Merge pull request #797 from nsajko/zero_one_identically_same_pullback

make `rrule` return identical pullback for `zero` as for `one`

Author: oxinabox

Project.toml

@@ -1,6 +1,6 @@
 name = "ChainRules"
 uuid = "082447d4-558c-5d27-93f4-14fc19e9eca2"
-version = "1.66.0"
+version = "1.67.0"
 
 [deps]
 Adapt = "79e6a3ab-5dfb-504d-930d-738a2a938a0e"

src/rulesets/Base/base.jl

@@ -11,7 +11,7 @@ function frule((_, _), ::typeof(zero), x)
 end
 
 function rrule(::typeof(zero), x)
-    zero_pullback(_) = (NoTangent(), ZeroTangent())
+    zero_pullback = Returns((NoTangent(), ZeroTangent()))
     return (zero(x), zero_pullback)
 end
 
@@ -22,7 +22,7 @@ function frule((_, _), ::typeof(one), x)
 end
 
 function rrule(::typeof(one), x)
-    one_pullback(_) = (NoTangent(), ZeroTangent())
+    one_pullback = Returns((NoTangent(), ZeroTangent()))
     return (one(x), one_pullback)
 end
 

test/rulesets/Base/base.jl

@@ -4,6 +4,7 @@ end
 
 @testset "base.jl" begin
     @testset "zero/one" begin
+        @test last(rrule(zero, 0.1)) === last(rrule(one, 0.2f0))
         for f in [zero, one]
             for x in [1.0, 1.0im, [10.0+im 11.0-im; 12.0+2im 13.0-3im]]
                 test_frule(f, x)