From faa33d4156dcdafdb1c536b5bc5e7dd6b36b6fca Mon Sep 17 00:00:00 2001
From: Sebastian Cao <cycsmail@gmail.com>
Date: Sun, 5 Jul 2026 21:26:48 +0800
Subject: [PATCH] Fix boolean-disjoint missing overlapping collinear lines

---
 packages/turf-boolean-disjoint/index.ts       | 13 +++++++++
 .../LineString/LineString-Overlap.geojson     | 27 +++++++++++++++++++
 2 files changed, 40 insertions(+)
 create mode 100644 packages/turf-boolean-disjoint/test/false/LineString/LineString/LineString-Overlap.geojson

diff --git a/packages/turf-boolean-disjoint/index.ts b/packages/turf-boolean-disjoint/index.ts
index 0b8158eb1b..ea3de597d3 100644
--- a/packages/turf-boolean-disjoint/index.ts
+++ b/packages/turf-boolean-disjoint/index.ts
@@ -125,6 +125,19 @@ function isLineOnLine(
   if (doLinesIntersect.features.length > 0) {
     return true;
   }
+  // lineIntersect() only reports points where segments cross, so collinear
+  // (partially) overlapping lines are missed. Check whether a vertex of either
+  // line lies on the other line to also catch those overlapping cases.
+  for (const coords of lineString1.coordinates) {
+    if (isPointOnLine(lineString2, { type: "Point", coordinates: coords })) {
+      return true;
+    }
+  }
+  for (const coords of lineString2.coordinates) {
+    if (isPointOnLine(lineString1, { type: "Point", coordinates: coords })) {
+      return true;
+    }
+  }
   return false;
 }
 
diff --git a/packages/turf-boolean-disjoint/test/false/LineString/LineString/LineString-Overlap.geojson b/packages/turf-boolean-disjoint/test/false/LineString/LineString/LineString-Overlap.geojson
new file mode 100644
index 0000000000..c591f5ef3e
--- /dev/null
+++ b/packages/turf-boolean-disjoint/test/false/LineString/LineString/LineString-Overlap.geojson
@@ -0,0 +1,27 @@
+{
+  "type": "FeatureCollection",
+  "features": [
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [4, 1],
+          [5, 4]
+        ]
+      }
+    },
+    {
+      "type": "Feature",
+      "properties": {},
+      "geometry": {
+        "type": "LineString",
+        "coordinates": [
+          [4, 1],
+          [6, 7]
+        ]
+      }
+    }
+  ]
+}