Method overwrite warning when building sysimg

[KristofferC]

WARNING: Method definition round(Real, Base.Rounding.RoundingMode{T} where T) in module Base at floatfuncs.jl:127 overwritten at floatfuncs.jl:135.

Touched in #26670 cc @simonbyrne

[simonbyrne]

The background is that we're exploiting #9498 to do dispatch on keyword arguments: the "user-facing" method is

julia/base/floatfuncs.jl

Lines 125 to 126 in a0b1e98

	function round(x::Real, r::RoundingMode=RoundNearest;
	digits::Union{Nothing,Integer}=nothing, sigdigits::Union{Nothing,Integer}=nothing, base=10)

which, depending on the arguments, will eventually call round(x,r) without keyword arguments.

To avoid recursive calls we also define a generic error:

julia/base/floatfuncs.jl

Line 135 in a0b1e98

round(x::Real, r::RoundingMode) = throw(MethodError(round, (x,r)))

which triggers the redefinition warning.

Unfortunately, I don't see a nice way to do it that doesn't trigger it. Any ideas?

[JeffBezanson]

Since we have

_round(x, r::RoundingMode, digits::Nothing, sigdigits::Nothing, base) = round(x, r)

it looks to me like it's never valid to be in the keyword arg definition with digits and sigdigits set to nothing. So an error could be thrown in that case, instead of defining the external error method?

[simonbyrne]

No that is valid: the intention is that each number type defines their own round(x,r) method, e.g.

julia/base/float.jl

Lines 358 to 365 in a0b1e98

	round(x::Float64, r::RoundingMode{:ToZero}) = trunc_llvm(x)
	round(x::Float32, r::RoundingMode{:ToZero}) = trunc_llvm(x)
	round(x::Float64, r::RoundingMode{:Down}) = floor_llvm(x)
	round(x::Float32, r::RoundingMode{:Down}) = floor_llvm(x)
	round(x::Float64, r::RoundingMode{:Up}) = ceil_llvm(x)
	round(x::Float32, r::RoundingMode{:Up}) = ceil_llvm(x)
	round(x::Float64, r::RoundingMode{:Nearest}) = rint_llvm(x)
	round(x::Float32, r::RoundingMode{:Nearest}) = rint_llvm(x)

[simonbyrne]

Ah, I misunderstood what you meant. That should work, thanks!