lib: replace use of static_cast for writable databases

static_cast is a bit tricky to understand and error prone, so add a
second pointer to (potentially the same) Xapian database object that
we know has the right subclass.

lib/add-message.cc

@@ -43,15 +43,12 @@ _notmuch_database_generate_thread_id (notmuch_database_t *notmuch)
     /* 16 bytes (+ terminator) for hexadecimal representation of
      * a 64-bit integer. */
     static char thread_id[17];
-    Xapian::WritableDatabase *db;
-
-    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
 
     notmuch->last_thread_id++;
 
     sprintf (thread_id, "%016" PRIx64, notmuch->last_thread_id);
 
-    db->set_metadata ("last_thread_id", thread_id);
+    notmuch->writable_xapian_db->set_metadata ("last_thread_id", thread_id);
 
     return thread_id;
 }
@@ -161,7 +158,7 @@ _resolve_message_id_to_thread_id_old (notmuch_database_t *notmuch,
      * can return the thread ID stored in the metadata. Otherwise, we
      * generate a new thread ID and store it there.
      */
-    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
+    db = notmuch->writable_xapian_db;
     metadata_key = _get_metadata_thread_id_key (ctx, message_id);
     thread_id_string = notmuch->xapian_db->get_metadata (metadata_key);
 
@@ -370,13 +367,9 @@ _consume_metadata_thread_id (void *ctx, notmuch_database_t *notmuch,
     if (stored_id.empty ()) {
 	return NULL;
     } else {
-	Xapian::WritableDatabase *db;
-
-	db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
-
 	/* Clear the metadata for this message ID. We don't need it
 	 * anymore. */
-	db->set_metadata (metadata_key, "");
+	notmuch->writable_xapian_db->set_metadata (metadata_key, "");
 
 	return talloc_strdup (ctx, stored_id.c_str ());
     }

lib/config.cc

@@ -45,15 +45,13 @@ notmuch_database_set_config (notmuch_database_t *notmuch,
 			     const char *value)
 {
     notmuch_status_t status;
-    Xapian::WritableDatabase *db;
 
     status = _notmuch_database_ensure_writable (notmuch);
     if (status)
 	return status;
 
     try {
-	db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
-	db->set_metadata (CONFIG_PREFIX + key, value);
+	notmuch->writable_xapian_db->set_metadata (CONFIG_PREFIX + key, value);
     } catch (const Xapian::Error &error) {
 	status = NOTMUCH_STATUS_XAPIAN_EXCEPTION;
 	notmuch->exception_reported = true;

lib/database-private.h

@@ -189,11 +189,11 @@ struct _notmuch_database {
 
     char *path;
 
-    notmuch_database_mode_t mode;
     int atomic_nesting;
     /* true if changes have been made in this atomic section */
     bool atomic_dirty;
     Xapian::Database *xapian_db;
+    Xapian::WritableDatabase *writable_xapian_db;
     bool open;
     /* Bit mask of features used by this database.  This is a
      * bitwise-OR of NOTMUCH_FEATURE_* values (above). */

lib/database.cc

@@ -72,7 +72,10 @@ _log_xapian_exception (const char *where, notmuch_database_t *notmuch,  const Xa
 notmuch_database_mode_t
 _notmuch_database_mode (notmuch_database_t *notmuch)
 {
-    return notmuch->mode;
+    if (notmuch->writable_xapian_db)
+	return NOTMUCH_DATABASE_MODE_READ_WRITE;
+    else
+	return NOTMUCH_DATABASE_MODE_READ_ONLY;
 }
 
 /* Here's the current schema for our database (for NOTMUCH_DATABASE_VERSION):
@@ -976,7 +979,7 @@ notmuch_database_open_verbose (const char *path,
 
     strip_trailing (notmuch->path, '/');
 
-    notmuch->mode = mode;
+    notmuch->writable_xapian_db = NULL;
     notmuch->atomic_nesting = 0;
     notmuch->view = 1;
     try {
@@ -984,8 +987,9 @@ notmuch_database_open_verbose (const char *path,
 	string last_mod;
 
 	if (mode == NOTMUCH_DATABASE_MODE_READ_WRITE) {
-	    notmuch->xapian_db = new Xapian::WritableDatabase (xapian_path,
-							       DB_ACTION);
+	    notmuch->writable_xapian_db = new Xapian::WritableDatabase (xapian_path,
+									DB_ACTION);
+	    notmuch->xapian_db = notmuch->writable_xapian_db;
 	} else {
 	    notmuch->xapian_db = new Xapian::Database (xapian_path);
 	}
@@ -1115,8 +1119,7 @@ notmuch_database_close (notmuch_database_t *notmuch)
 	     * cancel any outstanding transaction before closing. */
 	    if (_notmuch_database_mode (notmuch) == NOTMUCH_DATABASE_MODE_READ_WRITE &&
 		notmuch->atomic_nesting)
-		(static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db))
-		->cancel_transaction ();
+		notmuch->writable_xapian_db->cancel_transaction ();
 
 	    /* Close the database.  This implicitly flushes
 	     * outstanding changes. */
@@ -1454,7 +1457,7 @@ notmuch_database_upgrade (notmuch_database_t *notmuch,
     if (status)
 	return status;
 
