[PATCH 1/3] sparse-checkout: fix OOM error with mixed patterns

["Derrick Stolee via GitGitGadget" <gitgitgadget@gmail.com>]

From: Derrick Stolee <dstolee@microsoft.com>

Add a test to t1091-sparse-checkout-builtin.sh that would result in an
infinite loop and out-of-memory error before this change. The issue
relies on having non-cone-mode patterns while trying to modify the
patterns in cone-mode.

The fix is simple, allowing us to break from the loop when the input
path does not contain a slash, as the "dir" pattern we added does not.

This is only a fix to the critical out-of-memory error. A better
response to such a strange state will follow in a later change.

Reported-by: Calbabreaker <calbabreaker@gmail.com>
Helped-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
---
 builtin/sparse-checkout.c          | 2 +-
 t/t1091-sparse-checkout-builtin.sh | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
index 8ba9f13787b..b45fd97a98b 100644
--- a/builtin/sparse-checkout.c
+++ b/builtin/sparse-checkout.c
@@ -389,7 +389,7 @@ static void insert_recursive_pattern(struct pattern_list *pl, struct strbuf *pat
 		char *oldpattern = e->pattern;
 		size_t newlen;
 
-		if (slash == e->pattern)
+		if (!slash || slash == e->pattern)
 			break;
 
 		newlen = slash - e->pattern;
diff --git a/t/t1091-sparse-checkout-builtin.sh b/t/t1091-sparse-checkout-builtin.sh
index 38fc8340f5c..a429d2cc671 100755
--- a/t/t1091-sparse-checkout-builtin.sh
+++ b/t/t1091-sparse-checkout-builtin.sh
@@ -103,6 +103,14 @@ test_expect_success 'clone --sparse' '
 	check_files clone a
 '
 
+test_expect_success 'switching to cone mode with non-cone mode patterns' '
+	git init bad-patterns &&
+	git -C bad-patterns sparse-checkout init &&
+	git -C bad-patterns sparse-checkout add dir &&
+	git -C bad-patterns config core.sparseCheckoutCone true &&
+	git -C bad-patterns sparse-checkout add dir
+'
+
 test_expect_success 'interaction with clone --no-checkout (unborn index)' '
 	git clone --no-checkout "file://$(pwd)/repo" clone_no_checkout &&
 	git -C clone_no_checkout sparse-checkout init --cone &&
-- 
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