Move into nested docroot

web/core/lib/Drupal/Component/Diff/Diff.php

@@ -0,0 +1,172 @@
+<?php
+
+namespace Drupal\Component\Diff;
+
+use Drupal\Component\Diff\Engine\DiffEngine;
+
+/**
+ * Class representing a 'diff' between two sequences of strings.
+ * @todo document
+ * @subpackage DifferenceEngine
+ *
+ * Copied from https://www.drupal.org/project/diff which was based PHP diff
+ * engine for phpwiki. (Taken from phpwiki-1.3.3) The original code in phpwiki
+ * was copyright (C) 2000, 2001 Geoffrey T. Dairiki <dairiki@dairiki.org> and
+ * licensed under GPL.
+ */
+class Diff {
+
+  /**
+   * The list of differences as an array of diff operations.
+   *
+   * @var \Drupal\Component\Diff\Engine\DiffOp[]
+   */
+  protected $edits;
+
+  /**
+   * Constructor.
+   * Computes diff between sequences of strings.
+   *
+   * @param $from_lines array An array of strings.
+   *      (Typically these are lines from a file.)
+   * @param $to_lines array An array of strings.
+   */
+  public function __construct($from_lines, $to_lines) {
+    $eng = new DiffEngine();
+    $this->edits = $eng->diff($from_lines, $to_lines);
+    //$this->_check($from_lines, $to_lines);
+  }
+
+  /**
+   * Compute reversed Diff.
+   *
+   * SYNOPSIS:
+   *
+   *  $diff = new Diff($lines1, $lines2);
+   *  $rev = $diff->reverse();
+   * @return object A Diff object representing the inverse of the
+   *          original diff.
+   */
+  public function reverse() {
+    $rev = $this;
+    $rev->edits = array();
+    foreach ($this->edits as $edit) {
+      $rev->edits[] = $edit->reverse();
+    }
+    return $rev;
+  }
+
+  /**
+   * Check for empty diff.
+   *
+   * @return bool True iff two sequences were identical.
+   */
+  public function isEmpty() {
+    foreach ($this->edits as $edit) {
+      if ($edit->type != 'copy') {
+        return FALSE;
+      }
+    }
+    return TRUE;
+  }
+
+  /**
+   * Compute the length of the Longest Common Subsequence (LCS).
+   *
+   * This is mostly for diagnostic purposed.
+   *
+   * @return int The length of the LCS.
+   */
+  public function lcs() {
+    $lcs = 0;
+    foreach ($this->edits as $edit) {
+      if ($edit->type == 'copy') {
+        $lcs += sizeof($edit->orig);
+      }
+    }
+    return $lcs;
+  }
+
+  /**
+   * Gets the original set of lines.
+   *
+   * This reconstructs the $from_lines parameter passed to the
+   * constructor.
+   *
+   * @return array The original sequence of strings.
+   */
+  public function orig() {
+    $lines = array();
+
+    foreach ($this->edits as $edit) {
+      if ($edit->orig) {
+        array_splice($lines, sizeof($lines), 0, $edit->orig);
+      }
+    }
+    return $lines;
+  }
+
+  /**
+   * Gets the closing set of lines.
+   *
+   * This reconstructs the $to_lines parameter passed to the
+   * constructor.
+   *
+   * @return array The sequence of strings.
+   */
+  public function closing() {
+    $lines = array();
+
+    foreach ($this->edits as $edit) {
+      if ($edit->closing) {
+        array_splice($lines, sizeof($lines), 0, $edit->closing);
+      }
+    }
+    return $lines;
+  }
+
+  /**
+   * Check a Diff for validity.
+   *
+   * This is here only for debugging purposes.
+   */
+  public function check($from_lines, $to_lines) {
+    if (serialize($from_lines) != serialize($this->orig())) {
+      trigger_error("Reconstructed original doesn't match", E_USER_ERROR);
+    }
+    if (serialize($to_lines) != serialize($this->closing())) {
+      trigger_error("Reconstructed closing doesn't match", E_USER_ERROR);
+    }
+
+    $rev = $this->reverse();
+    if (serialize($to_lines) != serialize($rev->orig())) {
+      trigger_error("Reversed original doesn't match", E_USER_ERROR);
+    }
+    if (serialize($from_lines) != serialize($rev->closing())) {
+      trigger_error("Reversed closing doesn't match", E_USER_ERROR);
+    }
+
+
+    $prevtype = 'none';
+    foreach ($this->edits as $edit) {
+      if ( $prevtype == $edit->type ) {
+        trigger_error("Edit sequence is non-optimal", E_USER_ERROR);
+      }
+      $prevtype = $edit->type;
+    }
+
+    $lcs = $this->lcs();
+    trigger_error('Diff okay: LCS = ' . $lcs, E_USER_NOTICE);
+  }
+
+  /**
+   * Gets the list of differences as an array of diff operations.
+   *
+   * @return \Drupal\Component\Diff\Engine\DiffOp[]
+   *   The list of differences as an array of diff operations.
+   */
+  public function getEdits() {
+    return $this->edits;
+  }
+
+}

