ci: Limit depth of fetch for initial code checks

Rather than fetching the entire repository history, limit the fetch
depth to commits in the last 4 weeks. If a branch was branched longer
than 4 weeks ago, it seems reasonable to require it to be rebased before
it can be reviewed.

At the current rate of development, this reduces the bandwidth needed
for git pulls in the initial code checks from 73MB to 9MB.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

2 files changed, 29 insertions, 2 deletions

diff --git a/.gitlab-ci/run-check-todos.sh b/.gitlab-ci/run-check-todos.sh
index 8af102739..8a6a9bfda 100755
--- a/.gitlab-ci/run-check-todos.sh
+++ b/.gitlab-ci/run-check-todos.sh
@@ -2,11 +2,17 @@
 
 set -e
 
+ancestor_horizon=28  # days (4 weeks)
+
 # We need to add a new remote for the upstream target branch, since this script
 # could be running in a personal fork of the repository which has out of date
 # branches.
+#
+# Limit the fetch to a certain date horizon to limit the amount of data we get.
+# If the branch was forked from origin/master before this horizon, it should
+# probably be rebased.
 git remote add upstream https://gitlab.gnome.org/GNOME/glib.git
-git fetch upstream
+git fetch --shallow-since="$(date --date="${ancestor_horizon} days ago" +%Y-%m-%d)" upstream
 
 # 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
@@ -14,4 +20,11 @@ git fetch upstream
 # `${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}` is only defined if we’re running in
 # a merge request pipeline; fall back to `${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:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent HEAD) | head -1)
+if [ -z "${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"
+    echo "your clone, rebase, and re-push your branch."
+    exit 1
+fi
+
 ./.gitlab-ci/check-todos.py "${newest_common_ancestor_sha}"
diff --git a/.gitlab-ci/run-style-check-diff.sh b/.gitlab-ci/run-style-check-diff.sh
index 1f7b8c125..b308e7679 100755
--- a/.gitlab-ci/run-style-check-diff.sh
+++ b/.gitlab-ci/run-style-check-diff.sh
@@ -2,21 +2,35 @@
 
 set -e
 
+ancestor_horizon=28  # days (4 weeks)
+
 # Wrap everything in a subshell so we can propagate the exit status.
 (
 
 # We need to add a new remote for the upstream target branch, since this script
 # could be running in a personal fork of the repository which has out of date
 # branches.
+#
+# Limit the fetch to a certain date horizon to limit the amount of data we get.
+# If the branch was forked from origin/master before this horizon, it should
+# probably be rebased.
 git remote add upstream https://gitlab.gnome.org/GNOME/glib.git
-git fetch upstream
+git fetch --shallow-since="$(date --date="${ancestor_horizon} days ago" +%Y-%m-%d)" upstream
 
 # 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:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent HEAD) | head -1)
+if [ -z "${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"
+    echo "your clone, rebase, and re-push your branch."
+    exit 1
+fi
+
 git diff -U0 --no-color "${newest_common_ancestor_sha}" | ./clang-format-diff.py -binary "clang-format-7" -p1
 
 )