♻️ Simplify attachment previews by conforming Attachment to View

[YoungHypo]

This PR refactors the Attachment protocol to create a simpler and more idi-omatic SwiftUI API for rendering attachment previews.

The previous design required types conforming to Attachment to implement a previewView() function. The new approach removes this function and instead requires Attachment to conform directly to SwiftUI.View.

This change simplifies the implementation of custom attachments and makes the code in views that render them cleaner and more intuitive.

Key Changes

• Protocol Update: The Attachment protocol no longer has a previewView() requirement and now inherits from View.
• Simplified Views: Views like AttachmentPreviewCard and MessageComposerView now have a simpler generic constraint (<AttachmentType: Attachment & View>) and can render the attachment directly (e.g., attachment) instead
  of calling a function (attachment.previewView()).
• Concrete Types: ImageAttachment and EmptyAttachment have been updated to conform to View by implementing the required body property.

Before

// Protocol
public protocol Attachment: Identifiable, Hashable {
  @ViewBuilder
 func previewView() -> any View
}

// Usage in a view
struct AttachmentPreviewCard<AttachmentType: Attachment>: View {
  var attachment: AttachmentType
  // ...
  var body: some View {
    attachment.previewView()
  }
}

After

// Protocol
public protocol Attachment: Identifiable, Hashable, View {
}

// Usage in a view                                                                                                                                                                                                       
struct AttachmentPreviewCard<AttachmentType: Attachment>: View {                                                                                                                                                         
  var attachment: AttachmentType                                                                                                                                                                                         
  // ...                                                                                                                                                                                                                 
  var body: some View {                                                                                                                                                                                                  
    attachment                                                                                                                                                                                                           
  }                                                                                                                                                                                                                      
}

[gemini-code-assist]

Summary of Changes

Hello @YoungHypo, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request refactors the attachment preview rendering mechanism by introducing a previewView() method to the Attachment protocol. This change centralizes the view rendering logic within each attachment type, thereby simplifying the AttachmentPreviewCard which now directly displays the attachment's self-rendered preview. This approach enhances modularity and extensibility, making it easier to add new attachment types with custom preview displays.

Highlights

• Protocol Extension: The Attachment protocol has been extended to include a new previewView() method, allowing each attachment type to define its own preview rendering logic.
• Attachment Implementations: EmptyAttachment and ImageAttachment now implement the previewView() method, providing specific SwiftUI views for their respective previews.
• Simplified Preview Card: The AttachmentPreviewCard has been significantly simplified. It no longer contains conditional rendering logic for different attachment types but instead directly calls attachment.previewView(), delegating the preview rendering responsibility to the attachment itself.
• Visibility Change: The ConcentricClipShapeModifier struct has been made public.

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[gemini-code-assist]

Code Review

This pull request introduces a previewView() method to the Attachment protocol, allowing each attachment type to define its own SwiftUI preview. This is a good architectural improvement that simplifies AttachmentPreviewCard by removing conditional logic. The implementations for ImageAttachment and EmptyAttachment are included. My review includes a couple of suggestions to improve the design's flexibility and adhere to SwiftUI best practices. Specifically, I've noted that hardcoding the frame and style within ImageAttachment.previewView could limit reusability, and I've pointed out a redundant use of AnyView.

[YoungHypo]

@peterfriese da4bf21 moved EmptyAttachment and ImageAttachment away from inheriting View directly in the protocol. Instead, they now adopt View through extensions.
AttachmentPreviewCard still requires its generic type to conform to both Attachment and View, so the UI behaves exactly the same. The ConversationKitDemo app complied successfully and shown in the picture

[peterfriese]

LGTM, approved!