Unmuck some issues with viewing HEAD changes.

src/applications/diffusion/controller/change/DiffusionChangeController.php

@@ -23,14 +23,6 @@ class DiffusionChangeController extends DiffusionController {
 
     $content = array();
 
-    $content[] = $this->buildCrumbs(
-      array(
-        'branch' => true,
-        'path'   => true,
-        'view'   => 'change',
-      ));
-
-
     $diff_query = DiffusionDiffQuery::newFromDiffusionRequest($drequest);
     $changeset = $diff_query->loadChangeset();
 
@@ -39,6 +31,13 @@ class DiffusionChangeController extends DiffusionController {
     $changeset_view->setRenderURI(
       '/diffusion/'.$drequest->getRepository()->getCallsign().'/diff/');
 
+    $content[] = $this->buildCrumbs(
+      array(
+        'branch' => true,
+        'path'   => true,
+        'view'   => 'change',
+      ));
+
     // TODO: This is pretty awkward, unify the CSS between Diffusion and
     // Differential better.
     require_celerity_resource('differential-core-view-css');

src/applications/diffusion/query/diff/base/DiffusionDiffQuery.php

@@ -57,4 +57,18 @@ abstract class DiffusionDiffQuery {
   }
 
   abstract protected function executeQuery();
+
+  protected function getEffectiveCommit() {
+    $drequest = $this->getRequest();
+
+    $modified_query = DiffusionLastModifiedQuery::newFromDiffusionRequest(
+      $drequest);
+    list($commit) = $modified_query->loadLastModification();
+    if (!$commit) {
+      // TODO: Improve error messages here.
+      return null;
+    }
+    return $commit->getCommitIdentifier();
+  }
+
 }

src/applications/diffusion/query/diff/base/__init__.php

@@ -6,6 +6,7 @@
 
 
 
+phutil_require_module('phabricator', 'applications/diffusion/query/lastmodified/base');
 phutil_require_module('phabricator', 'applications/repository/constants/repositorytype');
 
 phutil_require_module('phutil', 'symbols');

src/applications/diffusion/query/diff/git/DiffusionGitDiffQuery.php

@@ -22,6 +22,17 @@ final class DiffusionGitDiffQuery extends DiffusionDiffQuery {
     $drequest = $this->getRequest();
     $repository = $drequest->getRepository();
 
+    if (!$drequest->getRawCommit()) {
+      $effective_commit = $this->getEffectiveCommit();
+      if (!$effective_commit) {
+        return null;
+      }
+      // TODO: This side effect is kind of skethcy.
+      $drequest->setCommit($effective_commit);
+    } else {
+      $effective_commit = $drequest->getCommit();
+    }
+
     $options = array(
       '-M',
       '-C',
@@ -36,8 +47,8 @@ final class DiffusionGitDiffQuery extends DiffusionDiffQuery {
     list($raw_diff) = execx(
       "(cd %s && git diff {$options} %s^ %s -- %s)",
       $repository->getDetail('local-path'),
-      $drequest->getCommit(),
-      $drequest->getCommit(),
+      $effective_commit,
+      $effective_commit,
       $drequest->getPath());
 
     $parser = new ArcanistDiffParser();

src/applications/diffusion/query/diff/svn/DiffusionSvnDiffQuery.php

@@ -21,6 +21,15 @@ final class DiffusionSvnDiffQuery extends DiffusionDiffQuery {
   protected function executeQuery() {
     $drequest = $this->getRequest();
 
+    if (!$drequest->getRawCommit()) {
+      $effective_commit = $this->getEffectiveCommit();
+      if (!$effective_commit) {
+        return null;
+      }
+      // TODO: Sketchy side effect.
+      $drequest->setCommit($effective_commit);
+    }
+
     $path_change_query = DiffusionPathChangeQuery::newFromDiffusionRequest(
       $drequest);
     $path_changes = $path_change_query->loadChanges();

src/applications/diffusion/request/base/DiffusionRequest.php

@@ -140,6 +140,11 @@ class DiffusionRequest {
     return $this->commit;
   }
 
+  public function setCommit($commit) {
+    $this->commit = $commit;
+    return $this;
+  }
+
   public function getCommitURIComponent($commit) {
     return $commit;
   }