Fix bugs with VF2Layout pass and Qiskit Aer 0.13

[chriseclectic]

Summary

Qiskit Aer 0.13 is incompatible with the pass manager generated by generate_preset_pass_manager due to bugs with how VF2Layout pass handles its Target, which does not contain a coupling map or qargs.

Details and comments

This fixes these so that VF2 will only use the target generated coupling map if it is not None, and doesn't error from trying to iterate over target.qargs that are also None in these cases.

[qiskit-bot]

One or more of the the following people are requested to review this:

• @Qiskit/terra-core

[coveralls]

Pull Request Test Coverage Report for Build 9426638631

Warning: This coverage report may be inaccurate.

This pull request's base commit is no longer the HEAD commit of its target branch. This means it includes changes from outside the original pull request, including, potentially, unrelated coverage changes.

• For more information on this, see Tracking coverage changes with pull request builds.
• To avoid this issue with future PRs, see these Recommended CI Configurations.
• For a quick fix, rebase this PR at GitHub. Your next report should be accurate.

Details

• 5 of 5 (100.0%) changed or added relevant lines in 2 files are covered.
• 51 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.004%) to 89.581%

---

Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	4	92.62%
qiskit/circuit/random/utils.py	5	95.69%
crates/qasm2/src/parse.rs	12	97.15%
qiskit/circuit/quantumcircuit.py	30	95.84%

Totals
Change from base Build 9410059639:	-0.004%
Covered Lines:	62446
Relevant Lines:	69709

---

💛 - Coveralls

[mtreinish]

I think this is fine as a workaround for this issue. It really is a weird edge case where you're giving it a target which doesn't have any constraints and then specifying with a lower priority argument the constraints to use. But that being said I think is probably safe from an interface perspective and won't have any backwards compatibility implications that I can think of.

The only things that I think are missing here are a unittest or two to cover this case and a release note to document the fix as it is an extension of the API semantics on the pass.

[1ucian0]

This also seems to affect stable/0.46.

[1ucian0]

@Mergifyio backport stable/0.46 stable/1.1

[mergify]

backport stable/0.46 stable/1.1

✅ Backports have been created

• #12536 Fix bugs with VF2Layout pass and Qiskit Aer 0.13 (backport #11585) has been created for branch stable/0.46
• #12537 Fix bugs with VF2Layout pass and Qiskit Aer 0.13 (backport #11585) has been created for branch stable/1.1

[ElePT]

I think this would be a good fix to include in the upcoming 1.1.1 release. @chriseclectic do you have time to add the required unit tests and release note within the next week/couple of weeks?

[1ucian0]

I'm adding the test and reno in few minutes done

[ElePT]

LGTM, I left a small suggestion for the reno.