web/core/lib/Drupal/Component/Diff/DiffFormatter.php

@@ -0,0 +1,197 @@
+<?php
+
+namespace Drupal\Component\Diff;
+
+use Drupal\Component\Diff\Engine\DiffOpCopy;
+
+/**
+ * A class to format Diffs
+ *
+ * This class formats the diff in classic diff format.
+ * It is intended that this class be customized via inheritance,
+ * to obtain fancier outputs.
+ * @todo document
+ * @private
+ * @subpackage DifferenceEngine
+ */
+class DiffFormatter {
+  /**
+   * Should a block header be shown?
+   */
+  public $show_header = TRUE;
+
+  /**
+   * Number of leading context "lines" to preserve.
+   *
+   * This should be left at zero for this class, but subclasses
+   * may want to set this to other values.
+   */
+  public $leading_context_lines = 0;
+
+  /**
+   * Number of trailing context "lines" to preserve.
+   *
+   * This should be left at zero for this class, but subclasses
+   * may want to set this to other values.
+   */
+  public $trailing_context_lines = 0;
+
+  /**
+   * The line stats.
+   *
+   * @var array
+   */
+  protected $line_stats = array(
+    'counter' => array('x' => 0, 'y' => 0),
+    'offset' => array('x' => 0, 'y' => 0),
+  );
+
+  /**
+   * Format a diff.
+   *
+   * @param \Drupal\Component\Diff\Diff $diff
+   *   A Diff object.
+   *
+   * @return string
+   *   The formatted output.
+   */
+  public function format(Diff $diff) {
+    $xi = $yi = 1;
+    $block = FALSE;
+    $context = array();
+
+    $nlead = $this->leading_context_lines;
+    $ntrail = $this->trailing_context_lines;
+
+    $this->_start_diff();
+
+    foreach ($diff->getEdits() as $edit) {
+      if ($edit->type == 'copy') {
+        if (is_array($block)) {
+          if (sizeof($edit->orig) <= $nlead + $ntrail) {
+            $block[] = $edit;
+          }
+          else {
+            if ($ntrail) {
+              $context = array_slice($edit->orig, 0, $ntrail);
+              $block[] = new DiffOpCopy($context);
+            }
+            $this->_block($x0, $ntrail + $xi - $x0, $y0, $ntrail + $yi - $y0, $block);
+            $block = FALSE;
+          }
+        }
+        $context = $edit->orig;
+      }
+      else {
+        if (!is_array($block)) {
+          $context = array_slice($context, sizeof($context) - $nlead);
+          $x0 = $xi - sizeof($context);
+          $y0 = $yi - sizeof($context);
+          $block = array();
+          if ($context) {
+            $block[] = new DiffOpCopy($context);
+          }
+        }
+        $block[] = $edit;
+      }
+
+      if ($edit->orig) {
+        $xi += sizeof($edit->orig);
+      }
+      if ($edit->closing) {
+        $yi += sizeof($edit->closing);
+      }
+    }
+
+    if (is_array($block)) {
+      $this->_block($x0, $xi - $x0, $y0, $yi - $y0, $block);
+    }
+    $end = $this->_end_diff();
+
+    if (!empty($xi)) {
+      $this->line_stats['counter']['x'] += $xi;
+    }
+    if (!empty($yi)) {
+      $this->line_stats['counter']['y'] += $yi;
+    }
+
+    return $end;
+  }
+
+  protected function _block($xbeg, $xlen, $ybeg, $ylen, &$edits) {
+    $this->_start_block($this->_block_header($xbeg, $xlen, $ybeg, $ylen));
+    foreach ($edits as $edit) {
+      if ($edit->type == 'copy') {
+        $this->_context($edit->orig);
+      }
+      elseif ($edit->type == 'add') {
+        $this->_added($edit->closing);
+      }
+      elseif ($edit->type == 'delete') {
+        $this->_deleted($edit->orig);
+      }
+      elseif ($edit->type == 'change') {
+        $this->_changed($edit->orig, $edit->closing);
+      }
+      else {
+        trigger_error('Unknown edit type', E_USER_ERROR);
+      }
+    }
+    $this->_end_block();
+  }
+
+  protected function _start_diff() {
+    ob_start();
+  }
+
+  protected function _end_diff() {
+    $val = ob_get_contents();
+    ob_end_clean();
+    return $val;
+  }
+
+  protected function _block_header($xbeg, $xlen, $ybeg, $ylen) {
+    if ($xlen > 1) {
+      $xbeg .= "," . ($xbeg + $xlen - 1);
+    }
+    if ($ylen > 1) {
+      $ybeg .= "," . ($ybeg + $ylen - 1);
+    }
+
+    return $xbeg . ($xlen ? ($ylen ? 'c' : 'd') : 'a') . $ybeg;
+  }
+
+  protected function _start_block($header) {
+    if ($this->show_header) {
+      echo $header . "\n";
+    }
+  }
+
+  protected function _end_block() {
+  }
+
+  protected function _lines($lines, $prefix = ' ') {
+    foreach ($lines as $line) {
+      echo "$prefix $line\n";
+    }
+  }
+
+  protected function _context($lines) {
+    $this->_lines($lines);
+  }
+
+  protected function _added($lines) {
+    $this->_lines($lines, '>');
+  }
+
+  protected function _deleted($lines) {
+    $this->_lines($lines, '<');
+  }
+
+  protected function _changed($orig, $closing) {
+    $this->_deleted($orig);
+    echo "---\n";
+    $this->_added($closing);
+  }
+
+}

