Qiskit / qiskit-terra / 5649294055

86%

main: 87%

push

github

Fix empty-barrier handling in OpenQASM 2 (#10469)

The new parser would allow a `barrier;` statement, implicitly
broadcasting it across all qubits in scope.  This is technically not
supported by the OpenQASM 2 specification, but is a useful
quality-of-life extension to the specification (in the same way that
Qiskit interprets barriers, and the OpenQASM 3 specification defines the
`barrier;` statement).  The precise rule is added to the new parser's
`strict` mode.

The OpenQASM 2 _exporter_ similarly should not have been putting out
`barrier;` statements.  These could only occur in Qiskit when a barrier
was explicitly constructed with zero elements (as opposed to the call
`QuantumCircuit.barrier()`, which has the all-in-scope behaviour), and
consequently have no actual meaning or effect.  The exporter is modified
to simply skip such instructions, for as long as Qiskit permits the
qubitless barrier statement.

11 of 11 new or added lines in 2 files covered. (100.0%)

73051 of 84997 relevant lines covered (85.95%)

60063.5 hits per line