Symlink forest should respect .bazelignore

[KrauseStefan]

Description of the bug:

The symlink forest does not respect the .bazelignore file, this was unexpected behavior, and in my situation led to non hermetic builds that poised a shared build cache.

In our case it was the node_modules folder that is moved from being referenced using the now deprecated/removed managed_directories feature (#15463)

It is ignored since we do not want Bazel to be able to depend on this folder even by accident, but since it is linked in it still can happen.

This does not fix hermitic problems for local/worker builds but it does remove one source.

What's the simplest, easiest way to reproduce this bug? Please provide a minimal example if possible.

clone the demo repo here and run ./demo.sh.
Note that the genrule can access the content of the ignored_directory even though it is in the .bazelignnore

https://github.com/KrauseStefan/bazel_issue_16842_demo/tree/main

Which operating system are you running Bazel on?

WSL / Native Windows

What is the output of bazel info release?

release 5.3.2

If bazel info release returns development version or (@non-git), tell us how you built Bazel.

No response

What's the output of git remote get-url origin; git rev-parse master; git rev-parse HEAD ?

No response

Have you found anything relevant by searching the web?

I tracked down the place where the symlinks are created, ignorering top level folders would have been easy but I realise that this would complicate the code a bit, so the question is also would you be interested in the .ignorebazel to be respected in context of the Symlink forest?

SymlinkForest.java:127

Extra context
Obviously a build cache can be poised any an almost infinite number of way when we update it from local developers machines with the local/worker strategy that is also why the cache is a dev only cache, CI has its own and uses the sandbox strateg.
There are some politics that prevent us from using the same cache as CI even if read-only.
Essentially a tradeoff between speed and hermicity.

I was very much in doubt if this should be a bug or a feature request, but decided on bug since this is mostly about unexpected behavior.

Any other information, logs, or outputs that you want to share?

No response

[sgowroji]

Hello @KrauseStefan, Could you please provide minimal steps followed to reproduce the above issue. Thanks!

[KrauseStefan]

I created a repo that reproduces the issues with a genrule, and updated the original post.

[KrauseStefan]

This has now been open for quite a while, is this something that has a realistic chance of getting fixed?
If not could you provide some pointers as to what an acceptable fix would need to do.

It would fix my immediate issue if the support was added for the root directory only, it seems like that would be pretty easy to just skip creating that symlink if it specifically is defined in the .ignorebazel.

Since it does not cover all cases will it need to be hidden behind a flag?

I'm not sure who to ping, so apologies if I picked the wrong person.
@meteorcloudy

[fmeum]

Have you tested Bazel 7 with e1fbc83? Sounds like it could have fixed the problem.

[KrauseStefan]

It seems you are right, closing.
Thank you 😃