From ae0712b657f769e299625351d22ca30e2d1ab288 Mon Sep 17 00:00:00 2001
From: Asheem Mamoowala <asheem.mamoowala@mapbox.com>
Date: Tue, 1 Aug 2017 16:43:11 -0700
Subject: [PATCH] Clone `layerObject` in `Style#addLayer` to prevent mutation
 of user data

---
 src/style/style.js            |  1 +
 test/unit/style/style.test.js | 17 +++++++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/src/style/style.js b/src/style/style.js
index 389ff5f45c0..9acb23e46d3 100644
--- a/src/style/style.js
+++ b/src/style/style.js
@@ -497,6 +497,7 @@ class Style extends Evented {
 
         if (typeof layerObject.source === 'object') {
             this.addSource(id, layerObject.source);
+            layerObject = util.clone(layerObject);
             layerObject = (util.extend(layerObject, {source: id}): any);
         }
 
diff --git a/test/unit/style/style.test.js b/test/unit/style/style.test.js
index 1aa99c0ceaf..86c5a9c79bd 100644
--- a/test/unit/style/style.test.js
+++ b/test/unit/style/style.test.js
@@ -723,6 +723,23 @@ test('Style#addLayer', (t) => {
         });
     });
 
+    t.test('#4040 does not mutate source property when provided inline', (t) => {
+        const style = new Style(createStyleJSON());
+        style.on('style.load', () => {
+            const source = {
+                "type": "geojson",
+                "data": {
+                    "type": "Point",
+                    "coordinates": [ 0, 0]
+                }
+            };
+            const layer = {id: 'inline-source-layer', type: 'circle', source: source };
+            style.addLayer(layer);
+            t.deepEqual(layer.source, source);
+            t.end();
+        });
+    });
+
     t.test('reloads source', (t) => {
         const style = new Style(util.extend(createStyleJSON(), {
             "sources": {