lib: support user prefix names in term generation

This should not change the indexing process yet as nothing calls
_notmuch_message_gen_terms with a user prefix name. On the other hand,
it should not break anything either.

_notmuch_database_prefix does a linear walk of the list of (built-in)
prefixes, followed by a logarithmic time search of the list of user
prefixes. The latter is probably not really noticable.

lib/database.cc

@@ -422,6 +422,26 @@ _find_prefix (const char *name)
     return "";
 }
 
+/* Like find prefix, but include the possibility of user defined
+ * prefixes specific to this database */
+
+const char *
+_notmuch_database_prefix (notmuch_database_t *notmuch, const char *name)
+{
+    unsigned int i;
+
+    /*XXX TODO: reduce code duplication */
+    for (i = 0; i < ARRAY_SIZE (prefix_table); i++) {
+	if (strcmp (name, prefix_table[i].name) == 0)
+	    return prefix_table[i].prefix;
+    }
+
+    if (notmuch->user_prefix)
+	return _notmuch_string_map_get (notmuch->user_prefix, name);
+
+    return NULL;
+}
+
 static const struct {
     /* NOTMUCH_FEATURE_* value. */
     _notmuch_features value;

lib/message.cc

@@ -1446,8 +1446,12 @@ _notmuch_message_gen_terms (notmuch_message_t *message,
     term_gen->set_termpos (message->termpos);
 
     if (prefix_name) {
+	const char *prefix = _notmuch_database_prefix (message->notmuch, prefix_name);
+	if (prefix == NULL)
+	    return NOTMUCH_PRIVATE_STATUS_BAD_PREFIX;
+
 	_notmuch_message_invalidate_metadata (message, prefix_name);
-	term_gen->index_text (text, 1, _find_prefix (prefix_name));
+	term_gen->index_text (text, 1, prefix);
     } else {
 	term_gen->index_text (text);
     }

lib/notmuch-private.h

@@ -136,6 +136,7 @@ typedef enum _notmuch_private_status {
     /* Then add our own private values. */
     NOTMUCH_PRIVATE_STATUS_TERM_TOO_LONG = NOTMUCH_STATUS_LAST_STATUS,
     NOTMUCH_PRIVATE_STATUS_NO_DOCUMENT_FOUND,
+    NOTMUCH_PRIVATE_STATUS_BAD_PREFIX,
 
     NOTMUCH_PRIVATE_STATUS_LAST_STATUS
 } notmuch_private_status_t;
@@ -181,6 +182,11 @@ typedef struct _notmuch_doc_id_set notmuch_doc_id_set_t;
 const char *
 _find_prefix (const char *name);
 
+/* Lookup a prefix value by name, including possibly user defined prefixes
+ */
+const char *
+_notmuch_database_prefix (notmuch_database_t  *notmuch, const char *name);
+
 char *
 _notmuch_message_id_compressed (void *ctx, const char *message_id);