Fix MacOS version detection

[fweikert]

#1542 relied on platform.mac_ver() to detect the MacOS version, which did not work as expected. Consequently, the previous PR led the CI to activate an incorrect version of Xcode. This behavior has been fixed by this change.

Related to #1431.

Users can still request a specific Xcode version in their CI config.

[brentleyjones]

Users can still request a specific Xcode version in their CI config.

Does that work though? Here we set Xcode 13, bazel still tried to use Xcode 14.2.

[fweikert]

Xcode support on Bazel CI basically means running the following two commands:

/usr/bin/sudo /usr/bin/xcode-select --switch /Applications/Xcode<$VERSION>.app
/usr/bin/sudo /usr/bin/xcodebuild -runFirstLaunch

However, rules_apple seems to be doing its own thing by setting the XCODE_VERSION_OVERRIDE env variable to whatever is returned by apple_common.XcodeVersionConfig. I'm not familiar enough with rules_apple to fix this.

[BalestraPatrick]

@fweikert Doesn't setting xcode_version: "13.0" run those two commands automatically though? We can see in our CI config that it's selecting 13.0, but right after xcode-locator says that no default version is selected: No default Xcode version is set with 'xcode-select', so I believe it's not actually selecting it correctly.

[meteorcloudy]

@fweikert I guess we can verify if xcrun xcodebuild -version returns the correct result after running

/usr/bin/sudo /usr/bin/xcode-select --switch /Applications/Xcode<$VERSION>.app
/usr/bin/sudo /usr/bin/xcodebuild -runFirstLaunch

IIUC, https://cs.opensource.google/bazel/bazel/+/master:tools/osx/xcode_configure.bzl;l=195-197, this is now rules_apple detects the default xcode version and uses it to populate XCODE_VERSION_OVERRIDE later?

[BalestraPatrick]

So I did some testing, and yes, the Xcode version is correctly selected, but it's an invalid Xcode version for the macOS version that the machine is on. At the moment, when we set xcode_version: "13.0", the CI machine selected is an iMac Pro that runs macOS 13.2, which doesn't support Xcode 13.x anymore. So yes, it's selected, but we can't use it for anything.

As mentioned in this comment, is there a way for us to run on the Mac Studio machines running Monterey instead of Ventura? In that way, we should be able to correctly use Xcode 13.0.

See here the build logs: bazelbuild/rules_apple#1820

[brentleyjones]

Seems if we set the xcode_version we aren't being routed to a machine that supports that version (sort of the opposite of what the logic here is touching). We want Xcode 13, which means we can't get placed on Ventura machines.

[meteorcloudy]

I'm not sure how well rules_apple works on Apple Silicon machines, if that's not a concern, you can simply change macos to macos_arm64 at https://github.com/bazelbuild/rules_apple/blob/master/.bazelci/presubmit.yml#LL6C20-L6C20, then all jobs will run on the MacStudio machines.

BTW, how soon will you move the Xcode 14? I guess at some point, we'll have to upgrade the OS of the MacStudio machines as well. Until the virtualization of the mac fleet is done, there is no easy way to switch OS versions for Mac machines on Bazel CI.