-    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
+    db = notmuch->writable_xapian_db;
 
     target_features = notmuch->features | NOTMUCH_FEATURES_CURRENT;
     new_features = NOTMUCH_FEATURES_CURRENT & ~notmuch->features;
@@ -1711,7 +1714,7 @@ notmuch_database_begin_atomic (notmuch_database_t *notmuch)
 	return NOTMUCH_STATUS_UPGRADE_REQUIRED;
 
     try {
-	(static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db))->begin_transaction (false);
+	notmuch->writable_xapian_db->begin_transaction (false);
     } catch (const Xapian::Error &error) {
 	_notmuch_database_log (notmuch, "A Xapian exception occurred beginning transaction: %s.\n",
 			       error.get_msg ().c_str ());
@@ -1736,7 +1739,7 @@ notmuch_database_end_atomic (notmuch_database_t *notmuch)
 	notmuch->atomic_nesting > 1)
 	goto DONE;
 
-    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
+    db = notmuch->writable_xapian_db;
     try {
 	db->commit_transaction ();
 

lib/directory.cc

@@ -99,7 +99,6 @@ _notmuch_directory_find_or_create (notmuch_database_t *notmuch,
 				   notmuch_find_flags_t flags,
 				   notmuch_status_t *status_ret)
 {
-    Xapian::WritableDatabase *db;
     notmuch_directory_t *directory;
     notmuch_private_status_t private_status;
     const char *db_path;
@@ -176,10 +175,10 @@ _notmuch_directory_find_or_create (notmuch_database_t *notmuch,
 	    directory->doc.add_value (NOTMUCH_VALUE_TIMESTAMP,
 				      Xapian::sortable_serialise (0));
 
-	    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
-
 	    directory->document_id = _notmuch_database_generate_doc_id (notmuch);
-	    db->replace_document (directory->document_id, directory->doc);
+	    directory->notmuch->
+		writable_xapian_db
+		-> replace_document (directory->document_id, directory->doc);
 	    talloc_free (local);
 	}
 
@@ -213,20 +212,18 @@ notmuch_directory_set_mtime (notmuch_directory_t *directory,
 			     time_t mtime)
 {
     notmuch_database_t *notmuch = directory->notmuch;
-    Xapian::WritableDatabase *db;
     notmuch_status_t status;
 
     status = _notmuch_database_ensure_writable (notmuch);
     if (status)
 	return status;
 
-    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
-
     try {
 	directory->doc.add_value (NOTMUCH_VALUE_TIMESTAMP,
 				  Xapian::sortable_serialise (mtime));
 
-	db->replace_document (directory->document_id, directory->doc);
+	directory->notmuch
+	    ->writable_xapian_db->replace_document (directory->document_id, directory->doc);
 
 	directory->mtime = mtime;
 
@@ -288,15 +285,14 @@ notmuch_status_t
 notmuch_directory_delete (notmuch_directory_t *directory)
 {
     notmuch_status_t status;
-    Xapian::WritableDatabase *db;
 
     status = _notmuch_database_ensure_writable (directory->notmuch);
     if (status)
 	return status;
 
     try {
-	db = static_cast <Xapian::WritableDatabase *> (directory->notmuch->xapian_db);
-	db->delete_document (directory->document_id);
+	directory->notmuch->
+	    writable_xapian_db->delete_document (directory->document_id);
     } catch (const Xapian::Error &error) {
 	_notmuch_database_log (directory->notmuch,
 			       "A Xapian exception occurred deleting directory entry: %s.\n",

lib/message.cc

@@ -1322,8 +1322,6 @@ _notmuch_message_upgrade_last_mod (notmuch_message_t *message)
 void
 _notmuch_message_sync (notmuch_message_t *message)
 {
-    Xapian::WritableDatabase *db;
-
     if (_notmuch_database_mode (message->notmuch) == NOTMUCH_DATABASE_MODE_READ_ONLY)
 	return;
 
@@ -1342,8 +1340,8 @@ _notmuch_message_sync (notmuch_message_t *message)
 				    _notmuch_database_new_revision (
 					message->notmuch)));
 
-    db = static_cast <Xapian::WritableDatabase *> (message->notmuch->xapian_db);
-    db->replace_document (message->doc_id, message->doc);
+    message->notmuch->writable_xapian_db->
+	replace_document (message->doc_id, message->doc);
     message->modified = false;
 }
 
@@ -1353,7 +1351,6 @@ notmuch_status_t
 _notmuch_message_delete (notmuch_message_t *message)
 {
     notmuch_status_t status;
-    Xapian::WritableDatabase *db;
     const char *mid, *tid, *query_string;
     notmuch_message_t *ghost;
     notmuch_private_status_t private_status;
@@ -1370,8 +1367,7 @@ _notmuch_message_delete (notmuch_message_t *message)
     if (status)
 	return status;
 
-    db = static_cast <Xapian::WritableDatabase *> (notmuch->xapian_db);
-    db->delete_document (message->doc_id);
+    message->notmuch->writable_xapian_db->delete_document (message->doc_id);
 
     /* if this was a ghost to begin with, we are done */
     private_status = _notmuch_message_has_term (message, "type", "ghost", &is_ghost);