Add notmuch_status_to_string function.

Be kind and let the user print error messages, not just error
codes.

database.cc

@@ -28,6 +28,26 @@
 
 using namespace std;
 
+const char *
+notmuch_status_to_string (notmuch_status_t status)
+{
+    switch (status) {
+    case NOTMUCH_STATUS_SUCCESS:
+	return "No error occurred";
+    case NOTMUCH_STATUS_XAPIAN_EXCEPTION:
+	return "A Xapian exception occurred";
+    case NOTMUCH_STATUS_FILE_NOT_EMAIL:
+	return "File is not an email";
+    case NOTMUCH_STATUS_NULL_POINTER:
+	return "Erroneous NULL pointer";
+    case NOTMUCH_STATUS_TAG_TOO_LONG:
+	return "Tag value is too long";
+    default:
+    case NOTMUCH_STATUS_LAST_STATUS:
+	return "Unknown error status value";
+    }
+}
+
 /* "128 bits of thread-id ought to be enough for anybody" */
 #define NOTMUCH_THREAD_ID_BITS	 128
 #define NOTMUCH_THREAD_ID_DIGITS (NOTMUCH_THREAD_ID_BITS / 4)

notmuch.c

@@ -527,8 +527,11 @@ restore_command (int argc, char *argv[])
 		    continue;
 		status = notmuch_message_add_tag (message, tag);
 		if (status) {
-		    fprintf (stderr, "Error applying tag %s to message %s.\n",
+		    fprintf (stderr,
+			     "Error applying tag %s to message %s:\n",
 			     tag, message_id);
+		    fprintf (stderr, "%s\n",
+			     notmuch_status_to_string (status));
 		}
 	    }
 

notmuch.h

@@ -49,6 +49,10 @@ typedef int notmuch_bool_t;
  *
  * NOTMUCH_STATUS_SUCCESS: No error occurred.
  *
+ * XXX: We don't really want to expose this lame XAPIAN_EXCEPTION
+ * value. Instead we should map to things like DATABASE_LOCKED or
+ * whatever.
+ *
  * NOTMUCH_STATUS_XAPIAN_EXCEPTION: A Xapian exception occurred
  *
  * NOTMUCH_STATUS_FILE_NOT_EMAIL: A file was presented that doesn't
@@ -72,6 +76,13 @@ typedef enum _notmuch_status {
     NOTMUCH_STATUS_LAST_STATUS
 } notmuch_status_t;
 
+/* Get a string representation of a notmuch_status_t value.
+ *
+ * The result is readonly.
+ */
+const char *
+notmuch_status_to_string (notmuch_status_t status);
+
 /* Various opaque data types. For each notmuch_<foo>_t see the various
  * notmuch_<foo> functions below. */
 typedef struct _notmuch_database notmuch_database_t;