From 5c04890c24e5f431c674a2d782adcb1469676bde Mon Sep 17 00:00:00 2001
From: Dhairya Gandhi <dhairya@juliacopmuting.com>
Date: Sat, 12 Dec 2020 20:43:34 +0530
Subject: [PATCH 1/5] add isderiving

---
 src/lib/utils.jl | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/src/lib/utils.jl b/src/lib/utils.jl
index 5d4634814..c4ad81ae4 100644
--- a/src/lib/utils.jl
+++ b/src/lib/utils.jl
@@ -111,3 +111,26 @@ a real.
      1  0
 """
 hessian(f, x::AbstractArray) = forward_jacobian(x -> gradient(f, x)[1], x)[2]
+
+"""
+   isderiving()
+
+Check whether the current function call is happening while taking the derivative.
+
+
+    julia> function f(x)
+             @show isderiving()
+           end
+    
+    f (generic function with 1 method)
+    
+    julia> f(3)
+    isderiving() = false
+    false
+    
+    julia> gradient(f, 4)
+    isderiving() = true
+    (nothing,)
+"""
+isderiving() = false
+@adjoint isderiving() = true, _ -> nothing

From 5c585681d0d3f5fc8c8611ddaa0c3f7382fe37a5 Mon Sep 17 00:00:00 2001
From: Dhairya Gandhi <dhairya@juliacopmuting.com>
Date: Sun, 13 Dec 2020 17:05:39 +0530
Subject: [PATCH 2/5] make isderiving for higher order differentiation

---
 src/lib/utils.jl | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/lib/utils.jl b/src/lib/utils.jl
index c4ad81ae4..82e02f3db 100644
--- a/src/lib/utils.jl
+++ b/src/lib/utils.jl
@@ -133,4 +133,6 @@ Check whether the current function call is happening while taking the derivative
     (nothing,)
 """
 isderiving() = false
+isderiving(x) = false
 @adjoint isderiving() = true, _ -> nothing
+@adjoint isderiving(x) = true, x -> (nothing,)

From 89458dbeb460d38389ef52ff7ccb57e924ee770b Mon Sep 17 00:00:00 2001
From: Dhairya Gandhi <dhairya@juliacopmuting.com>
Date: Sun, 13 Dec 2020 18:13:25 +0530
Subject: [PATCH 3/5] add 850 as a test

---
 test/tools.jl | 41 ++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 40 insertions(+), 1 deletion(-)

diff --git a/test/tools.jl b/test/tools.jl
index 921b8a56f..a27bcd451 100644
--- a/test/tools.jl
+++ b/test/tools.jl
@@ -22,4 +22,43 @@
   deleteat!(buff, 1)
   @test length(buff) == 1
   @test buff[1] === c
-end
\ No newline at end of file
+end
+
+@testset "isderiving" begin
+
+  function f(x)
+    if isderiving(x)
+      x^2
+    else
+      2x^2
+    end
+  end
+
+  # Test higher order derivatives
+  gs = gradient(4) do x
+    gradient(x) do y
+      f(y)
+    end[1]
+  end
+
+  @test gs == (2,)
+
+  struct Tester
+    cpu_offload::Float64
+  end
+
+  function Tester(p)
+      @show isderiving(p)
+      cpu_offload = isderiving(p) ? 0.0 : 0.2
+      Tester(cpu_offload)
+  end
+
+  function f(p)
+    sum(Tester(p).cpu_offload .* p)
+  end
+
+  p = [1.0]
+  gs = gradient(f, p)
+  @test gs[1] == [0.]
+
+end

From f022bbac45d4c52768b525c66cfad532d9f34cb7 Mon Sep 17 00:00:00 2001
From: Dhairya Gandhi <dhairya@juliacopmuting.com>
Date: Sun, 13 Dec 2020 18:20:33 +0530
Subject: [PATCH 4/5] qualify names in test

---
 test/tools.jl | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/test/tools.jl b/test/tools.jl
index a27bcd451..717612284 100644
--- a/test/tools.jl
+++ b/test/tools.jl
@@ -27,7 +27,7 @@ end
 @testset "isderiving" begin
 
   function f(x)
-    if isderiving(x)
+    if Zygote.isderiving(x)
       x^2
     else
       2x^2
@@ -48,8 +48,8 @@ end
   end
 
   function Tester(p)
-      @show isderiving(p)
-      cpu_offload = isderiving(p) ? 0.0 : 0.2
+      @show Zygote.isderiving(p)
+      cpu_offload = Zygote.isderiving(p) ? 0.0 : 0.2
       Tester(cpu_offload)
   end
 

From 453fe3a496595bc67bce6ecb32911cd1ba5fa6fe Mon Sep 17 00:00:00 2001
From: Dhairya Gandhi <dhairya@juliacomputing.com>
Date: Wed, 16 Dec 2020 16:40:15 +0530
Subject: [PATCH 5/5] Add the missing isderiving API to docstring

---
 src/lib/utils.jl | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/lib/utils.jl b/src/lib/utils.jl
index 82e02f3db..e51ff2d3c 100644
--- a/src/lib/utils.jl
+++ b/src/lib/utils.jl
@@ -114,6 +114,7 @@ hessian(f, x::AbstractArray) = forward_jacobian(x -> gradient(f, x)[1], x)[2]
 
 """
    isderiving()
+   isderiving(x)
 
 Check whether the current function call is happening while taking the derivative.