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

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

Index: third_party/WebKit/Source/core/editing/Editor.cpp
diff --git a/third_party/WebKit/Source/core/editing/Editor.cpp b/third_party/WebKit/Source/core/editing/Editor.cpp
index 79d38cb36fe377f0d516a531a5b4fb95d4f2a6f6..66ef6becc75e74660ceb48fa3497963f00e30c4b 100644
--- a/third_party/WebKit/Source/core/editing/Editor.cpp
+++ b/third_party/WebKit/Source/core/editing/Editor.cpp
@@ -201,6 +201,16 @@ EditorClient& Editor::client() const {
   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.
@@ -237,6 +247,17 @@ bool Editor::handleTextEvent(TextEvent* event) {
     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);
 }