From mboxrd@z Thu Jan  1 00:00:00 1970
From: Junio C Hamano <gitster@pobox.com>
Subject: Re: [PATCH] difftool: print list of valid tools with '--tool-help'
Date: Thu, 15 Mar 2012 16:18:00 -0700
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Cc: git@vger.kernel.org, David Aguilar <davvid@gmail.com>
To: Tim Henigan <tim.henigan@gmail.com>
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In-Reply-To: <1331850311-4620-1-git-send-email-tim.henigan@gmail.com> (Tim
 Henigan's message of "Thu, 15 Mar 2012 18:25:11 -0400")
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Tim Henigan <tim.henigan@gmail.com> writes:

> @@ -100,6 +101,15 @@ sub generate_command
>  		if ($arg eq '-h') {
>  			usage();
>  		}
> +		if ($arg eq '--tool-help') {
> +			my $gitpath = Git::exec_path();
> +			print "'git difftool --tool=<tool>' may be set to one of the following:\n";
> +			for (glob "$gitpath/mergetools/*") {
> +				next if /defaults$/;
> +				print "\t" . basename($_) . "\n";
> +			}

As this topic to show list of tools dynamically has plenty of time to be
in the mainline (it will be post 1.7.10), I would suggest a follow-up
series to this patch to do things like the following (just thinking
aloud):

 - define a new entry point to these mergetools/ scriptlets, let's call
   it "cando".  An entry for mergetools/kompare might look like this:

        cando () {
                type kompare >/dev/null && test -n "$DISPLAY"
        }

   that would yield true only when kompare is available and $DISPLAY is
   set.

 - instead of dumping everything in $gitpath/mergetools/*, check if each
   tool says it can be used in the user's environment.

        for (glob "$gitpath/mergetools/*") {
                next unless can_run($_);
                print ...
        }
        ...

   and "can_run" may look like this:

        sub can_run {
                my ($script) = @_;
             my $cmd = ". '$script' && cando";
             system('sh', '-c', $cmd) == 0;
        }

 - perhaps show the result in columnar layout.