fix the misplacement of adding slashes (gin-gonic#2847)

(cherry picked from commit 1c2aa59)

routes_test.go

@@ -481,6 +481,21 @@ func TestRouterNotFound(t *testing.T) {
 	router.GET("/a", func(c *Context) {})
 	w = performRequest(router, http.MethodGet, "/")
 	assert.Equal(t, http.StatusNotFound, w.Code)
+
+	// Reproduction test for the bug of issue #2843
+	router = New()
+	router.NoRoute(func(c *Context) {
+		if c.Request.RequestURI == "/login" {
+			c.String(200, "login")
+		}
+	})
+	router.GET("/logout", func(c *Context) {
+		c.String(200, "logout")
+	})
+	w = performRequest(router, http.MethodGet, "/login")
+	assert.Equal(t, "login", w.Body.String())
+	w = performRequest(router, http.MethodGet, "/logout")
+	assert.Equal(t, "logout", w.Body.String())
 }
 
 func TestRouterStaticFSNotFound(t *testing.T) {

tree.go

@@ -635,7 +635,8 @@ walk: // Outer loop for walking the tree
 		// Nothing found. We can recommend to redirect to the same URL with an
 		// extra trailing slash if a leaf exists for that path
 		value.tsr = path == "/" ||
-			(len(prefix) == len(path)+1 && n.handlers != nil)
+			(len(prefix) == len(path)+1 && prefix[len(path)] == '/' &&
+				path == prefix[:len(prefix)-1] && n.handlers != nil)
 		return
 	}
 }