Remove constexpr from _altBufferMarks

[PankajBhojwani]

Summary of the Pull Request

Compiler was raising the error: expression did not evaluate to a constant., causing the solution to fail when building. Removing this constexpr fixes it.

PR Checklist

• Closes #xxx
• CLA signed. If not, go over here and sign the CLA
• Tests added/passed
• Documentation updated. If checked, please file a pull request on our docs repo and link it here: #xxx
• Schema updated.
• I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

Validation Steps Performed

Solution builds now

[DHowett]

Huh. This was added for the audit mode build. Isn't this gonna make Audit fail?

Is this caused by a VS version disparity?

[lhecker]

The default constructor for std::vector is constexpr since C++20. This should work on any conforming C++20 compiler and unless I did something wrong, it did work in VS 17.3.6.

[lhecker]

For reference: https://godbolt.org/z/5qq667fq1

[PankajBhojwani]

Got on a call with @lhecker and turns out this repros on his machine as well (with VS 17.3.6)

[lhecker]

I figured it out... The debug version of std::vector allocates a 1-item backing storage even in the default constructor. The release one doesn't.

[DHowett]

Is it worth doing this?

static
#ifndef NDEBUG
constexpr
#else
const
#endif
std::vector foobarbaz{};

?

That way we keep the optimization on release without introducing a TLS storage check to make sure no two threads enter at the same time?

Or... is that moot because we're returning a const ref anyway?

[lhecker]

Or... is that moot because we're returning a const ref anyway?

I think it's moot because constexpr doesn't mean it's constexpr anyways. That's what consteval is for. 🥴 So I'm fairly confident that no matter whether we write constexpr or not, most of the time it should compile to the exact same thing.

[carlos-zamora]

@msftbot merge this in 10 minutes

[ghost]

Hello @carlos-zamora!

Because you've given me some instructions on how to help merge this pull request, I'll be modifying my merge approach. Here's how I understand your requirements for merging this pull request:

• I won't merge this pull request until after the UTC date Wed, 09 Nov 2022 21:20:23 GMT, which is in 10 minutes

If this doesn't seem right to you, you can tell me to cancel these instructions and use the auto-merge policy that has been configured for this repository. Try telling me "forget everything I just told you".