format-patch: teach --no-base

If `format.useAutoBase = true`, there was no way to override this from
the command-line. Teach the `--no-base` option in format-patch to
override `format.useAutoBase`.

Helped-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-format-patch.txt

@@ -333,11 +333,12 @@ you can use `--suffix=-patch` to get `0001-description-of-my-change-patch`.
   Output an all-zero hash in each patch's From header instead
   of the hash of the commit.
 
---base=<commit>::
+--[no-]base[=<commit>]::
 	Record the base tree information to identify the state the
 	patch series applies to.  See the BASE TREE INFORMATION section
 	below for details. If <commit> is "auto", a base commit is
-	automatically chosen.
+	automatically chosen. The `--no-base` option overrides a
+	`format.useAutoBase` configuration.
 
 --root::
 	Treat the revision argument as a <revision range>, even if it

builtin/log.c

@@ -1406,7 +1406,7 @@ static struct commit *get_base_commit(const char *base_commit,
 		base = lookup_commit_reference_by_name(base_commit);
 		if (!base)
 			die(_("unknown commit %s"), base_commit);
-	} else if ((base_commit && !strcmp(base_commit, "auto")) || base_auto) {
+	} else if ((base_commit && !strcmp(base_commit, "auto"))) {
 		struct branch *curr_branch = branch_get(NULL);
 		const char *upstream = branch_get_upstream(curr_branch, NULL);
 		if (upstream) {
@@ -1710,6 +1710,9 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	s_r_opt.def = "HEAD";
 	s_r_opt.revarg_opt = REVARG_COMMITTISH;
 
+	if (base_auto)
+		base_commit = "auto";
+
 	if (default_attach) {
 		rev.mime_boundary = default_attach;
 		rev.no_inline = 1;
@@ -1973,7 +1976,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	}
 
 	memset(&bases, 0, sizeof(bases));
-	if (base_commit || base_auto) {
+	if (base_commit) {
 		struct commit *base = get_base_commit(base_commit, list, nr);
 		reset_revision_walk();
 		clear_object_flags(UNINTERESTING);

t/t4014-format-patch.sh

@@ -1958,6 +1958,12 @@ test_expect_success 'format-patch --base overrides format.useAutoBase' '
 	test_cmp expect actual
 '
 
+test_expect_success 'format-patch --no-base overrides format.useAutoBase' '
+	test_config format.useAutoBase true &&
+	git format-patch --stdout --no-base -1 >patch &&
+	! grep "^base-commit:" patch
+'
+
 test_expect_success 'format-patch --base with --attach' '
 	git format-patch --attach=mimemime --stdout --base=HEAD~ -1 >patch &&
 	sed -n -e "/^base-commit:/s/.*/1/p" -e "/^---*mimemime--$/s/.*/2/p" \