Dropdown option is immediately selected due to order of processing touch events

[Adam13531]

Describe the bug

This bug seems to be a resurfacing of #1804; on mobile, when a dropdown would appear directly over where the user tapped to spawn the dropdown, a selection will be made immediately.

To Reproduce

(note: I did the following steps using this official sample, although I have a local repro too that I can provide if that's insufficient)

1. Do all of this either from a real mobile device or from Chrome's device emulation (DevTools → Toggle device toolbar)
2. Create 12 variables with any names (just so that they'll populate the dropdown menu)
3. Add a "set variable to" block to the canvas
4. Try opening the dropdown for that block

At this point, the dropdown will open and immediately choose the value underneath your finger/mouse.

Expected behavior

The dropdown stays open so that you can choose an option.

Screenshots

I have a video of myself reproing this: https://clips.twitch.tv/CheerfulCleverKleeOSfrog

Desktop (please complete the following information):

• OS: Windows
• Browser: Chrome
• Version: 79.0.3945.88

Smartphone (please complete the following information):

• Device: Google Pixel XL
• OS: Android 10
• Browser: Chrome
• Version: 79.0.3945.93

Additional context

We investigated, and the problem is that the dropdown menu is already drawn by the time the event is handled. We wrote a hack to work around this behavior by modifying Blockly directly to stop propagating the event:

--- a/core/components/menu/menuitem.js
+++ b/core/components/menu/menuitem.js
@@ -258,6 +258,29 @@ Blockly.MenuItem.prototype.setEnabled = function(enabled) {
  * @package
  */
 Blockly.MenuItem.prototype.handleClick = function(_e) {
+  var target = _e.currentTarget;
+  var parentMenu = this.getParent();
+
+  if (target &&
+    target.classList.contains("focused") &&
+    this.isEnabled() &&
+    parentMenu.getHighlighted() === null) {
+    return;
+  }
+
   if (this.isEnabled()) {
     this.setHighlighted(true);
     this.performActionInternal();

[samelhusseini]

Fixed.