Add basic version of NSError

Inspiration from:
- SSheldon/rust-objc-foundation#16
- https://github.com/nvzqz/fruity/tree/v0.3.0/src/foundation/ns_error
- https://github.com/ryanmcgrath/cacao/blob/02946476837e45ee381e37dde2946ed63b44dc31/src/error.rs

objc2/CHANGELOG_FOUNDATION.md

@@ -10,6 +10,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ### Added
 * Added `NSNumber`.
+* Added `NSError`.
 * Implement `UnwindSafe` and `RefUnwindSafe` for all objects.
 * Implemented `IntoIterator` for references to `NSArray`, `NSMutableArray`,
   `NSData` and `NSMutableData`.

objc2/src/foundation/error.rs

@@ -0,0 +1,162 @@
+use core::fmt;
+use core::panic::{RefUnwindSafe, UnwindSafe};
+
+use super::{NSCopying, NSDictionary, NSObject, NSString};
+use crate::extern_class;
+use crate::ffi::NSInteger;
+use crate::rc::{Id, Shared};
+use crate::{msg_send, msg_send_id};
+
+extern_class! {
+    /// Information about an error condition including a domain, a
+    /// domain-specific error code, and application-specific information.
+    ///
+    /// See also Apple's [documentation on error handling][err], and their
+    /// NSError [API reference][api].
+    ///
+    /// [err]: https://developer.apple.com/library/archive/documentation/Cocoa/Conceptual/ErrorHandlingCocoa/ErrorHandling/ErrorHandling.html#//apple_ref/doc/uid/TP40001806-CH201-SW1
+    /// [api]: https://developer.apple.com/documentation/foundation/nserror?language=objc
+    #[derive(PartialEq, Eq, Hash)]
+    unsafe pub struct NSError: NSObject;
+}
+
+// SAFETY: Error objects are immutable data containers.
+unsafe impl Sync for NSError {}
+unsafe impl Send for NSError {}
+
+impl UnwindSafe for NSError {}
+impl RefUnwindSafe for NSError {}
+
+pub type NSErrorUserInfoKey = NSString;
+pub type NSErrorDomain = NSString;
+
+/// Creation methods.
+impl NSError {
+    /// Construct a new [`NSError`] with the given code in the given domain.
+    pub fn new(code: NSInteger, domain: &NSString) -> Id<Self, Shared> {
+        unsafe { Self::with_user_info(code, domain, None) }
+    }
+
+    // TODO: Figure out safety of `user_info` dict!
+    unsafe fn with_user_info(
+        code: NSInteger,
+        domain: &NSString,
+        user_info: Option<&NSDictionary<NSErrorUserInfoKey, NSObject>>,
+    ) -> Id<Self, Shared> {
+        // SAFETY: `domain` and `user_info` are copied to the error object, so
+        // even if the `&NSString` came from a `&mut NSMutableString`, we're
+        // still good!
+        unsafe {
+            msg_send_id![
+                msg_send_id![Self::class(), alloc],
+                initWithDomain: domain,
+                code: code,
+                userInfo: user_info,
+            ]
+            .expect("unexpected NULL NSError")
+        }
+    }
+}
+
+/// Accessor methods.
+impl NSError {
+    pub fn domain(&self) -> Id<NSString, Shared> {
+        unsafe { msg_send_id![self, domain].expect("unexpected NULL NSError domain") }
+    }
+
+    pub fn code(&self) -> NSInteger {
+        unsafe { msg_send![self, code] }
+    }
+
+    pub fn user_info(&self) -> Option<Id<NSDictionary<NSErrorUserInfoKey, NSObject>, Shared>> {
+        unsafe { msg_send_id![self, userInfo] }
+    }
+
+    pub fn localized_description(&self) -> Id<NSString, Shared> {
+        unsafe {
+            msg_send_id![self, localizedDescription].expect(
+                "unexpected NULL localized description; a default should have been generated!",
+            )
+        }
+    }
+
+    // TODO: localizedRecoveryOptions
+    // TODO: localizedRecoverySuggestion
+    // TODO: localizedFailureReason
+    // TODO: helpAnchor
+    // TODO: +setUserInfoValueProviderForDomain:provider:
+    // TODO: +userInfoValueProviderForDomain:
+
+    // TODO: recoveryAttempter
+    // TODO: attemptRecoveryFromError:...
+
+    // TODO: Figure out if this is a good design, or if we should do something
+    // differently (like a Rusty name for the function, or putting a bunch of
+    // statics in a module instead)?
+    #[allow(non_snake_case)]
+    pub fn NSLocalizedDescriptionKey() -> &'static NSErrorUserInfoKey {
+        extern "C" {
+            #[link_name = "NSLocalizedDescriptionKey"]
+            static VALUE: &'static NSErrorUserInfoKey;
+        }
+        unsafe { VALUE }
+    }
+
+    // TODO: Other NSErrorUserInfoKey values
+    // TODO: NSErrorDomain values
+}
+
+impl fmt::Debug for NSError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_struct("NSError")
+            .field("domain", &self.domain())
+            .field("code", &self.code())
+            .field("user_info", &self.user_info())
+            .finish()
+    }
+}
+
+impl fmt::Display for NSError {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}", self.localized_description())
+    }
+}
+
+impl std::error::Error for NSError {}
+
+unsafe impl NSCopying for NSError {
+    type Ownership = Shared;
+    type Output = Self;
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use alloc::format;
+
+    use crate::ns_string;
+
+    #[test]
+    fn custom_domain() {
+        let error = NSError::new(42, ns_string!("MyDomain"));
+        assert_eq!(error.code(), 42);
+        assert_eq!(&*error.domain(), ns_string!("MyDomain"));
+        let expected = if cfg!(feature = "apple") {
+            "The operation couldn’t be completed. (MyDomain error 42.)"
+        } else {
+            "MyDomain 42"
+        };
+        assert_eq!(format!("{}", error), expected);
+    }
+
+    #[test]
+    fn basic() {
+        let error = NSError::new(-999, ns_string!("NSURLErrorDomain"));
+        let expected = if cfg!(feature = "apple") {
+            "The operation couldn’t be completed. (NSURLErrorDomain error -999.)"
+        } else {
+            "NSURLErrorDomain -999"
+        };
+        assert_eq!(format!("{}", error), expected);
+    }
+}

