Add unstable-extern-types feature

Author: madsmtm

.github/workflows/ci.yml

@@ -153,7 +153,7 @@ jobs:
       TESTARGS: ${{ matrix.dinghy && ' ' || '--no-fail-fast' }} ${{ matrix.test-args }}
       SOME_FEATURES: ${{ matrix.features || 'malloc,block,exception,foundation' }}
       FEATURES: ${{ matrix.features || 'malloc,block,exception,foundation,catch-all,verify_message,uuid' }}
-      UNSTABLE_FEATURES: ${{ matrix.unstable-features || 'unstable-autoreleasesafe,unstable-c-unwind' }}
+      UNSTABLE_FEATURES: ${{ matrix.unstable-features || 'unstable-autoreleasesafe,unstable-c-unwind,unstable-extern-types' }}
       CMD: cargo
 
     runs-on: ${{ matrix.os }}

objc-sys/Cargo.toml

@@ -33,26 +33,29 @@ default = ["std", "apple"]
 std = ["alloc"]
 alloc = []
 
-# Link to Apple's objc4
+# Link to Apple's objc4.
 apple = []
 
-# Link to GNUStep's libobjc2
+# Link to GNUStep's libobjc2.
 gnustep-1-7 = []
 gnustep-1-8 = ["gnustep-1-7"]
 gnustep-1-9 = ["gnustep-1-8"]
 gnustep-2-0 = ["gnustep-1-9"]
 gnustep-2-1 = ["gnustep-2-0"]
 
-# Link to Microsoft's libobjc2
+# Link to Microsoft's libobjc2.
 unstable-winobjc = ["gnustep-1-8"]
 
-# Link to ObjFW
+# Link to ObjFW.
 unstable-objfw = []
 
-# Use nightly c_unwind feature
+# Use nightly c_unwind feature.
 unstable-c-unwind = []
 
-# Private
+# Use nightly extern_types feature to mark opaque types as !Sized.
+unstable-extern-types = []
+
+# Private.
 unstable-exception = ["cc"]
 unstable-docsrs = []
 

objc-sys/src/lib.rs

@@ -28,6 +28,7 @@
 #![cfg_attr(feature = "unstable-c-unwind", feature(c_unwind))]
 #![cfg_attr(feature = "unstable-docsrs", feature(doc_auto_cfg, doc_cfg_hide))]
 #![cfg_attr(feature = "unstable-docsrs", doc(cfg_hide(doc)))]
+#![cfg_attr(feature = "unstable-extern-types", feature(extern_types))]
 
 // TODO: Remove this and add "no-std" category to Cargo.toml
 // Requires a better solution for C-types in `no_std` crates.
@@ -41,9 +42,6 @@ compile_error!("The `std` feature currently must be enabled.");
 #[doc = include_str!("../README.md")]
 extern "C" {}
 
-use core::cell::UnsafeCell;
-use core::marker::{PhantomData, PhantomPinned};
-
 macro_rules! generate_linking_tests {
     {
         extern $abi:literal {$(
@@ -170,9 +168,18 @@ pub use various::*;
 ///
 /// Downstream libraries can always manually opt in to these types afterwards.
 /// (It's also less of a breaking change on our part if we re-add these).
-///
-/// TODO: Replace this with `extern type` to also mark it as `!Sized`.
-type OpaqueData = UnsafeCell<PhantomData<(*const UnsafeCell<()>, PhantomPinned)>>;
+#[cfg(not(feature = "unstable-extern-types"))]
+type OpaqueData = core::cell::UnsafeCell<
+    core::marker::PhantomData<(
+        *const core::cell::UnsafeCell<()>,
+        core::marker::PhantomPinned,
+    )>,
+>;
+
+#[cfg(feature = "unstable-extern-types")]
+extern "C" {
+    type OpaqueData;
+}
 
 #[cfg(test)]
 mod tests {

objc2/CHANGELOG.md

@@ -16,6 +16,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 * **BREAKING**: Added required `ClassType::NAME` constant for statically
   determining the name of a specific class.
 * Allow directly specifying class name in declare_class! macro.
+* Added the `"unstable-extern-types"` feature flags to make relevant types
+  `!Sized`.
 
