Merge pull request #524 from JuliaDiff/mz/optout

`@opt_out of sum(array, array)`

Author: mzgubic

Project.toml

@@ -1,6 +1,6 @@
 name = "ChainRules"
 uuid = "082447d4-558c-5d27-93f4-14fc19e9eca2"
-version = "1.11.4"
+version = "1.11.5"
 
 [deps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"

src/rulesets/Base/mapreduce.jl

@@ -88,6 +88,17 @@ function rrule(
     return y, sum_pullback
 end
 
+# https://github.com/JuliaDiff/ChainRules.jl/issues/522
+# The rule above assumes `f` is callable. Arrays are not, this came up when summing
+# arrays with weights in StatsBase
+@opt_out ChainRulesCore.rrule(
+    config::RuleConfig{>:HasReverseMode},
+    ::typeof(sum),
+    x::AbstractArray,
+    y::AbstractArray;
+    dims=:
+)
+
 function frule(
     (_, _, Δx),
     ::typeof(sum),

test/rulesets/Base/mapreduce.jl

@@ -1,3 +1,7 @@
+# for sum(xs, weights) (#522)
+Base.sum(xs::AbstractArray, weights::AbstractArray) = dot(xs, weights)
+struct SumRuleConfig <: RuleConfig{Union{HasReverseMode}} end
+
 @testset "Maps and Reductions" begin
     @testset "sum(x; dims=$dims)" for dims in (:, 2, (1,3))
         # Forward
@@ -90,6 +94,14 @@
         @test_skip test_rrule(sum, iszero, randn(5))  # DimensionMismatch("second dimension of A, 1, does not match length of x, 0")
     end
 
+    # https://github.com/JuliaDiff/ChainRules.jl/issues/522
+    @testset "sum(xs, weights) (#522)" begin
+        xs = rand(5)
+        weights = rand(5)
+
+        @test rrule(SumRuleConfig(), Base.sum, xs, weights) isa Nothing
+    end
+
     @testset "prod" begin
         @testset "Array{$T}" for T in [Float64, ComplexF64]
             @testset "size = $sz, dims = $dims" for (sz, dims) in [