Merge pull request swiftlang#14690 from cwakamo/introducing-CustomPlaygroundDisplayConvertible

cwakamo · web-flow · commit 37f7493c8998 · 2018-02-21T16:09:06.000-08:00
This implements SE-0198 by introducing the `CustomPlaygroundDisplayConvertible` protocol and deprecating `PlaygroundQuickLook`/`CustomPlaygroundQuickLookable` in advance of removal from the standard library in the future.
diff --git a/stdlib/public/SDK/AppKit/AppKit.swift b/stdlib/public/SDK/AppKit/AppKit.swift
@@ -14,6 +14,7 @@ import Foundation
 @_exported import AppKit
 
 extension NSCursor : _DefaultCustomPlaygroundQuickLookable {
+  @available(*, deprecated, message: "NSCursor._defaultCustomPlaygroundQuickLook will be removed in a future Swift version")
   public var _defaultCustomPlaygroundQuickLook: PlaygroundQuickLook {
     return .image(image)
   }
@@ -24,6 +25,7 @@ internal struct _NSViewQuickLookState {
 }
 
 extension NSView : _DefaultCustomPlaygroundQuickLookable {
+  @available(*, deprecated, message: "NSView._defaultCustomPlaygroundQuickLook will be removed in a future Swift version")
   public var _defaultCustomPlaygroundQuickLook: PlaygroundQuickLook {
     // if you set NSView.needsDisplay, you can get yourself in a recursive scenario where the same view
     // could need to draw itself in order to get a QLObject for itself, which in turn if your code was
diff --git a/stdlib/public/SDK/CoreGraphics/CoreGraphics.swift b/stdlib/public/SDK/CoreGraphics/CoreGraphics.swift
@@ -232,6 +232,7 @@ extension CGPoint : CustomReflectable, CustomPlaygroundQuickLookable {
     return Mirror(self, children: ["x": x, "y": y], displayStyle: .`struct`)
   }
 
+  @available(*, deprecated, message: "CGPoint.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return .point(Double(x), Double(y))
   }
@@ -299,6 +300,7 @@ extension CGSize : CustomReflectable, CustomPlaygroundQuickLookable {
       displayStyle: .`struct`)
   }
 
+  @available(*, deprecated, message: "CGSize.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return .size(Double(width), Double(height))
   }
@@ -436,6 +438,7 @@ extension CGRect : CustomReflectable, CustomPlaygroundQuickLookable {
       displayStyle: .`struct`)
   }
 
+  @available(*, deprecated, message: "CGRect.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return .rectangle(
       Double(origin.x), Double(origin.y),
diff --git a/stdlib/public/SDK/Foundation/Date.swift b/stdlib/public/SDK/Foundation/Date.swift
@@ -280,6 +280,7 @@ extension Date : CustomPlaygroundQuickLookable {
         return df.string(from: self)
     }
     
+    @available(*, deprecated, message: "Date.customPlaygroundQuickLook will be removed in a future Swift version")
     public var customPlaygroundQuickLook: PlaygroundQuickLook {
         return .text(summary)
     }
diff --git a/stdlib/public/SDK/Foundation/NSDate.swift b/stdlib/public/SDK/Foundation/NSDate.swift
@@ -21,6 +21,7 @@ extension NSDate : CustomPlaygroundQuickLookable {
     return df.string(from: self as Date)
   }
 
+  @available(*, deprecated, message: "NSDate.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return .text(summary)
   }
diff --git a/stdlib/public/SDK/Foundation/NSRange.swift b/stdlib/public/SDK/Foundation/NSRange.swift
@@ -198,6 +198,7 @@ extension NSRange : CustomReflectable {
 }
 
 extension NSRange : CustomPlaygroundQuickLookable {
+    @available(*, deprecated, message: "NSRange.customPlaygroundQuickLook will be removed in a future Swift version")
     public var customPlaygroundQuickLook: PlaygroundQuickLook {
         return .range(Int64(location), Int64(length))
     }
diff --git a/stdlib/public/SDK/Foundation/NSString.swift b/stdlib/public/SDK/Foundation/NSString.swift
@@ -113,6 +113,7 @@ extension NSString {
 }
 