 ### Changed
 * **BREAKING**: Slightly changed when a type implements `?Sized` to support

objc2/Cargo.toml

@@ -47,6 +47,14 @@ malloc = ["malloc_buf"]
 # Expose features that requires creating blocks.
 block = ["block2"]
 
+# Runtime selection. See `objc-sys` for details.
+apple = ["objc-sys/apple", "objc2-encode/apple", "block2?/apple"]
+gnustep-1-7 = ["objc-sys/gnustep-1-7", "objc2-encode/gnustep-1-7", "block2?/gnustep-1-7"]
+gnustep-1-8 = ["gnustep-1-7", "objc-sys/gnustep-1-8", "objc2-encode/gnustep-1-8", "block2?/gnustep-1-8"]
+gnustep-1-9 = ["gnustep-1-8", "objc-sys/gnustep-1-9", "objc2-encode/gnustep-1-9", "block2?/gnustep-1-9"]
+gnustep-2-0 = ["gnustep-1-9", "objc-sys/gnustep-2-0", "objc2-encode/gnustep-2-0", "block2?/gnustep-2-0"]
+gnustep-2-1 = ["gnustep-2-0", "objc-sys/gnustep-2-1", "objc2-encode/gnustep-2-1", "block2?/gnustep-2-1"]
+
 # Make the `sel!` macro look up the selector statically.
 #
 # The plan is to enable this by default, but right now we are uncertain of
@@ -69,16 +77,13 @@ unstable-autoreleasesafe = []
 # `objc2-encode/unstable-c-unwind` to use this.
 unstable-c-unwind = []
 
-# For better documentation on docs.rs
-unstable-docsrs = []
+# Use nightly features to make Object and other types !Sized.
+#
+# You must manually enable `objc-sys/unstable-extern-types` to use this.
+unstable-extern-types = []
 
-# Runtime selection. See `objc-sys` for details.
-apple = ["objc-sys/apple", "objc2-encode/apple", "block2?/apple"]
-gnustep-1-7 = ["objc-sys/gnustep-1-7", "objc2-encode/gnustep-1-7", "block2?/gnustep-1-7"]
-gnustep-1-8 = ["gnustep-1-7", "objc-sys/gnustep-1-8", "objc2-encode/gnustep-1-8", "block2?/gnustep-1-8"]
-gnustep-1-9 = ["gnustep-1-8", "objc-sys/gnustep-1-9", "objc2-encode/gnustep-1-9", "block2?/gnustep-1-9"]
-gnustep-2-0 = ["gnustep-1-9", "objc-sys/gnustep-2-0", "objc2-encode/gnustep-2-0", "block2?/gnustep-2-0"]
-gnustep-2-1 = ["gnustep-2-0", "objc-sys/gnustep-2-1", "objc2-encode/gnustep-2-1", "block2?/gnustep-2-1"]
+# Private.
+unstable-docsrs = []
 
 [dependencies]
 malloc_buf = { version = "1.0", optional = true }

objc2/src/cache.rs

@@ -1,3 +1,4 @@
+use core::ffi::c_void;
 use core::ptr;
 use core::sync::atomic::{AtomicPtr, Ordering};
 
@@ -7,7 +8,7 @@ use crate::runtime::{Class, Sel};
 /// Allows storing a [`Sel`] in a static and lazily loading it.
 #[doc(hidden)]
 pub struct CachedSel {
-    ptr: AtomicPtr<ffi::objc_selector>,
+    ptr: AtomicPtr<c_void>,
 }
 
 impl CachedSel {
@@ -24,7 +25,7 @@ impl CachedSel {
     #[doc(hidden)]
     pub unsafe fn get(&self, name: &str) -> Sel {
         // `Relaxed` should be fine since `sel_registerName` is thread-safe.
-        let ptr = self.ptr.load(Ordering::Relaxed);
+        let ptr: *const ffi::objc_selector = self.ptr.load(Ordering::Relaxed).cast();
         unsafe { Sel::from_ptr(ptr) }.unwrap_or_else(|| {
             // The panic inside `Sel::register_unchecked` is unfortunate, but
             // strict correctness is more important than speed
@@ -34,7 +35,7 @@ impl CachedSel {
             // We know this, because we construct it in `sel!` ourselves
             let sel = unsafe { Sel::register_unchecked(name.as_ptr().cast()) };
             self.ptr
-                .store(sel.as_ptr() as *mut ffi::objc_selector, Ordering::Relaxed);
+                .store(sel.as_ptr() as *mut c_void, Ordering::Relaxed);
             sel
         })
     }
@@ -43,7 +44,7 @@ impl CachedSel {
 /// Allows storing a [`Class`] reference in a static and lazily loading it.
 #[doc(hidden)]
 pub struct CachedClass {
-    ptr: AtomicPtr<Class>,
+    ptr: AtomicPtr<c_void>,
 }
 
