Remove QPY warning on deserialising incomplete ParameterVectors

[jakelishman]

This warning was added with QPY v3¹ at a time when ParameterVector generated all its elements with unrelated UUIDs. Since qiskit-terra v0.25, we actually have had enough information to completely recreate an entire vector from a single element², and the circumstances needed to observe the incomplete behaviour are particularly convoluted, and unlikely in practice.

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Based on #16221.

The circumstances you can observe the bad behaviour are in the release note - it's pretty convoluted once #16221 is in place. I've separated off this PR from the others to discuss whether we truly want this. I think, with #16221 merged, the warning is no longer serving a meaningful purpose, and it costs us to maintain the tracking for it.

AI/LLM disclosure

• I didn't use LLM tooling, or only used it privately.
• I used the following tool to help write this PR description:
• I used the following tool to generate or modify code:

Footnotes

1. 5c4cd2b: Fix ParameterVector handling in QPY serialization (Fix ParameterVector handling in QPY serialization #7381) ↩

2. 5ab231d: Slightly optimize ParameterVector construction (Slightly optimize ParameterVector construction #10403) ↩

[coveralls]

Coverage Report for CI Build 26823200940

Warning

Build has drifted: This PR's base is out of sync with its target branch, so coverage data may include unrelated changes.
Quick fix: rebase this PR. Learn more →

Coverage increased (+0.07%) to 87.563%

Details

• Coverage increased (+0.07%) from the base build.
• Patch coverage: 6 of 6 lines across 2 files are fully covered (100%).
• 2761 coverage regressions across 91 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

2761 previously-covered lines in 91 files lost coverage.

Top 10 Files by Coverage Loss	Lines Losing Coverage	Coverage
crates/circuit/src/dag_circuit.rs	749	85.26%
crates/bindgen-cli/src/abi.rs	210	0.0%
crates/circuit/src/circuit_data.rs	210	86.72%
crates/circuit/src/operations.rs	130	82.58%
crates/cext/src/circuit.rs	121	79.58%
qiskit/synthesis/unitary/qsd.py	80	23.65%
crates/cext/src/dag.rs	75	85.27%
crates/transpiler/src/target/mod.rs	68	82.59%
crates/qpy/src/circuit_writer.rs	59	93.25%
crates/circuit/src/bit.rs	56	85.08%

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Coverage Stats

Relevant Lines:	123901
Covered Lines:	108491
Line Coverage:	87.56%
Coverage Strength:	964007.1 hits per line

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💛 - Coveralls

[qiskit-bot]

One or more of the following people are relevant to this code:

• @Qiskit/terra-core
• @mtreinish

[alexanderivrii]

Thanks Jake. This PR is a bit out of my comfort zone, but that was the point when we agreed on round robin.

AI/LLM disclaimer: I have first carefully looked at the changed myself, and then asked my new friend Claude to go over the changes together, so LGTM!

Though one general question: why was it necessary to do the change both in python and in rust: wouldn't just changing the rust code be enough?

And one typo (detected both by me and Claude).

[jakelishman]

why was it necessary to do the change both in python and in rust: wouldn't just changing the rust code be enough?

The Python code is still live code - the Rust reader only handles QPY >= v13. If it weren't live, we'd have deleted it from the repo.

[alexanderivrii]

Thanks for the quick reply!