[PATCH] git-am: Ignore whitespace before patches

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Change git-am to ignore whitespace (as defined by sh's read) at the
beginning of patches.

Empty lines are wont to creep in at the beginning of patches, here's
an example from a raw Gmail attachment:

    20 20 20 20 20 20 20 20  20 20 20 20 20 20 20 20  |                |
    20 20 20 20 20 20 20 20  20 20 20 20 20 20 20 0a  |               .|
    52 65 74 75 72 6e 2d 50  61 74 68 3a 20 3c 61 76  |Return-Path: <av|

Whitespace is also likely to appear if the user copy/pastes the patch
around, e.g. via a pastebin, or any any number of other cases. This
harms nothing and makes git-am's detection more fault tolerant.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 git-am.sh     |   16 +++++++++++++++-
 t/t4150-am.sh |   30 ++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 1 deletions(-)

diff --git a/git-am.sh b/git-am.sh
index 1056075..1b4baa8 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -172,7 +172,21 @@ check_patch_format () {
 	# otherwise, check the first few lines of the first patch to try
 	# to detect its format
 	{
-		read l1
+		while read -r line
+		do
+			case "$line" in
+				"")
+					# Just skip whitespace
+					continue
+					;;
+				*)
+					# First non-empty line
+					l1=$line
+					break
+					;;
+			esac
+		done
+
 		read l2
 		read l3
 		case "$l1" in
diff --git a/t/t4150-am.sh b/t/t4150-am.sh
index 810b04b..3d089de 100755
--- a/t/t4150-am.sh
+++ b/t/t4150-am.sh
@@ -318,6 +318,36 @@ test_expect_success 'am without --committer-date-is-author-date' '
 	test "$at" != "$ct"
 '
 
+test_expect_success 'am applying a patch that begins with an empty line' '
+	git checkout first &&
+	test_tick &&
+	echo > patch1-white &&
+	cat patch1 >> patch1-white &&
+	git am patch1-white &&
+	git cat-file commit HEAD | sed -e "/^\$/q" >head1 &&
+	at=$(sed -ne "/^author /s/.*> //p" head1) &&
+	ct=$(sed -ne "/^committer /s/.*> //p" head1) &&
+	test "$at" != "$ct"
+'
+
+test_expect_success 'am applying a patch that begins with many empty lines' '
+	git checkout first &&
+	test_tick &&
+	echo "   " > patch1-white2 &&
+	echo "  " >> patch1-white2 &&
+	echo " " >> patch1-white2 &&
+	echo "" >> patch1-white2 &&
+	echo " " >> patch1-white2 &&
+	echo "  " >> patch1-white2 &&
+	echo "   " >> patch1-white2 &&
+	cat patch1 >> patch1-white2 &&
+	git am patch1-white2 &&
+	git cat-file commit HEAD | sed -e "/^\$/q" >head1 &&
+	at=$(sed -ne "/^author /s/.*> //p" head1) &&
+	ct=$(sed -ne "/^committer /s/.*> //p" head1) &&
+	test "$at" != "$ct"
+'
+
 # This checks for +0000 because TZ is set to UTC and that should
 # show up when the current time is used. The date in message is set
 # by test_tick that uses -0700 timezone; if this feature does not
-- 
1.7.1.84.gd92f8