Bug 1540150 - Make it impossible to enter the native drag-drop loop in test automation. r=NeilDeakin

Differential Revision: https://phabricator.services.mozilla.com/D25428

--HG--
extra : moz-landing-system : lando

dom/events/test/test_bug1264380.html

@@ -13,37 +13,58 @@ function runTests()
 
   let iframe = document.createElement('iframe');
   document.body.appendChild(iframe);
-  iframe.contentDocument.body.innerHTML = '<div id="outter"/>';
+  iframe.contentDocument.body.innerHTML = '<div id="outer"/>';
 
   let iframeDoc = iframe.contentDocument;
   let iframeWin = iframe.contentWindow;
 
-  let shadow = iframeDoc.querySelector('#outter').attachShadow({mode: 'open'});
+  let shadow = iframeDoc.querySelector('#outer').attachShadow({mode: 'open'});
   let target = iframeDoc.createElement('a');
-  let linkText = iframeDoc.createTextNode("Drag me if you can!");
+
+  const TEXT = "Drag me if you can!";
+  let linkText = iframeDoc.createTextNode(TEXT);
   target.appendChild(linkText);
-  target.href = "http://www.mozilla.org/";
+
+  const URL = "http://www.mozilla.org/";
+  target.href = URL;
   shadow.appendChild(target);
 
-  let dataTransfer;
-  let trapDrag = function(event) {
-    ok(true, "Got dragstart event");
-    dataTransfer = event.dataTransfer;
-    ok(dataTransfer, "DataTransfer object is available.");
-    is(SpecialPowers.wrap(dataTransfer).mozItemCount, 1, "initial link item count");
-    is(dataTransfer.getData("text/uri-list"), "http://www.mozilla.org/", "link text/uri-list");
-    is(dataTransfer.getData("text/plain"), "http://www.mozilla.org/", "link text/plain");
+  // Some of the drag data we don't actually care about for this test,
+  // so we'll use this comparator function to ignore them.
+  function ignoreFunc(actualData, expectedData) {
+    return true;
   }
 
-  ok(!dragService.getCurrentSession(), "There shouldn't be a drag session!");
-  iframeWin.addEventListener("dragstart", trapDrag, true);
-  synthesizeMouse(target, 2, 2, { type: "mousedown" }, iframeWin);
-  synthesizeMouse(target, 11, 11, { type: "mousemove" }, iframeWin);
-  synthesizeMouse(target, 20, 20, { type: "mousemove" }, iframeWin);
-  iframeWin.removeEventListener("dragstart", trapDrag, true);
-  ok(dragService.getCurrentSession(), "Drag session is available.");
-  dragService.endDragSession(false);
-  ok(!dragService.getCurrentSession(), "There shouldn't be a drag session anymore!");
+  const EXPECTED_DRAG_DATA = [[{
+    type: "text/x-moz-url",
+    data: "",
+    eqTest: ignoreFunc,
+  }, {
+    type: "text/x-moz-url-data",
+    data: "",
+    eqTest: ignoreFunc,
+  }, {
+    type: "text/x-moz-url-desc",
+    data: "",
+    eqTest: ignoreFunc,
+  }, {
+    type: "text/uri-list",
+    data: URL,
+  }, {
+    type: "text/_moz_htmlinfo",
+    data: "",
+    eqTest: ignoreFunc,
+  }, {
+    type: "text/html",
+    data: "",
+    eqTest: ignoreFunc,
+  }, {
+    type: "text/plain",
+    data: URL,
+  }]];
+
+  let result = synthesizeDragStart(target, EXPECTED_DRAG_DATA, iframeWin);
+  is(result, null, "Should have gotten the expected drag data.");
   SimpleTest.finish();
 }
 

layout/generic/test/mochitest.ini

@@ -106,7 +106,7 @@ skip-if = os=='win'
 [test_image_selection.html]
 [test_image_selection_2.html]
 [test_invalidate_during_plugin_paint.html]
-skip-if = toolkit == 'android'
+skip-if = toolkit == 'android' || headless # Headless:Bug 1405871
 [test_intrinsic_size_on_loading.html]
 [test_movement_by_characters.html]
 [test_movement_by_words.html]

layout/generic/test/test_bug470212.html

@@ -26,6 +26,11 @@ function doShiftDrag(){
     // Drag canvas element starts with a mouse down event, combine with shift
     // key, follows by two mouse move events.
 
+    window.addEventListener("dragstart", e => {
+      e.preventDefault();
+      e.stopPropagation();
+    }, { once: true });
+
     // Press on left-top corner of the canvas element.
     wu.sendMouseEvent('mousedown',  canvasRect.left, canvasRect.top, 0, 1, 4);
     // Move to the center of this cavas element.

widget/nsBaseDragService.cpp

@@ -205,6 +205,23 @@ nsBaseDragService::InvokeDragSession(
     nsContentPolicyType aContentPolicyType = nsIContentPolicy::TYPE_OTHER) {
   AUTO_PROFILER_LABEL("nsBaseDragService::InvokeDragSession", OTHER);
 
+  // If you're hitting this, a test is causing the browser to attempt to enter
+  // the drag-drop native nested event loop, which will put the browser in a
+  // state that won't run tests properly until there's manual intervention
+  // to exit the drag-drop loop (either by moving the mouse or hitting escape),
+  // which can't be done from script since we're in the nested loop.
+  //
+  // The best way to avoid this is to catch the dragstart event on the item
+  // being dragged, and then to call preventDefault() and stopPropagating() on
+  // it. Alternatively, use EventUtils.synthesizeDragStart, which will do this
+  // for you.
+  if (XRE_IsParentProcess()) {
+    MOZ_ASSERT(
+        !xpc::IsInAutomation(),
+        "About to start drag-drop native loop on which will prevent later "
+        "tests from running properly.");
+  }
+
   NS_ENSURE_TRUE(aDOMNode, NS_ERROR_INVALID_ARG);
   NS_ENSURE_TRUE(mSuppressLevel == 0, NS_ERROR_FAILURE);