Merge #12098: [scripts] lint-whitespace: add param to check last N commits

8dbf740f8 [scripts] lint-whitespace: check last N commits or unstaged changes (Sjors Provoost)

Pull request description:

  E.g. before you push three commits to Github and upset Travis, check if you didn't make any whitespace mistakes:
  ```sh
  contrib/devtools/lint-whitespace.sh 3
  ```

  This is slightly more convenient than doing:
  ```sh
  TRAVIS_COMMIT_RANGE=HEAD~3...HEAD contrib/devtools/lint-whitespace.sh
  ```

Tree-SHA512: 5d9c1ae978ccbe59477e8cf53391e9bd697d2da87f417a2519264af560d4768138e0b2d320dd497a1f1e704e18ab279d724f523b57c17a80ccd753133a5445bf

contrib/devtools/lint-whitespace.sh

@@ -7,12 +7,26 @@
 # Check for new lines in diff that introduce trailing whitespace.
 
 # We can't run this check unless we know the commit range for the PR.
+
+while getopts "?" opt; do
+  case $opt in
+    ?)
+      echo "Usage: .lint-whitespace.sh [N]"
+      echo "       TRAVIS_COMMIT_RANGE='<commit range>' .lint-whitespace.sh"
+      echo "       .lint-whitespace.sh -?"
+      echo "Checks unstaged changes, the previous N commits, or a commit range."
+      echo "TRAVIS_COMMIT_RANGE='47ba2c3...ee50c9e' .lint-whitespace.sh"
+      exit 0
+    ;;
+  esac
+done
+
 if [ -z "${TRAVIS_COMMIT_RANGE}" ]; then
-  echo "Cannot run lint-whitespace.sh without commit range. To run locally, use:"
-  echo "TRAVIS_COMMIT_RANGE='<commit range>' .lint-whitespace.sh"
-  echo "For example:"
-  echo "TRAVIS_COMMIT_RANGE='47ba2c3...ee50c9e' .lint-whitespace.sh"
-  exit 1
+  if [ "$1" ]; then
+    TRAVIS_COMMIT_RANGE="HEAD~$1...HEAD"
+  else
+    TRAVIS_COMMIT_RANGE="HEAD"
+  fi
 fi
 
 showdiff() {