Feat(block2): Add new with_encoding unsafe block constructors

Signed-off-by: Paul Mabileau <paul.mabileau@harfanglab.fr>

crates/block2/Cargo.toml

@@ -59,6 +59,12 @@ unstable-private = []
 [dependencies]
 objc2 = { path = "../objc2", version = "0.5.2", default-features = false }
 
+[dev-dependencies.objc2-foundation]
+path = "../../framework-crates/objc2-foundation"
+version = "0.2.2"
+default-features = false
+features = ["NSError"]
+
 [package.metadata.docs.rs]
 default-target = "aarch64-apple-darwin"
 features = ["unstable-private"]

crates/block2/src/lib.rs

@@ -379,7 +379,7 @@ pub use self::block::Block;
 pub use self::global::GlobalBlock;
 pub use self::rc_block::RcBlock;
 pub use self::stack::StackBlock;
-pub use self::traits::{BlockFn, IntoBlock};
+pub use self::traits::{BlockFn, IntoBlock, ManualBlockEncoding};
 
 /// Deprecated alias for a `'static` `StackBlock`.
 #[deprecated = "renamed to `StackBlock`"]

crates/block2/src/rc_block.rs

@@ -7,6 +7,7 @@ use objc2::encode::{EncodeArguments, EncodeReturn};
 
 use crate::abi::BlockHeader;
 use crate::debug::debug_block_header;
+use crate::traits::{ManualBlockEncoding, NoBlockEncoding};
 use crate::{ffi, Block, IntoBlock, StackBlock};
 
 /// A reference-counted Objective-C block that is stored on the heap.
@@ -91,14 +92,58 @@ impl<F: ?Sized> RcBlock<F> {
     ///
     /// When the block is called, it will return the value that results from
     /// calling the closure.
-    //
+    #[inline]
+    pub fn new<'f, A, R, Closure>(closure: Closure) -> Self
+    where
+        A: EncodeArguments,
+        R: EncodeReturn,
+        Closure: IntoBlock<'f, A, R, Dyn = F>,
+    {
+        // SAFETY: no encoding is given.
+        unsafe { Self::with_encoding::<_, _, _, NoBlockEncoding<A, R>>(closure) }
+    }
+
+    /// Constructs a new [`RcBlock`] with the given function and encoding
+    /// information.
+    ///
+    /// See [`StackBlock::with_encoding`] as to why and how this could be
+    /// useful. The same requirements as [`Self::new`] apply here as well.
+    ///
+    /// # Safety
+    ///
+    /// The raw encoding string given through `E` must be correct with respect
+    /// to the given function's input and output types: see
+    /// [`ManualBlockEncoding`].
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use core::ffi::CStr;
+    /// # use block2::{Block, ManualBlockEncoding, RcBlock};
+    /// # use objc2_foundation::NSError;
+    /// #
+    /// struct MyBlockEncoding;
+    /// unsafe impl ManualBlockEncoding for MyBlockEncoding {
+    ///     type Arguments = (*mut NSError,);
+    ///     type Return = i32;
+    ///     const ENCODING_CSTR: &'static CStr = cr#"i16@?0@"NSError"8"#;
+    /// }
+    ///
+    /// let my_block = unsafe {
+    ///     RcBlock::with_encoding::<_, _, _, MyBlockEncoding>(|_err: *mut NSError| {
+    ///         42i32
+    ///     })
+    /// };
+    /// assert_eq!(my_block.call((std::ptr::null_mut(),)), 42);
+    /// ```
     // Note: Unsure if this should be #[inline], but I think it may be able to
     // benefit from not being so.
-    pub fn new<'f, A, R, Closure>(closure: Closure) -> Self
+    pub unsafe fn with_encoding<'f, A, R, Closure, E>(closure: Closure) -> Self
     where
         A: EncodeArguments,
         R: EncodeReturn,
         Closure: IntoBlock<'f, A, R, Dyn = F>,
+        E: ManualBlockEncoding<Arguments = A, Return = R>,
     {
         // SAFETY: The stack block is copied once below.
         //
@@ -108,7 +153,9 @@ impl<F: ?Sized> RcBlock<F> {
         //
         // Clang doesn't do this optimization either.
         // <https://github.com/llvm/llvm-project/blob/llvmorg-17.0.6/clang/lib/CodeGen/CGBlocks.cpp#L281-L284>
-        let block = unsafe { StackBlock::new_no_clone(closure) };
+        //
+        // Encoding safety is supposed to be upheld by the caller.
+        let block = unsafe { StackBlock::new_no_clone::<E>(closure) };
 
