Concise StandardGate::<ID> enums in Rust space

[Cryoris]

Summary

The Rust-side, internal StandardGate enum variants all repeat the fact that they are a gate. For example, the Hadamard is StandardGate::HGate instead of simply StandardGate::H. Being an enum variant, the fact that it is a gate is evident and always attached to the object. I suspect this is mainly a legacy naming from moving over from Python space (or maybe @mtreinish comes remembers 🙂)?

I'd suggest to shorten the enum variants to just the gate ID. This makes the code more concise and avoid redundant qualifiers. It also enables that gate enums in the C API, introduced in #14006, can be called QkGate_H instead of QkGate_HGate.

[qiskit-bot]

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

• @Cryoris
• @Qiskit/terra-core
• @ajavadia
• @levbishop

[coveralls]

Pull Request Test Coverage Report for Build 13896854086

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

• 712 of 754 (94.43%) changed or added relevant lines in 52 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.01%) to 88.102%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/accelerate/src/synthesis/multi_controlled/mcmt.rs	1	2	50.0%
crates/accelerate/src/unitary_synthesis.rs	12	13	92.31%
crates/accelerate/src/two_qubit_decompose.rs	29	31	93.55%
crates/accelerate/src/synthesis/evolution/pauli_network.rs	7	10	70.0%
crates/accelerate/src/commutation_checker.rs	0	35	0.0%

Totals
Change from base Build 13853660516:	-0.01%
Covered Lines:	72566
Relevant Lines:	82366

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💛 - Coveralls

[kevinhartman]

This seems like a nice improvement to me. Just a few minor comments.

(I didn't look too closely for typos--I assume you used an IDE to do symbolic renaming 😉)

[kevinhartman]

Is there a good reason it's Tdg and not TDG, or is that just historical?

[Cryoris]

There's a good historical reason 😛 See #3695 and the associated issue, we decided the naming norm is: a single uppercase letter per gate type (e.g. T for T-gate, C for controlled, R for a rotation, S for square root...) and dg being just an inverse qualifier remains lowercase. Ofc there are exceptions, like SwapGate (no single letter gate type), or SGate (which I guess would technically be SZ as square root of Z) but that's minimal 🙂

[kevinhartman]

This looks good to me.

I think it's important for consistent naming in our C-API, and @mtreinish could have arbitrarily chosen to do this in the original standard gates PR, so I feel confident to merge this without more consensus. We can always change this again if anyone comes up with a good reason.