Remove Bit.register and Bit.index, deprecated in 0.17 (released on April 01, 2021)

[1ucian0]

There is code released 28 month ago that needs to be removed.

• qiskit/circuit/bit.py:63 (register)
• qiskit/circuit/bit.py:85 (index)

This includes:

• Remove deprecated code and tests (if they only check the deprecation raise)
• tag the PR as Changelog: Removal
• create a release note in the category upgrade:. If you can include an example with an alternative for user to migrate to the new code, as this change might break users code.

[jakelishman]

Bit.register and Bit.index aren't really ready for removal yet - there's still code in Qiskit that uses them, and we know that there's code in backends and providers that uses them (despite them having issued warnings for years).

[1ucian0]

Good to know! I'm labelling this on hold. Do you know if there are issues open in those providers?

[1ucian0]

This is, at least, blocked on:

• Test raising "the property qiskit.circuit.bit.Bit.index is deprecated" #10749
• Bit.index is deprecated since Apr 2021 qiskit-ibm-provider#733
• Support new-style Bit in Pauli convertor from QuantumCircuit #10757
• Remove usage of deprecated Bit.index and Bit.register qiskit-community/qiskit-aqt-provider#80
• Fix deprecated behaviour in timeline drawer #10846

Any other issue that should be linked here? Either in Qiskit or not?

[1ucian0]

As I continue discovering instances of Bit.register and Bit.index, I think they can stay in ~=0.45 and be removed in ~=1.0. Setting that milestone for this one.