         // Transfer ownership from the stack to the heap.
         let mut block = ManuallyDrop::new(block);

crates/block2/src/stack.rs

@@ -1,4 +1,4 @@
-use core::ffi::c_void;
+use core::ffi::{c_void, CStr};
 use core::fmt;
 use core::marker::PhantomData;
 use core::mem::{self, MaybeUninit};
@@ -10,9 +10,11 @@ use std::os::raw::c_ulong;
 use objc2::encode::{EncodeArguments, EncodeReturn, Encoding, RefEncode};
 
 use crate::abi::{
-    BlockDescriptor, BlockDescriptorCopyDispose, BlockDescriptorPtr, BlockFlags, BlockHeader,
+    BlockDescriptor, BlockDescriptorCopyDispose, BlockDescriptorCopyDisposeSignature,
+    BlockDescriptorPtr, BlockDescriptorSignature, BlockFlags, BlockHeader,
 };
 use crate::debug::debug_block_header;
+use crate::traits::{ManualBlockEncoding, ManualBlockEncodingExt, NoBlockEncoding};
 use crate::{ffi, Block, IntoBlock};
 
 /// An Objective-C block constructed on the stack.
@@ -103,6 +105,17 @@ impl<'f, A, R, Closure> StackBlock<'f, A, R, Closure> {
         reserved: 0,
         size: Self::SIZE,
     };
+
+    /// The [`BlockDescriptorSignature`] corresponding to
+    /// [`Self::DESCRIPTOR_BASIC`] with the given `encoding` additionally set.
+    #[inline(always)]
+    const fn descriptor_basic_with_encoding(encoding: &'static CStr) -> BlockDescriptorSignature {
+        BlockDescriptorSignature {
+            reserved: Self::DESCRIPTOR_BASIC.reserved,
+            size: Self::DESCRIPTOR_BASIC.size,
+            encoding: encoding.as_ptr(),
+        }
+    }
 }
 
 // `StackBlock::new`
@@ -140,9 +153,30 @@ impl<'f, A, R, Closure: Clone> StackBlock<'f, A, R, Closure> {
         copy: Some(Self::clone_closure),
         dispose: Some(Self::drop_closure),
     };
+
+    /// The [`BlockDescriptorCopyDisposeSignature`] corresponding to
+    /// [`Self::DESCRIPTOR_WITH_CLONE`] with the given `encoding` additionally
+    /// set.
+    #[inline(always)]
+    const fn descriptor_with_clone_and_encoding(
+        encoding: &'static CStr,
+    ) -> BlockDescriptorCopyDisposeSignature {
+        BlockDescriptorCopyDisposeSignature {
+            reserved: Self::DESCRIPTOR_WITH_CLONE.reserved,
+            size: Self::DESCRIPTOR_WITH_CLONE.size,
+            copy: Self::DESCRIPTOR_WITH_CLONE.copy,
+            dispose: Self::DESCRIPTOR_WITH_CLONE.dispose,
+            encoding: encoding.as_ptr(),
+        }
+    }
 }
 
