Re: Bug in 'git am' when applying a broken patch

From: Junio C Hamano <gitster@pobox.com>
Date: Jun 1, 2015, 20:23 UTC
Message-ID: <xmqq8uc35gap.fsf@gitster.dls.corp.google.com>
In-Reply-To: <CAPig+cTc72npgXUA9EirGonrjwhXCROxn4cc=6=uPywers_h9w@mail.gmail.com>

Eric Sunshine <sunshine@sunshineco.com> writes:

> s/enw/new/

Heh, thanks; I wasn't planning to commit this one yet, but why not. Here is with an updated log message and a test.

-- >8 --
Subject: [PATCH] apply: reject a hunk that does not do anything

A hunk like this in a hand-edited patch without correctly adjusting the line counts:

     @@ -660,2 +660,2 @@ inline struct sk_buff *ieee80211_authentic...
             auth = (struct ieee80211_authentication *)
                     skb_put(skb, sizeof(struct ieee80211_authentication));
     -       some old text
     +       some new text
     --
     2.1.0

     dev mailing list

at the end of the input does not have a good way for us to diagnose it as a corrupt patch. We just read two context lines and discard the remainder as cruft, which we must do in order to ignore the e-mail footer. Notice that the patch does not change anything and signal an error.

Note that this fix will not help if the hand-edited hunk header were "@@ -660,3, +660,2" to include the removal. We would just remove the old text without adding the new one, and treat "+ some new text" and everything after that line as trailing cruft. So it is dubious that this patch alone would help very much in practice, but it may be better than nothing.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/apply.c        |  3 +++
 t/t4136-apply-check.sh | 13 +++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/builtin/apply.c b/builtin/apply.c
index 6696ea4..606eddd 100644
--- a/builtin/apply.c
+++ b/builtin/apply.c
@@ -1639,6 +1639,9 @@ static int parse_fragment(const char *line, unsigned long size,
 	}
 	if (oldlines || newlines)
 		return -1;
+	if (!deleted && !added)
+		return -1;
+
 	fragment->leading = leading;
 	fragment->trailing = trailing;
 
diff --git a/t/t4136-apply-check.sh b/t/t4136-apply-check.sh
index a321f7c..4b0a374 100755
--- a/t/t4136-apply-check.sh
+++ b/t/t4136-apply-check.sh
@@ -16,4 +16,17 @@ test_expect_success 'apply --check exits non-zero with unrecognized input' '
 	EOF
 '
 
+test_expect_success 'apply exits non-zero with no-op patch' '
+	cat >input <<-\EOF &&
+	diff --get a/1 b/1
+	index 6696ea4..606eddd 100644
+	--- a/1
+	+++ b/1
+	@@ -1,1 +1,1 @@
+	 1
+	EOF
+	test_must_fail git apply --stat input &&
+	test_must_fail git apply --check input
+'
+
 test_done

-- 
2.4.2-556-g58822d7