format-patch: escape "From " lines recognized by mailsplit mboxo

Users have mistakenly copied "From " lines into commit messages
in the past, and will certainly make the same mistakes in the
future.  Since not everyone uses mboxrd, yet, we should at least
prevent miss-split mails by always escaping "From " lines based
on the check used by mailsplit.

mailsplit will not perform unescaping by default, yet, as it
could cause further invocations of format-patch from old
versions of git to generate bad output.  Propagating the mboxo
escaping is preferable to miss-split patches.  Unescaping may
still be performed via "--mboxrd".

ref: https://public-inbox.org/git/20160606230248.GA15906@dcvr.yhbt.net/T/#u

Signed-off-by: Eric Wong <e@80x24.org>

2 files changed, 27 insertions, 3 deletions

diff --git a/pretty.c b/pretty.c
index 9fa42c2b4e..898c0a3ec6 100644
--- a/pretty.c
+++ b/pretty.c
@@ -10,6 +10,7 @@
 #include "color.h"
 #include "reflog-walk.h"
 #include "gpg-interface.h"
+#include "mailinfo.h"
 
 static char *user_format;
 static struct cmt_fmt_map {
@@ -1745,9 +1746,18 @@ void pp_remainder(struct pretty_print_context *pp,
                         strbuf_add_tabexpand(sb, pp->expand_tabs_in_log,
                                              line, linelen);
                 else {
-                        if (pp->fmt == CMIT_FMT_MBOXRD &&
-                                        is_mboxrd_from(line, linelen))
-                                strbuf_addch(sb, '>');
+                        switch (pp->fmt) {
+                        case CMIT_FMT_EMAIL:
+                                if (is_from_line(line, linelen))
+                                        strbuf_addch(sb, '>');
+                                break;
+                        case CMIT_FMT_MBOXRD:
+                                if (is_mboxrd_from(line, linelen))
+                                        strbuf_addch(sb, '>');
+                                break;
+                        default:
+                                break;
+                        }
 
                         strbuf_add(sb, line, linelen);
                 }
diff --git a/t/t4014-format-patch.sh b/t/t4014-format-patch.sh
index 1206c48392..8fa3982686 100755
--- a/t/t4014-format-patch.sh
+++ b/t/t4014-format-patch.sh
@@ -1606,4 +1606,18 @@ test_expect_success 'format-patch --pretty=mboxrd' '
         test_cmp expect actual
 '
 
+test_expect_success 'format-patch From escaping' '
+        cat >msg <<-INPUT_END &&
+        somebody pasted format-patch output into a body
+
+        From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+        INPUT_END
+
+        C=$(git commit-tree HEAD^^{tree} -p HEAD <msg) &&
+        git format-patch --stdout -1 $C~1..$C >patch &&
+        git grep -h --no-index \
+                ">From 0000000000000000000000000000000000000000 " \
+                patch
+'
+
 test_done