Merge branch 'dk/format-patch-ignore-diff-submodule' into maint

Setting diff.submodule to 'log' made "git format-patch" produce
broken patches.

* dk/format-patch-ignore-diff-submodule:
  format-patch: ignore diff.submodule setting
  t4255: test am submodule with diff.submodule

builtin/log.c

@@ -705,7 +705,7 @@ static int git_format_config(const char *var, const char *value, void *cb)
 		return 0;
 	}
 	if (!strcmp(var, "diff.color") || !strcmp(var, "color.diff") ||
-	    !strcmp(var, "color.ui")) {
+	    !strcmp(var, "color.ui") || !strcmp(var, "diff.submodule")) {
 		return 0;
 	}
 	if (!strcmp(var, "format.numbered")) {

t/t4255-am-submodule.sh

@@ -18,4 +18,76 @@ am_3way () {
 KNOWN_FAILURE_NOFF_MERGE_ATTEMPTS_TO_MERGE_REMOVED_SUBMODULE_FILES=1
 test_submodule_switch "am_3way"
 
+test_expect_success 'setup diff.submodule' '
+	test_commit one &&
+	INITIAL=$(git rev-parse HEAD) &&
+
+	git init submodule &&
+	(
+		cd submodule &&
+		test_commit two &&
+		git rev-parse HEAD >../initial-submodule
+	) &&
+	git submodule add ./submodule &&
+	git commit -m first &&
+
+	(
+		cd submodule &&
+		test_commit three &&
+		git rev-parse HEAD >../first-submodule
+	) &&
+	git add submodule &&
+	git commit -m second &&
+	SECOND=$(git rev-parse HEAD) &&
+
+	(
+		cd submodule &&
+		git mv two.t four.t &&
+		git commit -m "second submodule" &&
+		git rev-parse HEAD >../second-submodule
+	) &&
+	test_commit four &&
+	git add submodule &&
+	git commit --amend --no-edit &&
+	THIRD=$(git rev-parse HEAD) &&
+	git submodule update --init
+'
+
+run_test() {
+	START_COMMIT=$1 &&
+	EXPECT=$2 &&
+	# Abort any merges in progress: the previous
+	# test may have failed, and we should clean up.
+	test_might_fail git am --abort &&
+	git reset --hard $START_COMMIT &&
+	rm -f *.patch &&
+	git format-patch -1 &&
+	git reset --hard $START_COMMIT^ &&
+	git submodule update &&
+	git am *.patch &&
+	git submodule update &&
+	git -C submodule rev-parse HEAD >actual &&
+	test_cmp $EXPECT actual
+}
+
+test_expect_success 'diff.submodule unset' '
+	test_unconfig diff.submodule &&
+	run_test $SECOND first-submodule
+'
+
+test_expect_success 'diff.submodule unset with extra file' '
+	test_unconfig diff.submodule &&
+	run_test $THIRD second-submodule
+'
+
+test_expect_success 'diff.submodule=log' '
+	test_config diff.submodule log &&
+	run_test $SECOND first-submodule
+'
+
+test_expect_success 'diff.submodule=log with extra file' '
+	test_config diff.submodule log &&
+	run_test $THIRD second-submodule
+'
+
 test_done