Fix check-line-width CI script (#6326)

* Compare lines to the hash that the PR branched off from

* Use git merge-base to determine common ancestor

* Fixup

.maintain/gitlab/check_line_width.sh

@@ -10,14 +10,15 @@ BASE_BRANCH_NAME="master"
 LINE_WIDTH="120"
 GOOD_LINE_WIDTH="100"
 BASE_BRANCH="${BASE_ORIGIN}/${BASE_BRANCH_NAME}"
+git fetch ${BASE_ORIGIN} ${BASE_BRANCH_NAME} --depth 100
+BASE_HASH=$(git merge-base ${BASE_BRANCH} HEAD)
 
-git fetch ${BASE_ORIGIN} ${BASE_BRANCH_NAME} --depth 1
-git diff --name-only ${BASE_BRANCH} -- \*.rs | ( while read file
+git diff --name-only ${BASE_HASH} -- \*.rs | ( while read file
 do
  if [ ! -f ${file} ];
  then
  echo "Skipping removed file."
- elif git diff ${BASE_BRANCH} -- ${file} | grep -q "^+.\{$(( $LINE_WIDTH + 1 ))\}"
+ elif git diff ${BASE_HASH} -- ${file} | grep -q "^+.\{$(( $LINE_WIDTH + 1 ))\}"
  then
  if [ -z "${FAIL}" ]
  then
@@ -29,11 +30,11 @@ do
  FAIL="true"
  fi
  echo "| file: ${file}"
- git diff ${BASE_BRANCH} -- ${file} \
+ git diff ${BASE_HASH} -- ${file} \
  | grep -n "^+.\{$(( $LINE_WIDTH + 1))\}"
  echo "|"
  else
- if git diff ${BASE_BRANCH} -- ${file} | grep -q "^+.\{$(( $GOOD_LINE_WIDTH + 1 ))\}"
+ if git diff ${BASE_HASH} -- ${file} | grep -q "^+.\{$(( $GOOD_LINE_WIDTH + 1 ))\}"
  then
  if [ -z "${FAIL}" ]
  then
@@ -44,7 +45,7 @@ do
  echo "|"
  fi
  echo "| file: ${file}"
- git diff ${BASE_BRANCH} -- ${file} | grep -n "^+.\{$(( $GOOD_LINE_WIDTH + 1 ))\}"
+ git diff ${BASE_HASH} -- ${file} | grep -n "^+.\{$(( $GOOD_LINE_WIDTH + 1 ))\}"
  echo "|"
  fi
  fi