Submodules: Don't parse .gitmodules when it contains, merge conflicts

Commands like "git status", "git diff" and "git fetch" would fail when the
.gitmodules file contained merge conflicts because the config parser would
call die() when hitting the conflict markers:

    "fatal: bad config file line <n> in <path>/.gitmodules"

While this behavior was on the safe side, it is really unhelpful to the
user to have commands like status and diff fail, as these are needed to
find out what's going on. And the error message is only mildly helpful,
as it points to the right file but doesn't mention that it is unmerged.
Users of git gui were not shown any conflicts at all when this happened.

Improve the situation by checking if the index records .gitmodules as
unmerged. When that is the case we can't make any assumptions about the
configuration to be found there after the merge conflict is resolved by
the user, so assume that all recursion is disabled unless .git/config or
the global config say otherwise.

As soon as the merge conflict is resolved and the .gitmodules file has
been staged subsequent commands again honor any configuration done there.

Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

submodule.c

@@ -14,6 +14,15 @@ static struct string_list config_fetch_recurse_submodules_for_name;
 static struct string_list config_ignore_for_name;
 static int config_fetch_recurse_submodules = RECURSE_SUBMODULES_ON_DEMAND;
 static struct string_list changed_submodule_paths;
+/*
+ * The following flag is set if the .gitmodules file is unmerged. We then
+ * disable recursion for all submodules where .git/config doesn't have a
+ * matching config entry because we can't guess what might be configured in
+ * .gitmodules unless the user resolves the conflict. When a command line
+ * option is given (which always overrides configuration) this flag will be
+ * ignored.
+ */
+static int gitmodules_is_unmerged;
 
 static int add_submodule_odb(const char *path)
 {
@@ -63,6 +72,8 @@ void set_diffopt_flags_from_submodule_config(struct diff_options *diffopt,
 		ignore_option = unsorted_string_list_lookup(&config_ignore_for_name, path_option->util);
 		if (ignore_option)
 			handle_ignore_submodules_arg(diffopt, ignore_option->util);
+		else if (gitmodules_is_unmerged)
+			DIFF_OPT_SET(diffopt, IGNORE_SUBMODULES);
 	}
 }
 
@@ -82,9 +93,24 @@ void gitmodules_config(void)
 	const char *work_tree = get_git_work_tree();
 	if (work_tree) {
 		struct strbuf gitmodules_path = STRBUF_INIT;
+		int pos;
 		strbuf_addstr(&gitmodules_path, work_tree);
 		strbuf_addstr(&gitmodules_path, "/.gitmodules");
-		git_config_from_file(submodule_config, gitmodules_path.buf, NULL);
+		if (read_cache() < 0)
+			die("index file corrupt");
+		pos = cache_name_pos(".gitmodules", 11);
+		if (pos < 0) { /* .gitmodules not found or isn't merged */
+			pos = -1 - pos;
+			if (active_nr > pos) {  /* there is a .gitmodules */
+				const struct cache_entry *ce = active_cache[pos];
+				if (ce_namelen(ce) == 11 &&
+				    !memcmp(ce->name, ".gitmodules", 11))
+					gitmodules_is_unmerged = 1;
+			}
+		}
+
+		if (!gitmodules_is_unmerged)
+			git_config_from_file(submodule_config, gitmodules_path.buf, NULL);
 		strbuf_release(&gitmodules_path);
 	}
 }
@@ -434,7 +460,8 @@ int fetch_populated_submodules(int num_options, const char **options,
 					default_argv = "on-demand";
 				}
 			} else {
-				if (config_fetch_recurse_submodules == RECURSE_SUBMODULES_OFF)
+				if ((config_fetch_recurse_submodules == RECURSE_SUBMODULES_OFF) ||
+				    gitmodules_is_unmerged)
 					continue;
 				if (config_fetch_recurse_submodules == RECURSE_SUBMODULES_ON_DEMAND) {
 					if (!unsorted_string_list_lookup(&changed_submodule_paths, ce->name))

t/t7506-status-submodule.sh

@@ -196,7 +196,7 @@ AA .gitmodules
 A  sub1
 EOF
 
-test_expect_failure 'status with merge conflict in .gitmodules' '
+test_expect_success 'status with merge conflict in .gitmodules' '
 	git clone . super &&
 	test_create_repo_with_commit sub1 &&
 	test_tick &&
@@ -255,15 +255,15 @@ index badaa4c,44f999a..0000000
 ++>>>>>>> add_sub1
 EOF
 
-test_expect_failure 'diff with merge conflict in .gitmodules' '
+test_expect_success 'diff with merge conflict in .gitmodules' '
 	(
 		cd super &&
 		git diff >../diff_actual 2>&1
 	) &&
 	test_cmp diff_actual diff_expect
 '
 
-test_expect_failure 'diff --submodule with merge conflict in .gitmodules' '
+test_expect_success 'diff --submodule with merge conflict in .gitmodules' '
 	(
 		cd super &&
 		git diff --submodule >../diff_submodule_actual 2>&1