1 files changed, 100 insertions, 0 deletions
diff --git a/third_party/rust/objc_exception/src/lib.rs b/third_party/rust/objc_exception/src/lib.rs
new file mode 100644
index 0000000000..d381f60c70
--- /dev/null
+++ b/third_party/rust/objc_exception/src/lib.rs
@@ -0,0 +1,100 @@
+//! Rust interface for Objective-C's `@throw` and `@try`/`@catch` statements.
+
+use std::mem;
+use std::os::raw::{c_int, c_void};
+use std::ptr;
+
+#[link(name = "objc", kind = "dylib")]
+extern { }
+
+extern {
+    fn RustObjCExceptionThrow(exception: *mut c_void);
+    fn RustObjCExceptionTryCatch(try: extern fn(*mut c_void),
+            context: *mut c_void, error: *mut *mut c_void) -> c_int;
+}
+
+/// An opaque type representing any Objective-C object thrown as an exception.
+pub enum Exception { }
+
+/// Throws an Objective-C exception.
+/// The argument must be a pointer to an Objective-C object.
+///
+/// Unsafe because this unwinds from Objective-C.
+pub unsafe fn throw(exception: *mut Exception) -> ! {
+    RustObjCExceptionThrow(exception as *mut _);
+    unreachable!();
+}
+
+unsafe fn try_no_ret<F>(closure: F) -> Result<(), *mut Exception>
+        where F: FnOnce() {
+    extern fn try_objc_execute_closure<F>(closure: &mut Option<F>)
+            where F: FnOnce() {
+        // This is always passed Some, so it's safe to unwrap
+        let closure = closure.take().unwrap();
+        closure();
+    }
+
+    let f: extern fn(&mut Option<F>) = try_objc_execute_closure;
+    let f: extern 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 = RustObjCExceptionTryCatch(f, context, &mut exception);
+
+    if success == 0 {
+        Ok(())
+    } else {
+        Err(exception as *mut _)
+    }
+}
+
+/// Tries to execute the given closure and catches an Objective-C exception
+/// if one is thrown.
+///
+/// Returns a `Result` that is either `Ok` if the closure succeeded without an
+/// exception being thrown, or an `Err` with a pointer to an exception if one
+/// was thrown. The exception is retained and so must be released.
+///
+/// Unsafe because this encourages unwinding through the closure from
+/// Objective-C, which is not safe.
+pub unsafe fn try<F, R>(closure: F) -> Result<R, *mut Exception>
+        where F: FnOnce() -> R {
+    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 std::ptr;
+    use super::{throw, try};
+
+    #[test]
+    fn test_try() {
+        unsafe {
+            let s = "Hello".to_string();
+            let result = try(move || {
+                if s.len() > 0 {
+                    throw(ptr::null_mut());
+                }
+                s.len()
+            });
+            assert!(result.unwrap_err() == ptr::null_mut());
+
+            let mut s = "Hello".to_string();
+            let result = try(move || {
+                s.push_str(", World!");
+                s
+            });
+            assert!(result.unwrap() == "Hello, World!");
+        }
+    }
+}