ProgressJob column pruning in start!() causes spooky action at a distance

[impact-basin]

The invocation of filter!() in start!() is mutating.

Term.jl/src/progress.jl

Line 146 in 7cc1a29

filter!(c -> c != ProgressColumn, job.columns)

If I call addjob!() or swapjob!() with a vector of column elements, this pruning will mutate the vector at the callsite. This is spooky action at a distance and can lead to unexpected behaviour.

It is best if the vector is copied at the point of ProgressJob creation: specifically, this line:

Term.jl/src/progress.jl

Line 118 in 7cc1a29

columns,

should become

copy(columns),

and the same should be done for other mutable items passed across the interface.

In my use, a config array used for two, cases where N = nothing and N isa Integer, was being erroneously mutated -- the progress bars in the image linked in #279 were being spuriously deleted.

The last commit in PR #279 fixes this issue, but it may be desirable to patch this while you review the PR.