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, 15 insertions, 0 deletions

diff --git a/Documentation/git-format-patch.txt b/Documentation/git-format-patch.txt
index 39118774af..e394276b1a 100644
--- a/Documentation/git-format-patch.txt
+++ b/Documentation/git-format-patch.txt
@@ -187,6 +187,21 @@ will want to ensure that threading is disabled for `git send-email`.
 	The negated form `--no-cc` discards all `Cc:` headers added so
 	far (from config or command line).
 
+--from::
+--from=<ident>::
+	Use `ident` in the `From:` header of each commit email. If the
+	author ident of the commit is not textually identical to the
+	provided `ident`, place a `From:` header in the body of the
+	message with the original author. If no `ident` is given, use
+	the committer ident.
++
+Note that this option is only useful if you are actually sending the
+emails and want to identify yourself as the sender, but retain the
+original author (and `git am` will correctly pick up the in-body
+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`.
+
 --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.