Re: `git describe --dirty` doesn't consider untracked files to be dirty

Junio C Hamano [off-list ref] writes:

The first step would be to allow those who want their "git describe
--dirty --ignore=none" (untracked files are counted as dirtiness, to
be consistent with how "git diff" sees submodule directories by
default) to use presence of untracked files as dirty.  This is a
safe first step and can be done without breaking any existing users.

It is worse than I thought.  There is zero-th step we need to have,
to fix "git describe --dirty" itself.

Because the command internally uses "diff-index", and by default it
considers that a submodule with untracked path *is* dirty.  Because
of that, you get an inexplicable inconsistent behaviour.

 * If you start from a pristine checkout, and then add an untracked
   path to the current project, "git describe --dirty" won't give
   the -dirty suffix.

 * But if you add an untracked path in its submodule, the command
   does give you the -dirty suffix.

A fix, without the first-step to give the command configurable
definition of what makes a repository 'dirty', would probably look
like the attached untested patch.  A fix to "diff" machinery to make
"--ignore-submodules=untracked" the default would also make "describe"
internally consistent, too.

 builtin/describe.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/builtin/describe.c b/builtin/describe.c
index 7668591d57..af08d7d8cf 100644
--- a/builtin/describe.c
+++ b/builtin/describe.c

@@ -45,7 +45,7 @@ static struct commit_names commit_names;
 
 /* diff-index command arguments to check if working tree is dirty. */
 static const char *diff_index_args[] = {
-	"diff-index", "--quiet", "HEAD", "--", NULL
+	"diff-index", "--quiet", "--ignore-submodules=untracked", "HEAD", "--", NULL
 };
 
 struct commit_name {