Bug 1660363: Don't treat elements inside print preview documents as focusable. r=emilio,mstriemer

Previously, IsFocusable returned true on elements in print preview documents, but the element wouldn't accept focus.
This meant that when you tried to tab, focus would get stuck on the document.
Now, IsFocusable returns false.
Thus, tab doesn't try to stop on these elements and can move out of the document.

Differential Revision: https://phabricator.services.mozilla.com/D88000

dom/base/nsFocusManager.cpp

@@ -1939,14 +1939,6 @@ Element* nsFocusManager::FlushAndCheckIfFocusable(Element* aElement,
     return aElement;
   }
 
-  // cannot focus content in print preview mode. Only the root can be focused.
-  nsPresContext* presContext = presShell->GetPresContext();
-  if (presContext &&
-      presContext->Type() == nsPresContext::eContext_PrintPreview) {
-    LOGCONTENT("Cannot focus %s while in print preview", aElement)
-    return nullptr;
-  }
-
   nsIFrame* frame = aElement->GetPrimaryFrame();
   if (!frame) {
     LOGCONTENT("Cannot focus %s as it has no frame", aElement)

layout/generic/nsIFrame.cpp

@@ -9871,6 +9871,12 @@ bool nsIFrame::IsFocusable(int32_t* aTabIndex, bool aWithMouse) {
   }
   bool isFocusable = false;
 
+  // cannot focus content in print preview mode. Only the root can be focused,
+  // but that's handled elsewhere.
+  if (PresContext()->Type() == nsPresContext::eContext_PrintPreview) {
+    return false;
+  }
+
   if (mContent && mContent->IsElement() && IsVisibleConsideringAncestors() &&
       Style()->GetPseudoType() != PseudoStyleType::anonymousFlexItem &&
       Style()->GetPseudoType() != PseudoStyleType::anonymousGridItem &&

toolkit/components/printing/tests/browser_modal_print.js

@@ -70,3 +70,66 @@ add_task(async function testCancelButton() {
     helper.assertDialogHidden();
   });
 });
+
+add_task(async function testTabOrder() {
+  await PrintHelper.withTestPage(async helper => {
+    helper.assertDialogHidden();
+    await helper.startPrint();
+    helper.assertDialogVisible();
+
+    const printerPicker = helper.doc.getElementById("printer-picker");
+    is(
+      helper.doc.activeElement,
+      printerPicker,
+      "Initial focus on printer picker"
+    );
+
+    // Due to bug 1327274, if we shift+tab before print preview is initialized,
+    // focus will get trapped. Therefore, wait for initialization first.
+    await helper.win.PrintEventHandler._previewUpdatingPromise;
+    const previewBrowser = document.querySelector(".printPreviewBrowser");
+    ok(previewBrowser, "Got the print preview browser");
+    let focused = BrowserTestUtils.waitForEvent(previewBrowser, "focus");
+    EventUtils.synthesizeKey("KEY_Tab", { shiftKey: true });
+    await focused;
+    ok(true, "Print preview focused after shift+tab");
+
+    focused = BrowserTestUtils.waitForEvent(gNavToolbox, "focus", true);
+    EventUtils.synthesizeKey("KEY_Tab", { shiftKey: true });
+    await focused;
+    ok(true, "Toolbox focused after shift+tab");
+
+    focused = BrowserTestUtils.waitForEvent(previewBrowser, "focus");
+    EventUtils.synthesizeKey("KEY_Tab");
+    await focused;
+    ok(true, "Print preview focused after tab");
+
+    focused = BrowserTestUtils.waitForEvent(printerPicker, "focus");
+    EventUtils.synthesizeKey("KEY_Tab");
+    await focused;
+    ok(true, "Printer picker focused after tab");
+
+    const cancelButton = helper.doc.querySelector("button[name=cancel]");
+    ok(cancelButton, "Got the cancel button");
+    focused = BrowserTestUtils.waitForEvent(cancelButton, "focus");
+    cancelButton.focus();
+    await focused;
+    ok(true, "Cancel button focused");
+
+    focused = BrowserTestUtils.waitForEvent(gNavToolbox, "focus", true);
+    EventUtils.synthesizeKey("KEY_Tab");
+    await focused;
+    ok(true, "Toolbox focused after tab");
+
+    focused = BrowserTestUtils.waitForEvent(cancelButton, "focus");
+    EventUtils.synthesizeKey("KEY_Tab", { shiftKey: true });
+    await focused;
+    ok(true, "Cancel button focused after shift+tab");
+
+    await helper.withClosingFn(() => {
+      EventUtils.synthesizeKey("VK_ESCAPE", {});
+    });
+
+    helper.assertDialogHidden();
+  });
+});