Merge pull request #520 from JuliaDiff/ox/nprojrev

Don't ProjectTo in reverse or circshift

Author: oxinabox

Project.toml

@@ -1,6 +1,6 @@
 name = "ChainRules"
 uuid = "082447d4-558c-5d27-93f4-14fc19e9eca2"
-version = "1.11.1"
+version = "1.11.2"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/rulesets/Base/array.jl

@@ -303,10 +303,9 @@ function frule((_, xdot), ::typeof(reverse), x::AbstractArray, args...; kw...)
 end
 
 function rrule(::typeof(reverse), x::AbstractArray, args...; kw...)
-    project = ProjectTo(x)
     nots = map(_ -> NoTangent(), args)
     function reverse_pullback(dy)
-        dx = @thunk project(reverse(unthunk(dy), args...; kw...))
+        dx = @thunk reverse(unthunk(dy), args...; kw...)
         return (NoTangent(), dx, nots...)
     end
     return reverse(x, args...; kw...), reverse_pullback
@@ -321,9 +320,8 @@ function frule((_, xdot), ::typeof(circshift), x::AbstractArray, shifts)
 end
 
 function rrule(::typeof(circshift), x::AbstractArray, shifts)
-    project = ProjectTo(x)
     function circshift_pullback(dy)
-        dx = @thunk project(circshift(unthunk(dy), map(-, shifts)))
+        dx = @thunk circshift(unthunk(dy), map(-, shifts))
         # Note that circshift! is useless for InplaceableThunk, as it overwrites completely
         return (NoTangent(), dx, NoTangent())
     end

test/rulesets/Base/array.jl

@@ -171,7 +171,9 @@ end
 
         # Structured
         y, pb = rrule(reverse, Diagonal([1,2,3]))
-        @test unthunk(pb(rand(3,3))[2]) isa Diagonal
+        # We only preserve structure in this case if given structured tangent (no ProjectTo)
+        @test unthunk(pb(Diagonal([1.1, 2.1, 3.1]))[2]) isa Diagonal
+        @test unthunk(pb(rand(3, 3))[2]) isa AbstractArray
     end
 end