Conform 'AnyDifferentiable' and 'AnyDerivative' to 'CustomReflectable'.

'AnyDifferentiable' and 'AnyDerivative' should conform to 'CustomReflectable' to prevent leaking implementation details. The mirror should reflect its underlying value directly.

Resolves rdar://75496334.

Author: rxwei

stdlib/public/Differentiation/AnyDifferentiable.swift

@@ -102,6 +102,12 @@ public struct AnyDifferentiable: Differentiable {
   }
 }
 
+extension AnyDifferentiable: CustomReflectable {
+    public var customMirror: Mirror {
+        Mirror(reflecting: base)
+    }
+}
+
 //===----------------------------------------------------------------------===//
 // `AnyDerivative`
 //===----------------------------------------------------------------------===//
@@ -365,6 +371,12 @@ public struct AnyDerivative: Differentiable & AdditiveArithmetic {
   }
 }
 
+extension AnyDerivative: CustomReflectable {
+    public var customMirror: Mirror {
+        Mirror(reflecting: base)
+    }
+}
+
 //===----------------------------------------------------------------------===//
 // Helpers
 //===----------------------------------------------------------------------===//

test/AutoDiff/stdlib/anydifferentiable.swift

@@ -92,6 +92,16 @@ TypeErasureTests.test("AnyDifferentiable casting") {
   expectEqual(nil, genericAny.base as? Generic<Double>)
 }
 
+TypeErasureTests.test("AnyDifferentiable reflection") {
+  let originalVector = Vector(x: 1, y: 1)
+  let vector = AnyDifferentiable(originalVector)
+  let mirror = Mirror(reflecting: vector)
+  let children = Array(mirror.children)
+  expectEqual(2, children.count)
+  expectEqual(["x", "y"], children.map(\.label))
+  expectEqual([originalVector.x, originalVector.y], children.map { $0.value as! Float })
+}
+
 TypeErasureTests.test("AnyDerivative casting") {
   let tan = AnyDerivative(Vector.TangentVector(x: 1, y: 1))
   expectEqual(Vector.TangentVector(x: 1, y: 1), tan.base as? Vector.TangentVector)
@@ -107,6 +117,16 @@ TypeErasureTests.test("AnyDerivative casting") {
   expectEqual(nil, zero.base as? Generic<Float>.TangentVector)
 }
 
+TypeErasureTests.test("AnyDerivative reflection") {
+  let originalTan = Vector.TangentVector(x: 1, y: 1)
+  let tan = AnyDerivative(originalTan)
+  let mirror = Mirror(reflecting: tan)
+  let children = Array(mirror.children)
+  expectEqual(2, children.count)
+  expectEqual(["x", "y"], children.map(\.label))
+  expectEqual([originalTan.x, originalTan.y], children.map { $0.value as! Float })
+}
+
 TypeErasureTests.test("AnyDifferentiable differentiation") {
   // Test `AnyDifferentiable` initializer.
   do {