 extension NSString : CustomPlaygroundQuickLookable {
+  @available(*, deprecated, message: "NSString.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return .text(self as String)
   }
diff --git a/stdlib/public/SDK/Foundation/NSURL.swift b/stdlib/public/SDK/Foundation/NSURL.swift
@@ -13,6 +13,7 @@
 @_exported import Foundation // Clang module
 
 extension NSURL : CustomPlaygroundQuickLookable {
+  @available(*, deprecated, message: "NSURL.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     guard let str = absoluteString else { return .text("Unknown URL") }
     return .url(str)
diff --git a/stdlib/public/SDK/Foundation/URL.swift b/stdlib/public/SDK/Foundation/URL.swift
@@ -1202,6 +1202,7 @@ extension NSURL : _HasCustomAnyHashableRepresentation {
 }
 
 extension URL : CustomPlaygroundQuickLookable {
+    @available(*, deprecated, message: "URL.customPlaygroundQuickLook will be removed in a future Swift version")
     public var customPlaygroundQuickLook: PlaygroundQuickLook {
         return .url(absoluteString)
     }
diff --git a/stdlib/public/SDK/SpriteKit/SpriteKitQuickLooks.swift.gyb b/stdlib/public/SDK/SpriteKit/SpriteKitQuickLooks.swift.gyb
@@ -15,6 +15,7 @@
 % for Self in ['SKShapeNode', 'SKSpriteNode', 'SKTextureAtlas', 'SKTexture']:
 
 extension ${Self} : CustomPlaygroundQuickLookable {
+  @available(*, deprecated, message: "${Self}.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     let data = (self as AnyObject)._copyImageData?() as Data?
 
diff --git a/stdlib/public/SDK/UIKit/UIKit.swift b/stdlib/public/SDK/UIKit/UIKit.swift
@@ -231,6 +231,7 @@ internal struct _UIViewQuickLookState {
 }
 
 extension UIView : _DefaultCustomPlaygroundQuickLookable {
+  @available(*, deprecated, message: "UIView._defaultCustomPlaygroundQuickLook will be removed in a future Swift version")
   public var _defaultCustomPlaygroundQuickLook: PlaygroundQuickLook {
     if _UIViewQuickLookState.views.contains(self) {
       return .view(UIImage())
diff --git a/stdlib/public/core/CMakeLists.txt b/stdlib/public/core/CMakeLists.txt
@@ -173,6 +173,7 @@ set(SWIFTLIB_SOURCES
   CollectionOfOne.swift
   ExistentialCollection.swift.gyb
   Mirror.swift
+  PlaygroundDisplay.swift
   CommandLine.swift
   SliceBuffer.swift
   Tuple.swift.gyb
diff --git a/stdlib/public/core/GroupInfo.json b/stdlib/public/core/GroupInfo.json
@@ -155,6 +155,9 @@
     "CompilerProtocols.swift",
     "ShadowProtocols.swift"
   ],
+  "Playground": [
+    "PlaygroundDisplay.swift"
+  ],
   "Misc": [
     "AnyHashable.swift",
     "Interval.swift",
diff --git a/stdlib/public/core/Mirror.swift b/stdlib/public/core/Mirror.swift
@@ -661,7 +661,19 @@ internal extension Mirror {
 //===--- QuickLooks -------------------------------------------------------===//
 
