RFC: Deprecating generate-xcodeproj

[YOCKOW]

@broadway_lamb

If there was a way to pass the -DOPENCOMBINE_COMPATIBILITY_TEST argument to Xcode when opening Package.swift (or at least specify an .xcconfig file), I wouldn't complain.

As described in another topic, you can use $ OPENCOMBINE_COMPATIBILITY_TEST=1 open Package.swift.
Although all packages opened by Xcode at the same time are affected by the environment variable in that way.