Make Changeset ID for render cache explicit

Summary:
DifferentialChangesetParser currently takes the Changeset object to mean a bunch
of different and mutually conflicting things implicitly:

  - Changeset ID is used to access the render cache.
  - Changeset ID is also used to tell the ajax endpoint what to render when
clicking "show more".
  - Changeset object has the actual changes.
  - Changeset ID and "oldChangesetID" are used to choose where to show inline
comments and how to attach new ones.

This indirectly causes a bunch of problems, like T141 and T132. Move toward
making all these separate things explicit. I want to have the changeset object
only mean the actual changes to display.

Test Plan:
Looked at changesets and verified the render cache was accessed correctly (and
not accessed in other cases).

Reviewed By: tuomaspelkonen
Reviewers: jungejason, tuomaspelkonen, aran
CC: aran, epriestley, tuomaspelkonen
Differential Revision: 228

src/applications/differential/controller/changesetview/DifferentialChangesetViewController.php

@@ -48,6 +48,8 @@ class DifferentialChangesetViewController extends DifferentialController {
       $right_new = true;
       $left_source = $right->getID();
       $left_new = false;
+
+      $render_cache_key = $right->getID();
     } else if ($vs == -1) {
       $right = null;
       $left = $changeset;
@@ -56,6 +58,8 @@ class DifferentialChangesetViewController extends DifferentialController {
       $right_new = false;
       $left_source = $left->getID();
       $left_new = true;
+
+      $render_cache_key = null;
     } else {
       $right = $changeset;
       $left = $vs_changeset;
@@ -64,6 +68,8 @@ class DifferentialChangesetViewController extends DifferentialController {
       $right_new = true;
       $left_source = $left->getID();
       $left_new = true;
+
+      $render_cache_key = null;
     }
 
     if ($left) {
@@ -130,6 +136,7 @@ class DifferentialChangesetViewController extends DifferentialController {
 
     $parser = new DifferentialChangesetParser();
     $parser->setChangeset($changeset);
+    $parser->setRenderCacheKey($render_cache_key);
     $parser->setRightSideCommentMapping($right_source, $right_new);
     $parser->setLeftSideCommentMapping($left_source, $left_new);
     $parser->setWhitespaceMode($request->getStr('whitespace'));

src/applications/differential/parser/changeset/DifferentialChangesetParser.php

@@ -42,6 +42,8 @@ class DifferentialChangesetParser {
   protected $oldChangesetID = null;
   protected $noHighlight;
 
+  protected $renderCacheKey = null;
+
   private $handles;
   private $user;
 
@@ -66,6 +68,28 @@ class DifferentialChangesetParser {
 
   }
 
+  /**
+   * Set a key for identifying this changeset in the render cache. If set, the
+   * parser will attempt to use the changeset render cache, which can improve
+   * performance for frequently-viewed changesets.
+   *
+   * By default, there is no render cache key and parsers do not use the cache.
+   * This is appropriate for rarely-viewed changesets.
+   *
+   * NOTE: Currently, this key must be a valid Differential Changeset ID.
+   *
+   * @param   string  Key for identifying this changeset in the render cache.
+   * @return  this
+   */
+  public function setRenderCacheKey($key) {
+    $this->renderCacheKey = $key;
+    return $this;
+  }
+
+  private function getRenderCacheKey() {
+    return $this->renderCacheKey;
+  }
+
   public function setChangeset($changeset) {
     $this->changeset = $changeset;
 
@@ -427,7 +451,8 @@ class DifferentialChangesetParser {
   }
 
   public function loadCache() {
-    if (!$this->changesetID) {
+    $render_cache_key = $this->getRenderCacheKey();
+    if (!$render_cache_key) {
       return false;
     }
 
@@ -439,7 +464,7 @@ class DifferentialChangesetParser {
       $conn_r,
       'SELECT * FROM %T WHERE id = %d',
       $changeset->getTableName().'_parse_cache',
-      $this->changesetID);
+      $render_cache_key);
 
     if (!$data) {
       return false;
@@ -488,7 +513,8 @@ class DifferentialChangesetParser {
   }
 
   public function saveCache() {
-    if (!$this->changesetID) {
+    $render_cache_key = $this->getRenderCacheKey();
+    if (!$render_cache_key) {
       return false;
     }
 
@@ -516,7 +542,7 @@ class DifferentialChangesetParser {
         'INSERT INTO %T (id, cache) VALUES (%d, %s)
           ON DUPLICATE KEY UPDATE cache = VALUES(cache)',
         $changeset->getTableName().'_parse_cache',
-        $this->changesetID,
+        $render_cache_key,
         $cache);
     } catch (AphrontQueryException $ex) {
       // TODO: uhoh
@@ -705,8 +731,6 @@ EOSYNTHETIC;
 
     $this->tryCacheStuff();
 
-    $changeset_id = $this->changesetID;
-
     $feedback_mask = array();
 
     switch ($this->changeset->getFileType()) {