 /// The sum of types that can be used as a Quick Look representation.
+///
+/// - note: `PlaygroundQuickLook` is deprecated, and will be removed from the
+/// standard library in a future Swift release. Customizing display for in a
+/// playground is now done using the `CustomPlaygroundDisplayConvertible`
+/// protocol, which does not use the `PlaygroundQuickLook` enum. Please remove
+/// your uses of `PlaygroundQuickLook`, or conditionalize your use such that it
+/// is only present when compiling with Swift 4.0 or Swift 3.2 or earlier:
+///
+///     #if !(swift(>=4.1) || swift(>=3.3) && !swift(>=4.0))
+///       /* OK to use PlaygroundQuickLook */
+///     #endif
 @_fixed_layout // FIXME(sil-serialize-all)
+@available(*, deprecated, message: "PlaygroundQuickLook will be removed in a future Swift version. For customizing how types are presented in playgrounds, use CustomPlaygroundDisplayConvertible instead.")
 public enum PlaygroundQuickLook {
   /// Plain text.
   case text(String)
@@ -748,6 +760,7 @@ extension PlaygroundQuickLook {
   /// - Parameter subject: The instance to represent with the resulting Quick
   ///   Look.
   @_inlineable // FIXME(sil-serialize-all)
+  @available(*, deprecated, message: "PlaygroundQuickLook will be removed in a future Swift version.")
   public init(reflecting subject: Any) {
     if let customized = subject as? CustomPlaygroundQuickLookable {
       self = customized.customPlaygroundQuickLook
@@ -773,6 +786,23 @@ extension PlaygroundQuickLook {
 /// with the representation supplied for your type by default, you can make it
 /// conform to the `CustomPlaygroundQuickLookable` protocol and provide a
 /// custom `PlaygroundQuickLook` instance.
+///
+/// - note: `CustomPlaygroundQuickLookable` is deprecated, and will be removed
+/// from the standard library in a future Swift release. Please migrate to the
+/// `CustomPlaygroundDisplayConvertible` protocol instead, or conditionalize
+/// your conformance such that it is only present when compiling with Swift 4.0
+/// or Swift 3.2 or earlier:
+///
+///     #if swift(>=4.1) || swift(>=3.3) && !swift(>=4.0)
+///       // With Swift 4.1 and later (including Swift 3.3 and later), implement
+///       // CustomPlaygroundDisplayConvertible.
+///       extension MyType: CustomPlaygroundDisplayConvertible { /*...*/ }
+///     #else
+///       // Otherwise, on Swift 4.0 and Swift 3.2 and earlier,
+///       // implement CustomPlaygroundQuickLookable.
+///       extension MyType: CustomPlaygroundQuickLookable { /*...*/ }
+///     #endif
+@available(*, deprecated, message: "CustomPlaygroundQuickLookable will be removed in a future Swift version. For customizing how types are presented in playgrounds, use CustomPlaygroundDisplayConvertible instead.")
 public protocol CustomPlaygroundQuickLookable {
   /// A custom playground Quick Look for this instance.
   ///
@@ -784,6 +814,7 @@ public protocol CustomPlaygroundQuickLookable {
 
