Bug 1858804 - Make `TextControlState::GetIMEContentObserver()` return `nullptr` if it observes for `HTMLEditor` r=smaug

`<input>` and `<textarea>` can be an editing host. If so, setting focus to the elements causes `IMEContentObserver` observing HTML editing under the text control element instead of observing the native anonymous tree for the elements. Therefore, if `IMEContentObserver` observes it with `HTMLEditor`, it does not need to notify `IMEContentObserver` of the `value` changes. Differential Revision: https://phabricator.services.mozilla.com/D191163
2023-10-18 07:36:34 +00:00 · 2023-10-18 07:36:34 +00:00 · e5434d6609
--- a/dom/events/IMEContentObserver.h
+++ b/dom/events/IMEContentObserver.h
@ -152,6 +152,9 @@ class IMEContentObserver final : public nsStubMutationObserver,
    return mIMENotificationRequests &&
           mIMENotificationRequests->WantDuringDeactive();
  }
+  [[nodiscard]] bool EditorIsTextEditor() const {
+    return mEditorBase && mEditorBase->IsTextEditor();
+  }
  nsIWidget* GetWidget() const { return mWidget; }
  void SuppressNotifyingIME();
  void UnsuppressNotifyingIME();
--- a/dom/html/TextControlState.cpp
+++ b/dom/html/TextControlState.cpp
@ -3044,7 +3044,11 @@ IMEContentObserver* TextControlState::GetIMEContentObserver() const {
      mTextCtrlElement != IMEStateManager::GetFocusedElement()) {
    return nullptr;
  }
-  return IMEStateManager::GetActiveContentObserver();
+  IMEContentObserver* observer = IMEStateManager::GetActiveContentObserver();
+  // The text control element may be an editing host.  In this case, the
+  // observer does not observe the anonymous nodes under mTextCtrlElement.
+  // So, it means that the observer is not for ours.
+  return observer && observer->EditorIsTextEditor() ? observer : nullptr;
 }

 }  // namespace mozilla
--- a/testing/web-platform/tests/editing/crashtests/set-input-value-of-editing-host-after-changing-type.html
+++ b/testing/web-platform/tests/editing/crashtests/set-input-value-of-editing-host-after-changing-type.html
@ -0,0 +1,15 @@
+<!doctype html>
+<html>
+<head>
+<meta charset="utf-8">
+<script>
+document.addEventListener("DOMContentLoaded", () => {
+  const input = document.querySelector("input");
+  input.focus();
+  input.type = "text";
+  input.value = "new value";
+}, {once: true});
+</script>
+</head>
+<body><input type="button" contenteditable></body>
+</html>