Format operator does not detect negative zero (-0.0) sign

[He-Pin]

Summary

The format operator (%) does not correctly detect the sign of negative zero (-0.0). All format specifiers (%f, %e, %g) produce output without a minus sign for -0.0, while Python's equivalent produces -0.000000.

Reproduction

$ go-jsonnet -e '"%f" % (-0.0)'
"0.000000"

$ go-jsonnet -e '"%+f" % (-0.0)'
"+0.000000"

Expected (Python reference)

>>> "%f" % (-0.0)
'-0.000000'
>>> "%+f" % (-0.0)
'-0.000000'

Analysis

The issue is that the sign detection uses s < 0, which returns false for -0.0 in IEEE 754 floating point (-0.0 < 0 is false). The fix is to check the sign bit directly, e.g. using math.Signbit(s) in Go.

This affects %f, %e, %g, and their uppercase variants, as well as the + and (space) sign flags.

Version

go-jsonnet v0.22.0