Formatting fails for typemin(T<:Integer)

[jagot]

Consider

f = FormatExpr("{1:+d}")
for T in (Int8,Int16,Int32,Int64)
    @test format(f, typemin(T)) == string(typemin(T)) # Crashes
    @test format(f, typemax(T)) == "+"*string(typemax(T)) # Works
end

The first test (for typemin) crashes with the error

Error During Test at REPL[26]:2
  Test threw exception
  Expression: format(f, typemin(T)) == string(typemin(T))
  InexactError: check_top_bit(UInt32, -80)
  Stacktrace:
    [1] throw_inexacterror(f::Symbol, #unused#::Type{UInt32}, val::Int32)
      @ Core ./boot.jl:614
    [2] check_top_bit
      @ ./boot.jl:628 [inlined]
    [3] toUInt32
      @ ./boot.jl:727 [inlined]
    [4] UInt32
      @ ./boot.jl:768 [inlined]
    [5] +
      @ ./char.jl:242 [inlined]
    [6] _digitchar
      @ ~/.julia/packages/Formatting/BwWBf/src/fmtcore.jl:63 [inlined]
    [7] _pfmt_intdigits(out::IOBuffer, ax::Int8, op::Formatting._Dec)
      @ Formatting ~/.julia/packages/Formatting/BwWBf/src/fmtcore.jl:102
    [8] _pfmt_int(out::IOBuffer, sch::Char, ip::String, zs::Int64, ax::Int8, op::Formatting._Dec)
      @ Formatting ~/.julia/packages/Formatting/BwWBf/src/fmtcore.jl:89
    [9] _pfmt_i(out::IOBuffer, fs::FormatSpec, x::Int8, op::Formatting._Dec)
      @ Formatting ~/.julia/packages/Formatting/BwWBf/src/fmtcore.jl:126
   [10] printfmt(io::IOBuffer, fs::FormatSpec, x::Int8)
      @ Formatting ~/.julia/packages/Formatting/BwWBf/src/fmtspec.jl:182
   [11] printfmt(io::IOBuffer, fe::FormatExpr, args::Int8)
      @ Formatting ~/.julia/packages/Formatting/BwWBf/src/formatexpr.jl:147
   [12] sprint(::Function, ::FormatExpr, ::Vararg{Any}; context::Nothing, sizehint::Int64)
      @ Base ./strings/io.jl:114
   [13] sprint
      @ ./strings/io.jl:107 [inlined]
   [14] format(fe::FormatExpr, args::Int8)
      @ Formatting ~/.julia/packages/Formatting/BwWBf/src/formatexpr.jl:165

[jagot]

Digging a bit, it fails because we cannot compute the absolute value of typemin(i::Integer), since in two-complement binary representation, the absolute value of the minimum number is one larger than the maximum number:

julia> abs(typemin(Int8))
-128

This makes the following logic break:

Formatting.jl/src/fmtcore.jl

Lines 107 to 139 in e4c9f60

	function _pfmt_i(out::IO, fs::FormatSpec, x::Integer, op::Op) where {Op}
	# calculate actual length
	ax = abs(x)
	xlen = _ndigits(abs(x), op)
	# sign char
	sch = _signchar(x, fs.sign)
	if sch != '\0'
	xlen += 1
	end
	# prefix (e.g. 0x, 0b, 0o)
	ip = ""
	if fs.ipre
	ip = _ipre(op)
	xlen += length(ip)
	end
	# printing
	wid = fs.width
	if wid <= xlen
	_pfmt_int(out, sch, ip, 0, ax, op)
	elseif fs.zpad
	_pfmt_int(out, sch, ip, wid-xlen, ax, op)
	else
	a = fs.align
	if a == '<'
	_pfmt_int(out, sch, ip, 0, ax, op)
	_repprint(out, fs.fill, wid-xlen)
	else
	_repprint(out, fs.fill, wid-xlen)
	_pfmt_int(out, sch, ip, 0, ax, op)
	end
	end
	end

[ScottPJones]

Note that this is not broken if you use Format instead of Formatting