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-foundation/CHANGELOG.md

@@ -12,6 +12,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   `NSData` and `NSMutableData`.
 * Implemented `Extend` for `NSMutableArray`.
 * Add extra `Extend<&u8>` impl for `NSMutableData`.
+* Added `NSError`.
 
 ### Changed
 * Change selector syntax in `declare_class!` macro to be more Rust-like.

objc2-foundation/src/error.rs

@@ -0,0 +1,128 @@
+use core::fmt;
+use core::panic::{RefUnwindSafe, UnwindSafe};
+
+use objc2::ffi::NSInteger;
+use objc2::rc::{Id, Shared};
+use objc2::{msg_send, msg_send_id};
+
+use crate::{extern_class, NSCopying, NSDictionary, NSObject, NSString};
+
+extern_class! {
+    /// Information about an error condition including a domain, a
+    /// domain-specific error code, and application-specific information.
+    ///
+    /// See also [Apple's documentation][doc].
+    ///
+    /// [doc]: 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;
+}

objc2-foundation/src/lib.rs

@@ -55,6 +55,7 @@ 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, NSErrorUserInfoKey, NSLocalizedDescriptionKey};
 pub use self::exception::NSException;
 pub use self::geometry::{CGFloat, NSPoint, NSRect, NSSize};
 pub use self::mutable_array::NSMutableArray;
@@ -103,6 +104,7 @@ mod data;
 mod declare_macro;
 mod dictionary;
 mod enumerator;
+mod error;
 mod exception;
 mod geometry;
 mod macros;