GitLab

If the tag already exists (because the repo is reused), then git will
fail to create the tag by default.

Shellcheck wants you to quote all variables to prevent accidental
wordsplitting. But the arguments to `ap builddirs` should be splitted
because each package should be a separate argument.

23ae6625 (build.sh: fix shellcheck issues, 2020-02-03) did quote
`$aports`, breaking CI when trying to build multiple packages.

Undo that change and add comments to show that it should remain unquoted.

See merge request !5

Only when CI_DEBUG_BUILD is non-empty

Shellcheck flagged various issues, like quoting variables to prevent
splitting. Let's fix those.

Closes alpine/infra/infra#10670

See merge request !4

The testing repo is only available for edge, so do not add it to the
repositories file when building for stable releases.

Fixes: alpine/infra/infra#10670

Setting up a base build setup has been moved to a dedicated image called
alpinelinux/build-base. This allows that functionality be reused and
makes setting up this image simpler.

Because `set -u` is configured, the script will give an error when
trying to use a variable that is not defined.

Because the purpose this is meant to be an environment variable, we
cannot just set it empty, because it would overwrite the value from the
environment.

Define `CI_DEBUB_BUILD` as empty when it's not defined.

Only when CI_DEBUG_BUILD is non-empty, verbose logging will be enabled.

To make it easer to find out what's going on, print the commit graph of
the repo.

Merge requests can consist of packages from different repositories. Some
packages will depend on the packages that are just being built in a
higher repository.

The script currently only adds repos from the mirror, which will cause
build issues.

Add the local higher repositories to the repositories list.

A plain git diff will return changes both from the branch being merged,
as the target branch. Because we are only interested in changes from the
current branch, we need to do an asymmetric diff.

To make it clear in the build logs what is being built, provide the list
of changed aports that the build script is trying to build.

The CI job for merge requests is run in the forked project, meaning that
the target branch may be behind. This would result in more commits being
checked than intended.

Fetch the target branch from the upstream repository instead so that we
know the target branch is up-to-date and we can reliably get a list of
changed commits just for this merge request.

The basebranch might already exist. When trying to update the basebranch
when it's not fast-forwardable, git will throw an error.

Add a '+' to the fetch spec to tell git that it's allowed to force
overwrite the current ref.

See merge request !3

gitlab runs ci jobs with umask 0000 to prevent issues with file
permissions. sudo refuses to look at configuration files in
/etc/sudoers.d if it is world-writable.

Fix these permissions so that sudo still works.

Convert to alpine-gitlab-ci

See merge request !2

- Check if aport is enabled for current arch
- Display each aports status on a single line
- Make it clear which Drone variables are used

ref: alpinelinux/aports#7352

Do not use Drone's workspace but instead setup our own.
This means cloning a shallow copy of aports and git am the PR patch from github.