Adding ability to write diff artifacts to disk

Author: megs-seek

Sources/SnapshotTesting/AssertInlineSnapshot.swift

@@ -144,7 +144,13 @@ public func _verifyInlineSnapshot<Value>(
         if ProcessInfo.processInfo.environment.keys.contains("__XCODE_BUILT_PRODUCTS_DIR_PATHS") {
           XCTContext.runActivity(named: "Attached Failure Diff") { activity in
             attachments.forEach {
-              activity.add($0)
+              let data = snapshotting.diffing.toData($0.value)
+              let attachment = XCTAttachment(
+                data: data,
+                uniformTypeIdentifier: $0.uniformTypeIdentifier
+              )
+              attachment.name = $0.name
+              activity.add(attachment)
             }
           }
         }

Sources/SnapshotTesting/AssertSnapshot.swift

@@ -190,8 +190,9 @@ public func verifySnapshot<Value, Format>(
       }
 
       let testName = sanitizePathComponent(testName)
+      let snapshotFileName = "\(testName).\(identifier)"
       let snapshotFileUrl = snapshotDirectoryUrl
-        .appendingPathComponent("\(testName).\(identifier)")
+        .appendingPathComponent(snapshotFileName)
         .appendingPathExtension(snapshotting.pathExtension ?? "")
       let fileManager = FileManager.default
       try fileManager.createDirectory(at: snapshotDirectoryUrl, withIntermediateDirectories: true)
@@ -248,20 +249,37 @@ public func verifySnapshot<Value, Format>(
         fileURLWithPath: ProcessInfo.processInfo.environment["SNAPSHOT_ARTIFACTS"] ?? NSTemporaryDirectory(), isDirectory: true
       )
       let artifactsSubUrl = artifactsUrl.appendingPathComponent(fileName)
-      try fileManager.createDirectory(at: artifactsSubUrl, withIntermediateDirectories: true)
       let failedSnapshotFileUrl = artifactsSubUrl.appendingPathComponent(snapshotFileUrl.lastPathComponent)
-      try snapshotting.diffing.toData(diffable).write(to: failedSnapshotFileUrl)
+      try fileManager.createDirectory(at: artifactsSubUrl, withIntermediateDirectories: true)
 
       if !attachments.isEmpty {
         #if !os(Linux)
         if ProcessInfo.processInfo.environment.keys.contains("__XCODE_BUILT_PRODUCTS_DIR_PATHS") {
           XCTContext.runActivity(named: "Attached Failure Diff") { activity in
             attachments.forEach {
-              activity.add($0)
+              let data = snapshotting.diffing.toData($0.value)
+              let attachment = XCTAttachment(
+                data: data,
+                uniformTypeIdentifier: $0.uniformTypeIdentifier
+              )
+              attachment.name = $0.name
+              activity.add(attachment)
             }
           }
         }
         #endif
+
+        for (index, attachment) in attachments.enumerated() {
+          let snapshotArtifactUrl = artifactsSubUrl.appendingPathComponent(snapshotFileName)
+          try fileManager.createDirectory(at: snapshotArtifactUrl, withIntermediateDirectories: true)
+
+          let snapshotArtifactFileUrl = snapshotArtifactUrl
+            .appendingPathComponent(attachment.name ?? String(describing: index))
+            .appendingPathExtension(snapshotting.pathExtension ?? "")
+          try snapshotting.diffing.toData(attachment.value).write(to: snapshotArtifactFileUrl)
+        }
+      } else {
+        try snapshotting.diffing.toData(diffable).write(to: failedSnapshotFileUrl)
       }
 
       let diffMessage = diffTool

Sources/SnapshotTesting/Diffing.swift

@@ -10,7 +10,7 @@ public struct Diffing<Value> {
   public var fromData: (Data) -> Value
 
   /// Compares two values. If the values do not match, returns a failure message and artifacts describing the failure.
-  public var diff: (Value, Value) -> (String, [XCTAttachment])?
+  public var diff: (Value, Value) -> (String, [DiffingArtifact<Value>])?
 
   /// Creates a new `Diffing` on `Value`.
   ///
@@ -25,10 +25,38 @@ public struct Diffing<Value> {
   public init(
     toData: @escaping (_ value: Value) -> Data,
     fromData: @escaping (_ data: Data) -> Value,
-    diff: @escaping (_ lhs: Value, _ rhs: Value) -> (String, [XCTAttachment])?
+    diff: @escaping (_ lhs: Value, _ rhs: Value) -> (String, [DiffingArtifact<Value>])?
     ) {
     self.toData = toData
     self.fromData = fromData
     self.diff = diff
   }
 }
+
+public struct DiffingArtifact<Value> {
+    /// The name of artifact type, i.e. "reference", "failure", "patch", etc.
+    public var name: String?
+    
+    /// UTI (Uniform Type Identifier) of the payload data for an `XCTAttachment`.
+    public var uniformTypeIdentifier: String
+    
+    /// The value of the artifact.
+    public var value: Value
+    
+    /// Creates a new `DiffingArtifact` on `Value`.
+    ///
+    /// - Parameters:
+    ///   - name: The name of the artifact, to be written to disk and included
+    ///   as an `XCTAttachment`.
+    ///   - uniformTypeIdentifier: UTI for `XCTAttachment` payload representing the artifact.
+    ///   - value: The value to be written to disk and included as an `XCTAttachment` payload.
+    public init(
+        name: String? = nil,
+        uniformTypeIdentifier: String,
+        value: Value
+    ) {
+        self.name = name
+        self.uniformTypeIdentifier = uniformTypeIdentifier
+        self.value = value
+    }
+}

Sources/SnapshotTesting/Snapshotting/String.swift

@@ -20,7 +20,10 @@ extension Diffing where Value == String {
     let failure = hunks
       .flatMap { [$0.patchMark] + $0.lines }
       .joined(separator: "\n")
-    let attachment = XCTAttachment(data: Data(failure.utf8), uniformTypeIdentifier: "public.patch-file")
-    return (failure, [attachment])
+    let artifact = DiffingArtifact(
+      uniformTypeIdentifier: "public.patch-file",
+      value: failure
+    )
+    return (failure, [artifact])
   }
 }

Sources/SnapshotTesting/Snapshotting/UIImage.swift

@@ -20,15 +20,24 @@ extension Diffing where Value == UIImage {
       let message = new.size == old.size
         ? "Newly-taken snapshot does not match reference."
         : "Newly-taken snapshot@\(new.size) does not match reference@\(old.size)."
-      let oldAttachment = XCTAttachment(image: old)
-      oldAttachment.name = "reference"
-      let newAttachment = XCTAttachment(image: new)
-      newAttachment.name = "failure"
-      let differenceAttachment = XCTAttachment(image: difference)
-      differenceAttachment.name = "difference"
+      let oldArtifact = DiffingArtifact(
+        name: "reference",
+        uniformTypeIdentifier: "public.png",
+        value: old
+      )
+      let newArtifact = DiffingArtifact(
+        name: "failure",
+        uniformTypeIdentifier: "public.png",
+        value: new
+      )
+      let diffArtifact = DiffingArtifact(
+        name: "difference",
+        uniformTypeIdentifier: "public.png",
+        value: difference
+      )
       return (
         message,
-        [oldAttachment, newAttachment, differenceAttachment]
+        [oldArtifact, newArtifact, diffArtifact]
       )
     }
   }