format-patch: allow forcing the use of in-body From: header

Users may be authoring and committing their commits under the same
e-mail address they use to send their patches from, in which case
they shouldn't need to use the in-body From: line in their outgoing
e-mails.  At the receiving end, "git am" will use the address on the
"From:" header of the incoming e-mail and all should be well.

Some mailing lists, however, mangle the From: address from what the
original sender had; in such a situation, the user may want to add
the in-body "From:" header even for their own patches.

"git format-patch --[no-]force-in-body-from" was invented for such
users.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-format-patch.txt

@@ -275,6 +275,15 @@ header). Note also that `git send-email` already handles this
 transformation for you, and this option should not be used if you are
 feeding the result to `git send-email`.
 
+--[no-]force-in-body-from::
+	With the e-mail sender specified via the `--from` option, by
+	default, an in-body "From:" to identify the real author of
+	the commit is added at the top of the commit log message if
+	the sender is different from the author.  With this option,
+	the in-body "From:" is added even when the sender and the
+	author have the same name and address, which may help if the
+	mailing list software mangles the sender's identity.
+
 --add-header=<header>::
 	Add an arbitrary header to the email headers.  This is in addition
 	to any configured headers, and may be used multiple times.

builtin/log.c

@@ -52,6 +52,7 @@ static int default_encode_email_headers = 1;
 static int decoration_style;
 static int decoration_given;
 static int use_mailmap_config = 1;
+static unsigned int force_in_body_from;
 static const char *fmt_patch_subject_prefix = "PATCH";
 static int fmt_patch_name_max = FORMAT_PATCH_NAME_MAX_DEFAULT;
 static const char *fmt_pretty;
@@ -1897,6 +1898,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			   N_("show changes against <refspec> in cover letter or single patch")),
 		OPT_INTEGER(0, "creation-factor", &creation_factor,
 			    N_("percentage by which creation is weighted")),
+		OPT_BOOL(0, "force-in-body-from", &force_in_body_from,
+			 N_("show in-body From: even if identical to the e-mail header")),
 		OPT_END()
 	};
 
@@ -1940,6 +1943,8 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			     PARSE_OPT_KEEP_ARGV0 | PARSE_OPT_KEEP_UNKNOWN |
 			     PARSE_OPT_KEEP_DASHDASH);
 
+	rev.force_in_body_from = force_in_body_from;
+
 	/* Make sure "0000-$sub.patch" gives non-negative length for $sub */
 	if (fmt_patch_name_max <= strlen("0000-") + strlen(fmt_patch_suffix))
 		fmt_patch_name_max = strlen("0000-") + strlen(fmt_patch_suffix);

pretty.c

@@ -480,6 +480,8 @@ end:
 static int use_in_body_from(const struct pretty_print_context *pp,
 			    const struct ident_split *ident)
 {
+	if (pp->rev && pp->rev->force_in_body_from)
+		return 1;
 	if (ident_cmp(pp->from_ident, ident))
 		return 1;
 	return 0;

revision.h

@@ -221,6 +221,7 @@ struct rev_info {
 			missing_newline:1,
 			date_mode_explicit:1,
 			preserve_subject:1,
+			force_in_body_from:1,
 			encode_email_headers:1,
 			include_header:1;
 	unsigned int	disable_stdin:1;

t/t4014-format-patch.sh

@@ -1400,6 +1400,19 @@ test_expect_success '--from omits redundant in-body header' '
 	test_cmp expect patch.head
 '
 
+test_expect_success 'with --force-in-body-from, redundant in-body from is kept' '
+	git format-patch --force-in-body-from \
+		-1 --stdout --from="A U Thor <author@example.com>" >patch &&
+	cat >expect <<-\EOF &&
+	From: A U Thor <author@example.com>
+
+	From: A U Thor <author@example.com>
+
+	EOF
+	sed -ne "/^From:/p; /^$/p; /^---$/q" patch >patch.head &&
+	test_cmp expect patch.head
+'
+
 test_expect_success 'in-body headers trigger content encoding' '
 	test_env GIT_AUTHOR_NAME="éxötìc" test_commit exotic &&
 	test_when_finished "git reset --hard HEAD^" &&