absolutePath.js

function errorMessage(schema, data, message) {
  return {
    keyword: 'absolutePath',
    params: { absolutePath: data },
    message,
    parentSchema: schema,
  };
}

function getErrorFor(shouldBeAbsolute, data, schema) {
  const message = shouldBeAbsolute
    ? `The provided value ${JSON.stringify(data)} is not an absolute path!`
    : `A relative path is expected. However, the provided value ${JSON.stringify(
        data
      )} is an absolute path!`;

  return errorMessage(schema, data, message);
}

export default (ajv) => {
  ajv.addFormat('absolutePath', () => true);
  ajv.addKeyword('absolutePath', {
    errors: true,
    type: 'string',
    compile(expected, schema) {
      function callback(data) {
        let passes = true;
        const isExclamationMarkPresent = data.includes('!');
        const isCorrectAbsoluteOrRelativePath =
          expected === /^(?:[A-Za-z]:\\|\/)/.test(data);

        if (isExclamationMarkPresent) {
          callback.errors = [
            errorMessage(
              schema,
              data,
              `The provided value ${JSON.stringify(
                data
              )} contains exclamation mark (!) which is not allowed because it's reserved for loader syntax.`
            ),
          ];
          passes = false;
        }

        if (!isCorrectAbsoluteOrRelativePath) {
          callback.errors = [getErrorFor(expected, data, schema)];
          passes = false;
        }

        return passes;
      }

      callback.errors = [];

      return callback;
    },
  });

  return ajv;
};