Avoid exporting incorrect PyInit_* symbols (backport #12889)

[mergify]

Summary

Using the #[pymodule] derive macro in PyO3 0.21 always causes a PyInit_* symbol with a matching name to be exported in the output cdylib. This is required for the top-level module, in order for Python to import it---it needs to know which symbol in a shared library file it should call---but submodules must be manually initialised, so do not need it. Including it is typically harmless (and something we've been doing for a long time), but it is technically against the coding rules for CPython extensions¹.

Recent versions of abi3audit (0.0.11+) have tightened their symbol checkers to better match the CPython guidelines, which causes our wheels to be rejected by their audits. This is, in theory, not a break of abi3 because CPython could never introduce an API-elvel PyInit_* function themselves without causing problems, so there ought to be no problems for our users, even with future Python versions. That said, we still want to pass the audit, because the coding guidelines are useful.

This commit is not the cleanest way of doing things. PyO3 0.22 includes a #[pymodule(submodule)] option on the attribute macro, which lets us use all the standard code generation while suppressing the unnecessary PyInit_* symbol. When we are ready to move to PyO3 0.22, we probably want to revert this commit to switch to that form.

Details and comments

We found this during the deployment of 1.2.0rc1, since that's the most recent PyPI release since abi3audit released version 0.0.11. This commit creates a wheel that passes the audit at its current version 0.0.14.

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This is an automatic backport of pull request #12889 done by Mergify.

Footnotes

1. https://docs.python.org/3/c-api/intro.html ↩

[mergify]

Cherry-pick of 120b73d has failed:

On branch mergify/bp/stable/1.2/pr-12889
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Changes to be committed:
	modified:   crates/accelerate/src/convert_2q_block_matrix.rs
	modified:   crates/accelerate/src/dense_layout.rs
	modified:   crates/accelerate/src/error_map.rs
	modified:   crates/accelerate/src/euler_one_qubit_decomposer.rs
	modified:   crates/accelerate/src/isometry.rs
	modified:   crates/accelerate/src/nlayout.rs
	modified:   crates/accelerate/src/optimize_1q_gates.rs
	modified:   crates/accelerate/src/pauli_exp_val.rs
	modified:   crates/accelerate/src/results/mod.rs
	modified:   crates/accelerate/src/sabre/mod.rs
	modified:   crates/accelerate/src/sampled_exp_val.rs
	modified:   crates/accelerate/src/sparse_pauli_op.rs
	modified:   crates/accelerate/src/star_prerouting.rs
	modified:   crates/accelerate/src/stochastic_swap.rs
	modified:   crates/accelerate/src/synthesis/clifford/mod.rs
	modified:   crates/accelerate/src/synthesis/linear/mod.rs
	modified:   crates/accelerate/src/synthesis/mod.rs
	modified:   crates/accelerate/src/synthesis/permutation/mod.rs
	modified:   crates/accelerate/src/two_qubit_decompose.rs
	modified:   crates/accelerate/src/uc_gate.rs
	modified:   crates/accelerate/src/utils.rs
	modified:   crates/accelerate/src/vf2_layout.rs
	modified:   crates/circuit/src/lib.rs
	modified:   crates/qasm2/src/lib.rs
	modified:   crates/qasm3/src/lib.rs

Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	deleted by us:   crates/accelerate/src/target_transpiler/mod.rs
	both modified:   crates/pyext/src/lib.rs

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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[coveralls]

Pull Request Test Coverage Report for Build 10218833747

Details

• 40 of 40 (100.0%) changed or added relevant lines in 3 files are covered.
• No unchanged relevant lines lost coverage.
• Overall first build on mergify/bp/stable/1.2/pr-12889 at 89.972%

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Totals
Change from base Build 10218811685:	90.0%
Covered Lines:	66742
Relevant Lines:	74181

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💛 - Coveralls