"Have your CI verify your PR" recipe for GitLab CI

[scop]

The magic HEAD~..HEAD^2 recipe for checking commits in a PR does not work in GitLab CI, would be very nice to have one for it, too.

Sample MR in https://gitlab.com/scop/test/-/merge_requests/1, pipeline fail in https://gitlab.com/scop/test/-/jobs/12913721436#L41:

$ ./committed -vv --no-merge-commit HEAD~..HEAD^2
parent 1 does not exist; class=Invalid (3); code=NotFound (-3)

This is with the GitLab CI defaults for the checkout.

Some info what it does to check out is in https://gitlab.com/scop/test/-/jobs/12913721436#L13 but I don't know if that's verbose enough to be of any use. Making the output more verbose with CI_DEBUG_TRACE=true makes it non-public.

Let me know if I can provide some data to help come up with the recipe if you're interested in figuring it out -- I guess I could eventually come up with one myself that might take some time.

[epage]

Can you run in the job

git log --graph --oneline --decorate --all

[scop]

Sure, https://gitlab.com/scop/test/-/jobs/12981230680#L40

$ git log --graph --oneline --decorate --all
* a200d95 (HEAD, origin/test/committed) ...
* d5dfe15 ...
* 0812e06 ...
* 97ee2b1 ...
* 0793d9f mark checkout cwd safe
* b41a7b7 test: add GitLab CI config
* 86ab409 Initial commit

[epage]

Seems like this is going to require some gitlab specific variable to get the base sha.

[scop]

Looks like the variable is $CI_MERGE_REQUEST_DIFF_BASE_SHA, and the catch is that the pipeline must be a "merge request pipeline", not a branch one, refs

• https://docs.gitlab.com/ci/variables/predefined_variables/#predefined-variables-for-merge-request-pipelines
• https://docs.gitlab.com/ci/yaml/workflow/#switch-between-branch-pipelines-and-merge-request-pipelines

[scop]

So with that I suppose the recipe becomes just $CI_MERGE_REQUEST_DIFF_BASE_SHA..

Test pipeline/job making use of that at https://gitlab.com/scop/test/-/jobs/12992178198