web/core/lib/Drupal/Component/Diff/Engine/DiffEngine.php

@@ -0,0 +1,457 @@
+<?php
+
+namespace Drupal\Component\Diff\Engine;
+
+use Drupal\Component\Utility\Unicode;
+
+/**
+ * Class used internally by Diff to actually compute the diffs.
+ *
+ * The algorithm used here is mostly lifted from the perl module
+ * Algorithm::Diff (version 1.06) by Ned Konz, which is available at:
+ *   http://www.perl.com/CPAN/authors/id/N/NE/NEDKONZ/Algorithm-Diff-1.06.zip
+ *
+ * More ideas are taken from:
+ *   http://www.ics.uci.edu/~eppstein/161/960229.html
+ *
+ * Some ideas (and a bit of code) are from analyze.c, from GNU
+ * diffutils-2.7, which can be found at:
+ *   ftp://gnudist.gnu.org/pub/gnu/diffutils/diffutils-2.7.tar.gz
+ *
+ * closingly, some ideas (subdivision by NCHUNKS > 2, and some optimizations)
+ * are my own.
+ *
+ * Line length limits for robustness added by Tim Starling, 2005-08-31
+ *
+ * @author Geoffrey T. Dairiki, Tim Starling
+ * @private
+ * @subpackage DifferenceEngine
+ */
+class DiffEngine {
+
+  const USE_ASSERTS = FALSE;
+
+  const MAX_XREF_LENGTH = 10000;
+
+  public function diff($from_lines, $to_lines) {
+
+    $n_from = sizeof($from_lines);
+    $n_to = sizeof($to_lines);
+
+    $this->xchanged = $this->ychanged = array();
+    $this->xv = $this->yv = array();
+    $this->xind = $this->yind = array();
+    unset($this->seq);
+    unset($this->in_seq);
+    unset($this->lcs);
+
+    // Skip leading common lines.
+    for ($skip = 0; $skip < $n_from && $skip < $n_to; $skip++) {
+      if ($from_lines[$skip] !== $to_lines[$skip]) {
+        break;
+      }
+      $this->xchanged[$skip] = $this->ychanged[$skip] = FALSE;
+    }
+    // Skip trailing common lines.
+    $xi = $n_from;
+    $yi = $n_to;
+    for ($endskip = 0; --$xi > $skip && --$yi > $skip; $endskip++) {
+      if ($from_lines[$xi] !== $to_lines[$yi]) {
+        break;
+      }
+      $this->xchanged[$xi] = $this->ychanged[$yi] = FALSE;
+    }
+
+    // Ignore lines which do not exist in both files.
+    for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
+      $xhash[$this->_line_hash($from_lines[$xi])] = 1;
+    }
+
+    for ($yi = $skip; $yi < $n_to - $endskip; $yi++) {
+      $line = $to_lines[$yi];
+      if ($this->ychanged[$yi] = empty($xhash[$this->_line_hash($line)])) {
+        continue;
+      }
+      $yhash[$this->_line_hash($line)] = 1;
+      $this->yv[] = $line;
+      $this->yind[] = $yi;
+    }
+    for ($xi = $skip; $xi < $n_from - $endskip; $xi++) {
+      $line = $from_lines[$xi];
+      if ($this->xchanged[$xi] = empty($yhash[$this->_line_hash($line)])) {
+        continue;
+      }
+      $this->xv[] = $line;
+      $this->xind[] = $xi;
+    }
+
+    // Find the LCS.
+    $this->_compareseq(0, sizeof($this->xv), 0, sizeof($this->yv));
+
+    // Merge edits when possible
+    $this->_shift_boundaries($from_lines, $this->xchanged, $this->ychanged);
+    $this->_shift_boundaries($to_lines, $this->ychanged, $this->xchanged);
+
+    // Compute the edit operations.
+    $edits = array();
+    $xi = $yi = 0;
+    while ($xi < $n_from || $yi < $n_to) {
+      $this::USE_ASSERTS && assert($yi < $n_to || $this->xchanged[$xi]);
+      $this::USE_ASSERTS && assert($xi < $n_from || $this->ychanged[$yi]);
+
+      // Skip matching "snake".
+      $copy = array();
+      while ( $xi < $n_from && $yi < $n_to && !$this->xchanged[$xi] && !$this->ychanged[$yi]) {
+        $copy[] = $from_lines[$xi++];
+        ++$yi;
+      }
+      if ($copy) {
+        $edits[] = new DiffOpCopy($copy);
+      }
+      // Find deletes & adds.
+      $delete = array();
+      while ($xi < $n_from && $this->xchanged[$xi]) {
+        $delete[] = $from_lines[$xi++];
+      }
+      $add = array();
+      while ($yi < $n_to && $this->ychanged[$yi]) {
+        $add[] = $to_lines[$yi++];
+      }
+      if ($delete && $add) {
+        $edits[] = new DiffOpChange($delete, $add);
+      }
+      elseif ($delete) {
+        $edits[] = new DiffOpDelete($delete);
+      }
+      elseif ($add) {
+        $edits[] = new DiffOpAdd($add);
+      }
+    }
+    return $edits;
+  }
+
+  /**
+   * Returns the whole line if it's small enough, or the MD5 hash otherwise.
+   */
+  protected function _line_hash($line) {
+    if (Unicode::strlen($line) > $this::MAX_XREF_LENGTH) {
+      return md5($line);
+    }
+    else {
+      return $line;
+    }
+  }
+
+
+  /**
+   * Divide the Largest Common Subsequence (LCS) of the sequences
+   * [XOFF, XLIM) and [YOFF, YLIM) into NCHUNKS approximately equally
+   * sized segments.
+   *
+   * Returns (LCS, PTS).  LCS is the length of the LCS. PTS is an
+   * array of NCHUNKS+1 (X, Y) indexes giving the diving points between
+   * sub sequences.  The first sub-sequence is contained in [X0, X1),
+   * [Y0, Y1), the second in [X1, X2), [Y1, Y2) and so on.  Note
+   * that (X0, Y0) == (XOFF, YOFF) and
+   * (X[NCHUNKS], Y[NCHUNKS]) == (XLIM, YLIM).
+   *
+   * This function assumes that the first lines of the specified portions
+   * of the two files do not match, and likewise that the last lines do not
+   * match.  The caller must trim matching lines from the beginning and end
+   * of the portions it is going to specify.
+   */
+  protected function _diag($xoff, $xlim, $yoff, $ylim, $nchunks) {
+    $flip = FALSE;
+
+    if ($xlim - $xoff > $ylim - $yoff) {
+      // Things seems faster (I'm not sure I understand why)
+      // when the shortest sequence in X.
+      $flip = TRUE;
+      list($xoff, $xlim, $yoff, $ylim) = array($yoff, $ylim, $xoff, $xlim);
+    }
+
+    if ($flip) {
+      for ($i = $ylim - 1; $i >= $yoff; $i--) {
+        $ymatches[$this->xv[$i]][] = $i;
+      }
+    }
+    else {
+      for ($i = $ylim - 1; $i >= $yoff; $i--) {
+        $ymatches[$this->yv[$i]][] = $i;
+      }
+    }
+    $this->lcs = 0;
+    $this->seq[0] = $yoff - 1;
+    $this->in_seq = array();
+    $ymids[0] = array();
+
+    $numer = $xlim - $xoff + $nchunks - 1;
+    $x = $xoff;
+    for ($chunk = 0; $chunk < $nchunks; $chunk++) {
+      if ($chunk > 0) {
+        for ($i = 0; $i <= $this->lcs; $i++) {
+          $ymids[$i][$chunk - 1] = $this->seq[$i];
+        }
+      }
+
+      $x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $chunk) / $nchunks);
+      for ( ; $x < $x1; $x++) {
+        $line = $flip ? $this->yv[$x] : $this->xv[$x];
+        if (empty($ymatches[$line])) {
+          continue;
+        }
+        $matches = $ymatches[$line];
+        reset($matches);
+        while (list ($junk, $y) = each($matches)) {
+          if (empty($this->in_seq[$y])) {
+            $k = $this->_lcs_pos($y);
+            $this::USE_ASSERTS && assert($k > 0);
+            $ymids[$k] = $ymids[$k - 1];
+            break;
+          }
+        }
+        while (list ($junk, $y) = each($matches)) {
+          if ($y > $this->seq[$k - 1]) {
+            $this::USE_ASSERTS && assert($y < $this->seq[$k]);
+            // Optimization: this is a common case:
+            // next match is just replacing previous match.
+            $this->in_seq[$this->seq[$k]] = FALSE;
+            $this->seq[$k] = $y;
+            $this->in_seq[$y] = 1;
+          }
+          elseif (empty($this->in_seq[$y])) {
+            $k = $this->_lcs_pos($y);
+            $this::USE_ASSERTS && assert($k > 0);
