ChainRulesCore: frule(): explicitly fall-back to RuleConfig-less …

…version

```
Running tests:
1 ambiguities found. To get a list, set `broken = false`.
Ambiguity #1
frule(::ChainRulesCore.RuleConfig, args...) in ChainRulesCore at /home/runner/.julia/packages/ChainRulesCore/I1EbV/src/rules.jl:64
frule(::Any, ::typeof(Distributions.logpdf), d::Distributions.Uniform, x::Real) in Distributions.DistributionsChainRulesCoreExt at /home/runner/work/Distributions.jl/Distributions.jl/ext/DistributionsChainRulesCoreExt/univariate/continuous/uniform.jl:1

Possible fix, define
  frule(::ChainRulesCore.RuleConfig, ::typeof(Distributions.logpdf), ::Distributions.Uniform, ::Real)

Aqua: Test Failed at /home/runner/.julia/packages/Aqua/tHrmY/src/ambiguities.jl:78
  Expression: iszero(num_ambiguities)
Stacktrace:
 [1] _test_ambiguities(packages::Vector{Base.PkgId}; broken::Bool, kwargs::Base.Iterators.Pairs{Union{}, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
   @ Aqua ~/.julia/packages/Aqua/tHrmY/src/ambiguities.jl:78
 [2] _test_ambiguities
   @ ~/.julia/packages/Aqua/tHrmY/src/ambiguities.jl:69 [inlined]
 [3] test_ambiguities(packages::Module; kwargs::Base.Iterators.Pairs{Union{}, Union{}, Tuple{}, NamedTuple{(), Tuple{}}})
   @ Aqua ~/.julia/packages/Aqua/tHrmY/src/ambiguities.jl:28
 [4] test_ambiguities(packages::Module)
   @ Aqua ~/.julia/packages/Aqua/tHrmY/src/ambiguities.jl:28
 [5] macro expansion
   @ ~/work/Distributions.jl/Distributions.jl/test/aqua.jl:19 [inlined]
 [6] macro expansion
   @ /buildworker/worker/package_linux64/build/usr/share/julia/stdlib/v1.6/Test/src/Test.jl:1151 [inlined]
 [7] top-level scope
   @ ~/work/Distributions.jl/Distributions.jl/test/aqua.jl:9
```

ext/DistributionsChainRulesCoreExt/multivariate/dirichlet.jl

@@ -9,6 +9,9 @@ function ChainRulesCore.frule((_, Δalpha)::Tuple{Any,Any}, ::Type{DT}, alpha::A
     return d, Δd
 end
 
+ChainRulesCore.frule(::ChainRulesCore.RuleConfig, Δ, pdf::Type{DT}, alpha::AbstractVector{T}; check_args::Bool = true) where {T <: Real, DT <: Union{Dirichlet{T}, Dirichlet}} =
+    ChainRulesCore.frule(Δ, pdf, alpha, check_args=check_args)
+
 function ChainRulesCore.rrule(::Type{DT}, alpha::AbstractVector{T}; check_args::Bool = true) where {T <: Real, DT <: Union{Dirichlet{T}, Dirichlet}}
     d = DT(alpha; check_args=check_args)
     digamma_alpha0 = SpecialFunctions.digamma(d.alpha0)
@@ -33,6 +36,9 @@ function ChainRulesCore.frule((_, Δd, Δx)::Tuple{Any,Any,Any}, ::typeof(Distri
     return Ω, ΔΩ
 end
 
+ChainRulesCore.frule(::ChainRulesCore.RuleConfig, Δ, pdf::typeof(Distributions._logpdf), d::Dirichlet, x::AbstractVector{<:Real}) =
+    ChainRulesCore.frule(Δ, pdf, d, x)
+
 function ChainRulesCore.rrule(::typeof(Distributions._logpdf), d::T, x::AbstractVector{<:Real}) where {T<:Dirichlet}
     Ω = Distributions._logpdf(d, x)
     isfinite_Ω = isfinite(Ω)

ext/DistributionsChainRulesCoreExt/univariate/continuous/uniform.jl

@@ -12,6 +12,9 @@ function ChainRulesCore.frule((_, Δd, _), ::typeof(logpdf), d::Uniform, x::Real
     return Ω, ΔΩ
 end
 
+ChainRulesCore.frule(::ChainRulesCore.RuleConfig, Δ, pdf::typeof(logpdf), d::Uniform, x::Real) =
+    ChainRulesCore.frule(Δ, pdf, d, x)
+
 function ChainRulesCore.rrule(::typeof(logpdf), d::Uniform, x::Real)
     # Compute log probability
     a, b = params(d)

ext/DistributionsChainRulesCoreExt/univariate/discrete/poissonbinomial.jl

@@ -8,6 +8,8 @@ for f in (:poissonbinomial_pdf, :poissonbinomial_pdf_fft)
             A = Distributions.poissonbinomial_pdf_partialderivatives(p)
             return y, A' * Δp
         end
+        ChainRulesCore.frule(::ChainRulesCore.RuleConfig, Δ, pdf::typeof(Distributions.$f), p::AbstractVector{<:Real}) =
+            ChainRulesCore.frule(Δ, pdf, p)
         function ChainRulesCore.rrule(::typeof(Distributions.$f), p::AbstractVector{<:Real})
             y = Distributions.$f(p)
             A = Distributions.poissonbinomial_pdf_partialderivatives(p)