Allow custom struct args to grad_from_chainrules macro (#232)

* allow custom struct args to grad_from_chainrules

* fix test

* bump version

* fix test

* Update test/ChainRulesTests.jl

Co-authored-by: David Widmann <[email protected]>

* Update src/macros.jl

Co-authored-by: David Widmann <[email protected]>

* Update src/macros.jl

Co-authored-by: David Widmann <[email protected]>

---------

Co-authored-by: David Widmann <[email protected]>

Project.toml

@@ -1,6 +1,6 @@
 name = "ReverseDiff"
 uuid = "37e2e3b7-166d-5795-8a7a-e32c996b4267"
-version = "1.14.6"
+version = "1.15.0"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/macros.jl

@@ -317,9 +317,19 @@ macro grad_from_chainrules(fcall)
     Meta.isexpr(fcall, :call) && length(fcall.args) >= 2 ||
         error("`@grad_from_chainrules` has to be applied to a function signature")
     f = esc(fcall.args[1])
-    xs = fcall.args[2:end]
+    xs = map(fcall.args[2:end]) do x
+        if Meta.isexpr(x, :(::))
+            if length(x.args) == 1 # ::T without var name
+                return :($(gensym())::$(esc(x.args[1])))
+            else # x::T
+                @assert length(x.args) == 2
+                return :($(x.args[1])::$(esc(x.args[2])))
+            end
+        else
+            return x
+        end
+    end
     args_l, args_r, args_track, args_fixed, arg_types, kwargs = _make_fwd_args(f, xs)
-
     return quote
         $f($(args_l...)) = ReverseDiff.track($(args_r...))
         function ReverseDiff.track($(args_track...))

test/ChainRulesTests.jl

@@ -6,6 +6,9 @@ using DiffResults
 using ReverseDiff
 using Test
 
+struct MyStruct end
+f(::MyStruct, x) = sum(4x .+ 1)
+f(x, y::MyStruct) = sum(4x .+ 1)
 f(x) = sum(4x .+ 1)
 
 function ChainRulesCore.rrule(::typeof(f), x)
@@ -20,21 +23,37 @@ function ChainRulesCore.rrule(::typeof(f), x)
         rather than 4 when we compute the derivative of `f`, it means
         the importing mechanism works.
         =#
-        return ChainRulesCore.NoTangent(), fill(3 * d, size(x))
+        return NoTangent(), fill(3 * d, size(x))
+    end
+    return r, back
+end
+function ChainRulesCore.rrule(::typeof(f), ::MyStruct, x)
+    r = f(MyStruct(), x)
+    function back(d)
+        return NoTangent(), NoTangent(), fill(3 * d, size(x))
+    end
+    return r, back
+end
+function ChainRulesCore.rrule(::typeof(f), x, ::MyStruct)
+    r = f(x, MyStruct())
+    function back(d)
+        return NoTangent(), fill(3 * d, size(x)), NoTangent()
     end
     return r, back
 end
 
 ReverseDiff.@grad_from_chainrules f(x::ReverseDiff.TrackedArray)
-
+# test arg type hygiene
+ReverseDiff.@grad_from_chainrules f(::MyStruct, x::ReverseDiff.TrackedArray)
+ReverseDiff.@grad_from_chainrules f(x::ReverseDiff.TrackedArray, y::MyStruct)
 
 g(x, y) = sum(4x .+ 4y)
 
 function ChainRulesCore.rrule(::typeof(g), x, y)
     r = g(x, y)
     function back(d)
         # same as above, use 3 and 5 as the derivatives
-        return ChainRulesCore.NoTangent(), fill(3 * d, size(x)), fill(5 * d, size(x))
+        return NoTangent(), fill(3 * d, size(x)), fill(5 * d, size(x))
     end
     return r, back
 end
@@ -93,6 +112,19 @@ ReverseDiff.@grad_from_chainrules g(x::ReverseDiff.TrackedArray, y::ReverseDiff.
 
 end
 
+@testset "custom struct input" begin
+    input = rand(3, 3)
+    output, back = ChainRulesCore.rrule(f, MyStruct(), input);
+    _, _, d = back(1)
+    @test output == f(MyStruct(), input)
+    @test d == fill(3, size(input))
+
+    output, back = ChainRulesCore.rrule(f, input, MyStruct());
+    _, d, _ = back(1)
+    @test output == f(input, MyStruct())
+    @test d == fill(3, size(input))
+end
+
 ### Tape test
 @testset "Tape test: Ensure ordinary call is not tracked" begin
     tp = ReverseDiff.InstructionTape()
@@ -112,7 +144,7 @@ f_vararg(x, args...) = sum(4x .+ sum(args))
 function ChainRulesCore.rrule(::typeof(f_vararg), x, args...)
     r = f_vararg(x, args...)
     function back(d)
-        return ChainRulesCore.NoTangent(), fill(3 * d, size(x))
+        return NoTangent(), fill(3 * d, size(x))
     end
     return r, back
 end
@@ -136,7 +168,7 @@ f_kw(x, args...; k=1, kwargs...) = sum(4x .+ sum(args) .+ (k + kwargs[:j]))
 function ChainRulesCore.rrule(::typeof(f_kw), x, args...; k=1, kwargs...)
     r = f_kw(x, args...; k=k, kwargs...)
     function back(d)
-        return ChainRulesCore.NoTangent(), fill(3 * d, size(x))
+        return NoTangent(), fill(3 * d, size(x))
     end
     return r, back
 end
@@ -175,20 +207,20 @@ end
 ### Isolated Scope
 module IsolatedModuleForTestingScoping
 using ChainRulesCore
-using ReverseDiff: @grad_from_chainrules
+using ReverseDiff: ReverseDiff, @grad_from_chainrules
 
 f(x) = sum(4x .+ 1)
 
 function ChainRulesCore.rrule(::typeof(f), x)
     r = f(x)
     function back(d)
         # return a distinguishable but improper grad
-        return ChainRulesCore.NoTangent(), fill(3 * d, size(x))
+        return NoTangent(), fill(3 * d, size(x))
     end
     return r, back
 end
 
-@grad_from_chainrules f(x::TrackedArray)
+@grad_from_chainrules f(x::ReverseDiff.TrackedArray)
 
 module SubModule
 using Test