+                    //
+                    // This should become unnecessary after #563.
+                    if id.library_name() == "Metal" {
+                        if protocols.is_empty() {
+                            write!(f, ": ")?;
+                        } else {
+                            write!(f, "+ ")?;
+                        }
+                        write!(f, "IsRetainable")?;
+                    }
                     writeln!(f, " {{")?;
 
                     let required_items = self.required_items();

crates/objc2/src/__framework_prelude.rs

@@ -15,7 +15,7 @@ pub use crate::encode::{Encode, Encoding, RefEncode};
 pub use crate::ffi::{NSInteger, NSIntegerMax, NSUInteger, NSUIntegerMax, IMP};
 pub use crate::mutability::{
     Immutable, ImmutableWithMutableSubclass, InteriorMutable, IsIdCloneable, IsMainThreadOnly,
-    MainThreadOnly, Mutable, MutableWithImmutableSuperclass,
+    IsRetainable, MainThreadOnly, Mutable, MutableWithImmutableSuperclass,
 };
 pub use crate::rc::{Allocated, DefaultId, Id};
 pub use crate::runtime::{

crates/objc2/src/topics/about_generated/CHANGELOG.md

@@ -17,6 +17,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
   This means that they have the usual `ops::BitAnd`, `ops::BitOr`, `ops::Not`,
   etc. implementations that you would expect from an option enum.
+* Added optional support for a few methods depending on types from `libc`.
 * Added new framework crates:
   - `CoreBluetooth` / `objc2-core-bluetooth`.
   - `Virtualization` / `objc2-virtualization`.
@@ -40,21 +41,27 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   - `PhotosUI` / `objc2-photos-ui`.
   - `FinderSync` / `objc2-finder-sync`.
   - `Social` / `objc2-social`.
-* Added `objc2_quartz_core::CAMetalDrawable` and
-  `objc2_quartz_core::CAMetalLayer`.
-* Added methods to access `CALayer` from `objc2_app_kit::NSView`.
-* Added optional support for a few methods depending on types from `libc`.
-* Added `MTLCounterErrorValue`, `MTLCounterDontSample` and
-  `MTLTextureSwizzleChannelsDefault` Metal constants.
+* `objc2-quartz-core`: Added `CAMetalDrawable` and `CAMetalLayer`.
+* `objc2-app-kit`: Added methods to access `CALayer` from `NSView`.
+* `objc2-metal`: Added `MTLCounterErrorValue`, `MTLCounterDontSample` and
+  `MTLTextureSwizzleChannelsDefault` constants.
 
 ### Changed
 * Updated SDK from Xcode 15.3 to 15.4.
 
   View the release notes to learn more details:
   - [15.4](https://developer.apple.com/documentation/xcode-release-notes/xcode-15_4-release-notes)
 
+### Fixed
+* `objc2-metal`: All protocols are now marked as `IsRetainable`.
+
+  This may technically break your code if you had some custom object that
+  implements the protocol, but was marked with `Mutability = Mutable`, but
+  Metal protocols are assumed retainable by Objective-C code, so that'd have
+  been unsound anyway.
+
 ### Removed
-* `objc2_metal`: Removed internal `__MTLPackedFloat3` and made `MTLPackedFloat3` public.
+* `objc2-metal`: Removed internal `__MTLPackedFloat3` and made `MTLPackedFloat3` public.
 
 
 ## 0.2.0 - 2024-04-17