It should be returning twice the value, this is the half-angle. Sad that
this went unnoticed for so long, extra bad points for me to have a
complicated test but not actually verifying that the returned value
makes sense, sigh.
A *nasty* option would be to just fix it, but -- even though there's a
chance nonbody ever used it since nobody ever complained -- it would
introduce breakages to any code that fixed it and that's something to
definitely not do in a trusted codebase. So it's instead deprecated,
firing an annoying warning to whoever might have called it, and there's
a (temporary) replacement called halfAngle() that does exactly the same
but is named appropriately.
Then, once the deprecated angle() is removed (the usual deprecation
period, so a year or the span of two releases, whichever takes longer)
and enough time passes (so another year at least), I'll reintroduce it
with a correct return value.