+            $ymids[$k] = $ymids[$k - 1];
+          }
+        }
+      }
+    }
+
+    $seps[] = $flip ? array($yoff, $xoff) : array($xoff, $yoff);
+    $ymid = $ymids[$this->lcs];
+    for ($n = 0; $n < $nchunks - 1; $n++) {
+      $x1 = $xoff + (int)(($numer + ($xlim - $xoff) * $n) / $nchunks);
+      $y1 = $ymid[$n] + 1;
+      $seps[] = $flip ? array($y1, $x1) : array($x1, $y1);
+    }
+    $seps[] = $flip ? array($ylim, $xlim) : array($xlim, $ylim);
+
+    return array($this->lcs, $seps);
+  }
+
+  protected function _lcs_pos($ypos) {
+
+    $end = $this->lcs;
+    if ($end == 0 || $ypos > $this->seq[$end]) {
+      $this->seq[++$this->lcs] = $ypos;
+      $this->in_seq[$ypos] = 1;
+      return $this->lcs;
+    }
+
+    $beg = 1;
+    while ($beg < $end) {
+      $mid = (int)(($beg + $end) / 2);
+      if ($ypos > $this->seq[$mid]) {
+        $beg = $mid + 1;
+      }
+      else {
+        $end = $mid;
+      }
+    }
+
+    $this::USE_ASSERTS && assert($ypos != $this->seq[$end]);
+
+    $this->in_seq[$this->seq[$end]] = FALSE;
+    $this->seq[$end] = $ypos;
+    $this->in_seq[$ypos] = 1;
+    return $end;
+  }
+
+  /**
+   * Find LCS of two sequences.
+   *
+   * The results are recorded in the vectors $this->{x,y}changed[], by
+   * storing a 1 in the element for each line that is an insertion
+   * or deletion (ie. is not in the LCS).
+   *
+   * The subsequence of file 0 is [XOFF, XLIM) and likewise for file 1.
+   *
+   * Note that XLIM, YLIM are exclusive bounds.
+   * All line numbers are origin-0 and discarded lines are not counted.
+   */
+  protected function _compareseq($xoff, $xlim, $yoff, $ylim) {
+
+    // Slide down the bottom initial diagonal.
+    while ($xoff < $xlim && $yoff < $ylim && $this->xv[$xoff] == $this->yv[$yoff]) {
+      ++$xoff;
+      ++$yoff;
+    }
+
+    // Slide up the top initial diagonal.
+    while ($xlim > $xoff && $ylim > $yoff && $this->xv[$xlim - 1] == $this->yv[$ylim - 1]) {
+      --$xlim;
+      --$ylim;
+    }
+
+    if ($xoff == $xlim || $yoff == $ylim) {
+      $lcs = 0;
+    }
+    else {
+      // This is ad hoc but seems to work well.
+      //$nchunks = sqrt(min($xlim - $xoff, $ylim - $yoff) / 2.5);
+      //$nchunks = max(2, min(8, (int)$nchunks));
+      $nchunks = min(7, $xlim - $xoff, $ylim - $yoff) + 1;
+      list($lcs, $seps)
+      = $this->_diag($xoff, $xlim, $yoff, $ylim, $nchunks);
+    }
+
+    if ($lcs == 0) {
+      // X and Y sequences have no common subsequence:
+      // mark all changed.
+      while ($yoff < $ylim) {
+        $this->ychanged[$this->yind[$yoff++]] = 1;
+      }
+      while ($xoff < $xlim) {
+        $this->xchanged[$this->xind[$xoff++]] = 1;
+      }
+    }
+    else {
+      // Use the partitions to split this problem into subproblems.
+      reset($seps);
+      $pt1 = $seps[0];
+      while ($pt2 = next($seps)) {
+        $this->_compareseq ($pt1[0], $pt2[0], $pt1[1], $pt2[1]);
+        $pt1 = $pt2;
+      }
+    }
+  }
+
+  /**
+   * Adjust inserts/deletes of identical lines to join changes
+   * as much as possible.
+   *
+   * We do something when a run of changed lines include a
+   * line at one end and has an excluded, identical line at the other.
+   * We are free to choose which identical line is included.
+   * `compareseq' usually chooses the one at the beginning,
+   * but usually it is cleaner to consider the following identical line
+   * to be the "change".
+   *
+   * This is extracted verbatim from analyze.c (GNU diffutils-2.7).
+   */
+  protected function _shift_boundaries($lines, &$changed, $other_changed) {
+    $i = 0;
+    $j = 0;
+
+    $this::USE_ASSERTS && assert('sizeof($lines) == sizeof($changed)');
+    $len = sizeof($lines);
+    $other_len = sizeof($other_changed);
+
+    while (1) {
+      /*
+       * Scan forwards to find beginning of another run of changes.
+       * Also keep track of the corresponding point in the other file.
+       *
+       * Throughout this code, $i and $j are adjusted together so that
+       * the first $i elements of $changed and the first $j elements
+       * of $other_changed both contain the same number of zeros
+       * (unchanged lines).
+       * Furthermore, $j is always kept so that $j == $other_len or
+       * $other_changed[$j] == FALSE.
+       */
+      while ($j < $other_len && $other_changed[$j]) {
+        $j++;
+      }
+      while ($i < $len && !$changed[$i]) {
+        $this::USE_ASSERTS && assert('$j < $other_len && ! $other_changed[$j]');
+        $i++;
+        $j++;
+        while ($j < $other_len && $other_changed[$j]) {
+          $j++;
+        }
+      }
+
+      if ($i == $len) {
+        break;
+      }
+      $start = $i;
+
+      // Find the end of this run of changes.
+      while (++$i < $len && $changed[$i]) {
+        continue;
+      }
+
+      do {
+        /*
+         * Record the length of this run of changes, so that
+         * we can later determine whether the run has grown.
+         */
+        $runlength = $i - $start;
+
+        /*
+         * Move the changed region back, so long as the
+         * previous unchanged line matches the last changed one.
+         * This merges with previous changed regions.
+         */
+        while ($start > 0 && $lines[$start - 1] == $lines[$i - 1]) {
+          $changed[--$start] = 1;
+          $changed[--$i] = FALSE;
+          while ($start > 0 && $changed[$start - 1]) {
+            $start--;
+          }
+          $this::USE_ASSERTS && assert('$j > 0');
+          while ($other_changed[--$j]) {
+            continue;
+          }
+          $this::USE_ASSERTS && assert('$j >= 0 && !$other_changed[$j]');
+        }
+
+        /*
+         * Set CORRESPONDING to the end of the changed run, at the last
+         * point where it corresponds to a changed run in the other file.
+         * CORRESPONDING == LEN means no such point has been found.
+         */
+        $corresponding = $j < $other_len ? $i : $len;
+
+        /*
+         * Move the changed region forward, so long as the
+         * first changed line matches the following unchanged one.
+         * This merges with following changed regions.
+         * Do this second, so that if there are no merges,
+         * the changed region is moved forward as far as possible.
+         */
+        while ($i < $len && $lines[$start] == $lines[$i]) {
+          $changed[$start++] = FALSE;
+          $changed[$i++] = 1;
+          while ($i < $len && $changed[$i]) {
+            $i++;
+          }
+          $this::USE_ASSERTS && assert('$j < $other_len && ! $other_changed[$j]');
+          $j++;
+          if ($j < $other_len && $other_changed[$j]) {
+            $corresponding = $i;
+            while ($j < $other_len && $other_changed[$j]) {
+              $j++;
+            }
+          }
+        }
+      } while ($runlength != $i - $start);
+
+      /*
+       * If possible, move the fully-merged run of changes
+       * back to a corresponding run in the other file.
+       */
+      while ($corresponding < $i) {
+        $changed[--$start] = 1;
+        $changed[--$i] = 0;
+        $this::USE_ASSERTS && assert('$j > 0');
+        while ($other_changed[--$j]) {
+          continue;
+        }
+        $this::USE_ASSERTS && assert('$j >= 0 && !$other_changed[$j]');
+      }
+    }
+  }
+
+}

