End link files with a newline, tidy path handling

[chrisberkhout]

Summary

• Write a final newline when updating link files.
  This is particularly helpful when working with them in the terminal.
• Clarify and enforce requirements on CreateLinksFSFromPath arguments.
  The previous godoc, which said "workDir must be a path to a directory, relative to the repository root" was incorrect or at least misleading. Usually the repository root has a name that is absolute, and in that case workDir must also be an absolute path for filepath.Rel to succeed. The change clarifies the requirements, enforcement and error messages.

Related issues

• Closes Fix link inclusion during package build #2830

[teresaromero]

@chrisberkhout there is a side-effect for your changes, fields unit tests are failing because the path used for tests is relative.. could you review the change or update tests? also, when test pass we should trigger an integration job to check this does not break any package that might be using link files now. just write in a comment test integrations

[chrisberkhout]

test integrations

[elastic-vault-github-plugin-prod]

Created or updated PR in integrations repository to test this version. Check elastic/integrations#17731

[elasticmachine]

💛 Build succeeded, but was flaky

• Buildkite Build
• Commit: 09d02a3

Failed CI Steps

• :go: Integration test (with logstash): ti_misp

History

• 💔 Build #7393 failed 47e9df8

cc @chrisberkhout

[chrisberkhout]

The integrations tests fail for m365_defender, microsoft_defender_cloud and ti_abusech, but I'm not sure why and they pass for me locally. I suspect it's not this change. Everything else passes.

[jsoriano]

The integrations tests fail for m365_defender, microsoft_defender_cloud and ti_abusech, but I'm not sure why and they pass for me locally. I suspect it's not this change. Everything else passes.

Issues with these packages are hopefully fixed with elastic/integrations#17695.