Try fixing "user-facing"/default plan for real/complex integer|rationals ambig.

Author: nHackel

src/definitions.jl

@@ -260,6 +260,11 @@ bfft!
 for f in (:fft, :bfft, :ifft)
     pf = Symbol("plan_", f)
     @eval begin
+        $f(x::AbstractArray{<:Real}, region) = $f(complexfloat(x), region)
+        $pf(x::AbstractArray{<:Real}, region; kws...) = $pf(complexfloat(x), region; kws...)
+        $f(x::AbstractArray{<:Complex{<:Union{Integer,Rational}}}, region) = $f(complexfloat(x), region)
+        $pf(x::AbstractArray{<:Complex{<:Union{Integer,Rational}}}, region; kws...) = $pf(complexfloat(x), region; kws...)
+        # These methods run into ambig. if a backend does not specialise T further
         $f(b::AbstractFFTBackend, x::AbstractArray{<:Real}, region) = $f(b, complexfloat(x), region)
         $pf(b::AbstractFFTBackend, x::AbstractArray{<:Real}, region; kws...) = $pf(b, complexfloat(x), region; kws...)
         $f(b::AbstractFFTBackend, x::AbstractArray{<:Complex{<:Union{Integer,Rational}}}, region) = $f(b, complexfloat(x), region)

test/TestPlans.jl

@@ -34,10 +34,10 @@ Base.ndims(::InverseTestPlan{T,N}) where {T,N} = N
 AbstractFFTs.AdjointStyle(::TestPlan) = AbstractFFTs.FFTAdjointStyle()
 AbstractFFTs.AdjointStyle(::InverseTestPlan) = AbstractFFTs.FFTAdjointStyle()
 
-function AbstractFFTs.plan_fft(::TestBackend, x::AbstractArray{T}, region; kwargs...) where {T <: Complex}
+function AbstractFFTs.plan_fft(::TestBackend, x::AbstractArray{T}, region; kwargs...) where {T}
     return TestPlan{T}(region, size(x))
 end
-function AbstractFFTs.plan_bfft(::TestBackend, x::AbstractArray{T}, region; kwargs...) where {T <: Complex}
+function AbstractFFTs.plan_bfft(::TestBackend, x::AbstractArray{T}, region; kwargs...) where {T}
     return InverseTestPlan{T}(region, size(x))
 end