Failures while running tests are reported as branch being out-of-date

[nwiltsie]

From https://github.com/uclahs-cds/pipeline-call-mtSNV/pull/165#issuecomment-2065479844.

The Nextflow run died due to a missing file, and the actions/upload-artifact step complained that there were no files to upload.

In the summary step, the command to check if files changed between the merge commit and the branch tip failed - not because there were differences, but because there were no files to be checked:

2024-04-18T23:24:31.6649211Z [command]/usr/bin/git ls-files --modified -- configtest*.json **/configtest*.json
2024-04-18T23:24:31.6802962Z [command]/usr/bin/git diff-tree HEAD cc2bcea5d27ae44814dc88f8f97d8dac104f680b --exit-code --name-status -- 
2024-04-18T23:24:31.6843427Z fatal: empty string is not a valid pathspec. please use . instead if you meant to match all paths
2024-04-18T23:24:32.4297973Z ##[error]Need to merge tests

---

Weirdly I can't replicate that error locally - there's something odd going on with that.

$ git diff-tree HEAD cc2bcea5d27ae44814dc88f8f97d8dac104f680b --exit-code --name-status -- && echo "No failure"
No failure

[nwiltsie]

Ah, nevermind, the workflow is explicitly passing an empty string - nothing odd going on with that.

$ git diff-tree HEAD cc2bcea5d27ae44814dc88f8f97d8dac104f680b --exit-code --name-status -- ""
fatal: empty string is not a valid pathspec. please use . instead if you meant to match all paths

[nwiltsie]

This came up again with uclahs-cds/pipeline-call-sSV#187 (comment). Here was the chain of events:

gitGraph
    commit id: "  "
    commit id: "   "
    branch mmootor-filter-gridss
    checkout mmootor-filter-gridss
    commit id: "Add required parameter"
    checkout main
    branch nwiltsie-modernize
    commit id: "Tests updated"
    checkout main
    merge nwiltsie-modernize
    checkout mmootor-filter-gridss
    merge main type: REVERSE id: "Tests failed"

Loading

When I merged main into mmootor-filter-gridss, the tests failed due to the addition of a new required parameter, but the workflow reported that main needed to be merged...

I'm not sure if the changes on nwiltsie-modernize were relevant at all - I don't remember the specifics of how the "need to merge main" check is done.