web/core/lib/Drupal/Component/Diff/Engine/DiffOp.php

@@ -0,0 +1,27 @@
+<?php
+
+namespace Drupal\Component\Diff\Engine;
+
+/**
+ * @todo document
+ * @private
+ * @subpackage DifferenceEngine
+ */
+class DiffOp {
+  public $type;
+  public $orig;
+  public $closing;
+
+  public function reverse() {
+    trigger_error('pure virtual', E_USER_ERROR);
+  }
+
+  public function norig() {
+    return $this->orig ? sizeof($this->orig) : 0;
+  }
+
+  public function nclosing() {
+    return $this->closing ? sizeof($this->closing) : 0;
+  }
+
+}

web/core/lib/Drupal/Component/Diff/Engine/DiffOpAdd.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Drupal\Component\Diff\Engine;
+
+/**
+ * @todo document
+ * @private
+ * @subpackage DifferenceEngine
+ */
+class DiffOpAdd extends DiffOp {
+  public $type = 'add';
+
+  public function __construct($lines) {
+    $this->closing = $lines;
+    $this->orig = FALSE;
+  }
+
+  public function reverse() {
+    return new DiffOpDelete($this->closing);
+  }
+
+}

web/core/lib/Drupal/Component/Diff/Engine/DiffOpChange.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Drupal\Component\Diff\Engine;
+
+/**
+ * @todo document
+ * @private
+ * @subpackage DifferenceEngine
+ */
+class DiffOpChange extends DiffOp {
+  public $type = 'change';
+
+  public function __construct($orig, $closing) {
+    $this->orig = $orig;
+    $this->closing = $closing;
+  }
+
+  public function reverse() {
+    return new DiffOpChange($this->closing, $this->orig);
+  }
+
+}

web/core/lib/Drupal/Component/Diff/Engine/DiffOpCopy.php

@@ -0,0 +1,25 @@
+<?php
+
+namespace Drupal\Component\Diff\Engine;
+
+/**
+ * @todo document
+ * @private
+ * @subpackage DifferenceEngine
+ */
+class DiffOpCopy extends DiffOp {
+  public $type = 'copy';
+
+  public function __construct($orig, $closing = FALSE) {
+    if (!is_array($closing)) {
+      $closing = $orig;
+    }
+    $this->orig = $orig;
+    $this->closing = $closing;
+  }
+
+  public function reverse() {
+    return new DiffOpCopy($this->closing, $this->orig);
+  }
+
+}

web/core/lib/Drupal/Component/Diff/Engine/DiffOpDelete.php

@@ -0,0 +1,22 @@
+<?php
+
+namespace Drupal\Component\Diff\Engine;
+
+/**
+ * @todo document
+ * @private
+ * @subpackage DifferenceEngine
+ */
+class DiffOpDelete extends DiffOp {
+  public $type = 'delete';
+
+  public function __construct($lines) {
+    $this->orig = $lines;
+    $this->closing = FALSE;
+  }
+
+  public function reverse() {
+    return new DiffOpAdd($this->orig);
+  }
+
+}

web/core/lib/Drupal/Component/Diff/Engine/HWLDFWordAccumulator.php

@@ -0,0 +1,79 @@
+<?php
+
+namespace Drupal\Component\Diff\Engine;
+
+use Drupal\Component\Utility\Unicode;
+
+/**
+ * Additions by Axel Boldt follow, partly taken from diff.php, phpwiki-1.3.3
+ */
+
+/**
+ * @todo document
+ * @private
+ * @subpackage DifferenceEngine
+ */
+class HWLDFWordAccumulator {
+
+  /**
+   * An iso-8859-x non-breaking space.
+   */
+  const NBSP = '&#160;';
+
+  protected $lines = array();
+
+  protected $line = '';
+
+  protected $group = '';
+
+  protected $tag = '';
+
+  protected function _flushGroup($new_tag) {
+    if ($this->group !== '') {
+      if ($this->tag == 'mark') {
+        $this->line = $this->line . '<span class="diffchange">' . $this->group . '</span>';
+      }
+      else {
+        $this->line = $this->line . $this->group;
+      }
+    }
+    $this->group = '';
+    $this->tag = $new_tag;
+  }
+
+  protected function _flushLine($new_tag) {
+    $this->_flushGroup($new_tag);
+    if ($this->line != '') {
+      array_push($this->lines, $this->line);
+    }
+    else {
+      // make empty lines visible by inserting an NBSP
+      array_push($this->lines, $this::NBSP);
+    }
+    $this->line = '';
+  }
+
+  public function addWords($words, $tag = '') {
+    if ($tag != $this->tag) {
+      $this->_flushGroup($tag);
+    }
+    foreach ($words as $word) {
+      // new-line should only come as first char of word.
+      if ($word == '') {
+        continue;
+      }
+      if ($word[0] == "\n") {
+        $this->_flushLine($tag);
+        $word = Unicode::substr($word, 1);
+      }
+      assert(!strstr($word, "\n"));
+      $this->group .= $word;
+    }
+  }
+
+  public function getLines() {
+    $this->_flushLine('~done');
+    return $this->lines;
+  }
+
+}

