Fix image loading crashes

Sources/SnapshotTesting/AssertSnapshot.swift

@@ -276,7 +276,7 @@ public func verifySnapshot<Value, Format>(
     }
 
     let data = try Data(contentsOf: snapshotFileUrl)
-    let reference = snapshotting.diffing.fromData(data)
+    let reference = try snapshotting.diffing.fromData(data)
 
     guard let (failureMessage, attachments) = snapshotting.diffing.diff(reference, diffable) else {
       return nil

Sources/SnapshotTesting/Diffing.swift

@@ -7,7 +7,7 @@ public struct Diffing<Value> {
   public var toData: (Value) throws -> Data
 
   /// Produces a value _from_ data.
-  public var fromData: (Data) -> Value
+  public var fromData: (Data) throws -> Value
 
   /// Compares two values. If the values do not match, returns a failure message and artifacts
   /// describing the failure.
@@ -26,7 +26,7 @@ public struct Diffing<Value> {
   ///   - rhs: Another value to compare.
   public init(
     toData: @escaping (_ value: Value) throws -> Data,
-    fromData: @escaping (_ data: Data) -> Value,
+    fromData: @escaping (_ data: Data) throws -> Value,
     diff: @escaping (_ lhs: Value, _ rhs: Value) -> (String, [XCTAttachment])?
   ) {
     self.toData = toData

Sources/SnapshotTesting/Extensions/Data+XImage.swift

@@ -0,0 +1,21 @@
+import Foundation
+
+extension Data {
+#if os(iOS) || os(tvOS)
+    func image(scale: CGFloat) throws -> XImage {
+        let image = XImage(data: self, scale: scale)
+        guard let image else {
+            throw ImageConversionError.invalidImageData
+        }
+        return image
+    }
+#elseif os(macOS)
+    func image() throws -> XImage {
+        let image = XImage(data: self)
+        guard let image else {
+            throw ImageConversionError.invalidImageData
+        }
+        return image
+    }
+#endif
+}

Sources/SnapshotTesting/Snapshotting/ImageConversionError.swift

@@ -3,6 +3,7 @@ import Foundation
 
 enum ImageConversionError: Error {
   case cgImageConversionFailed
+  case invalidImageData
   case pngDataConversionFailed
   case zeroHeight
   case zeroSize
@@ -14,6 +15,8 @@ extension ImageConversionError: LocalizedError {
     switch self {
     case .cgImageConversionFailed, .pngDataConversionFailed:
       return "Snapshot could not be processed"
+    case .invalidImageData:
+      return "Invalid image data"
     case .zeroHeight:
       return "Snapshot has a height of zero"
     case .zeroSize:

Sources/SnapshotTesting/Snapshotting/NSImage.swift

@@ -18,7 +18,7 @@
     public static func image(precision: Float = 1, perceptualPrecision: Float = 1) -> Diffing {
       return .init(
         toData: convertToData,
-        fromData: { NSImage(data: $0)! }
+        fromData: { try $0.image() }
       ) { old, new in
         do {
           let result = try compare(old, new, precision: precision, perceptualPrecision: perceptualPrecision)

Sources/SnapshotTesting/Snapshotting/UIImage.swift

@@ -22,7 +22,7 @@
     ) -> Diffing {
       Diffing(
         toData: convertToData,
-        fromData: { UIImage(data: $0, scale: scale)! }
+        fromData: { try $0.image(scale: scale) }
       ) { old, new in
         do {
           let result = try compare(old, new, precision: precision, perceptualPrecision: perceptualPrecision)

Tests/SnapshotTestingTests/SnapshotTestingTests.swift

@@ -1137,6 +1137,13 @@ final class SnapshotTestingTests: XCTestCase {
       XCTAssertEqual(firstLine, "[macos] Snapshot size (123.0, 123.0) is unequal to expected size (100.0, 100.0)")
       #endif
     }
+
+    func testImageSnapshot_whenReferenceImageLoadingFails() {
+      let size = CGSize(width: 100, height: 100)
+      let view = XView(frame: .init(origin: .zero, size: size))
+      let message = verifySnapshot(of: view, as: .image)
+      XCTAssertEqual(message, "Invalid image data")
+    }
   #endif
 
 #if canImport(SwiftUI)