LibGUI+HackStudio: Fix cursor appearance and crash while debugging

HackStudio uses a TreeView to display the list of current variables
while debugging, and when the program completes, it sets that view's
model to a null model. This would trip an assertion if the TreeView
had something selected at the time, so this patch lessens the
assertion into a simple null check.

Additionally, the cursor would look laggy when moving about the
editor because the code was waiting for a window repaint to update
the cursor's look when it makes more sense to update the cursor
when it actually moves. This change also requires the base
GUI::TextEditor to expose a getter to tell if its currently in a drag
selection.

Finally, requesting a context menu in the line ruler on the side of
the editor would also place/remove breakpoints, which was counter
intuitive, so this requires a left click to modify breakpoint placement.

4 files changed, 12 insertions, 11 deletions

diff --git a/DevTools/HackStudio/Editor.cpp b/DevTools/HackStudio/Editor.cpp
index 697d811ceb..9520298a72 100644
--- a/DevTools/HackStudio/Editor.cpp
+++ b/DevTools/HackStudio/Editor.cpp
@@ -107,11 +107,6 @@ void Editor::paint_event(GUI::PaintEvent& event)
         painter.draw_rect(rect, palette().selection());
     }
 
-    if (m_hovering_lines_ruler)
-        window()->set_override_cursor(GUI::StandardCursor::Arrow);
-    else if (m_hovering_editor)
-        window()->set_override_cursor(m_hovering_link && m_holding_ctrl ? GUI::StandardCursor::Hand : GUI::StandardCursor::IBeam);
-
     if (ruler_visible()) {
         size_t first_visible_line = text_position_at(event.rect().top_left()).line();
         size_t last_visible_line = text_position_at(event.rect().bottom_right()).line();
@@ -217,12 +212,16 @@ void Editor::mousemove_event(GUI::MouseEvent& event)
     if (!highlighter)
         return;
 
-    auto ruler_line_rect = ruler_content_rect(text_position.line());
-    m_hovering_lines_ruler = (event.position().x() < ruler_line_rect.width());
-
     bool hide_tooltip = true;
     bool is_over_link = false;
 
+    auto ruler_line_rect = ruler_content_rect(text_position.line());
+    auto hovering_lines_ruler = (event.position().x() < ruler_line_rect.width());
+    if (hovering_lines_ruler && !is_in_drag_select())
+        window()->set_override_cursor(GUI::StandardCursor::Arrow);
+    else if (m_hovering_editor)
+        window()->set_override_cursor(m_hovering_link && m_holding_ctrl ? GUI::StandardCursor::Hand : GUI::StandardCursor::IBeam);
+
     for (auto& span : document().spans()) {
         if (span.range.contains(m_previous_text_position) && !span.range.contains(text_position)) {
             if (highlighter->is_navigatable(span.data) && span.is_underlined) {
@@ -272,7 +271,7 @@ void Editor::mousedown_event(GUI::MouseEvent& event)
 
     auto text_position = text_position_at(event.position());
     auto ruler_line_rect = ruler_content_rect(text_position.line());
-    if (event.position().x() < ruler_line_rect.width()) {
+    if (event.button() == GUI::MouseButton::Left && event.position().x() < ruler_line_rect.width()) {
         if (!m_breakpoint_lines.contains_slow(text_position.line())) {
             m_breakpoint_lines.append(text_position.line());
             on_breakpoint_change(wrapper().filename_label().text(), text_position.line(), BreakpointChange::Added);
diff --git a/DevTools/HackStudio/Editor.h b/DevTools/HackStudio/Editor.h
index 69561b39ce..0d83145660 100644
--- a/DevTools/HackStudio/Editor.h
+++ b/DevTools/HackStudio/Editor.h
@@ -77,7 +77,6 @@ private:
     bool m_hovering_editor { false };
     bool m_hovering_link { false };
     bool m_holding_ctrl { false };
-    bool m_hovering_lines_ruler { false };
 
     Vector<size_t> m_breakpoint_lines;
     Optional<size_t> m_execution_position;
diff --git a/Libraries/LibGUI/TextEditor.h b/Libraries/LibGUI/TextEditor.h
index a6138ecde9..901345b7e9 100644
--- a/Libraries/LibGUI/TextEditor.h
+++ b/Libraries/LibGUI/TextEditor.h
@@ -129,6 +129,8 @@ public:
     const SyntaxHighlighter* syntax_highlighter() const;
     void set_syntax_highlighter(OwnPtr<SyntaxHighlighter>);
 
+    bool is_in_drag_select() const { return m_in_drag_select; }
+
 protected:
     explicit TextEditor(Type = Type::MultiLine);
 
diff --git a/Libraries/LibGUI/TreeView.cpp b/Libraries/LibGUI/TreeView.cpp
index 7c1d62df35..016037d6cb 100644
--- a/Libraries/LibGUI/TreeView.cpp
+++ b/Libraries/LibGUI/TreeView.cpp
@@ -377,7 +377,8 @@ void TreeView::did_update_model(unsigned flags)
 void TreeView::did_update_selection()
 {
     AbstractView::did_update_selection();
-    ASSERT(model());
+    if (!model())
+        return;
     auto index = selection().first();
     if (!index.is_valid())
         return;