Merge pull request #57 from madsmtm/exception-merge

Move `objc2_exception` into `objc2::exception`

.github/workflows/apple.yml

@@ -76,4 +76,4 @@ jobs:
       with:
         command: test
         # Not using --all-features because some features are nightly-only
-        args: --verbose --no-fail-fast --features block,exception,verify_message
+        args: --verbose --no-fail-fast --features block,exception,catch_all,verify_message

.github/workflows/gnustep.yml

@@ -114,4 +114,4 @@ jobs:
       with:
         command: test
         # Not using --all-features because some features are nightly-only
-        args: --verbose --no-fail-fast --features gnustep-1-9,block,exception,verify_message
+        args: --verbose --no-fail-fast --features gnustep-1-9,block,exception,catch_all,verify_message

.travis-disabled.yml

@@ -23,8 +23,8 @@ jobs:
     script:
     - cargo test --workspace --verbose
     - # TODO: cargo test --workspace --verbose --all-features
-    - # objc2_exception doesn't work on 32bit?
-      cargo test --workspace --exclude objc2_exception --verbose -Z build-std --target i686-apple-darwin
+    - # exception doesn't work on 32bit?
+      cargo test --workspace --verbose -Z build-std --target i686-apple-darwin
     - # TODO: cargo test --workspace --verbose --all-features -Z build-std --target i686-apple-darwin
 
   - name: MacOS 11.3

Cargo.toml

@@ -4,7 +4,6 @@ members = [
     "objc2_block",
     "objc2_block_sys",
     "objc2_encode",
-    "objc2_exception",
     "objc2_foundation",
     "objc2_sys",
     "objc2_test_utils",

objc2/Cargo.toml

@@ -24,12 +24,18 @@ exclude = [
 build = "build.rs"
 
 [features]
-exception = ["objc2_exception"]
+# Enables `objc2::exception::throw` and `objc2::exception::catch`
+exception = ["cc"]
+
+# Wrap every `objc2::msg_send` call in a `@try/@catch` block
+catch_all = ["exception"]
 verify_message = []
 unstable_autoreleasesafe = []
 
 [dependencies]
 malloc_buf = "1.0"
 objc2_sys = { path = "../objc2_sys" }
 objc2_encode = { path = "../objc2_encode" }
-objc2_exception = { path = "../objc2_exception", optional = true }
+
+[build-dependencies]
+cc = { version = "1", optional = true }

objc2/README.md

@@ -94,7 +94,7 @@ decl.register();
 
 By default, if the `msg_send!` macro causes an exception to be thrown, this
 will unwind into Rust resulting in unsafe, undefined behavior.
-However, this crate has an `"exception"` feature which, when enabled, wraps
+However, this crate has an `"catch_all"` feature which, when enabled, wraps
 each `msg_send!` in a `@try`/`@catch` and panics if an exception is caught,
 preventing Objective-C from unwinding into Rust.
 

objc2/build.rs

@@ -6,4 +6,18 @@ fn main() {
 
     let runtime = env::var("DEP_OBJC_RUNTIME").unwrap();
     println!("cargo:rustc-cfg={}", runtime);
+
+    #[cfg(feature = "exception")]
+    {
+        println!("cargo:rerun-if-changed=extern/exception.m");
+
+        let mut builder = cc::Build::new();
+        builder.file("extern/exception.m");
+
+        for flag in env::var("DEP_OBJC_CC_ARGS").unwrap().split(' ') {
+            builder.flag(flag);
+        }
+
+        builder.compile("librust_objc_try_catch_exception.a");
+    }
 }

objc2_exception/extern/exception.m → objc2/extern/exception.m

@@ -1,7 +1,7 @@
 // Don't include any headers, cross compilation is difficult to set up
 // properly in such situations.
 
