fix: Ignore C4668 when preprocessing via MSVC

[Alexei-Barnes]

This fixes #1725.

[sylvestre]

is it possible to add a test for this? thanks

[Alexei-Barnes]

Absolutely, I'm on vacation right now without access to a computer I could run the tests on. Back home around the 7th of May. Happy to amend this with a test then.

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -0.04 ⚠️

Comparison is base (7416904) 29.44% compared to head (071d680) 29.40%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1730      +/-   ##
==========================================
- Coverage   29.44%   29.40%   -0.04%     
==========================================
  Files          49       49              
  Lines       17713    17713              
  Branches     8547     8547              
==========================================
- Hits         5215     5209       -6     
  Misses       7347     7347              
- Partials     5151     5157       +6     

Impacted Files	Coverage Δ
src/compiler/msvc.rs	45.01% <ø> (ø)

... and 9 files with indirect coverage changes

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[Alexei-Barnes]

@sylvestre I've written a minimal integration test to verify the behaviour.

There aren't currently any unit tests for the msvc preprocessing method. I could add one if required, but it might require other changes to make the preprocessing method more testable.

[Alexei-Barnes]

Updated the test just now to actually use sccache 😅
Should now actually test the intended behaviour. I also threw in a direct call to cl.exe just to show the preprocessing error in the output that we're trying to avoid. Maybe we should run this new test on unfixed code first to establish a baseline negative result?

[Alexei-Barnes]

Removed the additional call to cl that shows the 4668 warning because it terminates the build, and it isn't necessary.

[Alexei-Barnes]

Oh interesting, the test failed! Will investigate tomorrow.

[Alexei-Barnes]

OK the test revealed that simply changing the warning to level 4 isn't enough, it must be entirely disabled. I've updated the code, test should pass in CI now.

[Alexei-Barnes]

Test passing now 👍