lib: cache user prefixes in database object

This will be used to avoid needing a database access to resolve a db
prefix from the corresponding UI prefix (e.g. when indexing). Arguably
the setup of the separate header map does not belong here, since it is
about indexing rather than querying, but we currently don't have any
other indexing setup to do.

lib/database-private.h

@@ -221,6 +221,11 @@ struct _notmuch_database {
     Xapian::ValueRangeProcessor *value_range_processor;
     Xapian::ValueRangeProcessor *date_range_processor;
     Xapian::ValueRangeProcessor *last_mod_range_processor;
+
+    /* XXX it's slightly gross to use two parallel string->string maps
+     * here, but at least they are small */
+    notmuch_string_map_t *user_prefix;
+    notmuch_string_map_t *user_header;
 };
 
 /* Prior to database version 3, features were implied by the database

lib/database.cc

@@ -334,6 +334,14 @@ _setup_user_query_fields (notmuch_database_t *notmuch)
     notmuch_config_list_t *list;
     notmuch_status_t status;
 
+    notmuch->user_prefix = _notmuch_string_map_create (notmuch);
+    if (notmuch->user_prefix == NULL)
+	return NOTMUCH_STATUS_OUT_OF_MEMORY;
+
+    notmuch->user_header = _notmuch_string_map_create (notmuch);
+    if (notmuch->user_header == NULL)
+	return NOTMUCH_STATUS_OUT_OF_MEMORY;
+
     status = notmuch_database_get_config_list (notmuch, CONFIG_HEADER_PREFIX, &list);
     if (status)
 	return status;
@@ -345,6 +353,14 @@ _setup_user_query_fields (notmuch_database_t *notmuch)
 	const char *key = notmuch_config_list_key (list)
 	    + sizeof (CONFIG_HEADER_PREFIX) - 1;
 
+	_notmuch_string_map_append (notmuch->user_prefix,
+				    key,
+				    _user_prefix (notmuch, key));
+
+	_notmuch_string_map_append (notmuch->user_header,
+				    key,
+				    notmuch_config_list_value (list));
+
 	query_field.name = talloc_strdup (notmuch, key);
 	query_field.prefix = _user_prefix (notmuch, key);
 	query_field.flags = NOTMUCH_FIELD_PROBABILISTIC

lib/notmuch-private.h

@@ -678,6 +678,8 @@ struct _notmuch_indexopts {
 
 #define CONFIG_HEADER_PREFIX "index.header."
 
+#define EMPTY_STRING(s) ((s)[0] == '\0')
+
 NOTMUCH_END_DECLS
 
 #ifdef __cplusplus

lib/thread.cc

@@ -30,8 +30,6 @@
 #define THREAD_DEBUG(format, ...) do {} while (0) /* ignored */
 #endif
 
-#define EMPTY_STRING(s) ((s)[0] == '\0')
-
 struct _notmuch_thread {
     notmuch_database_t *notmuch;
     char *thread_id;