non-sensical MethodError

[simonster]

The tests for DSP.jl master are currently failing with a MethodError (JuliaDSP/DSP.jl#19):

 ERROR: no method convert(Type{Array{Complex{Float64},1}}, Array{Float64,1})

That method definitely exists: We are importing convert from Base before extending it, and inserting print(code_lowered(convert, (Type{Array{Complex{Float64},1}}, Array{Float64,1}))) above the line that throws shows the method source. git bisect shows that the error first appears with 6002358 (cc @JeffBezanson).

[johnmyleswhite]

Maybe related to the convert issue I raised a week or two ago?

[simonster]

For the method that's throwing, code_typed shows:

code_typed(convert, (Type{ZPKFilter}, TFFilter{Float64}))
1-element Array{Any,1}:
 :($(Expr(:lambda, {:#s68,:f}, {{:k,:b,:z,:p},{{:#s68,Type{ZPKFilter{Z,P,K}},0},{:f,TFFilter{Float64},0},{:k,Float64,18},{:b,Poly{Float64},18},{:z,Array{Complex{Float64},1},18},{:p,Array{Complex{Float64},1},18}},{}}, quote  # /Users/simon/.julia/DSP/src/filter_design.jl, line 107:
        k = arrayref(top(getfield)(top(getfield)(f::TFFilter{Float64},:b)::Poly{Float64},:a)::Array{Float64,1},top(box)(Int64,top(add_int)(1,top(getfield)(top(getfield)(f::TFFilter{Float64},:b)::Poly{Float64},:nzfirst)::Int64))::Int64)::Float64 # line 108:
        b = /(top(getfield)(f::TFFilter{Float64},:b)::Poly{Float64},k::Float64)::Poly{Float64} # line 109:
        z = convert_default($(Array{Complex{Float64},1}),roots(b::Poly{Float64})::AbstractArray{T,N},convert)::Array{Complex{Float64},1} # line 110:
        p = convert_default($(Array{Complex{Float64},1}),roots(top(getfield)(f::TFFilter{Float64},:a)::Poly{Float64})::AbstractArray{T,N},convert)::Array{Complex{Float64},1} # line 111:
        return $(Expr(:new, ZPKFilter{Complex{Float64},Complex{Float64},Float64}, :(z::Array{Complex{Float64},1}), :(p::Array{Complex{Float64},1}), :(k::Float64)))::ZPKFilter{Complex{Float64},Complex{Float64},Float64}
    end)))

It fails at the convert_default line there, since Array{Float64,1} is not a subtype of Array{Complex{Float64},1}. With the previous (working) commit, code_typed shows:

code_typed(convert, (Type{ZPKFilter}, TFFilter{Float64}))
1-element Array{Any,1}:
 :($(Expr(:lambda, {:#s62,:f}, {{:k,:b,:z,:p},{{:#s62,Type{ZPKFilter{Z,P,K}},0},{:f,TFFilter{Float64},0},{:k,Float64,18},{:b,Poly{Float64},18},{:z,Array{Complex{Float64},1},18},{:p,Array{Complex{Float64},1},18}},{}}, quote  # /Users/simon/.julia/DSP/src/filter_design.jl, line 107:
        k = arrayref(top(getfield)(top(getfield)(f::TFFilter{Float64},:b)::Poly{Float64},:a)::Array{Float64,1},top(box)(Int64,top(add_int)(1,top(getfield)(top(getfield)(f::TFFilter{Float64},:b)::Poly{Float64},:nzfirst)::Int64))::Int64)::Float64 # line 108:
        b = /(top(getfield)(f::TFFilter{Float64},:b)::Poly{Float64},k::Float64)::Poly{Float64} # line 109:
        z = convert($(Array{Complex{Float64},1}),roots(b::Poly{Float64})::Array{T,1})::Array{Complex{Float64},1} # line 110:
        p = convert($(Array{Complex{Float64},1}),roots(top(getfield)(f::TFFilter{Float64},:a)::Poly{Float64})::Array{T,1})::Array{Complex{Float64},1} # line 111:
        return $(Expr(:new, ZPKFilter{Complex{Float64},Complex{Float64},Float64}, :(z::Array{Complex{Float64},1}), :(p::Array{Complex{Float64},1}), :(k::Float64)))::ZPKFilter{Complex{Float64},Complex{Float64},Float64}
    end)))

[simonster]

Reduced test case:

julia> f() = convert(Vector{Complex128}, AbstractArray[[1.0]][1]);

julia> f()
ERROR: no method convert(Type{Array{Complex{Float64},1}}, Array{Float64,1})
 in f at none:1

This fails both before and after 6002358 (and all the way back to at least 0.2). The reason git bisect picked out 6002358 is that type inference for roots(Poly{Float64}) now gives a less specific return type (AbstractArray{T,N} instead of Array{T,1}), which seems to have exposed this bug.