From de0d754693530a562bc9da2ecd1a7556ca7328e2 Mon Sep 17 00:00:00 2001
From: Symmetricity <184246+Symmetricity@users.noreply.github.com>
Date: Thu, 28 May 2026 14:33:17 +0200
Subject: [PATCH] Fix UsedWays bounds check

UsedWays stores relation-used way ids in a vector<bool>. The old exact-size check treated wayid == size() as valid and then indexed one past the vector.

Resize when the requested id is equal to the current size, and treat the same boundary as absent when reading. Add coverage for the first and exact-size insert cases.

Co-authored-by: Codex <noreply@openai.com>
---
 Makefile                |  5 +++++
 include/osm_store.h     |  4 ++--
 test/osm_store.test.cpp | 27 +++++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 2 deletions(-)
 create mode 100644 test/osm_store.test.cpp

diff --git a/Makefile b/Makefile
index 38908e07..b08088f2 100644
--- a/Makefile
+++ b/Makefile
@@ -149,6 +149,7 @@ test: \
 	test_significant_tags \
 	test_sorted_node_store \
 	test_sorted_way_store \
+	test_osm_store \
 	test_tile_coordinates_set
 
 test_append_vector: \
@@ -188,6 +189,10 @@ test_options_parser: \
 	test/options_parser.test.o
 	$(CXX) $(CXXFLAGS) -o test.options_parser $^ $(INC) $(LIB) $(LDFLAGS) && ./test.options_parser
 
+test_osm_store: \
+	test/osm_store.test.o
+	$(CXX) $(CXXFLAGS) -o test.osm_store $^ $(INC) $(LIB) $(LDFLAGS) && ./test.osm_store
+
 test_pooled_string: \
 	src/mmap_allocator.o \
 	src/pooled_string.o \
diff --git a/include/osm_store.h b/include/osm_store.h
index 171e9386..ce54cd0f 100644
--- a/include/osm_store.h
+++ b/include/osm_store.h
@@ -78,13 +78,13 @@ class UsedWays {
 	// Mark a way as used
 	void insert(WayID wayid) {
 		std::lock_guard<std::mutex> lock(mutex);
-		if (wayid>usedList.size()) usedList.resize(wayid+256);
+		if (wayid>=usedList.size()) usedList.resize(wayid+256);
 		usedList[wayid] = true;
 	}
 	
 	// See if a way is used
 	bool at(WayID wayid) const {
-		return (wayid>usedList.size()) ? false : usedList[wayid];
+		return (wayid>=usedList.size()) ? false : usedList[wayid];
 	}
 	
 	void clear() {
diff --git a/test/osm_store.test.cpp b/test/osm_store.test.cpp
new file mode 100644
index 00000000..61eca883
--- /dev/null
+++ b/test/osm_store.test.cpp
@@ -0,0 +1,27 @@
+#include <iostream>
+#include "external/minunit.h"
+#include "osm_store.h"
+
+MU_TEST(test_usedways_grows_for_first_index) {
+	UsedWays usedWays;
+	usedWays.insert(0);
+	mu_check(usedWays.at(0));
+}
+
+MU_TEST(test_usedways_grows_at_current_size) {
+	UsedWays usedWays;
+	usedWays.insert(0);
+	usedWays.insert(256);
+	mu_check(usedWays.at(256));
+}
+
+MU_TEST_SUITE(test_suite_osm_store) {
+	MU_RUN_TEST(test_usedways_grows_for_first_index);
+	MU_RUN_TEST(test_usedways_grows_at_current_size);
+}
+
+int main() {
+	MU_RUN_SUITE(test_suite_osm_store);
+	MU_REPORT();
+	return MU_EXIT_CODE;
+}