simpler

Author: nsajko

src/ChainRulesCore.jl

@@ -2,7 +2,7 @@ module ChainRulesCore
 using Base.Broadcast: broadcasted, Broadcasted, broadcastable, materialize, materialize!
 using Base.Meta
 using LinearAlgebra
-using Compat: hasfield, hasproperty, ismutabletype
+using Compat: hasfield, hasproperty, ismutabletype, Returns
 
 export frule, rrule  # core function
 # rule configurations

src/rule_definition_tools.jl

@@ -418,14 +418,6 @@ function _nondiff_frule_expr(__source__, primal_sig_parts, primal_invoke)
     end
 end
 
-struct NonDiffPullback{T<:Tuple{Vararg{NoTangent}}} <: Function
-    v::T
-end
-
-function (@nospecialize pb::NonDiffPullback)(@nospecialize ::Any)
-    return pb.v
-end
-
 function tuple_expression(primal_sig_parts)
     has_vararg = _isvararg(primal_sig_parts[end])
     return if !has_vararg
@@ -444,7 +436,7 @@ function _nondiff_rrule_expr(__source__, primal_sig_parts, primal_invoke)
     tup_expr = tuple_expression(primal_sig_parts)
     primal_name = first(primal_invoke.args)
     pullback_expr = @strip_linenos quote
-        NonDiffPullback($(tup_expr))
+        Returns($(tup_expr))
     end
 
     @gensym kwargs

test/rule_definition_tools.jl

@@ -42,18 +42,6 @@ end
 
 @testset "rule_definition_tools.jl" begin
     @testset "@non_differentiable" begin
-        @testset "`NonDiffPullback`" begin
-            NDP = ChainRulesCore.NonDiffPullback
-            for i in 0:5
-                tup = ntuple((_ -> NoTangent()), i)
-                ndp = NDP(tup)
-                @test ndp === @inferred NDP(tup)
-                @test tup === @inferred ndp(:arbitrary)
-                @test_throws MethodError ndp()
-                @test_throws MethodError ndp(1, 2)
-            end
-        end
-
         @testset "issue #678: identical pullback objects" begin
             issue_678_f(::Any) = nothing
             issue_678_g(::Any) = nothing