 // A workaround for <rdar://problem/26182650>
 // FIXME(ABI)#50 (Dynamic Dispatch for Class Extensions) though not if it moves out of stdlib.
+@available(*, deprecated, message: "_DefaultCustomPlaygroundQuickLookable will be removed in a future Swift version. For customizing how types are presented in playgrounds, use CustomPlaygroundDisplayConvertible instead.")
 public protocol _DefaultCustomPlaygroundQuickLookable {
   var _defaultCustomPlaygroundQuickLook: PlaygroundQuickLook { get }
 }
diff --git a/stdlib/public/core/Mirrors.swift.gyb b/stdlib/public/core/Mirrors.swift.gyb
@@ -48,6 +48,7 @@ extension ${Type[0]} : CustomReflectable {
 extension ${Type[0]} : CustomPlaygroundQuickLookable {
   /// A custom playground Quick Look for the `${Type[0]}` instance.
   @_inlineable // FIXME(sil-serialize-all)
+  @available(*, deprecated, message: "${Type[0]}.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return ${Type[1]}(${Type[2]})
   }
diff --git a/stdlib/public/core/PlaygroundDisplay.swift b/stdlib/public/core/PlaygroundDisplay.swift
@@ -0,0 +1,63 @@
+//===--- PlaygroundDisplay.swift ------------------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+/// A type that supplies a custom description for playground logging.
+///
+/// All types have a default description for playgrounds. This protocol
+/// allows types to provide custom descriptions which are then logged in
+/// place of the original instance.
+///
+/// Playground logging can generate, at a minimum, a structured description
+/// of any type. Playground logging is also capable of generating a richer,
+/// more specialized description of core types -- for instance, the contents
+/// of a `String` are logged, as are the components of an `NSColor` or
+/// `UIColor`.
+///
+/// The current playground logging implementation logs specialized
+/// descriptions of at least the following types:
+///
+/// - `String` and `NSString`
+/// - `Int` and `UInt` (including the sized variants)
+/// - `Float` and `Double`
+/// - `Bool`
+/// - `Date` and `NSDate`
+/// - `NSAttributedString`
+/// - `NSNumber`
+/// - `NSRange`
+/// - `URL` and `NSURL`
+/// - `CGPoint`, `CGSize`, and `CGRect`
+/// - `NSColor`, `UIColor`, `CGColor`, and `CIColor`
+/// - `NSImage`, `UIImage`, `CGImage`, and `CIImage`
+/// - `NSBezierPath` and `UIBezierPath`
+/// - `NSView` and `UIView`
+///
+/// Playground logging may also be able to support specialized descriptions
+/// of other types.
+///
+/// Implementors of `CustomPlaygroundDisplayConvertible` may return a value of
+/// one of the above types to also receive a specialized log description.
+/// Implementors may also return any other type, and playground logging will
+/// generated structured logging for the returned value.
+///
+/// - note: `CustomPlaygroundDisplayConvertible` conformances chain -- that is,
+///   if `playgroundDescription` returns an instance which itself conforms to
+///   `CustomPlaygroundDisplayConvertible`, then playground logging will ask for
+///   that instance's `playgroundDescription` and so on. It is permissible for
+///   playground logging implementations to place a reasonable limit on this
+///   kind of chaining to prevent infinite loops.
+public protocol CustomPlaygroundDisplayConvertible {
+  /// Returns the custom playground description for this instance.
+  ///
+  /// If this type has value semantics, the instance returned should be
+  /// unaffected by subsequent mutations if possible.
+  var playgroundDescription: Any { get }
+}
diff --git a/stdlib/public/core/StringUTF16.swift b/stdlib/public/core/StringUTF16.swift
@@ -447,6 +447,7 @@ extension String.UTF16View : CustomReflectable {
 
 extension String.UTF16View : CustomPlaygroundQuickLookable {
   @_inlineable // FIXME(sil-serialize-all)
+  @available(*, deprecated, message: "UTF16View.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return .text(description)
   }
diff --git a/stdlib/public/core/StringUTF8.swift b/stdlib/public/core/StringUTF8.swift
@@ -634,6 +634,7 @@ extension String.UTF8View : CustomReflectable {
 
 extension String.UTF8View : CustomPlaygroundQuickLookable {
   @_inlineable // FIXME(sil-serialize-all)
+  @available(*, deprecated, message: "UTF8View.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return .text(description)
   }
diff --git a/stdlib/public/core/StringUnicodeScalarView.swift b/stdlib/public/core/StringUnicodeScalarView.swift
@@ -544,6 +544,7 @@ extension String.UnicodeScalarView : CustomReflectable {
 
 extension String.UnicodeScalarView : CustomPlaygroundQuickLookable {
   @_inlineable // FIXME(sil-serialize-all)
+  @available(*, deprecated, message: "UnicodeScalarView.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return .text(description)
   }
diff --git a/stdlib/public/core/Substring.swift.gyb b/stdlib/public/core/Substring.swift.gyb
@@ -338,6 +338,7 @@ extension Substring : CustomReflectable {
 
 extension Substring : CustomPlaygroundQuickLookable {
   @_inlineable // FIXME(sil-serialize-all)
+  @available(*, deprecated, message: "Substring.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return String(self).customPlaygroundQuickLook
   }
diff --git a/stdlib/public/core/UnsafePointer.swift.gyb b/stdlib/public/core/UnsafePointer.swift.gyb
@@ -1004,6 +1004,7 @@ extension ${Self} : CustomPlaygroundQuickLookable {
   }
 
