Ensure Lightning adheres to C++17 modernization standard with clang-tidy

[mlxd]

Context: To ensure modern C++ standards, we require testing of newly added code to ensure it is standards-conforming with all newly supported features. This PR enables clang-tidy with warnings-as-errors support for a variety of tidy options as defined from here

Description of the Change: Add CI-enabled checking of code-base builds with clang-tidy for the following options:

clang-tidy \
-extra-arg=-std=c++17 \
-warnings-as-errors=* \
-header-filter=.* \
-checks=-*,-llvmlibc-*,clang-analyzer-*,modernize-*,clang-analyzer-cplusplus*,openmp-*,performance-*,portability-*,readability-*

Benefits: This will ensure our codebase uses non-legacy and/or deprecated language features, as well as ensuring strict conformance to the modern C++ standard (currently C++17). In addition, this can prevent compiler-specific bugs being uncaught, which can be difficult to find between compiler versions.

Possible Drawbacks: May add additional development time to new features as developer become comfortable with the requirements of the standard.

Related GitHub Issues:

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit .github/CHANGELOG.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[codecov]

Codecov Report

Merging #153 (972bf34) into master (238f4d0) will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##            master      #153   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            4         4           
  Lines          182       182           
=========================================
  Hits           182       182           

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[github-actions]

Test Report (C++) on Ubuntu

       1 files  ±0         1 suites  ±0   0s ⏱️ ±0s
   327 tests ±0     327 ✔️ ±0  0 💤 ±0  0 ❌ ±0 
1 185 runs  ±0  1 185 ✔️ ±0  0 💤 ±0  0 ❌ ±0 

Results for commit 972bf34. ± Comparison against base commit 238f4d0.

This pull request removes 9 and adds 9 tests. Note that renamed tests count towards both.

runner.global ‑ AdjointJacobian::adjointJacobian/Decomposed Rot gate, non computational basis state
runner.global ‑ AdjointJacobian::adjointJacobian/Mixed gradient, tensor expval
runner.global ‑ AdjointJacobian::adjointJacobian/Multiple RX gradient, single expval per wire
runner.global ‑ AdjointJacobian::adjointJacobian/Multiple RX gradient, single expval per wire, subset of params
runner.global ‑ AdjointJacobian::adjointJacobian/Multiple RX gradient, tensor expval
runner.global ‑ AdjointJacobian::adjointJacobian/RX gradient
runner.global ‑ AdjointJacobian::adjointJacobian/RY gradient
runner.global ‑ AdjointJacobian::adjointJacobian/Single RX gradient, 2 expval
runner.global ‑ AdjointJacobian::adjointJacobian/Trainable params subset

runner.global ‑ AdjointJacobian::adjointJacobian Decomposed Rot gate, non computational basis state
runner.global ‑ AdjointJacobian::adjointJacobian Mixed Ops, Obs and TParams
runner.global ‑ AdjointJacobian::adjointJacobian Op=Mixed, Obs=[XXX]
runner.global ‑ AdjointJacobian::adjointJacobian Op=RX, Obs=Z
runner.global ‑ AdjointJacobian::adjointJacobian Op=RX, Obs=[Z,Z]
runner.global ‑ AdjointJacobian::adjointJacobian Op=RY, Obs=X
runner.global ‑ AdjointJacobian::adjointJacobian Op=[RX,RX,RX], Obs=[Z,Z,Z]
runner.global ‑ AdjointJacobian::adjointJacobian Op=[RX,RX,RX], Obs=[Z,Z,Z], TParams=[0,2]
runner.global ‑ AdjointJacobian::adjointJacobian Op=[RX,RX,RX], Obs=[ZZZ]

♻️ This comment has been updated with latest results.

[mlxd]

As an example of the usefulness of the above changes.

[maliasadi]

Great PR! I didn't know that clang-tidy is this powerful really.

[mlxd]

Hi @maliasadi , what changes were made to the clang-tidy files? I am having a hard time tracking and comparing them. These are auto-generated with 1 or 2 minor amendments, so I'm having a tough time comparing the new changes you added.

Were yours autogenerated too?

[maliasadi]

Hi @maliasadi , what changes were made to the clang-tidy files? I am having a hard time tracking and comparing them. These are auto-generated with 1 or 2 minor amendments, so I'm having a tough time comparing the new changes you added.

Were yours autogenerated too?

I only re-ordered them w.r.t. their categories and didn't add any new checks there.

[mlxd]

I only re-ordered them w.r.t. their categories and didn't add any new checks there.

Ah okay. I think we can undo these commits, as any further edits to the autogenerated files will cause a large number of line-changes here. The config used to get these is clang-tidy -extra-arg=-std=c++17 -warnings-as-errors=* -header-filter=.* -checks=-*,-llvmlibc-*,modernize-*,clang-analyzer-cplusplus*,openmp-*,performance-*,portability-*,readability-* --dump-config with an edit made to the expected complexity number. Can you revert them?

[trbromley]

Thanks @mlxd, looks great and amazing to see the speedup! I wonder if it's worth discussing next time we meet about some of the new concepts that may be unfamiliar (at least to me), such as [[nodiscard]].

[mlxd]

Thanks for the reviews and suggestions all!