dedent function

String dedent(String text)

Remove any common leading whitespace from every line in text. This can be used to make triple-quoted strings line up with the left edge of the display, while still presenting them in the source code in indented form. Note that tabs and spaces are both treated as whitespace, but they are not equal: the lines " hello" and "\thello" are considered to have no common leading whitespace. Entirely blank lines are normalized to a newline character.

Implementation

String dedent(String text) {
  var _whitespaceOnlyRe = new RegExp(r"^[ \t]+$", multiLine: true);
  var _leadingWhitespaceRe =
      new RegExp(r"(^[ \t]*)(?:[^ \t\n])", multiLine: true);

  // Look for the longest leading string of spaces and tabs common to
  // all lines.
  String? margin;
  text = text.replaceAll(_whitespaceOnlyRe, '');
  var indents = _leadingWhitespaceRe.allMatches(text);

  for (var _indent in indents) {
    String indent = text.substring(_indent.start, _indent.end - 1);
    if (margin == null) {
      margin = indent;
    }

    // Current line more deeply indented than previous winner:
    // no change (previous winner is still on top).
    else if (indent.startsWith(margin)) {
    }

    // Current line consistent with and no deeper than previous winner:
    // it's the new winner.
    else if (margin.startsWith(indent)) {
      margin = indent;
    }

    // Find the largest common whitespace between current line and previous
    // winner.
    else {
      var it = zip([margin.split(''), indent.split('')]).toList();
      for (var i = 0; i < it.length; i++) {
        if (it[0] != it[1]) {
          var till = (i == 0) // compensate for lack of [:-1] Python syntax
              ? margin!.length - 1
              : i - 1;
          margin = margin!.substring(0, till);
          break;
        }
      }
    } // else
  }

  // sanity check (testing/debugging only)
  var debug = false;
  if (debug && margin != null && margin != '') {
    for (var line in text.split('\n')) {
      assert(line == "" || line.startsWith(margin),
          "Sanity check failed: line = $line, margin = $margin");
    }
  }

  if (margin != null && margin != "") {
    var r = new RegExp(r"^" + margin,
        multiLine: true); // python r"(?m)^" illegal in js regex so leave it out
    text = text.replaceAll(r, '');
  }
  return text;
}