Bazel CI fails after updating Swift 5.2.5 to 5.4.2 in Ubuntu

[philwo]

Hi,

after upgrading Swift in our Bazel CI Ubuntu Docker containers from 5.2.5 to 5.4.2 rules_swift started failing with "No 'swiftc' executable found in $PATH". See: https://buildkite.com/bazel/rules-swift-swift/builds/2704#0330f7fc-fc2a-462c-a6d5-4c584173e5f1

However, a swiftc binary is definitely in the PATH:

$ docker run --rm -it gcr.io/bazel-public/ubuntu1804-java11 /bin/bash
root@4b105b952bb8:/# which swiftc
/opt/swift-5.4.2-RELEASE-ubuntu18.04/usr/bin/swiftc
root@4b105b952bb8:/# swiftc --version
Swift version 5.4.2 (swift-5.4.2-RELEASE)
Target: x86_64-unknown-linux-gnu

Do you want to debug this? Should I rollback the upgrade?

Also, I'm curious, do you have plans for using remote repositories to download Swift SDKs instead of relying on the system to provide them (or maybe does this feature already exist and we could use it somehow on Bazel CI?)?

[keith]

I don't see what about this image update could have broken this, but repository_ctx.which clearly isn't returning swiftc even if it should. After hardcoding the expected values I hit another interesting failures:

Error forking process '/opt/swift-5.4.2-RELEASE-ubuntu18.04/usr/bin/swiftc'. No such file or directory

https://buildkite.com/bazel/rules-swift-swift/builds/2713#1209b2ff-7544-4c43-8bec-1b0d88c3d306

It seems like that change must have introduced something strange here. The permissions on those files look fine to me.

It also doesn't appear like these actions are running remotely, or in the sandbox (since we're using a persistent worker)

Any other ideas here?

[keith]

We kinda punted on downloading the toolchain directly since no one has been asking for it #4

[philwo]

@keith Mhm... very strange. Thanks for doing these checks. I'll have another look later today!

[keith]

Avoided via #672