Add a RefPosition table to hold branch/tag positions once the RefCursor table is split

Summary:
Ref T11823. Currently, we have a "RefCursor" table which stores rows like `<branch or tag name, commit it is pointing at>` with some more data.

Because Mercurial can have a single branch pointing at several different places, this table must allow multiple rows with the same branch or tag name.

Among other things, this means there isn't a single PHID which can be used to identify a branch name in a stable way. However, we have several UIs where we want to be able to do this.

Some specific examples where we run into trouble: in Mercurial, if there are 5 heads for "default", that means there are 5 phids. And currently, if someone deletes a branch, we lose the PHID for it. Instead, we'd rather retain it so the whole world doesn't break if you accidentally delete a branch and then fix it a little later.

(I'll likely hold this until the rest of the logic is fleshed out a little more in followup changes.)

Test Plan: Ran `bin/storage upgrade`, saw the table get created without warnings.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T11823

Differential Revision: https://secure.phabricator.com/D18602

resources/sql/autopatches/20170914.ref.01.position.sql

@@ -0,0 +1,6 @@
+CREATE TABLE {$NAMESPACE}_repository.repository_refposition (
+  id INT UNSIGNED NOT NULL AUTO_INCREMENT PRIMARY KEY,
+  cursorID INT UNSIGNED NOT NULL,
+  commitIdentifier VARCHAR(40) NOT NULL COLLATE {$COLLATE_TEXT},
+  isClosed BOOL NOT NULL
+) ENGINE=InnoDB, COLLATE {$COLLATE_TEXT};

src/__phutil_library_map__.php

@@ -3863,6 +3863,7 @@ phutil_register_library_map(array(
     'PhabricatorRepositoryRefCursorPHIDType' => 'applications/repository/phid/PhabricatorRepositoryRefCursorPHIDType.php',
     'PhabricatorRepositoryRefCursorQuery' => 'applications/repository/query/PhabricatorRepositoryRefCursorQuery.php',
     'PhabricatorRepositoryRefEngine' => 'applications/repository/engine/PhabricatorRepositoryRefEngine.php',
+    'PhabricatorRepositoryRefPosition' => 'applications/repository/storage/PhabricatorRepositoryRefPosition.php',
     'PhabricatorRepositoryRepositoryPHIDType' => 'applications/repository/phid/PhabricatorRepositoryRepositoryPHIDType.php',
     'PhabricatorRepositorySchemaSpec' => 'applications/repository/storage/PhabricatorRepositorySchemaSpec.php',
     'PhabricatorRepositorySearchEngine' => 'applications/repository/query/PhabricatorRepositorySearchEngine.php',
@@ -9434,6 +9435,7 @@ phutil_register_library_map(array(
     'PhabricatorRepositoryRefCursorPHIDType' => 'PhabricatorPHIDType',
     'PhabricatorRepositoryRefCursorQuery' => 'PhabricatorCursorPagedPolicyAwareQuery',
     'PhabricatorRepositoryRefEngine' => 'PhabricatorRepositoryEngine',
+    'PhabricatorRepositoryRefPosition' => 'PhabricatorRepositoryDAO',
     'PhabricatorRepositoryRepositoryPHIDType' => 'PhabricatorPHIDType',
     'PhabricatorRepositorySchemaSpec' => 'PhabricatorConfigSchemaSpec',
     'PhabricatorRepositorySearchEngine' => 'PhabricatorApplicationSearchEngine',

src/applications/repository/storage/PhabricatorRepositoryRefPosition.php

@@ -0,0 +1,26 @@
+<?php
+
+final class PhabricatorRepositoryRefPosition
+  extends PhabricatorRepositoryDAO {
+
+  protected $cursorID;
+  protected $commitIdentifier;
+  protected $isClosed = 0;
+
+  protected function getConfiguration() {
+    return array(
+      self::CONFIG_TIMESTAMPS => false,
+      self::CONFIG_COLUMN_SCHEMA => array(
+        'commitIdentifier' => 'text40',
+        'isClosed' => 'bool',
+      ),
+      self::CONFIG_KEY_SCHEMA => array(
+        'key_position' => array(
+          'columns' => array('cursorID', 'commitIdentifier'),
+          'unique' => true,
+        ),
+      ),
+    ) + parent::getConfiguration();
+  }
+
+}