#87474 by webernet. Move the log message field from book to node module.

modules/book/book.module

@@ -232,13 +232,6 @@ function book_form(&$node) {
   );
   $form['body_filter']['format'] = filter_form($node->format);
 
-  $form['log'] = array(
-    '#type' => 'textarea',
-    '#title' => t('Log message'),
-    '#weight' => 5,
-    '#description' => t('An explanation of the additions or updates being made to help other authors understand your motivations.'),
-  );
-
   if (user_access('administer nodes')) {
     $form['weight'] = array('#type' => 'weight',
       '#title' => t('Weight'),

modules/node/node.module

@@ -571,12 +571,18 @@ function node_save(&$node) {
   // Split off revisions data to another structure
   $revisions_table_values = array('nid' => $node->nid, 'vid' => $node->vid,
                      'title' => $node->title, 'body' => $node->body,
-                     'teaser' => $node->teaser, 'log' => $node->log, 'timestamp' => $node->changed,
+                     'teaser' => $node->teaser, 'timestamp' => $node->changed,
                      'uid' => $user->uid, 'format' => $node->format);
   $revisions_table_types = array('nid' => '%d', 'vid' => '%d',
                      'title' => "'%s'", 'body' => "'%s'",
-                     'teaser' => "'%s'", 'log' => "'%s'", 'timestamp' => '%d',
+                     'teaser' => "'%s'", 'timestamp' => '%d',
                      'uid' => '%d', 'format' => '%d');
+  if (!empty($node->log)) {
+    // Only store the log message if there's something to store; this prevents existing
+    // log messages from being unintentionally overwritten by a blank message.
+    $revisions_table_values['log'] = $node->log;
+    $revisions_table_types['log'] = "'%s'";
+  }
   $node_table_values = array('nid' => $node->nid, 'vid' => $node->vid,
                     'title' => $node->title, 'type' => $node->type, 'uid' => $node->uid,
                     'status' => $node->status, 'created' => $node->created,
@@ -1955,6 +1961,18 @@ function node_form($node, $form_values = NULL) {
   }
   $form['#node'] = $node;
 
+  // Add a log field if the "Create new revisions" option is checked, or if the
+  // current user has the ability to check that option.
+  if ($node->revision || user_access('administer nodes')) {
+    $form['log'] = array(
+      '#type' => 'textarea',
+      '#title' => t('Log message'),
+      '#rows' => 2,
+      '#weight' => 20,
+      '#description' => t('An explanation of the additions or updates being made to help other authors understand your motivations.'),
+    );
+  }
+
   // Node author information for administrators
   $form['author'] = array(
     '#type' => 'fieldset',