Re: [PATCH] make config --add behave correctly for empty and NULL values

Tanay Abhra <tanayabh@gmail.com> writes:

Thanks; this is a good find.

This is a tangent, but people please stop starting their sentence with a somewhat irritating "Currently"; it does not help both current and future readers very much without some mention of version numbers.

I suspect this bug dates back to pretty much day one of "git config" (dates at least back to 1.5.3).

Yuck, but we cannot pass NULL or some other special value that look more meaningful to signal the fact that we do not want to match anything, so this seems to be the easiest way out.

Are we sure that "a^", which cannot be true for any string, will not be caught by anybody's regcomp() as an error? I know regcomp() accepts the expression and regexec() fails to match with GNU libc, but that is not the whole of the world.

At least, please make it clear for those who read this code later what is going on with this magic "a^", perhaps with

	#define REGEXP_THAT_NEVER_MATCHES "a^"
	...
        return git_config_set_multivar_in_file(given_config_source.file,
                                              argv[0], value,
                                              REGEXP_THAT_NEVER_MATCHES, 0);
and/or with in-code comment.

	/*
         * set_multivar_in_file() removes existing values that match
         * the value_regexp argument and then adds this new value;
         * pass a pattern that never matches anything, as we do not
         * want to remove any existing value.
         */
	return git_config_set_multivar_in_file(given_config_source.file,
                                              argv[0], value,
                                              REGEXP_THAT_NEVER_MATCHES, 0);

To be honest, I'd rather see this done "right", by giving an option to the caller to tell the function not to call regcomp/regexec in matches().

 * Define a global exported via cache.h and defined in config.c

	extern const char CONFIG_SET_MULTIVAR_NO_REPLACE[];

   and pass it from this calling site, instead of an arbitrary
   literal string e.g. "a^"

 * Add a bit to the "store" struct, e.g. "unsigned value_never_matches:1";

 * In git_config_set_multivar_in_file() implementation, check for
   this constant address and set store.value_never_matches to true;

 * in matches(), check this bit and always return "No, this existing
   value do not match" when it is set.

or something like that.

The fact that you do a check is important, but it equally if not more important what you do with the result. "Check for a NULL and consider it as not matching" is probably what you meant, but I'd like to double check.