round(pi, base=10) broken

[martinholters]

julia> round(pi)
3.0

julia> round(pi, digits=0)
3.0

julia> round(pi, digits=0, base=10)
3.0

julia> round(pi, base=10)
ERROR: MethodError: no method matching round(::Irrational{:π}, ::RoundingMode{:Nearest})
Closest candidates are:
  round(::Irrational, ::RoundingMode) at irrationals.jl:137
  round(::Real, ::RoundingMode; digits, sigdigits, base) at floatfuncs.jl:127
  round(::Number, ::Any) at deprecated.jl:53
  ...
Stacktrace:
 [1] _round(::Irrational{:π}, ::RoundingMode{:Nearest}, ::Nothing, ::Nothing, ::Int64) at ./floatfuncs.jl:137
#...

The error is a straight lie:

julia> round(pi, RoundingMode{:Nearest}())
3.0

Explicitly thrown here:

julia/base/floatfuncs.jl

Lines 136 to 137 in b6a60dd

	# if we hit this method, it means that no `round(x, r)` method is defined
	_round(x::Real, r::RoundingMode, digits::Nothing, sigdigits::Nothing, base) = throw(MethodError(round, (x,r)))

[simonbyrne]

Note that the current docstring doesn't actually mention this as an option. Do we want to allow it, or should we just throw a better error message?