web/core/lib/Drupal/Component/Diff/LICENSE.txt

@@ -0,0 +1,339 @@
+        GNU GENERAL PUBLIC LICENSE
+           Version 2, June 1991
+
+ Copyright (C) 1989, 1991 Free Software Foundation, Inc.,
+ 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
+          Preamble
+
+  The licenses for most software are designed to take away your
+freedom to share and change it.  By contrast, the GNU General Public
+License is intended to guarantee your freedom to share and change free
+software--to make sure the software is free for all its users.  This
+General Public License applies to most of the Free Software
+Foundation's software and to any other program whose authors commit to
+using it.  (Some other Free Software Foundation software is covered by
+the GNU Lesser General Public License instead.)  You can apply it to
+your programs, too.
+
+  When we speak of free software, we are referring to freedom, not
+price.  Our General Public Licenses are designed to make sure that you
+have the freedom to distribute copies of free software (and charge for
+this service if you wish), that you receive source code or can get it
+if you want it, that you can change the software or use pieces of it
+in new free programs; and that you know you can do these things.
+
+  To protect your rights, we need to make restrictions that forbid
+anyone to deny you these rights or to ask you to surrender the rights.
+These restrictions translate to certain responsibilities for you if you
+distribute copies of the software, or if you modify it.
+
+  For example, if you distribute copies of such a program, whether
+gratis or for a fee, you must give the recipients all the rights that
+you have.  You must make sure that they, too, receive or can get the
+source code.  And you must show them these terms so they know their
+rights.
+
+  We protect your rights with two steps: (1) copyright the software, and
+(2) offer you this license which gives you legal permission to copy,
+distribute and/or modify the software.
+
+  Also, for each author's protection and ours, we want to make certain
+that everyone understands that there is no warranty for this free
+software.  If the software is modified by someone else and passed on, we
+want its recipients to know that what they have is not the original, so
+that any problems introduced by others will not reflect on the original
+authors' reputations.
+
+  Finally, any free program is threatened constantly by software
+patents.  We wish to avoid the danger that redistributors of a free
+program will individually obtain patent licenses, in effect making the
+program proprietary.  To prevent this, we have made it clear that any
+patent must be licensed for everyone's free use or not licensed at all.
+
+  The precise terms and conditions for copying, distribution and
+modification follow.
+
+        GNU GENERAL PUBLIC LICENSE
+   TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION
+
+  0. This License applies to any program or other work which contains
+a notice placed by the copyright holder saying it may be distributed
+under the terms of this General Public License.  The "Program", below,
+refers to any such program or work, and a "work based on the Program"
+means either the Program or any derivative work under copyright law:
+that is to say, a work containing the Program or a portion of it,
+either verbatim or with modifications and/or translated into another
+language.  (Hereinafter, translation is included without limitation in
+the term "modification".)  Each licensee is addressed as "you".
+
+Activities other than copying, distribution and modification are not
+covered by this License; they are outside its scope.  The act of
+running the Program is not restricted, and the output from the Program
+is covered only if its contents constitute a work based on the
+Program (independent of having been made by running the Program).
+Whether that is true depends on what the Program does.
+
+  1. You may copy and distribute verbatim copies of the Program's
+source code as you receive it, in any medium, provided that you
+conspicuously and appropriately publish on each copy an appropriate
+copyright notice and disclaimer of warranty; keep intact all the
+notices that refer to this License and to the absence of any warranty;
+and give any other recipients of the Program a copy of this License
+along with the Program.
+
+You may charge a fee for the physical act of transferring a copy, and
+you may at your option offer warranty protection in exchange for a fee.
+
+  2. You may modify your copy or copies of the Program or any portion
+of it, thus forming a work based on the Program, and copy and
+distribute such modifications or work under the terms of Section 1
+above, provided that you also meet all of these conditions:
+
+    a) You must cause the modified files to carry prominent notices
+    stating that you changed the files and the date of any change.
+
+    b) You must cause any work that you distribute or publish, that in
+    whole or in part contains or is derived from the Program or any
+    part thereof, to be licensed as a whole at no charge to all third
+    parties under the terms of this License.
+
+    c) If the modified program normally reads commands interactively
+    when run, you must cause it, when started running for such
+    interactive use in the most ordinary way, to print or display an
+    announcement including an appropriate copyright notice and a
+    notice that there is no warranty (or else, saying that you provide
+    a warranty) and that users may redistribute the program under
+    these conditions, and telling the user how to view a copy of this
+    License.  (Exception: if the Program itself is interactive but
+    does not normally print such an announcement, your work based on
+    the Program is not required to print an announcement.)
+
+These requirements apply to the modified work as a whole.  If
+identifiable sections of that work are not derived from the Program,
+and can be reasonably considered independent and separate works in
+themselves, then this License, and its terms, do not apply to those
+sections when you distribute them as separate works.  But when you
+distribute the same sections as part of a whole which is a work based
+on the Program, the distribution of the whole must be on the terms of
+this License, whose permissions for other licensees extend to the
+entire whole, and thus to each and every part regardless of who wrote it.
+
+Thus, it is not the intent of this section to claim rights or contest
+your rights to work written entirely by you; rather, the intent is to
+exercise the right to control the distribution of derivative or
+collective works based on the Program.
+
+In addition, mere aggregation of another work not based on the Program
+with the Program (or with a work based on the Program) on a volume of
+a storage or distribution medium does not bring the other work under
+the scope of this License.
+
+  3. You may copy and distribute the Program (or a work based on it,
+under Section 2) in object code or executable form under the terms of
+Sections 1 and 2 above provided that you also do one of the following:
+
+    a) Accompany it with the complete corresponding machine-readable
+    source code, which must be distributed under the terms of Sections
+    1 and 2 above on a medium customarily used for software interchange; or,
+
+    b) Accompany it with a written offer, valid for at least three
+    years, to give any third party, for a charge no more than your
+    cost of physically performing source distribution, a complete
+    machine-readable copy of the corresponding source code, to be
+    distributed under the terms of Sections 1 and 2 above on a medium
+    customarily used for software interchange; or,
+
+    c) Accompany it with the information you received as to the offer
+    to distribute corresponding source code.  (This alternative is
+    allowed only for noncommercial distribution and only if you
+    received the program in object code or executable form with such
+    an offer, in accord with Subsection b above.)
+