objc2/src/foundation/mod.rs

@@ -33,6 +33,7 @@ pub use self::copying::{NSCopying, NSMutableCopying};
 pub use self::data::NSData;
 pub use self::dictionary::NSDictionary;
 pub use self::enumerator::{NSEnumerator, NSFastEnumeration, NSFastEnumerator};
+pub use self::error::{NSError, NSErrorDomain, NSErrorUserInfoKey};
 pub use self::exception::NSException;
 pub use self::geometry::{CGFloat, NSPoint, NSRect, NSSize};
 pub use self::mutable_array::NSMutableArray;
@@ -72,6 +73,7 @@ mod copying;
 mod data;
 mod dictionary;
 mod enumerator;
+mod error;
 mod exception;
 mod geometry;
 mod mutable_array;
@@ -134,6 +136,7 @@ mod tests {
         // TODO: Figure out if Send + Sync is safe?
         // assert_auto_traits::<NSEnumerator<NSString>>();
         // assert_auto_traits::<NSFastEnumerator<NSArray<NSString, Shared>>>();
+        assert_auto_traits::<NSError>();
         assert_auto_traits::<NSException>();
         assert_auto_traits::<CGFloat>();
         assert_auto_traits::<NSPoint>();

test-ui/ui/msg_send_id_invalid_return.stderr

@@ -22,10 +22,10 @@ error[E0277]: the trait bound `objc2::runtime::Class: Message` is not satisfied
              NSAttributedString
              NSData
              NSDictionary<K, V>
+             NSError
              NSException
              NSMutableArray<T, O>
-             NSMutableAttributedString
-           and 10 others
+           and 11 others
    = note: required because of the requirements on the impl of `MsgSendId<&objc2::runtime::Class, Id<objc2::runtime::Class, Shared>>` for `RetainSemantics<true, false, false, false>`
    = note: this error originates in the macro `msg_send_id` (in Nightly builds, run with -Z macro-backtrace for more info)
 
@@ -50,10 +50,10 @@ error[E0277]: the trait bound `objc2::runtime::Class: Message` is not satisfied
              NSAttributedString
              NSData
              NSDictionary<K, V>
+             NSError
              NSException
              NSMutableArray<T, O>
-             NSMutableAttributedString
-           and 10 others
+           and 11 others
    = note: required because of the requirements on the impl of `MsgSendId<&objc2::runtime::Class, Id<Allocated<objc2::runtime::Class>, Shared>>` for `RetainSemantics<false, true, false, false>`
    = note: this error originates in the macro `msg_send_id` (in Nightly builds, run with -Z macro-backtrace for more info)