Add CI with branch status checks against upstream master branch

.gitlab-ci.yml

+stages:
+  - checkRepository
+
+RebaseCheck:
+  stage: checkRepository
+  tags:
+    - CbmRoot
+  only:
+    refs:
+      - merge_requests
+    variables:
+      - $CI_MERGE_REQUEST_PROJECT_PATH == "CbmSoft/cbmroot_geometry" && $CI_MERGE_REQUEST_TARGET_BRANCH_NAME == "master"
+  script:
+    # Get the upstream repository manually. I did not find any other way to have it for
+    # comparison
+    # Check if a rebase is needed
+    # If a rebase is needed stop immediately
+    - scripts/connect_upstream_repo.sh $CI_MERGE_REQUEST_PROJECT_URL
+    - git fetch upstream
+    - hash1=$(git show-ref upstream/master | cut -f1 -d' ')
+    - hash2=$(git merge-base upstream/master origin/$CI_MERGE_REQUEST_SOURCE_BRANCH_NAME)
+    - echo "${hash1}"
+    - echo "${hash2}"
+    - if [ "${hash1}" = "${hash2}" ]; then
+    -   echo "No rebase required"
+    -   exit 0
+    - else
+    -   echo "The Merge Request is not up-to-date"
+    -   echo "Rebase is required"
+    -   exit 1
+    - fi
+
+LinearHistCheck:
+  stage: checkRepository
+  tags:
+    - CbmRoot
+  only:
+    refs:
+      - merge_requests
+    variables:
+      - $CI_MERGE_REQUEST_PROJECT_PATH == "CbmSoft/cbmroot_geometry" && $CI_MERGE_REQUEST_TARGET_BRANCH_NAME == "master"
+  script:
+    # Get the upstream repository manually. I did not find any other way to have it for
+    # comparison
+    # Check if the history introduced by the MR is linear (no branch loop in fork)
+    # If not linear stop immediately
+    - scripts/connect_upstream_repo.sh $CI_MERGE_REQUEST_PROJECT_URL
+    - git fetch upstream
+    - count=$(git rev-list --min-parents=2 --count upstream/master..HEAD)
+    - echo "${count}"
+    - if [ 0 = "${count}" ]; then
+    -   echo "History introduced in fork is linear"
+    -   exit 0
+    - else
+    -   echo "History introduced in fork is not linear"
+    -   echo "${count} merge commits must be removed or the other new commits have to be replayed in a new branch"
+    -   exit 1
+    - fi

ci_scripts/connect_upstream_repo.sh

+#!/bin/bash
+
+upstream_repo=$1
+
+bla=$(git remote -v | grep upstream)
+if [ $? -eq 0 ]; then
+  echo "Remote link upstream already exist"
+  bla=$(git remote -v | grep upstream | grep $upstream_repo)
+  if [ $? -eq 0 ]; then
+    echo "Remote link upstream already exist and points to the correct repo"
+    # dont do anything
+  else
+    echo "Remote link upstream already exist and points to the wrong repo"
+    git remote rm upstream
+    git remote add upstream $upstream_repo
+  fi
+else
+  echo "Remote repo has to be connected"
+  git remote add upstream $upstream_repo
+fi
+