GitHub Actions issues not triggering

[zooba]

Something has happened to the source checker task, e.g. python/cpython#21748

Run if [ -z "GITHUB_BASE_REF" ]; then
  if [ -z "GITHUB_BASE_REF" ]; then
    echo '::set-output name=run_tests::true'
  else
    git fetch origin $GITHUB_BASE_REF --depth=1
    git diff --name-only origin/$GITHUB_BASE_REF... | grep -qvE '(\.rst$|^Doc|^Misc)' && echo '::set-output name=run_tests::true' || true
  fi
  shell: /bin/bash -e {0}
From https://github.com/python/cpython
 * branch            master     -> FETCH_HEAD
 * [new branch]      master     -> origin/master
fatal: origin/master...HEAD: no merge base

I'm not sure what this error means, but because the failure is treated as a success, the checks decide they don't need to run and so we get all green with no CI!

[brettcannon]

Did we shove all of these into a single file with this trick due to requiring status checks that don't get run blocks a PR?

[vstinner]

Something has happened to the source checker task, e.g. python/cpython#21748

I confirmed that it worked well since May ( https://bugs.python.org/issue40548 ) but it started to fail with fatal: origin/master...HEAD: no merge base. I'm not sure why it stopped working.

I'm not sure if git fetch fails or if git diff fails.

cc @FFY00

[vstinner]

Did we shove all of these into a single file with this trick due to requiring status checks that don't get run blocks a PR?

I understood that @FFY00 chose to use a separated job to check if a PR is a "doc only" to easy maintenance of the check: the job uses Linux and reuses services like uses: actions/checkout@v2 (rather than having to implement the check for Windows, macOS, Linux, ...)

The advantage is to not even start other jobs if it's a doc-only PR. It reduces resource consumption.

[vstinner]

Oh! I can reproduce the issue with Git 2.28 (on Fedora Rawhide), but not with Git 2.26 (Fedora 32). Script to reproduce the issue:

set -e -x
DIR=clone_python
export GITHUB_BASE_REF=master

rm -rf $DIR
git init $DIR
cd $DIR
git remote add origin https://github.com/python/cpython

git fetch --no-tags --prune --depth=1 origin +fe42ecf3c875b31a281ecb5b4e257655cf820134:refs/remotes/pull/21748/merge
git fetch origin master --depth=1
git checkout --force refs/remotes/pull/21748/merge

git diff --name-only origin/master... | cat

git diff --name-only origin/master... fails with fatal: origin/master...HEAD: no merge base.

But git diff --name-only origin/master..refs/remotes/pull/21748/merge works as expected.

[vstinner]

Difference between 2 dots (..) and 3 dots (...):
https://matthew-brett.github.io/pydagogue/git_diff_dots.html

It seems like using 2 dots should be enough for the workflow job, since GitHub starts by merging master into the PR anyway.

[vstinner]

I didn't find any obvious change on the "merge-base" command in the Git 2.28 changelog, but this version contains many changes, so I'm not surprised that the behavior changed.

[vstinner]

Git 2.28 changelog:

• https://github.blog/2020-07-27-highlights-from-git-2-28/
• https://lore.kernel.org/git/xmqq5za8hpir.fsf@gitster.c.googlers.com/

[vstinner]

I proposed python/cpython#21806 to replace "..." (3 dots) with ".." (2 dots).

[FFY00]

Sorry for the delay! I wasn't able to look at this earlier.

See my comment in python/cpython#21806 (comment).

[vstinner]

My python/cpython#21806 was merged into master and then backported to 3.8 and 3.9 branches. I close the issue.