From 971a55f7e061309589f7a188b4b1ed8ebc2b2dae Mon Sep 17 00:00:00 2001
From: Isaac Brodsky <isaac@isaacbrodsky.com>
Date: Fri, 26 Jun 2026 10:21:36 -0700
Subject: [PATCH] Cover a case in compactCells with invalid input

---
 src/apps/testapps/testBBoxInternal.c |  2 +-
 src/apps/testapps/testCompactCells.c | 13 +++++++++++++
 src/h3lib/lib/h3Index.c              |  2 +-
 3 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/src/apps/testapps/testBBoxInternal.c b/src/apps/testapps/testBBoxInternal.c
index 15068626cc..1c2e89048e 100644
--- a/src/apps/testapps/testBBoxInternal.c
+++ b/src/apps/testapps/testBBoxInternal.c
@@ -350,7 +350,7 @@ SUITE(BBox) {
                  "bboxHexEstimate of invalid resolution fails");
     }
 
-    TEST(bboxHexEstimate_invalidRes) {
+    TEST(bboxHexEstimate_invalidLatitudeDifference) {
         int64_t numHexagons;
         BBox bbox = {1.0, 1.0, 0.0, 1.0};
         t_assert(bboxHexEstimate(&bbox, 1, &numHexagons) == E_FAILED,
diff --git a/src/apps/testapps/testCompactCells.c b/src/apps/testapps/testCompactCells.c
index bab73abc28..39cd5f364a 100644
--- a/src/apps/testapps/testCompactCells.c
+++ b/src/apps/testapps/testCompactCells.c
@@ -441,6 +441,19 @@ SUITE(compactCells) {
         t_assertSuccess(H3_EXPORT(compactCells)(bad, output, numHex));
     }
 
+    TEST(compactCells_parentError3) {
+        const int numHex = 3;
+        H3Index bad[] = {0x81283ffffffffff, 0, 0};
+        H3Index output[] = {0, 0, 0};
+
+        t_assertSuccess(H3_EXPORT(compactCells)(bad, output, numHex));
+        t_assert(output[0] == 0x81283ffffffffff,
+                 "output contains expected cell");
+        for (int i = 1; i < numHex; i++) {
+            t_assert(output[i] == 0, "output contains nulls");
+        }
+    }
+
     TEST(uncompactCells_wrongRes) {
         int numHex = 3;
         H3Index someHexagons[] = {0, 0, 0};
diff --git a/src/h3lib/lib/h3Index.c b/src/h3lib/lib/h3Index.c
index 64c11c9ef5..436a0363fd 100644
--- a/src/h3lib/lib/h3Index.c
+++ b/src/h3lib/lib/h3Index.c
@@ -590,7 +590,7 @@ H3Error H3_EXPORT(compactCells)(const H3Index *h3Set, H3Index *compactedSet,
             // to track how many times a parent is duplicated
             for (int64_t i = 0; i < numRemainingHexes; i++) {
                 H3Index currIndex = remainingHexes[i];
-                // TODO: This case is coverable (reachable by fuzzer)
+                // Can occur if 0 is passed in to the input to this function.
                 if (currIndex != 0) {
                     // If the reserved bits were set by the caller, the
                     // algorithm below may encounter undefined behavior