#883 - Intersection of two polygons does not detect tighter constraints correctly

[schillic]

Closes #883.

[mforets]

This example now returns a bounds error:

ph = convert(HPolygon, p)
qh = convert(HPolygon, q)
intersection(ph, qh)

BoundsError: attempt to access 5-element Array{HalfSpace{Float64},1} at index [7:7]

Stacktrace:
 [1] throw_boundserror(::Array{HalfSpace{Float64},1}, ::Tuple{UnitRange{Int64}}) at ./abstractarray.jl:492
 [2] checkbounds at ./abstractarray.jl:457 [inlined]
 [3] getindex(::Array{HalfSpace{Float64},1}, ::UnitRange{Int64}) at ./array.jl:737
 [4] (::getfield(LazySets, Symbol("#add_remaining_constraints!#75")))(::Array{HalfSpace{Float64},1}, ::Int64, ::Array{HalfSpace{Float64},1}, ::Int64, ::Int64) at /Users/forets/.julia/dev/LazySets/src/concrete_intersection.jl:133
 [5] (::getfield(LazySets, Symbol("#choose_first_diff_dir!#76")){getfield(LazySets, Symbol("#add_remaining_constraints!#75"))})(::Array{HalfSpace{Float64},1}, ::Int64, ::Int64, ::Int64, ::Array{HalfSpace{Float64},1}, ::Array{HalfSpace{Float64},1}, ::Int64) at /Users/forets/.julia/dev/LazySets/src/concrete_intersection.jl:141
 [6] intersection(::HPolygon{Float64}, ::HPolygon{Float64}) at /Users/forets/.julia/dev/LazySets/src/concrete_intersection.jl:207
 [7] top-level scope at In[79]:3

[schillic]

Thanks, I had introduced a new bug. This is fixed now and a new unit test checks it.

[mforets]

Ok. Now it returns the same peaked object as before, so the fix should be somewhere else. BTW note that

function intersection2(P1, P2)
    P = HPolygon()
    addconstraint!.(P, constraints_list(P1))
    addconstraint!.(P, constraints_list(P2))
    return P
end

runs in 2.875 ms (797 allocations: 50.73 KiB) for that example, whereas intersection takes
2.226 μs (3 allocations: 288 bytes) 💯