Slight VersionSet refactoring, test intersect(::VersionSet, ::VersionSet)

[carlobaldassi]

• Enforce VectorSet normalization in constructor (fixes equality testing and generally makes more sense)
• Improve VectorSet normalization code (faster, fewer allocations),
• Test VectorSet intersections (including the empty cases which were at the root of issue Failure in pkg tests #20566)

[tkelman]

I'd word this as "The only purpose of the fusing check is to avoid extra allocations"

[tkelman]

why isn't this defined outside the type block?

[carlobaldassi]

To avoid going through normalize! by calling new directly (the idea being that vset.intervals is already normalized, being an invariant of the type, so we can safely just copy it and save time). It's the equivalent of a copy constructor of C++, except that I think this is more idiomatic Julia (I had initially written VersionSet(::VersionSet), but it didn't seem right).

[tkelman]

neither ∅ nor ∪ display properly in the windows console

[carlobaldassi]

Not sure what to do here. ∪ was already there, but now it's more exposed to the user through the backtrace printing. Should I set them to empty and U on Windows? E.g.:

const _empty_symbol = @static is_windows() ? "empty" : "∅"
const _union_symbol = @static is_windows() ? " U " : " ∪ "
show(io::IO, s::VersionSet) = isempty(s) ? print(io, _empty_symbol) :
                                           join(io, s.intervals, _union_symbol)

Other suggestions?

[vtjnash]

I would suggest printing VersionSet(∅ empty) / VersionSet(union of v"1.1.1" ∪ v"1.1.2" ∪ ...) everywhere. This helps both terminals that can't interpret unicode, and people who don't recognize it either.

[carlobaldassi]

That seems way too verbose, considering that it's going to be shown to users in backtrace error messages like these:

version range [0.0.0,0.2.0) ∪ [0.3.0,∞) required by package SomePackage, whose allowed version range is [0.1.0,0.1.2) ∪ [0.1.4,∞):

etc.

[tkelman]

could just say "or"

[nalimilan]

s/intersetct/intersect/

[carlobaldassi]

Rebased and addressed comments.