Bug 1686361 - [marionette] Sync synthesizeMouseAtPoint from EventUtils.js. r=marionette-reviewers,whimboo

Currently the default value of buttons is set to
MOUSE_BUTTONS_NOT_SPECIFIED, which defers calculation of the value to
the DOMWindowUtils GetButtonsFlagForButton function. This calculates a
default value based upon the value of the button key.

By specifying a default button value of 0, which has a meaning of
ePrimary, the buttons value is calculated as the
ePrimaryFlag (1), suggesting that a button was pressed.

This patch changes the behaviour to set the value of buttons based on
the original value of button before the default was applied. The value
of buttons also considers the event type to ensure that a mousedown
event has a default value calculated by DOMWindowUtils.

With the new behaviour:
- if a value was explicitly set for buttons, this is used
- if a value was explicitly set for button, then the not-specified
  constant is used to defer calculation to DOMWindowUtils
- if an event type was specified and that event type was not the
  'mousedown' event, then the no-button constant is used
- if an event type was not specified or it was for the 'mousedown'
  event, then the not-specified constant is used to defer calculation to
  DOMWindowUtils

Differential Revision: https://phabricator.services.mozilla.com/D105877

testing/marionette/event.js

@@ -178,11 +178,21 @@ event.synthesizeMouseAtPoint = function(left, top, opts, win) {
   } else {
     isWidgetEventSynthesized = false;
   }
-  let buttons;
-  if ("buttons" in opts) {
-    buttons = opts.buttons;
-  } else {
-    buttons = domutils.MOUSE_BUTTONS_NOT_SPECIFIED;
+
+  function computeButtons(aEvent, utils) {
+    if (typeof aEvent.buttons != "undefined") {
+      return aEvent.buttons;
+    }
+
+    if (typeof aEvent.button != "undefined") {
+      return utils.MOUSE_BUTTONS_NOT_SPECIFIED;
+    }
+
+    if (typeof aEvent.type != "undefined" && aEvent.type != "mousedown") {
+      return utils.MOUSE_BUTTONS_NO_BUTTON;
+    }
+
+    return utils.MOUSE_BUTTONS_NOT_SPECIFIED;
   }
 
   if ("type" in opts && opts.type) {
@@ -198,7 +208,7 @@ event.synthesizeMouseAtPoint = function(left, top, opts, win) {
       inputSource,
       isDOMEventSynthesized,
       isWidgetEventSynthesized,
-      buttons
+      computeButtons(opts, domutils)
     );
   } else {
     domutils.sendMouseEvent(
@@ -213,7 +223,7 @@ event.synthesizeMouseAtPoint = function(left, top, opts, win) {
       inputSource,
       isDOMEventSynthesized,
       isWidgetEventSynthesized,
-      buttons
+      computeButtons(Object.assign({ type: "mousedown" }, opts), domutils)
     );
     domutils.sendMouseEvent(
       "mouseup",
@@ -227,7 +237,7 @@ event.synthesizeMouseAtPoint = function(left, top, opts, win) {
       inputSource,
       isDOMEventSynthesized,
       isWidgetEventSynthesized,
-      buttons
+      computeButtons(Object.assign({ type: "mouseup" }, opts), domutils)
     );
   }
 };

testing/marionette/interaction.js

@@ -184,8 +184,6 @@ async function webdriverClickElement(el, a11y) {
       clickPoint.y,
       {
         type: "mousemove",
-        // Remove buttons attribute with https://bugzilla.mozilla.org/show_bug.cgi?id=1686361
-        buttons: 0,
       },
       win
     );