Method buildExpr_

src/service/variable-source.js:280–318

* @param {!Array } keys * @param {!{[key: string]: boolean}=} opt_allowlist Optional allowlist of names * that can be substituted. * @return {!RegExp} * @private

(keys, opt_allowlist)

   * @private
   */
  buildExpr_(keys, opt_allowlist) {
    // If a allowlist is present, the keys must belong to the allowlist.
    // We filter the keys one last time to ensure no unallowlisted key is
    // allowed.
    if (this.getUrlMacroAllowlist_()) {
      keys = keys.filter((key) => this.getUrlMacroAllowlist_().includes(key));
    }
    // If a allowlist is passed into the call to GlobalVariableSource.expand_
    // then we only resolve values contained in the allowlist.
    if (opt_allowlist) {
      keys = keys.filter((key) => opt_allowlist[key]);
    }
    if (keys.length === 0) {
      const regexThatMatchesNothing = /_^/g; // lgtm [js/regex/unmatchable-caret]
      return regexThatMatchesNothing;
    }
    // The keys must be sorted to ensure that the longest keys are considered
    // first. This avoids a problem where a RANDOM conflicts with RANDOM_ONE.
    keys.sort((s1, s2) => s2.length - s1.length);
    // Keys that start with a `$` need to be escaped so that they do not
    // interfere with the regex that is constructed.
    const escaped = keys.map((key) => {
      if (key[0] === '$') {
        return '\\' + key;
      }
      return key;
    });

    const all = escaped.join('|');
    // Match the given replacement patterns, as well as optionally
    // arguments to the replacement behind it in parentheses.
    // Example string that match
    // FOO_BAR
    // FOO_BAR(arg1)
    // FOO_BAR(arg1,arg2)
    // FOO_BAR(arg1, arg2)
    const regexStr = '\\$?(' + all + ')';
    return new RegExp(regexStr, 'g');
  }

  /**
   * For email documents, all URL macros are disallowed by default.