Insert a line break when space is inserted at the top of wrapped lines

third_party/WebKit/Source/core/editing/Editor.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 183 matching lines @@
   DEFINE_STATIC_LOCAL(EmptyEditorClient, client, ());
   return client;
 }
 
 EditorClient& Editor::client() const {
   if (Page* page = frame().page())
     return page->editorClient();
   return emptyEditorClient();
 }
 
+static bool isCaretAtStartOfWrappedLine(const FrameSelection& selection) {
+  if (!selection.isCaret())
+    return false;
+  if (selection.affinity() != TextAffinity::Downstream)
+    return false;
+  const Position& position = selection.start();
+  return !inSameLine(PositionWithAffinity(position, TextAffinity::Upstream),
+                     PositionWithAffinity(position, TextAffinity::Downstream));
+}
+
 bool Editor::handleTextEvent(TextEvent* event) {
   // Default event handling for Drag and Drop will be handled by DragController
   // so we leave the event for it.
   if (event->isDrop())
     return false;
 
   // Default event handling for IncrementalInsertion will be handled by
   // TypingCommand::insertText(), so we leave the event for it.
   if (event->isIncrementalInsertion())
     return false;
@@ skipping 16 matching lines @@
     return true;
   }
 
   String data = event->data();
   if (data == "\n") {
     if (event->isLineBreak())
       return insertLineBreak();
     return insertParagraphSeparator();
   }
 
+  // Typing spaces at the beginning of wrapped line is confusing, because
+  // inserted spaces would appear in the previous line.
+  // Insert a line break automatically so that the spaces appear at the caret.
+  // TODO(kojii): rich editing has the same issue, but has more options and
+  // needs coordination with JS. Enable for plaintext only for now and collect
+  // feedback.
+  if (data == " " && !canEditRichly() &&
+      isCaretAtStartOfWrappedLine(frame().selection())) {
+    insertLineBreak();
+  }
+
   return insertTextWithoutSendingTextEvent(EditCommandSource::kMenuOrKeyBinding,
                                            data, false, event);
 }
 
 bool Editor::canEdit() const {
   return frame().selection().rootEditableElement();
 }
 
 bool Editor::canEditRichly() const {
   return frame().selection().isContentRichlyEditable();
@@ skipping 1457 matching lines @@
 }
 
 DEFINE_TRACE(Editor) {
   visitor->trace(m_frame);
   visitor->trace(m_lastEditCommand);
   visitor->trace(m_undoStack);
   visitor->trace(m_mark);
 }
 
 }  // namespace blink