fix(route): redirectSlash bug (#3227)

fixes https://github.com/gin-gonic/gin/issues/2959
fixes https://github.com/gin-gonic/gin/issues/2282
fixes https://github.com/gin-gonic/gin/issues/2211

tree.go

@@ -107,7 +107,8 @@ func countSections(path string) uint16 {
 type nodeType uint8
 
 const (
-	root nodeType = iota + 1
+	static nodeType = iota
+	root
 	param
 	catchAll
 )
@@ -173,6 +174,7 @@ walk:
 			child := node{
 				path:      n.path[i:],
 				wildChild: n.wildChild,
+				nType:     static,
 				indices:   n.indices,
 				children:  n.children,
 				handlers:  n.handlers,
@@ -604,6 +606,11 @@ walk: // Outer loop for walking the tree
 				return
 			}
 
+			if path == "/" && n.nType == static {
+				value.tsr = true
+				return
+			}
+
 			// No handle found. Check if a handle for this path + a
 			// trailing slash exists for trailing slash recommendation
 			for i, c := range []byte(n.indices) {