From bbe47331a57458adf0c29a4143a77150424a6e15 Mon Sep 17 00:00:00 2001
From: Frederic Martinsons <frederic.martinsons@sigfox.com>
Date: Mon, 11 Jan 2021 17:04:52 +0100
Subject: [PATCH] It seems the gitlab CI performs only a shallow clone of
 1-depth and so checkout only the HEAD of the branch. This leads to not being
 able to find an ancestor since there is only one new commit. I presume that
 when it worked, it was because of specific settings of some users.

Now we fetch (with the same depth as the target branch) the source branch
and use it to compare sha1 and find the common ancestor.

Closes #2292

Signed-off-by: Frederic Martinsons <frederic.martinsons@sigfox.com>
---
 .gitlab-ci/search-common-ancestor.sh | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/.gitlab-ci/search-common-ancestor.sh b/.gitlab-ci/search-common-ancestor.sh
index d09f7d3f8..76521f402 100755
--- a/.gitlab-ci/search-common-ancestor.sh
+++ b/.gitlab-ci/search-common-ancestor.sh
@@ -17,9 +17,15 @@ git fetch --shallow-since="$(date --date="${ancestor_horizon} days ago" +%Y-%m-%
 # Work out the newest common ancestor between the detached HEAD that this CI job
 # has checked out, and the upstream target branch (which will typically be
 # `upstream/master` or `upstream/glib-2-62`).
-# `${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}` is only defined if we’re running in
-# a merge request pipeline; fall back to `${CI_DEFAULT_BRANCH}` otherwise.
-newest_common_ancestor_sha=$(diff --old-line-format='' --new-line-format='' <(git rev-list --first-parent "upstream/${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent HEAD) | head -1)
+# `${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}` or `${CI_MERGE_REQUEST_SOURCE_BRANCH_NAME}`
+# are only defined if we’re running in a merge request pipeline,
+# fall back to `${CI_DEFAULT_BRANCH}` or `${CI_COMMIT_BRANCH}` respectively
+# otherwise.
+
+source_branch="${CI_MERGE_REQUEST_SOURCE_BRANCH_NAME:-${CI_COMMIT_BRANCH}}"
+git fetch --shallow-since="$(date --date="${ancestor_horizon} days ago" +%Y-%m-%d)" origin "${source_branch}"
+
+newest_common_ancestor_sha=$(diff --old-line-format='' --new-line-format='' <(git rev-list --first-parent "upstream/${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent "origin/${source_branch}") | head -1)
 if [ -z "${newest_common_ancestor_sha}" ]; then
     echo "Couldn’t find common ancestor with upstream master. This typically"
     echo "happens if you branched from master a long time ago. Please update"