Error for thread/group size with different integer types

[eschnett]

This fails:

julia> function f() end
julia> @metal threads=(Int64(1), Int32(1)) f()

with:

ERROR: MethodError: Cannot `convert` an object of type Tuple{Int64, Int32} to an object of type UInt64
The function `convert` exists, but no method is defined for this combination of argument types.

Closest candidates are:
  convert(::Type{UInt64}, ::ObjectiveC.OS.OSSignpost)
   @ ObjectiveC ~/.julia/packages/ObjectiveC/C7BVt/src/os.jl:170
  convert(::Type{UInt64}, ::LLVM.OrcTargetAddress)
   @ LLVM ~/.julia/packages/LLVM/joxPv/src/orc.jl:217
  convert(::Type{T}, ::IntervalArithmetic.ExactReal) where T<:Real
   @ IntervalArithmetic ~/.julia/packages/IntervalArithmetic/hLM2A/src/intervals/exact_literals.jl:111
  ...

Stacktrace:
 [1] Metal.MTL.MTLSize(w::Tuple{Int64, Int32}, h::Int64, d::Int64)
   @ Metal.MTL ~/.julia/packages/Metal/UcSBS/lib/mtl/size.jl:10

[eschnett]

I am using Metal 1.3.0.

[tgymnich]

Metal currently expects the threads tuple elements to have the same type, so

julia> function f() end
julia> @metal threads=(1,1) f()

should work.

[eschnett]

Yes, this works. (My issues that it doesn't work when the tuple elements have different types.)

[tgymnich]

Why is that an issue?

[eschnett]

It is unexpected and inconvenient. I encountered this by accident and was then confused by the error message. I assumed that this was a case that was unintentionally not handled.

[tgymnich]

I guess thats fair #425