comprehension failure in global scope

[stevengj]

using Color
m = 2
[RGB(i/m,0,0) for i=1:m]

gives

`_convert` has no method matching _convert(::Type{RGB{Float64}}, ::RGB{Float64})
while loading In[15], in expression starting on line 2
 in convert at /home/juser/.julia/v0.3/Color/src/conversions.jl:32
 in setindex! at array.jl:307
 in anonymous at no file

changing m to const eliminates the problem, so I'm guessing that this is some type-inference problem with globals. But it doesn't seem like this should give an error in any case.

[simonster]

I think this is a reduced test case:

abstract A{T}
immutable B{T<:Integer} <: A{T}; end
Base.convert(::Type{B}, c::B) = c
Base.convert{T}(::Type{B}, c::A{T}) = error("should not be called")

julia> @which convert(B{TypeVar(:T,Top)}, B{Int}())
convert(::Type{B{T<:Integer}},c::B{T<:Integer}) at none:3

julia> convert(B{TypeVar(:T,Top)}, B{Int}())
ERROR: should not be called
 in convert at none:4

There's clearly something weird going on since the method returned by @which is not actually the method that gets called. In the code for the comprehension it's also a bit weird that code_typed(RGB, (Any, Int, Int)) is inferred as RGB{T<:Top}, since RGB is constrained as RGB{T<:Fractional}.

[timholy]

Likely also the cause of #8618.

[jakebolewski]

This is fixed now, due to the resolution of #8631