Fix #27 - mixup in lifiting of getfield

Author: Keno

src/stage1/generated.jl

@@ -380,7 +380,7 @@ lifted_getfield(x::ZeroTangent, s) = ZeroTangent()
 lifted_getfield(x::NoTangent, s) = NoTangent()
 
 function lifted_getfield(x::Tangent, s)
-    z = getfield(ChainRulesCore.backing(x), s)
+    z = getfield(ChainRulesCore.backing(ChainRulesCore.canonicalize(x)), s)
     z
 end
 

test/runtests.jl

@@ -182,5 +182,10 @@ end
 @test bwd(x->f_crit_edge(false, true, true, x))(1.0) == 12.0
 @test bwd(x->f_crit_edge(false, false, true, x))(1.0) == 4.0
 
+# Issue #27 - Mixup in lifting of getfield
+let var"'" = bwd
+    @test (x->x^5)''(1.0) == 20.
+    @test (x->x^5)'''(1.0) == 60.
+end
 
 include("pinn.jl")