Implement rough content-aware inline adjustment rules for ghosts

Summary:
Ref T7447. Fixes T7600. This likely needs significant adjustment, but implements content-aware comment porting for line changes.

Specifically, this moves lines around to adjust their position considering added and removed lines between the diffs and across rebases.

It does not try to do any actual content (line against line) matching.

Test Plan:
  - Unit tests.
  - Poking around in the web UI seems to generate mostly reasonable-ish results?
  - This may be a huge step backward in some cases that I just haven't hit.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: yelirekim, epriestley

Maniphest Tasks: T7600, T7447

Differential Revision: https://secure.phabricator.com/D12741

src/applications/differential/query/DifferentialInlineCommentQuery.php

@@ -323,6 +323,7 @@ final class DifferentialInlineCommentQuery
               'new' => $is_new,
               'reason' => $reason,
               'href' => $href,
+              'originalID' => $changeset->getID(),
             ));
 
         $results[] = $inline;
@@ -348,6 +349,107 @@ final class DifferentialInlineCommentQuery
       }
     }
 
+    // Adjust inline line numbers to account for content changes across
+    // updates and rebases.
+    $plan = array();
+    $need = array();
+    foreach ($results as $inline) {
+      $ghost = $inline->getIsGhost();
+      if (!$ghost) {
+        // If this isn't a "ghost" inline, ignore it.
+        continue;
+      }
+
+      $src_id = $ghost['originalID'];
+      $dst_id = $inline->getChangesetID();
+
+      $xforms = array();
+
+      // If the comment is on the right, transform it through the inverse map
+      // back to the left.
+      if ($inline->getIsNewFile()) {
+        $xforms[] = array($src_id, $src_id, true);
+      }
+
+      // Transform it across rebases.
+      $xforms[] = array($src_id, $dst_id, false);
+
+      // If the comment is on the right, transform it back onto the right.
+      if ($inline->getIsNewFile()) {
+        $xforms[] = array($dst_id, $dst_id, false);
+      }
+
+      $key = array();
+      foreach ($xforms as $xform) {
+        list($u, $v, $inverse) = $xform;
+
+        $short = $u.'/'.$v;
+        $need[$short] = array($u, $v);
+
+        $part = $u.($inverse ? '<' : '>').$v;
+        $key[] = $part;
+      }
+      $key = implode(',', $key);
+
+      if (empty($plan[$key])) {
+        $plan[$key] = array(
+          'xforms' => $xforms,
+          'inlines' => array(),
+        );
+      }
+
+      $plan[$key]['inlines'][] = $inline;
+    }
+
+    if ($need) {
+      $maps = DifferentialLineAdjustmentMap::loadMaps($need);
+    } else {
+      $maps = array();
+    }
+
+    foreach ($plan as $step) {
+      $xforms = $step['xforms'];
+
+      $chain = null;
+      foreach ($xforms as $xform) {
+        list($u, $v, $inverse) = $xform;
+        $map = idx(idx($maps, $u, array()), $v);
+        if (!$map) {
+          continue 2;
+        }
+
+        if ($inverse) {
+          $map = DifferentialLineAdjustmentMap::newInverseMap($map);
+        } else {
+          $map = clone $map;
+        }
+
+        if ($chain) {
+          $chain->addMapToChain($map);
+        } else {
+          $chain = $map;
+        }
+      }
+
+      foreach ($step['inlines'] as $inline) {
+        $head_line = $inline->getLineNumber();
+        $tail_line = ($head_line + $inline->getLineLength());
+
+        $head_info = $chain->mapLine($head_line, false);
+        $tail_info = $chain->mapLine($tail_line, true);
+
+        list($head_deleted, $head_offset, $head_line) = $head_info;
+        list($tail_deleted, $tail_offset, $tail_line) = $tail_info;
+
+        if ($head_offset !== false) {
+          $inline->setLineNumber($head_line + 1 + $head_offset);
+        } else {
+          $inline->setLineNumber($head_line);
+          $inline->setLineLength($tail_line - $head_line);
+        }
+      }
+    }
+
     return $results;
   }