-/// We're linking to `libobjc` so this should be available.
+/// We're linking to `libobjc` in build.rs, so this should be available.
 ///
 /// See <https://clang.llvm.org/docs/AutomaticReferenceCounting.html#arc-runtime-objc-retain>.
 id objc_retain(id value);

objc2/src/exception.rs

@@ -1,10 +1,87 @@
+//! Objective-C's @throw and @try/@catch.
+//!
+//! This is only available when the `exception` feature is enabled.
+//!
+//! See the following links for more information:
+//! - <https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Exceptions/Tasks/HandlingExceptions.html>
+//! - <https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ObjectiveC/Chapters/ocExceptionHandling.html>
+//! - <https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/Exceptions/Exceptions.html>
+//! - <https://llvm.org/docs/ExceptionHandling.html>
+
+use core::ffi::c_void;
+use core::mem;
+use core::ptr;
 use core::ptr::NonNull;
+use std::os::raw::c_uchar;
 
 use crate::rc::{Id, Shared};
 use crate::runtime::Object;
-use objc2_exception::r#try;
 
-// Comment copied from `objc2_exception`
+use objc2_sys::{objc_exception_throw, objc_object};
+
+extern "C" {
+    fn rust_objc_try_catch_exception(
+        f: extern "C" fn(*mut c_void),
+        context: *mut c_void,
+        error: *mut *mut objc_object,
+    ) -> c_uchar;
+}
+
+/// Throws an Objective-C exception.
+///
+/// The argument must be a pointer to an Objective-C object.
+///
+/// # Safety
+///
+/// This unwinds from Objective-C, and the exception must be caught using an
+/// Objective-C exception handler like [`catch`] (and specifically not
+/// [`catch_unwind`]).
+///
+/// This also invokes undefined behaviour until `C-unwind` is stabilized, see
+/// [RFC-2945].
+///
+/// [`catch_unwind`]: std::panic::catch_unwind
+/// [RFC-2945]: https://rust-lang.github.io/rfcs/2945-c-unwind-abi.html
+#[inline]
+pub unsafe fn throw(exception: Option<&Id<Object, Shared>>) -> ! {
+    let exception = match exception {
+        Some(id) => &**id as *const Object as *mut objc_object,
+        None => ptr::null_mut(),
+    };
+    objc_exception_throw(exception)
+}
+
+unsafe fn try_no_ret<F: FnOnce()>(closure: F) -> Result<(), Option<Id<Object, Shared>>> {
+    extern "C" fn try_objc_execute_closure<F: FnOnce()>(closure: &mut Option<F>) {
+        // This is always passed Some, so it's safe to unwrap
+        let closure = closure.take().unwrap();
+        closure();
+    }
+
+    let f: extern "C" fn(&mut Option<F>) = try_objc_execute_closure;
+    let f: extern "C" fn(*mut c_void) = mem::transmute(f);
+    // Wrap the closure in an Option so it can be taken
+    let mut closure = Some(closure);
+    let context = &mut closure as *mut _ as *mut c_void;
+
+    let mut exception = ptr::null_mut();
+    let success = rust_objc_try_catch_exception(f, context, &mut exception);
+
+    if success == 0 {
+        Ok(())
+    } else {
+        // SAFETY:
+        // The exception is always a valid object (or NULL, but that has been
+        // checked).
+        //
+        // The ownership is safe as Shared; Objective-C code throwing an
+        // exception knows that they don't hold sole access to that exception
+        // instance any more, and Rust code is forbidden by requiring a Shared
+        // Id in `throw` (instead of just a shared reference, which could have
+        // come from an Owned Id).
+        Err(NonNull::new(exception as *mut Object).map(|e| Id::new(e)))
+    }
+}
 