+The source code for a work means the preferred form of the work for
+making modifications to it.  For an executable work, complete source
+code means all the source code for all modules it contains, plus any
+associated interface definition files, plus the scripts used to
+control compilation and installation of the executable.  However, as a
+special exception, the source code distributed need not include
+anything that is normally distributed (in either source or binary
+form) with the major components (compiler, kernel, and so on) of the
+operating system on which the executable runs, unless that component
+itself accompanies the executable.
+
+If distribution of executable or object code is made by offering
+access to copy from a designated place, then offering equivalent
+access to copy the source code from the same place counts as
+distribution of the source code, even though third parties are not
+compelled to copy the source along with the object code.
+
+  4. You may not copy, modify, sublicense, or distribute the Program
+except as expressly provided under this License.  Any attempt
+otherwise to copy, modify, sublicense or distribute the Program is
+void, and will automatically terminate your rights under this License.
+However, parties who have received copies, or rights, from you under
+this License will not have their licenses terminated so long as such
+parties remain in full compliance.
+
+  5. You are not required to accept this License, since you have not
+signed it.  However, nothing else grants you permission to modify or
+distribute the Program or its derivative works.  These actions are
+prohibited by law if you do not accept this License.  Therefore, by
+modifying or distributing the Program (or any work based on the
+Program), you indicate your acceptance of this License to do so, and
+all its terms and conditions for copying, distributing or modifying
+the Program or works based on it.
+
+  6. Each time you redistribute the Program (or any work based on the
+Program), the recipient automatically receives a license from the
+original licensor to copy, distribute or modify the Program subject to
+these terms and conditions.  You may not impose any further
+restrictions on the recipients' exercise of the rights granted herein.
+You are not responsible for enforcing compliance by third parties to
+this License.
+
+  7. If, as a consequence of a court judgment or allegation of patent
+infringement or for any other reason (not limited to patent issues),
+conditions are imposed on you (whether by court order, agreement or
+otherwise) that contradict the conditions of this License, they do not
+excuse you from the conditions of this License.  If you cannot
+distribute so as to satisfy simultaneously your obligations under this
+License and any other pertinent obligations, then as a consequence you
+may not distribute the Program at all.  For example, if a patent
+license would not permit royalty-free redistribution of the Program by
+all those who receive copies directly or indirectly through you, then
+the only way you could satisfy both it and this License would be to
+refrain entirely from distribution of the Program.
+
+If any portion of this section is held invalid or unenforceable under
+any particular circumstance, the balance of the section is intended to
+apply and the section as a whole is intended to apply in other
+circumstances.
+
+It is not the purpose of this section to induce you to infringe any
+patents or other property right claims or to contest validity of any
+such claims; this section has the sole purpose of protecting the
+integrity of the free software distribution system, which is
+implemented by public license practices.  Many people have made
+generous contributions to the wide range of software distributed
+through that system in reliance on consistent application of that
+system; it is up to the author/donor to decide if he or she is willing
+to distribute software through any other system and a licensee cannot
+impose that choice.
+
+This section is intended to make thoroughly clear what is believed to
+be a consequence of the rest of this License.
+
+  8. If the distribution and/or use of the Program is restricted in
+certain countries either by patents or by copyrighted interfaces, the
+original copyright holder who places the Program under this License
+may add an explicit geographical distribution limitation excluding
+those countries, so that distribution is permitted only in or among
+countries not thus excluded.  In such case, this License incorporates
+the limitation as if written in the body of this License.
+
+  9. The Free Software Foundation may publish revised and/or new versions
+of the General Public License from time to time.  Such new versions will
+be similar in spirit to the present version, but may differ in detail to
+address new problems or concerns.
+
+Each version is given a distinguishing version number.  If the Program
+specifies a version number of this License which applies to it and "any
+later version", you have the option of following the terms and conditions
+either of that version or of any later version published by the Free
+Software Foundation.  If the Program does not specify a version number of
+this License, you may choose any version ever published by the Free Software
+Foundation.
+
+  10. If you wish to incorporate parts of the Program into other free
+programs whose distribution conditions are different, write to the author
+to ask for permission.  For software which is copyrighted by the Free
+Software Foundation, write to the Free Software Foundation; we sometimes
+make exceptions for this.  Our decision will be guided by the two goals
+of preserving the free status of all derivatives of our free software and
+of promoting the sharing and reuse of software generally.
+
+          NO WARRANTY
+
+  11. BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY
+FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW.  EXCEPT WHEN
+OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES
+PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED
+OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  THE ENTIRE RISK AS
+TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU.  SHOULD THE
+PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING,
+REPAIR OR CORRECTION.
+
+  12. IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR
+REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES,
+INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING
+OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED
+TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY
+YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER
+PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE
+POSSIBILITY OF SUCH DAMAGES.
+
+         END OF TERMS AND CONDITIONS
+
+      How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+convey the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License along
+    with this program; if not, write to the Free Software Foundation, Inc.,
+    51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program is interactive, make it output a short notice like this
+when it starts in an interactive mode:
+
+    Gnomovision version 69, Copyright (C) year name of author
+    Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, the commands you use may
+be called something other than `show w' and `show c'; they could even be
+mouse-clicks or menu items--whatever suits your program.
+
+You should also get your employer (if you work as a programmer) or your
+school, if any, to sign a "copyright disclaimer" for the program, if
+necessary.  Here is a sample; alter the names:
+
+  Yoyodyne, Inc., hereby disclaims all copyright interest in the program
+  `Gnomovision' (which makes passes at compilers) written by James Hacker.
+
+  <signature of Ty Coon>, 1 April 1989
+  Ty Coon, President of Vice
+
+This General Public License does not permit incorporating your program into
+proprietary programs.  If your program is a subroutine library, you may
+consider it more useful to permit linking proprietary applications with the
+library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.

