---

yaml
---
r: 340371
b: refs/heads/rxwei-patch-1
c: 1782d72
h: refs/heads/master
i:
  340369: 1b991aa
  340367: cba1b78

Author: rxwei

[refs]

@@ -1015,7 +1015,7 @@ refs/tags/swift-DEVELOPMENT-SNAPSHOT-2018-08-18-a: b10b1fce14385faa6d44f6b933e95
 refs/heads/rdar-43033749-fix-batch-mode-no-diags-swift-5.0-branch: a14e64eaad30de89f0f5f0b2a782eed7ecdcb255
 refs/heads/revert-19006-error-bridging-integer-type: 8a9065a3696535305ea53fe9b71f91cbe6702019
 refs/heads/revert-19050-revert-19006-error-bridging-integer-type: ecf752d54b05dd0a20f510f0bfa54a3fec3bcaca
-refs/heads/rxwei-patch-1: aa6d64c6cca590d93805d8253b5ab9963e91d84f
+refs/heads/rxwei-patch-1: 1782d725aba57c23f44249844c560a53ed27c21b
 refs/heads/shahmishal-patch-1: e58ec0f7488258d42bef51bc3e6d7b3dc74d7b2a
 refs/heads/typelist-existential: 4046359efd541fb5c72d69a92eefc0a784df8f5e
 refs/tags/swift-4.2-DEVELOPMENT-SNAPSHOT-2018-08-20-a: 4319ba09e4fb8650ee86061075c74a016b6baab9

branches/rxwei-patch-1/stdlib/public/core/AutoDiff.swift

@@ -140,12 +140,24 @@ public extension Differentiable where TangentVector == Self {
 }
 
 public extension Differentiable {
-  /// Identity function that stops gradients from propagating.
+  /// Identity function that stops derivatives from propagating.
+  @inlinable
   @inline(__always)
   @_semantics("autodiff.nonvarying")
   func withoutDerivative() -> Self { return self }
 }
 
+/// Applies the given closure `body` to `x`. When used in a context where `x` is
+/// being differentiated with respect to, this function will not produce any
+/// derivative at `x`.
+// FIXME: Support throws-rethrows.
+@inlinable
+@inline(__always)
+@_semantics("autodiff.nonvarying")
+public func withoutDerivative<T, R>(at x: T, in body: (T) -> R) -> R {
+  body(x)
+}
+
 //===----------------------------------------------------------------------===//
 // Functional utilities
 //===----------------------------------------------------------------------===//

branches/rxwei-patch-1/test/AutoDiff/custom_derivatives.swift

@@ -87,4 +87,12 @@ CustomDerivativesTests.test("ModifyGradientOfSum") {
   })
 }
 
+CustomDerivativesTests.test("WithoutDerivative") {
+  expectEqual(0, gradient(at: Float(4)) { x in
+    withoutDerivative(at: x) { x in
+      sinf(x) + cosf(x)
+    }
+  })
+}
+
 runAllTests()