Flash message if drag not allowed because of a hidden connection

(closes #4493)

data/core.yaml

@@ -19,6 +19,8 @@ en:
       tail: Click to add nodes to your area. Click the first node to finish the area.
     draw_line:
       tail: "Click to add more nodes to the line. Click on other lines to connect to them, and double-click to end the line."
+    drag_node:
+      connected_to_hidden: This can't be edited because it is connected to a hidden feature.
   operations:
     add:
       annotation:

dist/locales/en.json

@@ -25,6 +25,9 @@
             },
             "draw_line": {
                 "tail": "Click to add more nodes to the line. Click on other lines to connect to them, and double-click to end the line."
+            },
+            "drag_node": {
+                "connected_to_hidden": "This can't be edited because it is connected to a hidden feature."
             }
         },
         "operations": {

modules/modes/drag_node.js

@@ -28,6 +28,7 @@ import {
 import { geoChooseEdge } from '../geo';
 import { osmNode } from '../osm';
 import { utilEntitySelector } from '../util';
+import { uiFlash } from '../ui';
 
 
 export function modeDragNode(context) {
@@ -106,11 +107,14 @@ export function modeDragNode(context) {
 
     function start(entity) {
         wasMidpoint = entity.type === 'midpoint';
+        var hasHidden = context.features().hasHiddenConnections(entity, context.graph());
+        isCancelled = d3_event.sourceEvent.shiftKey || hasHidden;
 
-        isCancelled = d3_event.sourceEvent.shiftKey ||
-            context.features().hasHiddenConnections(entity, context.graph());
 
         if (isCancelled) {
+            if (hasHidden) {
+                uiFlash().text(t('modes.drag_node.connected_to_hidden'))();
+            }
             return behavior.cancel();
         }