teach format-patch to place other authors into in-body "From"

Format-patch generates emails with the "From" address set to the
author of each patch. If you are going to send the emails, however,
you would want to replace the author identity with yours (if they
are not the same), and bump the author identity to an in-body
header.

Normally this is handled by git-send-email, which does the
transformation before sending out the emails. However, some
workflows may not use send-email (e.g., imap-send, or a custom
script which feeds the mbox to a non-git MUA). They could each
implement this feature themselves, but getting it right is
non-trivial (one must canonicalize the identities by reversing any
RFC2047 encoding or RFC822 quoting of the headers, which has caused
many bugs in send-email over the years).

This patch takes a different approach: it teaches format-patch a
"--from" option which handles the ident check and in-body header
while it is writing out the email.  It's much simpler to do at this
level (because we haven't done any quoting yet), and any workflow
based on format-patch can easily turn it on.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 24 insertions, 0 deletions

diff --git a/builtin/log.c b/builtin/log.c
index e3222ed9f9..2625f9881a 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -1112,6 +1112,21 @@ static int cc_callback(const struct option *opt, const char *arg, int unset)
 	return 0;
 }
 
+static int from_callback(const struct option *opt, const char *arg, int unset)
+{
+	char **from = opt->value;
+
+	free(*from);
+
+	if (unset)
+		*from = NULL;
+	else if (arg)
+		*from = xstrdup(arg);
+	else
+		*from = xstrdup(git_committer_info(IDENT_NO_DATE));
+	return 0;
+}
+
 int cmd_format_patch(int argc, const char **argv, const char *prefix)
 {
 	struct commit *commit;
@@ -1134,6 +1149,7 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 	int quiet = 0;
 	int reroll_count = -1;
 	char *branch_name = NULL;
+	char *from = NULL;
 	const struct option builtin_format_patch_options[] = {
 		{ OPTION_CALLBACK, 'n', "numbered", &numbered, NULL,
 			    N_("use [PATCH n/m] even with a single patch"),
@@ -1177,6 +1193,9 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 			    0, to_callback },
 		{ OPTION_CALLBACK, 0, "cc", NULL, N_("email"), N_("add Cc: header"),
 			    0, cc_callback },
+		{ OPTION_CALLBACK, 0, "from", &from, N_("ident"),
+			    N_("set From address to <ident> (or committer ident if absent)"),
+			    PARSE_OPT_OPTARG, from_callback },
 		OPT_STRING(0, "in-reply-to", &in_reply_to, N_("message-id"),
 			    N_("make first mail a reply to <message-id>")),
 		{ OPTION_CALLBACK, 0, "attach", &rev, N_("boundary"),
@@ -1264,6 +1283,11 @@ int cmd_format_patch(int argc, const char **argv, const char *prefix)
 
 	rev.extra_headers = strbuf_detach(&buf, NULL);
 
+	if (from) {
+		if (split_ident_line(&rev.from_ident, from, strlen(from)))
+			die(_("invalid ident line: %s"), from);
+	}
+
 	if (start_number < 0)
 		start_number = 1;