Prepare to record selection changes as perceived by the user

To be able to undo selection changes, we want to record selections
from all commands that modify selections. Each such command will get
its own private copy of the selections object.

This copy will live until the command is finished executing.
All child commands that are run while the command is executing,
will also use the same copy, because to the user it's all just one
selection change anyway.

Add an RAII object in all places where we might modify selections.
The next commit will use this to create the private selections copy
in the constructor (if there is none) and remove redundant history
items in the destructor.

We could avoid the RAII object in some places but that seems worse.
For lifetimes that don't correspond to a lexical scope, we use a
std::unique_ptr. For lambdas that require conversion to std::function,
we use std::shared_ptr because we need something that's copyable.

src/commands.cc

@@ -2009,6 +2009,7 @@ void context_wrap(const ParametersParser& parser, Context& context, StringView d
 
     ScopedSetBool disable_history(c.history_disabled());
     ScopedEdition edition{c};
+    ScopedSelectionEdition selection_edition{c};
 
     if (parser.get_switch("itersel"))
     {
@@ -2523,6 +2524,7 @@ const CommandDesc select_cmd = {
         else if (parser.get_switch("display-column"))
             column_type = ColumnType::DisplayColumn;
         ColumnCount tabstop = context.options()["tabstop"].get<int>();
+        ScopedSelectionEdition selection_edition{context};
         context.selections_write_only() = selection_list_from_strings(buffer, column_type, parser.positionals_from(0), timestamp, 0, tabstop);
     }
 };

src/context.hh

@@ -180,5 +180,19 @@ private:
     SafePtr<Buffer> m_buffer;
 };
 
+struct ScopedSelectionEdition
+{
+    ScopedSelectionEdition(Context& context)
+        : m_context{context},
+          m_buffer{context.has_buffer() ? &context.buffer() : nullptr} {}
+    ScopedSelectionEdition(ScopedSelectionEdition&& other) : m_context{other.m_context}, m_buffer{other.m_buffer}
+    { other.m_buffer = nullptr; }
+
+    ~ScopedSelectionEdition() {}
+private:
+    Context& m_context;
+    SafePtr<Buffer> m_buffer;
+};
+
 }
 #endif // context_hh_INCLUDED

src/input_handler.cc

@@ -93,67 +93,75 @@ struct MouseHandler
 
         Buffer& buffer = context.buffer();
         BufferCoord cursor;
-        auto& selections = context.selections();
         constexpr auto modifiers = Key::Modifiers::Control | Key::Modifiers::Alt | Key::Modifiers::Shift | Key::Modifiers::MouseButtonMask;
         switch ((key.modifiers & ~modifiers).value)
         {
         case Key::Modifiers::MousePress:
             switch (key.mouse_button())
             {
-            case Key::MouseButton::Right:
-                m_dragging = false;
+            case Key::MouseButton::Right: {
+                m_dragging.reset();
                 cursor = context.window().buffer_coord(key.coord());
+                ScopedSelectionEdition selection_edition{context};
+                auto& selections = context.selections();
                 if (key.modifiers & Key::Modifiers::Control)
                     selections = {{selections.begin()->anchor(), cursor}};
                 else
                     selections.main() = {selections.main().anchor(), cursor};
                 selections.sort_and_merge_overlapping();
                 return true;
+            }
 
-            case Key::MouseButton::Left:
-                m_dragging = true;
+            case Key::MouseButton::Left: {
+                m_dragging.reset(new ScopedSelectionEdition{context});
                 m_anchor = context.window().buffer_coord(key.coord());
                 if (not (key.modifiers & Key::Modifiers::Control))
                     context.selections_write_only() = { buffer, m_anchor};
                 else
                 {
+                    auto& selections = context.selections();
                     size_t main = selections.size();
                     selections.push_back({m_anchor});
                     selections.set_main_index(main);
                     selections.sort_and_merge_overlapping();
                 }
                 return true;
+            }
 
             default: return true;
             }
 
-        case Key::Modifiers::MouseRelease:
+        case Key::Modifiers::MouseRelease: {
             if (not m_dragging)
                 return true;
-            m_dragging = false;
+            auto& selections = context.selections();
             cursor = context.window().buffer_coord(key.coord());
             selections.main() = {buffer.clamp(m_anchor), cursor};
             selections.sort_and_merge_overlapping();
+            m_dragging.reset();
             return true;
+        }
 
-        case Key::Modifiers::MousePos:
+        case Key::Modifiers::MousePos: {
             if (not m_dragging)
                 return true;
             cursor = context.window().buffer_coord(key.coord());
+            auto& selections = context.selections();
             selections.main() = {buffer.clamp(m_anchor), cursor};
             selections.sort_and_merge_overlapping();
             return true;
+        }
 
         case Key::Modifiers::Scroll:
-            scroll_window(context, static_cast<int32_t>(key.key), m_dragging);
+            scroll_window(context, static_cast<int32_t>(key.key), (bool)m_dragging);
             return true;
 
         default: return false;
         }
     }
 
 private:
-    bool m_dragging = false;
+    std::unique_ptr<ScopedSelectionEdition> m_dragging;
     BufferCoord m_anchor;
 };
 
@@ -1199,6 +1207,7 @@ class Insert : public InputMode
     Insert(InputHandler& input_handler, InsertMode mode, int count)
         : InputMode(input_handler),
           m_edition(context()),
+          m_selection_edition(context()),
           m_completer(context()),
           m_restore_cursor(mode == InsertMode::Append),
           m_auto_complete{context().options()["autocomplete"].get<AutoComplete>() & AutoComplete::Insert},
@@ -1549,6 +1558,7 @@ class Insert : public InputMode
     }
 
     ScopedEdition   m_edition;
+    ScopedSelectionEdition m_selection_edition;
     InsertCompleter m_completer;
     const bool      m_restore_cursor;
     bool            m_auto_complete;
@@ -1806,6 +1816,7 @@ void scroll_window(Context& context, LineCount offset, bool mouse_dragging)
 
     win_pos.line = clamp(win_pos.line + offset, 0_line, line_count-1);
 
+    ScopedSelectionEdition selection_edition{context};
     SelectionList& selections = context.selections();
     Selection& main_selection = selections.main();
     const BufferCoord anchor = main_selection.anchor();