LibGUI+TextEditor: Make TextDocument modified state track undo stack

This was quite unreliable before. Changes to the undo stack's modified
state are now reflected in the document's modified state, and the
GUI::TextEditor widget has its undo/redo actions updated automatically.

UndoStack is still a bit hard to understand due to the lazy coalescing
of commands, and that's something we should improve upon (e.g with more
explicit, incremental command merging.) But for now, this is a nice
improvement and undo/redo finally behaves in a way that feels natural.

1 files changed, 5 insertions, 0 deletions

diff --git a/Userland/Libraries/LibGUI/TextEditor.cpp b/Userland/Libraries/LibGUI/TextEditor.cpp
index bd9b9754e9..7e1582562d 100644
--- a/Userland/Libraries/LibGUI/TextEditor.cpp
+++ b/Userland/Libraries/LibGUI/TextEditor.cpp
@@ -1638,6 +1638,11 @@ void TextEditor::document_did_update_undo_stack()
 {
     m_undo_action->set_enabled(can_undo());
     m_redo_action->set_enabled(can_redo());
+
+    // FIXME: This is currently firing more often than it should.
+    //        Ideally we'd only send this out when the undo stack modified state actually changes.
+    if (on_modified_change)
+        on_modified_change(document().is_modified());
 }
 
 void TextEditor::document_did_set_text()