--- /dev/null	2005-11-20 21:22:37.000000000 -0600
+++ compat/category_compat_forum.info	2007-02-08 10:32:23.000000000 -0600
@@ -0,0 +1,5 @@
+; $Id$
+name = Category compatibility: Forum
+description = Compatibility routines to improve compatibility with the Forum module.
+package = Category
+dependencies = category forum
--- /dev/null	2005-11-20 21:22:37.000000000 -0600
+++ compat/category_compat_forum.module	2007-02-08 11:34:17.000000000 -0600
@@ -0,0 +1,62 @@
+<?php
+// $Id$
+
+/**
+ * @file
+ * Compatibility routines for forum.module.
+ */
+
+/**
+ * Implementation of hook_nodeapi().
+ */
+function category_compat_forum_nodeapi(&$node, $op, $teaser = NULL, $page = NULL) {
+  if ($node->type == 'forum') {
+    switch ($op) {
+      case 'validate':
+        if ($node->category) {
+          // Since forum can't directly file errors anymore, it's our job.
+          $container = variable_get('forum_nav_vocabulary', '');
+          $cats = variable_get('forum_containers', array()); // Ironically, forum compensates for taxonomy's limitations.
+          foreach ($node->category as $cat) {
+            $cat = category_get_category($cat);
+            if ($cat->cnid == $container) {
+              if (in_array($cat->cid, $cats)) {
+                form_set_error('category', t('The item %forum is only a container for forums. Please select one of the forums below it.', array('%forum' => $cat->title)));
+              }
+            }
+          }
+        }
+        break;
+      case 'prepare':
+        if (!$node->nid) {
+          // New topic. Attempt to grab our cid.
+          if (is_numeric(arg(3))) {
+            // These will be picked up during render.
+            $node->category[arg(3)]->cnid = _forum_get_vid();
+            $node->category[arg(3)]->cid = arg(3);
+          }
+        }
+        break;
+    }
+  }
+}
+
+/**
+ * Implementation of hook_link_alter().
+ * Links to forum categories need to point to forum/
+ * to ensure proper display.
+ */
+function category_compat_forum_link_alter(&$node, &$links) {
+  if ($node->type == 'forum') {
+    foreach ($links as $module => $link) {
+      if (strpos($module, 'category_cat_')===0) {
+        // Link back to the forum page.
+        $cat = str_replace('node/', '', $link['href']);
+        $cat = category_get_category($cat);
+        if ($cat->cnid == _forum_get_vid()) {
+          $links[$module]['href'] = str_replace('node', 'forum', $link['href']);
+        }
+      }
+    }
+  }
+}