-impl<'f, A, R, Closure> StackBlock<'f, A, R, Closure> {
+impl<'f, A, R, Closure> StackBlock<'f, A, R, Closure>
+where
+    A: EncodeArguments,
+    R: EncodeReturn,
+    Closure: IntoBlock<'f, A, R> + Clone,
+{
     /// Construct a `StackBlock` with the given closure.
     ///
     /// Note that this requires [`Clone`], as a C block is generally assumed
@@ -154,21 +188,90 @@ impl<'f, A, R, Closure> StackBlock<'f, A, R, Closure> {
     ///
     /// [`RcBlock::new`]: crate::RcBlock::new
     #[inline]
-    pub fn new(closure: Closure) -> Self
+    pub fn new(closure: Closure) -> Self {
+        // SAFETY: no encoding is given.
+        unsafe { Self::with_encoding::<NoBlockEncoding<A, R>>(closure) }
+    }
+
+    /// Constructs a new [`StackBlock`] with the given function and encoding
+    /// information.
+    ///
+    /// Some particular newer-ish Apple Objective-C APIs expect the block they
+    /// are given to be created with encoding information set in the block
+    /// object itself and crash the calling process if they fail to find it,
+    /// which renders them pretty much unusable with only [`Self::new`] that
+    /// currently does not set such encoding information. This is for example
+    /// the case in [`FileProvider`] for [`NSFileProviderManager`]'s
+    /// [`reimportItemsBelowItemWithIdentifier:completionHandler:`] and
+    /// [`waitForStabilizationWithCompletionHandler:`], but also in
+    /// [`NetworkExtension`] for [`NEFilterDataProvider`]'s
+    /// [`applySettings:completionHandler`]. A complete list of such APIs may
+    /// not be easily obtained, though.
+    ///
+    /// This encoding information string could technically be generated at
+    /// compile time using the generic parameters already available to
+    /// [`Self::new`]. However, doing so would require some constant evaluation
+    /// features that are yet to be implemented and stabilized in the Rust
+    /// compiler. This function is therefore exposed in the meantime so users
+    /// may still be able to call the concerned APIs by providing the raw
+    /// encoding information string themselves, thus obtaining a block
+    /// containing it and working with these APIs.
+    ///
+    /// The same requirements as [`Self::new`] apply here as well.
+    ///
+    /// [`FileProvider`]: https://developer.apple.com/documentation/fileprovider?language=objc
+    /// [`NSFileProviderManager`]: https://developer.apple.com/documentation/fileprovider/nsfileprovidermanager?language=objc
+    /// [`reimportItemsBelowItemWithIdentifier:completionHandler:`]: https://developer.apple.com/documentation/fileprovider/nsfileprovidermanager/reimportitems(below:completionhandler:)?language=objc
+    /// [`waitForStabilizationWithCompletionHandler:`]: https://developer.apple.com/documentation/fileprovider/nsfileprovidermanager/waitforstabilization(completionhandler:)?language=objc
+    /// [`NetworkExtension`]: https://developer.apple.com/documentation/networkextension?language=objc
+    /// [`NEFilterDataProvider`]: https://developer.apple.com/documentation/networkextension/nefilterdataprovider?language=objc
+    /// [`applySettings:completionHandler`]: https://developer.apple.com/documentation/networkextension/nefilterdataprovider/3181998-applysettings?language=objc
+    ///
+    /// # Safety
+    ///
+    /// The raw encoding string given through `E` must be correct with respect
+    /// to the given function's input and output types: see
+    /// [`ManualBlockEncoding`].
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use core::ffi::CStr;
+    /// # use block2::{Block, ManualBlockEncoding, StackBlock};
+    /// # use objc2_foundation::NSError;
+    /// #
+    /// struct MyBlockEncoding;
+    /// unsafe impl ManualBlockEncoding for MyBlockEncoding {
+    ///     type Arguments = (*mut NSError,);
+    ///     type Return = i32;
+    ///     const ENCODING_CSTR: &'static CStr = cr#"i16@?0@"NSError"8"#;
+    /// }
+    ///
+    /// let my_block = unsafe {
+    ///     StackBlock::with_encoding::<MyBlockEncoding>(|_err: *mut NSError| {
+    ///         42i32
+    ///     })
+    /// };
+    /// assert_eq!(my_block.call((std::ptr::null_mut(),)), 42);
+    /// ```
+    #[inline]
+    pub unsafe fn with_encoding<E>(closure: Closure) -> Self
     where
-        A: EncodeArguments,
-        R: EncodeReturn,
-        Closure: IntoBlock<'f, A, R> + Clone,
+        E: ManualBlockEncoding<Arguments = A, Return = R>,
     {
         let header = BlockHeader {
             isa: unsafe { ptr::addr_of!(ffi::_NSConcreteStackBlock) },
-            // TODO: Add signature.
-            flags: BlockFlags::BLOCK_HAS_COPY_DISPOSE,
+            flags: BlockFlags::BLOCK_HAS_COPY_DISPOSE
+                | if !E::is_none() {
+                    BlockFlags::BLOCK_HAS_SIGNATURE
+                } else {
+                    BlockFlags::EMPTY
+                },
             reserved: MaybeUninit::new(0),
             invoke: Some(Closure::__get_invoke_stack_block()),
             // TODO: Use `Self::DESCRIPTOR_BASIC` when `F: Copy`
             // (probably only possible with specialization).
-            descriptor: BlockDescriptorPtr {
+            descriptor: if E::is_none() {
                 // SAFETY: The descriptor must (probably) point to `static`
                 // memory, as Objective-C code may assume the block's
                 // descriptor to be alive past the lifetime of the block
@@ -184,7 +287,16 @@ impl<'f, A, R, Closure> StackBlock<'f, A, R, Closure> {
                 // does not contain `UnsafeCell` (it does not).
                 //
                 // [promotion]: https://doc.rust-lang.org/reference/destructors.html#constant-promotion
-                with_copy_dispose: &Self::DESCRIPTOR_WITH_CLONE,
+                BlockDescriptorPtr {
+                    with_copy_dispose: &Self::DESCRIPTOR_WITH_CLONE,
+                }
+            } else {
+                // SAFETY: promotion is guaranteed with the used inline const.
+                BlockDescriptorPtr {
+                    with_copy_dispose_signature: &const {
+                        Self::descriptor_with_clone_and_encoding(E::ENCODING_CSTR)
+                    },
+                }
             },
         };
         Self {
@@ -195,11 +307,11 @@ impl<'f, A, R, Closure> StackBlock<'f, A, R, Closure> {
     }
 }
 