web/core/lib/Drupal/Component/Diff/MappedDiff.php

@@ -0,0 +1,56 @@
+<?php
+
+namespace Drupal\Component\Diff;
+
+/**
+ * FIXME: bad name.
+ * @todo document
+ * @private
+ * @subpackage DifferenceEngine
+ */
+class MappedDiff extends Diff {
+
+  /**
+   * Constructor.
+   *
+   * Computes diff between sequences of strings.
+   *
+   * This can be used to compute things like
+   * case-insensitive diffs, or diffs which ignore
+   * changes in white-space.
+   *
+   * @param $from_lines array An array of strings.
+   *   (Typically these are lines from a file.)
+   * @param $to_lines array An array of strings.
+   * @param $mapped_from_lines array This array should
+   *   have the same size number of elements as $from_lines.
+   *   The elements in $mapped_from_lines and
+   *   $mapped_to_lines are what is actually compared
+   *   when computing the diff.
+   * @param $mapped_to_lines array This array should
+   *   have the same number of elements as $to_lines.
+   */
+  public function __construct($from_lines, $to_lines, $mapped_from_lines, $mapped_to_lines) {
+
+    assert(sizeof($from_lines) == sizeof($mapped_from_lines));
+    assert(sizeof($to_lines) == sizeof($mapped_to_lines));
+
+    parent::__construct($mapped_from_lines, $mapped_to_lines);
+
+    $xi = $yi = 0;
+    for ($i = 0; $i < sizeof($this->edits); $i++) {
+      $orig = &$this->edits[$i]->orig;
+      if (is_array($orig)) {
+        $orig = array_slice($from_lines, $xi, sizeof($orig));
+        $xi += sizeof($orig);
+      }
+
+      $closing = &$this->edits[$i]->closing;
+      if (is_array($closing)) {
+        $closing = array_slice($to_lines, $yi, sizeof($closing));
+        $yi += sizeof($closing);
+      }
+    }
+  }
+
+}

web/core/lib/Drupal/Component/Diff/README.txt

@@ -0,0 +1,12 @@
+The Drupal Diff Component
+
+Thanks for using this Drupal component.
+
+You can participate in its development on Drupal.org, through our issue system:
+https://www.drupal.org/project/issues/drupal
+
+You can get the full Drupal repo here:
+https://www.drupal.org/project/drupal/git-instructions
+
+You can browse the full Drupal repo here:
+http://cgit.drupalcode.org/drupal

web/core/lib/Drupal/Component/Diff/TESTING.txt

@@ -0,0 +1,18 @@
+HOW-TO: Test this Drupal component
+
+In order to test this component, you'll need to get the entire Drupal repo and
+run the tests there.
+
+You'll find the tests under core/tests/Drupal/Tests/Component.
+
+You can get the full Drupal repo here:
+https://www.drupal.org/project/drupal/git-instructions
+
+You can find more information about running PHPUnit tests with Drupal here:
+https://www.drupal.org/node/2116263
+
+Each component in the Drupal\Component namespace has its own annotated test
+group. You can use this group to run only the tests for this component. Like
+this:
+
+$ ./vendor/bin/phpunit -c core --group Diff

web/core/lib/Drupal/Component/Diff/WordLevelDiff.php

@@ -0,0 +1,82 @@
+<?php
+
+namespace Drupal\Component\Diff;
+
+use Drupal\Component\Diff\Engine\HWLDFWordAccumulator;
+use Drupal\Component\Utility\Unicode;
+
+/**
+ * @todo document
+ * @private
+ * @subpackage DifferenceEngine
+ */
+class WordLevelDiff extends MappedDiff {
+
+  const MAX_LINE_LENGTH = 10000;
+
+  public function __construct($orig_lines, $closing_lines) {
+    list($orig_words, $orig_stripped) = $this->_split($orig_lines);
+    list($closing_words, $closing_stripped) = $this->_split($closing_lines);
+
+    parent::__construct($orig_words, $closing_words, $orig_stripped, $closing_stripped);
+  }
+
+  protected function _split($lines) {
+    $words = array();
+    $stripped = array();
+    $first = TRUE;
+    foreach ($lines as $line) {
+      // If the line is too long, just pretend the entire line is one big word
+      // This prevents resource exhaustion problems
+      if ( $first ) {
+        $first = FALSE;
+      }
+      else {
+        $words[] = "\n";
+        $stripped[] = "\n";
+      }
+      if (Unicode::strlen($line) > $this::MAX_LINE_LENGTH) {
+        $words[] = $line;
+        $stripped[] = $line;
+      }
+      else {
+        if (preg_match_all('/ ( [^\S\n]+ | [0-9_A-Za-z\x80-\xff]+ | . ) (?: (?!< \n) [^\S\n])? /xs', $line, $m)) {
+          $words = array_merge($words, $m[0]);
+          $stripped = array_merge($stripped, $m[1]);
+        }
+      }
+    }
+    return array($words, $stripped);
+  }
+
+  public function orig() {
+    $orig = new HWLDFWordAccumulator();
+
+    foreach ($this->edits as $edit) {
+      if ($edit->type == 'copy') {
+        $orig->addWords($edit->orig);
+      }
+      elseif ($edit->orig) {
+        $orig->addWords($edit->orig, 'mark');
+      }
+    }
+    $lines = $orig->getLines();
+    return $lines;
+  }
+
+  public function closing() {
+    $closing = new HWLDFWordAccumulator();
+
+    foreach ($this->edits as $edit) {
+      if ($edit->type == 'copy') {
+        $closing->addWords($edit->closing);
+      }
+      elseif ($edit->closing) {
+        $closing->addWords($edit->closing, 'mark');
+      }
+    }
+    $lines = $closing->getLines();
+    return $lines;
+  }
+
+}

web/core/lib/Drupal/Component/Diff/composer.json

@@ -0,0 +1,16 @@
+{
+  "name": "drupal/core-diff",
+  "description": "Diff.",
+  "keywords": ["drupal"],
+  "homepage": "https://www.drupal.org/project/drupal",
+  "license": "GPL-2.0+",
+  "require": {
+    "php": ">=5.5.9",
+    "drupal/utility": "~8.2"
+  },
+  "autoload": {
+    "psr-4": {
+      "Drupal\\Component\\Diff\\": ""
+    }
+  }
+}