Which command should handle broken symlinks

[dhadka]

Describe the bug

https://github.com/actions/runner/blob/main/src/Runner.Sdk/Util/WhichUtil.cs should detect and ignore broken symlinks. This should be considered a bug as calling the native which command will detect and ignore the broken symlink.

To Reproduce

See https://github.com/dhadka/repro-broken-symlink/actions/runs/3106185147/jobs/5032737959 for an example. Here I'm creating a broken symlink for pwsh and then trying to run Powershell using shell: pwsh and through bash with run: pwsh -Command ....

shell: pwsh fails because it's using the custom WhichUtil implementation, matches the broken symlink, and fails with An error occurred trying to start process '/usr/local/bin/pwsh' with working directory '/home/runner/work/repro-broken-symlink/repro-broken-symlink'. No such file or directory

run: pwsh -Command ... works fine as it uses the system's which command that ignores the broken symlink.

Expected behavior

If the target of the symlink does not exist, WhichUtil should skip it and locate any other matches on the PATH.

Runner Version and Platform

Latest Version

OS of the machine running the runner? Ubuntu

What's not working?

See repro above.

Job Log Output

See repro above.

Runner and Worker's Diagnostic Logs

N/A

[nikola-jokic]

Thank you, @dhadka, for reporting this! I applied correct labels and added this issue to the board. ☺️

[fhammerl]

We could fail if the path returned by which is a broken symlink.

In other words, after the runner code invokes which to get the path to the executable, we could enforce that it in fact exists.

[eli-entelis]

Hi, I am a first time contributor, I would like to take this issue. Would appreciate any help on where to start

[fhammerl]

Hello @Eliminator1999. Let me know if you'd like me to assign you to this issue.

High level goal

Make the runner work the same as which. which ignores broken symlinks, while the runner treats them as if they were executables.

Code location and whatnot

By default, running which -a pwsh would ignore broken symlinks.

• The runner doesn't run which directly, rather it tries to simulate it.
• The runner loops through all segments in $PATH and tries to see if the command pwsh is present.
• Seems like if the result is a symlink, we should try and assert that it points to a real file.
  Consider multi-level symlinks as well.

Pre-requisites

Are you already familiar with how Actions works and how to use self-hosted runners?

Next, I'd recommend checking out our contribution document.
Here's some more specific docs if you're using vscode

[eli-entelis]

thank you @fhammerl, yes please assign this to me, and thanks for all the info!

[eli-entelis]

@fhammerl @nikola-jokic , can someone please review the pr #2196? thank you

[fhammerl]

PR merged