[PATCH 3/3] builtin/describe: introduce --submodule-error-as-dirty flag

[Stefan Beller <sbeller@google.com>]

git-describe tells you the version number you're at, or errors out, e.g.
when you run it outside of a repository, which may happen when downloading
a tar ball instead of using git to obtain the source code.

To keep this property of only erroring out, when not in a repository,
severe submodule errors must be downgraded to reporting them gently
instead of having git-describe error out completely.

This patch helps to fix the root cause in [1], which tries to work around
this situation.

[1] ("Work around git describe bug for build.")
https://gerrit-review.googlesource.com/#/c/99851/

Signed-off-by: Stefan Beller <sbeller@google.com>
---
 builtin/describe.c  | 17 ++++++++++-------
 t/t6120-describe.sh | 17 +++++++++++++++++
 2 files changed, 27 insertions(+), 7 deletions(-)

diff --git a/builtin/describe.c b/builtin/describe.c
index 76c18059bf..569fef9ecf 100644
--- a/builtin/describe.c
+++ b/builtin/describe.c
@@ -31,13 +31,9 @@ static int have_util;
 static struct string_list patterns = STRING_LIST_INIT_NODUP;
 static struct string_list exclude_patterns = STRING_LIST_INIT_NODUP;
 static int always;
+static int gentle_submodule_errors;
 static const char *dirty;
 
-/* diff-index command arguments to check if working tree is dirty. */
-static const char *diff_index_args[] = {
-	"diff-index", "--quiet", "HEAD", "--", NULL
-};
-
 struct commit_name {
 	struct hashmap_entry entry;
 	struct object_id peeled;
@@ -442,6 +438,8 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 			   N_("do not consider tags matching <pattern>")),
 		OPT_BOOL(0, "always",        &always,
 			N_("show abbreviated commit object as fallback")),
+		OPT_BOOL(0, "submodule-error-as-dirty", &gentle_submodule_errors,
+			N_("show abbreviated commit object as fallback")),
 		{OPTION_STRING, 0, "dirty",  &dirty, N_("mark"),
 			N_("append <mark> on dirty working tree (default: \"-dirty\")"),
 			PARSE_OPT_OPTARG, NULL, (intptr_t) "-dirty"},
@@ -496,6 +494,12 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 		if (dirty) {
 			static struct lock_file index_lock;
 			int fd;
+			struct argv_array args = ARGV_ARRAY_INIT;
+
+			argv_array_push(&args, "diff-index");
+			if (gentle_submodule_errors)
+				argv_array_push(&args, "--gentle-submodule-errors");
+			argv_array_pushl(&args, "--quiet", "HEAD", "--", NULL);
 
 			read_cache_preload(NULL);
 			refresh_index(&the_index, REFRESH_QUIET|REFRESH_UNMERGED,
@@ -504,8 +508,7 @@ int cmd_describe(int argc, const char **argv, const char *prefix)
 			if (0 <= fd)
 				update_index_if_able(&the_index, &index_lock);
 
-			if (!cmd_diff_index(ARRAY_SIZE(diff_index_args) - 1,
-					    diff_index_args, prefix))
+			if (!cmd_diff_index(args.argc, args.argv, prefix))
 				dirty = NULL;
 		}
 		describe("HEAD", 1);
diff --git a/t/t6120-describe.sh b/t/t6120-describe.sh
index 167491fd5b..99e5ba44b7 100755
--- a/t/t6120-describe.sh
+++ b/t/t6120-describe.sh
@@ -233,4 +233,21 @@ test_expect_success 'describe --contains and --no-match' '
 	test_cmp expect actual
 '
 
+test_expect_success 'setup and absorb a submodule' '
+	test_create_repo sub1 &&
+	test_commit -C sub1 initial &&
+	git submodule add ./sub1 &&
+	git submodule absorbgitdirs &&
+	git commit -a -m "add submodule"
+'
+
+test_expect_success 'describe chokes on severly broken submodules' '
+	mv .git/modules/sub1/ .git/modules/sub_moved &&
+	test_must_fail git describe --dirty
+'
+test_expect_success 'describe ignoring a borken submodule' '
+	git describe --dirty --submodule-error-as-dirty >out &&
+	grep dirty out
+'
+
 test_done
-- 
2.12.0.402.g4b3201c2d6.dirty