   @_inlineable // FIXME(sil-serialize-all)
+  @available(*, deprecated, message: "${Self}.customPlaygroundQuickLook will be removed in a future Swift version")
   public var customPlaygroundQuickLook: PlaygroundQuickLook {
     return .text(summary)
   }
diff --git a/stdlib/public/core/UnsafeRawPointer.swift.gyb b/stdlib/public/core/UnsafeRawPointer.swift.gyb
@@ -996,6 +996,7 @@ extension Unsafe${Mutable}RawPointer : CustomReflectable {
 extension Unsafe${Mutable}RawPointer : CustomPlaygroundQuickLookable {
   @_inlineable // FIXME(sil-serialize-all)
   @_versioned // FIXME(sil-serialize-all)
+  @available(*, deprecated, message: "Unsafe${Mutable}RawPointer.customPlaygroundQuickLook will be removed in a future Swift version")
   internal var summary: String {
     let selfType = "${Self}"
     let ptrValue = UInt64(

Original file line number	Diff line number	Diff line change
`@@ -14,6 +14,7 @@ import Foundation`
`14`	`14`	`@_exported import AppKit`
`15`	`15`
`16`	`16`	`extension NSCursor : _DefaultCustomPlaygroundQuickLookable {`
	`17`	`+ @available(*, deprecated, message: "NSCursor._defaultCustomPlaygroundQuickLook will be removed in a future Swift version")`
`17`	`18`	`public var _defaultCustomPlaygroundQuickLook: PlaygroundQuickLook {`
`18`	`19`	`return .image(image)`
`19`	`20`	`}`
`@@ -24,6 +25,7 @@ internal struct _NSViewQuickLookState {`
`24`	`25`	`}`
`25`	`26`
`26`	`27`	`extension NSView : _DefaultCustomPlaygroundQuickLookable {`
	`28`	`+ @available(*, deprecated, message: "NSView._defaultCustomPlaygroundQuickLook will be removed in a future Swift version")`
`27`	`29`	`public var _defaultCustomPlaygroundQuickLook: PlaygroundQuickLook {`
`28`	`30`	`// if you set NSView.needsDisplay, you can get yourself in a recursive scenario where the same view`
`29`	`31`	`// could need to draw itself in order to get a QLObject for itself, which in turn if your code was`
Original file line number	Diff line number	Diff line change
`@@ -232,6 +232,7 @@ extension CGPoint : CustomReflectable, CustomPlaygroundQuickLookable {`
`232`	`232`	return Mirror(self, children: ["x": x, "y": y], displayStyle: .`struct`)
`233`	`233`	`}`
`234`	`234`
	`235`	`+ @available(*, deprecated, message: "CGPoint.customPlaygroundQuickLook will be removed in a future Swift version")`
`235`	`236`	`public var customPlaygroundQuickLook: PlaygroundQuickLook {`
`236`	`237`	`return .point(Double(x), Double(y))`
`237`	`238`	`}`
`@@ -299,6 +300,7 @@ extension CGSize : CustomReflectable, CustomPlaygroundQuickLookable {`
`299`	`300`	displayStyle: .`struct`)
`300`	`301`	`}`
`301`	`302`
	`303`	`+ @available(*, deprecated, message: "CGSize.customPlaygroundQuickLook will be removed in a future Swift version")`
`302`	`304`	`public var customPlaygroundQuickLook: PlaygroundQuickLook {`
`303`	`305`	`return .size(Double(width), Double(height))`
`304`	`306`	`}`
`@@ -436,6 +438,7 @@ extension CGRect : CustomReflectable, CustomPlaygroundQuickLookable {`
`436`	`438`	displayStyle: .`struct`)
`437`	`439`	`}`
`438`	`440`
	`441`	`+ @available(*, deprecated, message: "CGRect.customPlaygroundQuickLook will be removed in a future Swift version")`
