Segfault after deepcopy of MixedIntegerLinearProgram #15159
Description
I wanted to make a copy of a linear program and modify the copy somewhat further. Using deepcopy I get a segfault (tested under 5.12.beta4) running the following:
sage: p = MixedIntegerLinearProgram()
sage: w = p.new_variable()
sage: q = deepcopy(p)
sage: q.add_constraint(w[0] >= 0)
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Unhandled SIGSEGV: A segmentation fault occurred in Sage.
This probably occurred because a *compiled* component of Sage has a bug
in it and is not properly wrapped with sig_on(), sig_off(). You might
want to run Sage under gdb with 'sage -gdb' to debug this.
Sage will now terminate.
------------------------------------------------------------------------
The same segfault happens when one instead defines a new variable for the new linear program and tries to add constraints in terms of that variable:
sage: p = MixedIntegerLinearProgram()
sage: q = deepcopy(p)
sage: w = q.new_variable()
sage: q.add_constraint(w[0] >= 0)
Everything works well when using copy instead of deepcopy. Nevertheless, could this be related to #11588?
Depends on #20414
Component: linear programming
Reviewer: Travis Scrimshaw
Issue created by migration from https://trac.sagemath.org/ticket/15159