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, 43 insertions, 0 deletions

diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index 58d4180..668933b 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -972,6 +972,49 @@ test_expect_success 'empty subject prefix does not have extra space' '
 	test_cmp expect actual
 '
 
+test_expect_success '--from=ident notices bogus ident' '
+	test_must_fail git format-patch -1 --stdout --from=foo >patch
+'
+
+test_expect_success '--from=ident replaces author' '
+	git format-patch -1 --stdout --from="Me <me@example.com>" >patch &&
+	cat >expect <<-\EOF &&
+	From: Me <me@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 '--from uses committer ident' '
+	git format-patch -1 --stdout --from >patch &&
+	cat >expect <<-\EOF &&
+	From: C O Mitter <committer@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' '
+	GIT_AUTHOR_NAME="éxötìc" test_commit exotic &&
+	test_when_finished "git reset --hard HEAD^" &&
+	git format-patch -1 --stdout --from >patch &&
+	cat >expect <<-\EOF &&
+	From: C O Mitter <committer@example.com>
+	Content-Type: text/plain; charset=UTF-8
+
+	From: éxötìc <author@example.com>
+
+	EOF
+	sed -ne "/^From:/p; /^$/p; /^Content-Type/p; /^---$/q" <patch >patch.head &&
+	test_cmp expect patch.head
+'
+
 append_signoff()
 {
 	C=$(git commit-tree HEAD^^{tree} -p HEAD) &&