Decide how to support `cxxLanguageStandard` in a Swift manifest.

[cgrindel]

The problem is that we do not want to add it to the cxxopts for each target. It would override the values in the .bazelrc. Also, I think that you do not want modules linked with different standards.

• Should we output cxxLanguageStandard values as we come across them?
• Should we scan all of the manifests and pick the highest one?
• How should we tell the client?
  • We can print the value(s) from Starlark, but they could be easily missed in the output.
  • We can analyze the manifests during update-repos and print a suggested .bazelrc entry.

Example:

• firebase/abseil-cpp-SwiftPM

[keith]

I think you probably do want to override the global ones for each target as this could be saying "it's only compatible with this version". At the very least that's likely the only version it's tested with.

If that became a big issue cargo raze has a clever system for overriding things like this

[cgrindel]

Interesting. I thought it best practice to specify -std=XXX once for the whole project. It definitely would not be difficult to specify it at the target level.

[keith]

I agree with that for all your own code but yea I think for third parties like this it's more complicated. I think many bazel libraries just throw this in their Copts as well for the same reason but I'd have to double check in envoy how many do