Add a full `fs.FS` implementation to `runfiles`

[fmeum]

What type of PR is this?

Feature

What does this PR do? Why is it needed?

Runfiles instances now implement fs.FS in a platform-agnostic way, regardless of whether they are manifest- or directory-based. This is meant to finally provide a full replacement for runfiles functionality offered by the legacy bazel package.

Which issues(s) does this PR fix?

Fixes #3375 Fixes #3830

Other notes for review

[fmeum]

cc @sluongng

[fmeum]

Thanks, I addressed your comments and am debugging the remaining test failure on Windows.

[fmeum]

The remaining test failure is a very reasonable one: The logic fails to account for runfiles that are linked under a basename that differs from that of the underlying file. This will require some more tweaks.

[fmeum]

@meteorcloudy The new macOS machines frequently run into timeouts: https://buildkite.com/bazel/rules-go-golang/builds/6622#01908e0d-57ff-4850-8b3c-cb9fe2fff52f

Are we perhaps lacking any settings?

[meteorcloudy]

@fmeum Yes, please check https://github.com/bazelbuild/continuous-integration/issues/1981#issuecomment-2217609837

[meteorcloudy]

@fmeum To unblock this, you can also temporarily switch back to the old Mac fleet by using macos_legacy or macos_arm64_legacy.

The timeout looks weird, does it look like some network issue? One major difference is that the new Mac fleet is ipv6 only, not sure if it's relevant.

[fmeum]

@meteorcloudy Thanks, I'll go with this workaround for now until I can properly investigate this (limited to GitHub web UI right now).

The failing test downloads a few old Go releases from the official download page, I don't know why this would cause issues. The relevant tests are tagged local.

[meteorcloudy]

One major difference is that the new Mac fleet is ipv6 only, not sure if it's relevant.

Indeed it's caused by the ipv6-only network.

• We are setting --host_jvm_args=-Djava.net.preferIPv6Addresses=true in /private/etc/bazel.bazelrc on the Mac VMs.
• But it only affected the outer Bazel, inner Bazel running in the test has --nosystem_rc specified.
• I can confirm after adding this flag in the go code, the three timeout tests are passing. Also on macos_arm64.

I'll let you decide how to inject this for macos ci, here is an example for Bazel's integration test https://github.com/bazelbuild/bazel/commit/2c51a0c8590e73c88d6a678f1b0583c6aee313c3