Subject: [PATCH v4 1/3] apply: report the location of corrupt patches

From: Jialong Wang <[email-masked]>
Date: Tue, 17 Mar 2026 12:23:19 -0400

When parsing a corrupt patch, git apply reports only the line number.
That does not tell the user which input the line number refers to.

Include the patch input path in the error message so the reported
location is easier to use.

Reset the line number for each patch input so the reported location stays
correct when multiple input files are provided.

Add tests for file input, standard input, multiple patch inputs, and
existing binary-diff corrupt patch cases.

Signed-off-by: Jialong Wang <[email-masked]>
---
 apply.c                |  4 +++-
 t/t4012-diff-binary.sh |  4 ++--
 t/t4100-apply-stat.sh  | 38 +++++++++++++++++++++++++++++++++++++-
 3 files changed, 42 insertions(+), 4 deletions(-)

diff --git a/apply.c b/apply.c
index b6dd1066a0..b7b0a201b3 100644
--- a/apply.c
+++ b/apply.c
@@ -1875,7 +1875,8 @@ static int parse_single_patch(struct apply_state *state,
 		len = parse_fragment(state, line, size, patch, fragment);
 		if (len <= 0) {
 			free(fragment);
-			return error(_("corrupt patch at line %d"), state->linenr);
+			return error(_("corrupt patch at %s:%d"),
+				     state->patch_input_file, state->linenr);
 		}
 		fragment->patch = line;
 		fragment->size = len;
@@ -4825,6 +4826,7 @@ static int apply_patch(struct apply_state *state,
 	int flush_attributes = 0;
 
 	state->patch_input_file = filename;
+	state->linenr = 1;
 	if (read_patch_file(&buf, fd) < 0)
 		return -128;
 	offset = 0;
diff --git a/t/t4012-diff-binary.sh b/t/t4012-diff-binary.sh
index d1d30ac2a9..97b5ac0407 100755
--- a/t/t4012-diff-binary.sh
+++ b/t/t4012-diff-binary.sh
@@ -68,7 +68,7 @@ test_expect_success 'apply detecting corrupt patch correctly' '
 	sed -e "s/-CIT/xCIT/" <output >broken &&
 	test_must_fail git apply --stat --summary broken 2>detected &&
 	detected=$(cat detected) &&
-	detected=$(expr "$detected" : "error.*at line \\([0-9]*\\)\$") &&
+	detected=$(expr "$detected" : "error.*broken:\\([0-9]*\\)\$") &&
 	detected=$(sed -ne "${detected}p" broken) &&
 	test "$detected" = xCIT
 '
@@ -77,7 +77,7 @@ test_expect_success 'apply detecting corrupt patch correctly' '
 	git diff --binary | sed -e "s/-CIT/xCIT/" >broken &&
 	test_must_fail git apply --stat --summary broken 2>detected &&
 	detected=$(cat detected) &&
-	detected=$(expr "$detected" : "error.*at line \\([0-9]*\\)\$") &&
+	detected=$(expr "$detected" : "error.*broken:\\([0-9]*\\)\$") &&
 	detected=$(sed -ne "${detected}p" broken) &&
 	test "$detected" = xCIT
 '
diff --git a/t/t4100-apply-stat.sh b/t/t4100-apply-stat.sh
index a5664f3eb3..b19fc9fe50 100755
--- a/t/t4100-apply-stat.sh
+++ b/t/t4100-apply-stat.sh
@@ -48,7 +48,43 @@ test_expect_success 'applying a hunk header which overflows fails' '
 	+b
 	EOF
 	test_must_fail git apply patch 2>err &&
-	echo "error: corrupt patch at line 4" >expect &&
+	echo "error: corrupt patch at patch:4" >expect &&
+	test_cmp expect err
+'
+
+test_expect_success 'applying a hunk header which overflows from stdin fails' '
+	cat >patch <<-\EOF &&
+	diff -u a/file b/file
+	--- a/file
+	+++ b/file
+	@@ -98765432109876543210 +98765432109876543210 @@
+	-a
+	+b
+	EOF
+	test_must_fail git apply <patch 2>err &&
+	echo "error: corrupt patch at <stdin>:4" >expect &&
+	test_cmp expect err
+'
+
+test_expect_success 'applying multiple patches reports the corrupted input' '
+	cat >good.patch <<-\EOF &&
+	diff -u a/file b/file
+	--- a/file
+	+++ b/file
+	@@ -1 +1 @@
+	-a
+	+b
+	EOF
+	cat >bad.patch <<-\EOF &&
+	diff -u a/file b/file
+	--- a/file
+	+++ b/file
+	@@ -98765432109876543210 +98765432109876543210 @@
+	-a
+	+b
+	EOF
+	test_must_fail git apply --stat --summary good.patch bad.patch 2>err &&
+	echo "error: corrupt patch at bad.patch:4" >expect &&
 	test_cmp expect err
 '
 test_done
-- 
2.51.0