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Add a cross-import overlay with AppKit to allow attaching NSImages. #869

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@grynspan grynspan commented Dec 19, 2024

This PR adds on to the Core Graphics cross-import overlay added in #827 to allow attaching instances of NSImage to a test.

NSImage is a more complicated animal because it is not Sendable, but we don't want to make a (potentially very expensive) deep copy of its data until absolutely necessary. So we check inside the image to see if its contained representations are known to be safely copyable (i.e. copies made with NSCopying do not share any mutable state with their originals.) If it looks safe to make a copy of the image by calling copy(), we do so; otherwise, we try to make a deep copy of the image.

Due to how Swift implements polymorphism in protocol requirements, and because we don't really know what they're doing, subclasses of NSImage just get a call to copy() instead of deep introspection.

UIImage support will be implemented in a separate PR.

Note

Attachments remain an experimental feature.

Checklist:

  • Code and documentation should follow the style of the Style Guide.
  • If public symbols are renamed or modified, DocC references should be updated.

This PR adds on to the Core Graphics cross-import overlay added in #827 to allow attaching
instances of `NSImage` to a test.

`NSImage` is a more complicated animal because it is not `Sendable`, but we don't want to
make a (potentially very expensive) deep copy of its data until absolutely necessary. So
we check inside the image to see if its contained representations are known to be safely
copyable (i.e. copies made with `NSCopying` do not share any mutable state with their
originals.) If it looks safe to make a copy of the image by calling `copy()`, we do so;
otherwise, we try to make a deep copy of the image.

Due to how Swift implements polymorphism in protocol requirements, and because we don't
really know what they're doing, subclasses of `NSImage` just get a call to `copy()`
instead of deep introspection.

`UIImage` support will be implemented in a separate PR.

> [!NOTE]
> Attachments remain an experimental feature.
@grynspan grynspan added enhancement New feature or request darwin 🍎 macOS, iOS, watchOS, tvOS, and visionOS support public-api Affects public API attachments/activities 🖇️ Work related to attachments and/or activities labels Dec 19, 2024
@grynspan grynspan added this to the Swift 6.x milestone Dec 19, 2024
@grynspan grynspan self-assigned this Dec 19, 2024
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