🩹 Fix: Unintended overwritten bind variables (#2240)

* bindMap key value should only be set when not already present

* add comment

Co-authored-by: Clark Winters <clwinters8@gmail.com>

ctx.go

@@ -1437,7 +1437,10 @@ func (c *Ctx) renderExtensions(bind interface{}) {
 		// Bind view map
 		if c.viewBindMap != nil {
 			for _, v := range c.viewBindMap.D {
-				bindMap[v.Key] = v.Value
+				// make sure key does not exist already
+				if _, ok := bindMap[v.Key]; !ok {
+					bindMap[v.Key] = v.Value
+				}
 			}
 		}
 

ctx_test.go

@@ -2851,6 +2851,29 @@ func Test_Ctx_RenderWithBind(t *testing.T) {
 
 }
 
+func Test_Ctx_RenderWithOverwrittenBind(t *testing.T) {
+	t.Parallel()
+
+	app := New()
+	c := app.AcquireCtx(&fasthttp.RequestCtx{})
+
+	err := c.Bind(Map{
+		"Title": "Hello, World!",
+	})
+	utils.AssertEqual(t, nil, err)
+	defer app.ReleaseCtx(c)
+	err = c.Render("./.github/testdata/index.tmpl", Map{
+		"Title": "Hello from Fiber!",
+	})
+
+	buf := bytebufferpool.Get()
+	_, _ = buf.WriteString("overwrite")
+	defer bytebufferpool.Put(buf)
+
+	utils.AssertEqual(t, nil, err)
+	utils.AssertEqual(t, "<h1>Hello from Fiber!</h1>", string(c.Response().Body()))
+}
+
 func Test_Ctx_RenderWithBindLocals(t *testing.T) {
 	t.Parallel()