Re: [PATCH] difftool: print list of valid tools with '--tool-help'

On Thu, Mar 15, 2012 at 7:18 PM, Junio C Hamano [off-list ref] wrote:

Tim Henigan [off-list ref] writes:

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.

I experimented with this a bit and came up with the following idea
(not protected for GMail whitespace mangling):

# The following is to be added to 'git-difftool.perl'
sub print_tool_help
{
	my ($cmd, @found, @notfound);
	my $gitpath = Git::exec_path();

	for (glob "$gitpath/mergetools/*") {
		my $tool = basename($_);
		next if ($tool eq "defaults");

		$cmd  = '. "$(git --exec-path)/git-mergetool--lib"';
		$cmd .= " && get_merge_tool_path $tool >/dev/null 2>&1";
		if (system('sh', '-c', $cmd) == 0) {
			push(@found, $tool);
		} else {
			push(@notfound, $tool);
		}
	}

	print "'git difftool --tool=<tool>' may be set to one of the following:\n";
	print "\t$_\n" for (@found);

	print "\nThe following are valid tools, but not currently installed:\n";
	print "\t$_\n" for (@notfound);

	exit(0);
}

Rather than create a new entry point, I used the existing
'get_merge_tool_path' that resides in 'git-mergetool--lib' to
determine if a given tool is actually installed on the system.

The '$DISPLAY' variable is lost in this implementation, but honestly I
don't understand how it was intended to be used.

Does this look useful?