help: handle NULL value for alias.* config

When showing all config with "git help --all", we print the list of
defined aliases. But our config callback to do so does not check for a
NULL value, meaning a config block like:

  [alias]
  foo

will cause us to segfault. We should detect and complain about this in
the usual way.

Since this command is purely informational (and we aren't trying to run
the alias), we could perhaps just generate a warning and continue. But
this sort of misconfiguration should be pretty rare, and the error
message we will produce points directly to the line of config that needs
to be fixed. So just generating the usual error should be OK.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/help.c b/help.c
index 6d2ebfbd2a45f134bc45c039cb4cf26b402b8f6c..2dbe57b413b2a8f2e8262fb2c022711aa2d60a2a 100644 (file)
--- a/help.c
+++ b/help.c
@@ -464,8 +464,11 @@ static int get_alias(const char *var, const char *value,
 {
        struct string_list *list = data;
 
-       if (skip_prefix(var, "alias.", &var))
+       if (skip_prefix(var, "alias.", &var)) {
+               if (!value)
+                       return config_error_nonbool(var);
                string_list_append(list, var)->util = xstrdup(value);
+       }
 
        return 0;
 }