am: learn passing -b to mailinfo

git-am could pass -k to mailinfo, but not -b.  Introduce an option
that does so.  We change the meaning of the 'keep' state file, but are
careful not to cause a problem unless you downgrade in the middle of
an 'am' run.

This uncovers a bug in mailinfo -b, hence the failing test.

Signed-off-by: Thomas Rast <trast@student.ethz.ch>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-am.txt

@@ -39,6 +39,9 @@ OPTIONS
 --keep::
 	Pass `-k` flag to 'git mailinfo' (see linkgit:git-mailinfo[1]).
 
+--keep-non-patch::
+	Pass `-b` flag to 'git mailinfo' (see linkgit:git-mailinfo[1]).
+
 --keep-cr::
 --no-keep-cr::
 	With `--keep-cr`, call 'git mailsplit' (see linkgit:git-mailsplit[1])

git-am.sh

@@ -15,6 +15,7 @@ q,quiet         be quiet
 s,signoff       add a Signed-off-by line to the commit message
 u,utf8          recode into utf8 (default)
 k,keep          pass -k flag to git-mailinfo
+keep-non-patch  pass -b flag to git-mailinfo
 keep-cr         pass --keep-cr flag to git-mailsplit for mbox format
 no-keep-cr      do not pass --keep-cr flag to git-mailsplit independent of am.keepcr
 c,scissors      strip everything before a scissors line
@@ -345,6 +346,8 @@ do
 		utf8= ;;
 	-k|--keep)
 		keep=t ;;
+	--keep-non-patch)
+		keep=b ;;
 	-c|--scissors)
 		scissors=t ;;
 	--no-scissors)
@@ -522,16 +525,25 @@ case "$resolved" in
 	fi
 esac
 
+# Now, decide what command line options we will give to the git
+# commands we invoke, based on the result of parsing command line
+# options and previous invocation state stored in $dotest/ files.
+
 if test "$(cat "$dotest/utf8")" = t
 then
 	utf8=-u
 else
 	utf8=-n
 fi
-if test "$(cat "$dotest/keep")" = t
-then
-	keep=-k
-fi
+keep=$(cat "$dotest/keep")
+case "$keep" in
+t)
+	keep=-k ;;
+b)
+	keep=-b ;;
+*)
+	keep= ;;
+esac
 case "$(cat "$dotest/keepcr")" in
 t)
 	keepcr=--keep-cr ;;

t/t4150-am.sh

@@ -219,7 +219,7 @@ test_expect_success 'am stays in branch' '
 
 test_expect_success 'am --signoff does not add Signed-off-by: line if already there' '
 	git format-patch --stdout HEAD^ >patch3 &&
-	sed -e "/^Subject/ s,\[PATCH,Re: Re: Re: & 1/5 v2," patch3 >patch4 &&
+	sed -e "/^Subject/ s,\[PATCH,Re: Re: Re: & 1/5 v2] [foo," patch3 >patch4 &&
 	rm -fr .git/rebase-apply &&
 	git reset --hard &&
 	git checkout HEAD^ &&
@@ -241,7 +241,17 @@ test_expect_success 'am --keep really keeps the subject' '
 	git am --keep patch4 &&
 	! test -d .git/rebase-apply &&
 	git cat-file commit HEAD >actual &&
-	grep "Re: Re: Re: \[PATCH 1/5 v2\] third" actual
+	grep "Re: Re: Re: \[PATCH 1/5 v2\] \[foo\] third" actual
+'
+
+test_expect_failure 'am --keep-non-patch really keeps the non-patch part' '
+	rm -fr .git/rebase-apply &&
+	git reset --hard &&
+	git checkout HEAD^ &&
+	git am --keep-non-patch patch4 &&
+	! test -d .git/rebase-apply &&
+	git cat-file commit HEAD >actual &&
+	grep "^\[foo\] third" actual
 '
 
 test_expect_success 'am -3 falls back to 3-way merge' '