git pre-commit hook to lint .travis.yml using api.travis-ci.org/lint

pre-commit

#!/bin/sh
#
# A hook to check for lint warnings when .travis.yml is modified
# by uploading it to api.travis-ci.org/lint.
#
# A similar result could be achieved by uploading the configuration
# to https://lint.travis-ci.org/ before commiting.

# Redirect output to stderr.
exec 1>&2

# Is .travis.yml among the the modified files?
if git diff --cached --name-only | grep --quiet ".travis.yml"; then

  cat <<EOF

Uploading .travis.yml to api.travis-ci.org/lint to check for lint warnings.
If you know what you are doing you can disable this check using:

  git commit --no-verify

EOF

  # Upload .travis.yml to the Travis API lint endpoint.
  JSON_RESPONSE=$(curl -L -T .travis.yml --max-time 15 https://api.travis-ci.org/lint)
  CURL_EXIT_CODE=$?
  # TODO: report a different error for exit code 28 (timeout)
  # The timeout could be a temporary issue where the user could try again.
  if [ "$CURL_EXIT_CODE" -ne 0 ]; then
    cat <<EOF

Error: curl failed with exit code $CURL_EXIT_CODE uploading .travis.yml to api.travis-ci.org/lint.
You can also check your .travis.yml configuration on https://lint.travis-ci.org/
If you know what you are doing you can disable this check using:

  git commit --no-verify

EOF
    exit 1
  fi

  # Use POSIX substring parameter expansion to check for warnings in the response.
  # http://pubs.opengroup.org/onlinepubs/009695399/utilities/xcu_chap02.html#tag_02_06_02
  #
  # Example response without warnings:
  # {
  #   "lint" : {
  #      "warnings" : []
  #   }
  # }
  #
  # Example response with warnings:
  # {
  #   "lint": {
  #     "warnings": [
  #       {
  #         "key": ["jdk"],
  #         "message": "specified jdk, but ruby does not include jruby"
  #       }
  #     ]
  #   }
  # }
  # https://docs.travis-ci.com/api#linting
  if [ "${JSON_RESPONSE#*"message"}" != "$JSON_RESPONSE" ]; then
    cat << EOF

Error: api.travis-ci.org/lint returned the following response:

EOF

    # Try a few commands to pretty print the JSON response.
    # If none are available, fallback to printing the raw response.
    # The /dev/null redirects hide "command not found" messages.
    echo $JSON_RESPONSE | {
    jq . 2>/dev/null \
      || python -m json.tool 2>/dev/null | { pygmentize -g 2>/dev/null || cat; } 2>/dev/null \
      || json_pp 2>/dev/null \
      || cat; \
    }

    # Abort commit
    exit 1
  fi
fi

# Proceed with commit
exit 0