 /// Tries to execute the given closure and catches an Objective-C exception
 /// if one is thrown.
@@ -15,14 +92,64 @@ use objc2_exception::r#try;
 ///
 /// # Safety
 ///
-/// The given closure must not panic.
+/// The given closure must not panic (e.g. normal Rust unwinding into this
+/// causes undefined behaviour).
 ///
 /// Additionally, this unwinds through the closure from Objective-C, which is
 /// undefined behaviour until `C-unwind` is stabilized, see [RFC-2945].
 ///
 /// [RFC-2945]: https://rust-lang.github.io/rfcs/2945-c-unwind-abi.html
-pub unsafe fn catch_exception<R>(
-    closure: impl FnOnce() -> R,
-) -> Result<R, Option<Id<Object, Shared>>> {
-    r#try(closure).map_err(|e| NonNull::new(e).map(|e| Id::new(e.cast())))
+pub unsafe fn catch<R>(closure: impl FnOnce() -> R) -> Result<R, Option<Id<Object, Shared>>> {
+    let mut value = None;
+    let result = {
+        let value_ref = &mut value;
+        try_no_ret(move || {
+            *value_ref = Some(closure());
+        })
+    };
+    // If the try succeeded, this was set so it's safe to unwrap
+    result.map(|_| value.unwrap())
+}
+
+#[cfg(test)]
+mod tests {
+    use alloc::string::ToString;
+
+    use super::*;
+
+    #[test]
+    fn test_catch() {
+        let mut s = "Hello".to_string();
+        let result = unsafe {
+            catch(move || {
+                s.push_str(", World!");
+                s
+            })
+        };
+        assert_eq!(result.unwrap(), "Hello, World!");
+    }
+
+    #[test]
+    fn test_throw_catch_none() {
+        let s = "Hello".to_string();
+        let result = unsafe {
+            catch(move || {
+                if !s.is_empty() {
+                    throw(None);
+                }
+                s.len()
+            })
+        };
+        assert!(result.unwrap_err().is_none());
+    }
+
+    #[test]
+    fn test_throw_catch_object() {
+        let obj: Id<Object, Shared> = unsafe { Id::new(msg_send![class!(NSObject), new]) };
+
+        let result = unsafe { catch(|| throw(Some(&obj))) };
+        let e = result.unwrap_err().unwrap();
+        // Compare pointers
+        assert_eq!(&*e as *const Object, &*obj as *const Object);
+    }
 }

objc2/src/lib.rs

@@ -32,7 +32,7 @@ the [`declare`](declare/index.html) module.
 
 By default, if the `msg_send!` macro causes an exception to be thrown, this
 will unwind into Rust resulting in unsafe, undefined behavior.
-However, this crate has an `"exception"` feature which, when enabled, wraps
+However, this crate has an `"catch_all"` feature which, when enabled, wraps
 each `msg_send!` in a `@try`/`@catch` and panics if an exception is caught,
 preventing Objective-C from unwinding into Rust.
 
@@ -90,7 +90,7 @@ mod cache;
 pub mod declare;
 mod encode;
 #[cfg(feature = "exception")]
-mod exception;
+pub mod exception;
 mod message;
 pub mod rc;
 pub mod runtime;

objc2/src/macros.rs

@@ -78,7 +78,7 @@ Variadic arguments are not currently supported.
 
 # Panics
 
-Panics if the `exception` feature is enabled and the Objective-C method throws
+Panics if the `catch_all` feature is enabled and the Objective-C method throws
 an exception.
 
 And panics if the `verify_message` feature is enabled and the Objective-C

objc2/src/message/mod.rs

@@ -8,10 +8,10 @@ use crate::rc::{Id, Ownership};
 use crate::runtime::{Class, Imp, Object, Sel};
 use crate::{Encode, EncodeArguments, RefEncode};
 
-#[cfg(feature = "exception")]
+#[cfg(feature = "catch_all")]
 unsafe fn conditional_try<R: Encode>(f: impl FnOnce() -> R) -> Result<R, MessageError> {
     use alloc::borrow::ToOwned;
-    crate::exception::catch_exception(f).map_err(|exception| {
+    crate::exception::catch(f).map_err(|exception| {
         if let Some(exception) = exception {
             MessageError(alloc::format!("Uncaught exception {:?}", exception))
         } else {
@@ -20,7 +20,7 @@ unsafe fn conditional_try<R: Encode>(f: impl FnOnce() -> R) -> Result<R, Message
     })
 }
 
-#[cfg(not(feature = "exception"))]
+#[cfg(not(feature = "catch_all"))]
 #[inline(always)]
 unsafe fn conditional_try<R: Encode>(f: impl FnOnce() -> R) -> Result<R, MessageError> {
     Ok(f())
@@ -300,7 +300,7 @@ An error encountered while attempting to send a message.
 
 Currently, an error may be returned in two cases:
 
-* an Objective-C exception is thrown and the `exception` feature is enabled
+* an Objective-C exception is thrown and the `catch_all` feature is enabled
 * the encodings of the arguments do not match the encoding of the method
   and the `verify_message` feature is enabled
 */