`439`	`442`	`public var customPlaygroundQuickLook: PlaygroundQuickLook {`
`440`	`443`	`return .rectangle(`
`441`	`444`	`Double(origin.x), Double(origin.y),`
Original file line number	Diff line number	Diff line change
`@@ -280,6 +280,7 @@ extension Date : CustomPlaygroundQuickLookable {`
`280`	`280`	`return df.string(from: self)`
`281`	`281`	`}`
`282`	`282`
	`283`	`+ @available(*, deprecated, message: "Date.customPlaygroundQuickLook will be removed in a future Swift version")`
`283`	`284`	`public var customPlaygroundQuickLook: PlaygroundQuickLook {`
`284`	`285`	`return .text(summary)`
`285`	`286`	`}`
Original file line number	Diff line number	Diff line change
`@@ -21,6 +21,7 @@ extension NSDate : CustomPlaygroundQuickLookable {`
`21`	`21`	`return df.string(from: self as Date)`
`22`	`22`	`}`
`23`	`23`
	`24`	`+ @available(*, deprecated, message: "NSDate.customPlaygroundQuickLook will be removed in a future Swift version")`
`24`	`25`	`public var customPlaygroundQuickLook: PlaygroundQuickLook {`
`25`	`26`	`return .text(summary)`
`26`	`27`	`}`
Original file line number	Diff line number	Diff line change
`@@ -198,6 +198,7 @@ extension NSRange : CustomReflectable {`
`198`	`198`	`}`
`199`	`199`
`200`	`200`	`extension NSRange : CustomPlaygroundQuickLookable {`
	`201`	`+ @available(*, deprecated, message: "NSRange.customPlaygroundQuickLook will be removed in a future Swift version")`
`201`	`202`	`public var customPlaygroundQuickLook: PlaygroundQuickLook {`
`202`	`203`	`return .range(Int64(location), Int64(length))`
`203`	`204`	`}`
Original file line number	Diff line number	Diff line change
`@@ -113,6 +113,7 @@ extension NSString {`
`113`	`113`	`}`
`114`	`114`
`115`	`115`	`extension NSString : CustomPlaygroundQuickLookable {`
	`116`	`+ @available(*, deprecated, message: "NSString.customPlaygroundQuickLook will be removed in a future Swift version")`
`116`	`117`	`public var customPlaygroundQuickLook: PlaygroundQuickLook {`
`117`	`118`	`return .text(self as String)`
`118`	`119`	`}`
Original file line number	Diff line number	Diff line change
`@@ -1202,6 +1202,7 @@ extension NSURL : _HasCustomAnyHashableRepresentation {`
`1202`	`1202`	`}`
`1203`	`1203`
`1204`	`1204`	`extension URL : CustomPlaygroundQuickLookable {`
	`1205`	`+ @available(*, deprecated, message: "URL.customPlaygroundQuickLook will be removed in a future Swift version")`
`1205`	`1206`	`public var customPlaygroundQuickLook: PlaygroundQuickLook {`
`1206`	`1207`	`return .url(absoluteString)`
`1207`	`1208`	`}`
Original file line number	Diff line number	Diff line change
`@@ -231,6 +231,7 @@ internal struct _UIViewQuickLookState {`
`231`	`231`	`}`
`232`	`232`
`233`	`233`	`extension UIView : _DefaultCustomPlaygroundQuickLookable {`
	`234`	`+ @available(*, deprecated, message: "UIView._defaultCustomPlaygroundQuickLook will be removed in a future Swift version")`
`234`	`235`	`public var _defaultCustomPlaygroundQuickLook: PlaygroundQuickLook {`
`235`	`236`	`if _UIViewQuickLookState.views.contains(self) {`
`236`	`237`	`return .view(UIImage())`