-// `RcBlock::new`
+// `RcBlock::with_encoding`
 impl<'f, A, R, Closure> StackBlock<'f, A, R, Closure> {
     crate::__c_unwind! {unsafe extern "C" fn empty_clone_closure(_dst: *mut c_void, _src: *const c_void) {
         // We do nothing, the closure has been `memmove`'d already, and
-        // ownership will be passed in `RcBlock::new`.
+        // ownership will be passed in `RcBlock::with_encoding`.
     }}
 
     const DESCRIPTOR_WITH_DROP: BlockDescriptorCopyDispose = BlockDescriptorCopyDispose {
@@ -209,34 +321,71 @@ impl<'f, A, R, Closure> StackBlock<'f, A, R, Closure> {
         dispose: Some(Self::drop_closure),
     };
 
+    /// The [`BlockDescriptorCopyDisposeSignature`] corresponding to
+    /// [`Self::DESCRIPTOR_WITH_DROP`] with the given `encoding` additionally
+    /// set.
+    #[inline(always)]
+    const fn descriptor_with_drop_and_encoding(
+        encoding: &'static CStr,
+    ) -> BlockDescriptorCopyDisposeSignature {
+        BlockDescriptorCopyDisposeSignature {
+            reserved: Self::DESCRIPTOR_WITH_DROP.reserved,
+            size: Self::DESCRIPTOR_WITH_DROP.size,
+            copy: Self::DESCRIPTOR_WITH_DROP.copy,
+            dispose: Self::DESCRIPTOR_WITH_DROP.dispose,
+            encoding: encoding.as_ptr(),
+        }
+    }
+
     /// # Safety
     ///
-    /// `_Block_copy` must be called on the resulting stack block only once.
+    ///  * `_Block_copy` must be called on the resulting stack block only once.
+    ///  * Encoding must be correct with respect to the given function's input
+    ///    and output types: see [`ManualBlockEncoding`].
     #[inline]
-    pub(crate) unsafe fn new_no_clone(closure: Closure) -> Self
+    pub(crate) unsafe fn new_no_clone<E>(closure: Closure) -> Self
     where
         A: EncodeArguments,
         R: EncodeReturn,
         Closure: IntoBlock<'f, A, R>,
+        E: ManualBlockEncoding<Arguments = A, Return = R>,
     {
         // Don't need to emit copy and dispose helpers if the closure
         // doesn't need it.
-        //
-        // TODO: Add signature.
         let flags = if mem::needs_drop::<Self>() {
             BlockFlags::BLOCK_HAS_COPY_DISPOSE
         } else {
             BlockFlags::EMPTY
+        } | if !E::is_none() {
+            BlockFlags::BLOCK_HAS_SIGNATURE
+        } else {
+            BlockFlags::EMPTY
         };
         // See discussion in `new` above with regards to the safety of the
         // pointer to the descriptor.
         let descriptor = if mem::needs_drop::<Self>() {
+            if E::is_none() {
+                // SAFETY: see above.
+                BlockDescriptorPtr {
+                    with_copy_dispose: &Self::DESCRIPTOR_WITH_DROP,
+                }
+            } else {
+                // SAFETY: promotion is guaranteed with the used inline const.
+                BlockDescriptorPtr {
+                    with_copy_dispose_signature: &const {
+                        Self::descriptor_with_drop_and_encoding(E::ENCODING_CSTR)
+                    },
+                }
+            }
+        } else if E::is_none() {
+            // SAFETY: see above.
             BlockDescriptorPtr {
-                with_copy_dispose: &Self::DESCRIPTOR_WITH_DROP,
+                basic: &Self::DESCRIPTOR_BASIC,
             }
         } else {
+            // SAFETY: promotion is guaranteed with the used inline const.
             BlockDescriptorPtr {
-                basic: &Self::DESCRIPTOR_BASIC,
+                with_signature: &const { Self::descriptor_basic_with_encoding(E::ENCODING_CSTR) },
             }
         };