Convert irrational manually with oftype

Author: devmotion

src/chainrules.jl

@@ -40,7 +40,7 @@ ChainRulesCore.@scalar_rule(erf(x, y), (- (2 * exp(-x^2)) / sqrtπ, (2 * exp(-y^
 ChainRulesCore.@scalar_rule(erfc(x), - (2 * exp(-x^2)) / sqrtπ)
 ChainRulesCore.@scalar_rule(logerfc(x), - (2 * exp(-x^2 - Ω)) / sqrtπ)
 ChainRulesCore.@scalar_rule(erfcinv(x), - (sqrtπ * (exp(Ω^2) / 2)))
-ChainRulesCore.@scalar_rule(erfcx(x), 2 * x * Ω - 2 / sqrtπ)
+ChainRulesCore.@scalar_rule(erfcx(x), 2 * (x * Ω - inv(oftype(Ω, sqrtπ))))
 ChainRulesCore.@scalar_rule(logerfcx(x), 2 * (x - exp(-Ω) / sqrtπ))
 ChainRulesCore.@scalar_rule(erfi(x), (2 * exp(x^2)) / sqrtπ)
 ChainRulesCore.@scalar_rule(erfinv(x), sqrtπ * (exp(Ω^2) / 2))

test/chainrules.jl

@@ -147,7 +147,7 @@
     # https://github.com/JuliaMath/SpecialFunctions.jl/issues/307
     @testset "promotions" begin
         # one argument
-        for f in (erf, erfc, logerfc, erfcinv, logerfcx, erfi, erfinv, sinint)
+        for f in (erf, erfc, logerfc, erfcinv, erfcx, logerfcx, erfi, erfinv, sinint)
             _, ẏ = frule((NoTangent(), 1f0), f, 1f0)
             @test ẏ isa Float32
             _, back = rrule(f, 1f0)
@@ -161,13 +161,5 @@
         _, back = rrule(erf, 1f0, 1f0)
         _, x̄ = back(1f0)
         @test x̄ isa Float32
-
-        # currently broken, can be fixed if `invsqrtπ` is available:
-        # https://github.com/JuliaMath/IrrationalConstants.jl/pull/8#issuecomment-925828753
-        _, ẏ = frule((NoTangent(), 1f0), erfcx, 1f0)
-        @test_broken ẏ isa Float32
-        _, back = rrule(erfcx, 1f0)
-        _, x̄ = back(1f0)
-        @test x̄ isa Float32
     end
 end