 impl CachedClass {
@@ -60,12 +61,12 @@ impl CachedClass {
     #[doc(hidden)]
     pub unsafe fn get(&self, name: &str) -> Option<&'static Class> {
         // `Relaxed` should be fine since `objc_getClass` is thread-safe.
-        let ptr = self.ptr.load(Ordering::Relaxed);
+        let ptr: *const Class = self.ptr.load(Ordering::Relaxed).cast();
         if let Some(cls) = unsafe { ptr.as_ref() } {
             Some(cls)
         } else {
             let ptr: *const Class = unsafe { ffi::objc_getClass(name.as_ptr().cast()) }.cast();
-            self.ptr.store(ptr as *mut Class, Ordering::Relaxed);
+            self.ptr.store(ptr as *mut c_void, Ordering::Relaxed);
             unsafe { ptr.as_ref() }
         }
     }

objc2/src/foundation/array.rs

@@ -63,6 +63,8 @@ __inner_extern_class!(
 );
 
 // SAFETY: Same as Id<T, O> (which is what NSArray effectively stores).
+//
+// Duplicated here, rustdoc doesn't show these otherwise.
 unsafe impl<T: ?Sized + Message + Sync + Send> Sync for NSArray<T, Shared> {}
 unsafe impl<T: ?Sized + Message + Sync + Send> Send for NSArray<T, Shared> {}
 unsafe impl<T: ?Sized + Message + Sync> Sync for NSArray<T, Owned> {}

objc2/src/foundation/mutable_array.rs

@@ -35,7 +35,7 @@ __inner_extern_class!(
 
 // SAFETY: Same as NSArray<T, O>
 //
-// Put here because rustdoc doesn't show these otherwise
+// Duplicated here, rustdoc doesn't show these otherwise.
 unsafe impl<T: ?Sized + Message + Sync + Send> Sync for NSMutableArray<T, Shared> {}
 unsafe impl<T: ?Sized + Message + Sync + Send> Send for NSMutableArray<T, Shared> {}
 unsafe impl<T: ?Sized + Message + Sync> Sync for NSMutableArray<T, Owned> {}

objc2/src/foundation/set.rs

@@ -28,7 +28,9 @@ __inner_extern_class!(
     }
 );
 
-// SAFETY: Same as NSArray<T, O>
+// SAFETY: Same as Id<T, O>.
+//
+// Duplicated here, rustdoc doesn't show these otherwise.
 unsafe impl<T: ?Sized + Message + Sync + Send> Sync for NSSet<T, Shared> {}
 unsafe impl<T: ?Sized + Message + Sync + Send> Send for NSSet<T, Shared> {}
 unsafe impl<T: ?Sized + Message + Sync> Sync for NSSet<T, Owned> {}

objc2/src/lib.rs

@@ -167,6 +167,7 @@
 )]
 #![cfg_attr(feature = "unstable-c-unwind", feature(c_unwind))]
 #![cfg_attr(feature = "unstable-docsrs", feature(doc_auto_cfg))]
+#![cfg_attr(feature = "unstable-extern-types", feature(extern_types, ptr_metadata))]
 #![warn(elided_lifetimes_in_paths)]
 #![warn(missing_docs)]
 #![deny(non_ascii_idents)]
@@ -186,7 +187,10 @@ compile_error!("The `std` feature currently must be enabled.");
 extern crate alloc;
 extern crate std;
 
+#[cfg(not(feature = "unstable-extern-types"))]
 pub(crate) use core::marker::Sized as Thin;
+#[cfg(feature = "unstable-extern-types")]
+pub(crate) use core::ptr::Thin;
 
 // The example uses NSObject without doing the __gnustep_hack
 #[cfg(all(feature = "apple", doctest))]