[gtk/ci-style] ci: Create new origin for forks

[Emmanuele Bassi <ebassi src gnome org>]

commit 6bdca276a2318fa1fd2f9f9df7a475c52bb44a33
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Sun Jun 28 14:01:19 2020 +0100

    ci: Create new origin for forks
    
    We don't need to create a new remote and fetch its master if we're
    checking a merge request done on the upstream repository.

 .gitlab-ci/run-style-check-diff.sh | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)
---
diff --git a/.gitlab-ci/run-style-check-diff.sh b/.gitlab-ci/run-style-check-diff.sh
index 35a1bb4a39..42ef5d9fee 100755
--- a/.gitlab-ci/run-style-check-diff.sh
+++ b/.gitlab-ci/run-style-check-diff.sh
@@ -4,8 +4,15 @@ set -e
 
 # We need to add a new remote for the upstream master, since this script could
 # be running in a personal fork of the repository which has out of date branches.
-git remote add upstream https://gitlab.gnome.org/GNOME/gtk.git
-git fetch upstream
+if [ "${CI_PROJECT_NAMESPACE}" != "GNOME" ]; then
+    echo "Retrieving the current upstream repository from ${CI_PROJECT_NAMESPACE}/${CI_PROJECT_NAME}..."
+    git remote add upstream https://gitlab.gnome.org/GNOME/gtk.git
+    git fetch upstream
+    ORIGIN="upstream"
+else
+    echo "Reusing the existing repository on ${CI_PROJECT_NAMESPACE}/${CI_PROJECT_NAME}"
+    ORIGIN="origin"
+fi
 
 # 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
@@ -13,7 +20,7 @@ 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:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent HEAD) 
| head -1)
+newest_common_ancestor_sha=$(diff --old-line-format='' --new-line-format='' <(git rev-list --first-parent 
"${ORIGIN}/${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent HEAD) 
| head -1)
 git diff -U0 --no-color "${newest_common_ancestor_sha}" | .gitlab-ci/clang-format-diff.py -binary 
"clang-format" -p1
 exit_status=$?