Fix: Relax Interner trait bounds for borrowed elements

[raynelfss]

Summary

Fix trait bounds in certain methods of Interner to allow for the use of elements that satisfy the trait bounds of Equivalent<T> in IndexMap.

Details and comments

In a very special edge case for the Interner a user was not able to check if it contained an instance of String from an &str. The following commits relax the trait bounds on the contains, try_key, and insert methods, to allow for more flexibility by behaving similarly to the trait Equivalent<T> from IndexMap.

[qiskit-bot]

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

• @Qiskit/terra-core

[coveralls]

Pull Request Test Coverage Report for Build 13931421405

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.

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Details

• 5 of 15 (33.33%) changed or added relevant lines in 1 file are covered.
• 50 unchanged lines in 5 files lost coverage.
• Overall coverage decreased (-0.02%) to 88.07%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/circuit/src/interner.rs	5	15	33.33%

Files with Coverage Reduction	New Missed Lines	%
crates/accelerate/src/unitary_synthesis.rs	1	94.69%
crates/qasm2/src/lex.rs	4	93.23%
qiskit/transpiler/passes/scheduling/time_unit_conversion.py	9	92.31%
crates/qasm2/src/parse.rs	12	97.15%
crates/circuit/src/bit.rs	24	87.14%

Totals
Change from base Build 13905217637:	-0.02%
Covered Lines:	72612
Relevant Lines:	82448

---

💛 - Coveralls

[kevinhartman]

Maybe we can instead reexport indexmap's Equivalent with pub use indexmap::Equivalent in this file? And then just use it in these method bounds so it's easier to understand what's happening.

[raynelfss]

I tried putting in Q: Equivalent<T> alone, but then the compiler will complain because, to satisfy the trait bounds of Q: Equivalent<T>, Q needs to be: Q: ?Sized + ToOwned, and T needs to satisfy T: Borrow<Q> as a minimum. The rest is more specificity to mention that the owned versions of both T and Q need to be of the same base type.

Bringing those trait bounds in already makes using Q: Equivalent<T> redundant, but it is implicitly satisfied. Is there an easier wa of conveying this?

[kevinhartman]

Maybe this would work?

pub fn try_key<Q>(&self, value: &Q) -> Option<Interned<T>>
    where
        Q: ?Sized + Hash + Equivalent<T::Owned>,
    {
        todo!()
    }

[raynelfss]

This works as long as we also specify that T: Borrow<Q>. Unfortunately, though, it's still not enough for the insert method. Fixed in d5161e3!