Treat existence of managed directories as a part of repository dirtiness.

[irengrig]

• If managed directory is declared for the external repository and does not exist (probably was deleted by user), make external repository dirty and re-fetch it.
• Add tests to demonstrate the added behavior to ManagedDirectoriesBlackBoxTest.
• Closes Managed directories should rerun repository rule if directory is deleted or timestamp changes #8487.

[Globegitter]

@irengrig will this be cherry picked into the 0.26 and/or 0.27 release?

[irengrig]

Asked for cherry-pick into 0.27, as 0.26.1 is already out.

[dslomov]

@alexeagle do we absolutely need this cherry-picked for 0.27? Or is it ok for this fix to be in 0.28?

[laurentlb]

When you think a bug should be a release blocker, please add the release blocker label (if you can) and cc the release manager (the person assigned to the release tracking issue).

The bug was filed 9 days ago. If it was critical, it would have been useful to mention it earlier.

[alexeagle]

We haven't been able to adopt the managed_directories feature, so this bug is a show-stopper for us. So it is quite important for us to have it fixed in next release, yes. Is it risky/difficult to cherry-pick?

reasoning:
Node developers are accustomed to problems with their third-party deps, and their instinctive reaction is to delete them and re-install. If you do this after Bazel has installed the deps, that deletion destroys the BUILD files we wrote, and then the re-install does not re-create them. The error doesn't give any hint that you need to bazel clean --expunge to fix the wrong state of the managed directory, so users get stuck. For now we don't recommend they use the feature because it's so hard to recover from this common situation. This means they still have to install all of their dependencies twice which makes Bazel seem much slower than existing tooling.

[dslomov]

@alexeagle what if we fix it in 0.28 (July) release?

[alexeagle]

Then it is another month before we can finish rolling out the feature, which makes me worry we'll miss other problems that require some dogfooder adoption.
In the meantime we have already switched our documentation and quickstart to managed directories so we have users getting really confused - have seen a few already and we anticipate more.

[laurentlb]

Related discussion around release frequency: https://groups.google.com/d/msg/bazel-dev/Ez4B3N_YEQY/PVzVJZL3BAAJ

[dslomov]

@laurentlb what do you think about cherry-picking this given @alexeagle comments?