Add support for target column preservation

Fixes #64

src/buffer.cc

@@ -137,14 +137,14 @@ ByteCoord Buffer::offset_coord(ByteCoord coord, CharCount offset)
     return {coord.line, line.byte_count_to(character)};
 }
 
-ByteCoord Buffer::offset_coord(ByteCoord coord, LineCount offset)
+ByteCoordAndTarget Buffer::offset_coord(ByteCoordAndTarget coord, LineCount offset)
 {
-    auto character = m_lines[coord.line].char_count_to(coord.column);
+    auto character = coord.target == -1 ? m_lines[coord.line].char_count_to(coord.column) : coord.target;
     auto line = Kakoune::clamp(coord.line + offset, 0_line, line_count()-1);
     auto& content = m_lines[line];
 
     character = std::max(0_char, std::min(character, content.char_length() - 2));
-    return {line, content.byte_count_to(character)};
+    return {line, content.byte_count_to(character), character};
 }
 
 String Buffer::string(ByteCoord begin, ByteCoord end) const

src/buffer.hh

@@ -136,7 +136,7 @@ public:
     ByteCoord clamp(ByteCoord coord) const;
 
     ByteCoord offset_coord(ByteCoord coord, CharCount offset);
-    ByteCoord offset_coord(ByteCoord coord, LineCount offset);
+    ByteCoordAndTarget offset_coord(ByteCoordAndTarget coord, LineCount offset);
 
     const String& name() const { return m_name; }
     String display_name() const;

src/coord.hh

@@ -99,6 +99,19 @@ struct CharCoord : LineAndColumn<CharCoord, LineCount, CharCount>
         : LineAndColumn(line, column) {}
 };
 
+struct ByteCoordAndTarget : ByteCoord
+{
+    [[gnu::always_inline]]
+    constexpr ByteCoordAndTarget(LineCount line = 0, ByteCount column = 0, CharCount target = -1)
+        : ByteCoord(line, column), target(target) {}
+
+    [[gnu::always_inline]]
+    constexpr ByteCoordAndTarget(ByteCoord coord, CharCount target = -1)
+        : ByteCoord(coord), target(target) {}
+
+    CharCount target;
+};
+
 }
 
 #endif // coord_hh_INCLUDED

src/highlighters.cc

@@ -580,7 +580,7 @@ void highlight_selections(const Context& context, HighlightFlags flags, DisplayB
         auto& sel = context.selections()[i];
         const bool forward = sel.anchor() <= sel.cursor();
         ByteCoord begin = forward ? sel.anchor() : buffer.char_next(sel.cursor());
-        ByteCoord end   = forward ? sel.cursor() : buffer.char_next(sel.anchor());
+        ByteCoord end   = forward ? (ByteCoord)sel.cursor() : buffer.char_next(sel.anchor());
 
         const bool primary = (i == context.selections().main_index());
         Face sel_face = get_face(primary ? "PrimarySelection" : "SecondarySelection");

src/selection.hh

@@ -21,10 +21,10 @@ struct Selection
     void merge_with(const Selection& range);
 
     ByteCoord& anchor() { return m_anchor; }
-    ByteCoord& cursor() { return m_cursor; }
+    ByteCoordAndTarget& cursor() { return m_cursor; }
 
     const ByteCoord& anchor() const { return m_anchor; }
-    const ByteCoord& cursor() const { return m_cursor; }
+    const ByteCoordAndTarget& cursor() const { return m_cursor; }
 
     CaptureList& captures() { return m_captures; }
     const CaptureList& captures() const { return m_captures; }
@@ -42,7 +42,7 @@ struct Selection
 
 private:
     ByteCoord m_anchor;
-    ByteCoord m_cursor;
+    ByteCoordAndTarget m_cursor;
 
     CaptureList m_captures;
 };

src/selectors.hh

@@ -18,7 +18,11 @@ inline void clear_selections(SelectionList& selections)
 inline void flip_selections(SelectionList& selections)
 {
     for (auto& sel : selections)
-        std::swap(sel.anchor(), sel.cursor());
+    {
+        ByteCoord tmp = sel.anchor();
+        sel.anchor() = sel.cursor();
+        sel.cursor() = tmp;
+    }
     selections.check_invariant();
 }
 

src/window.cc

@@ -253,7 +253,7 @@ ByteCoord Window::offset_coord(ByteCoord coord, CharCount offset)
     return buffer().offset_coord(coord, offset);
 }
 
-ByteCoord Window::offset_coord(ByteCoord coord, LineCount offset)
+ByteCoordAndTarget Window::offset_coord(ByteCoordAndTarget coord, LineCount offset)
 {
     auto line = clamp(coord.line + offset, 0_line, buffer().line_count()-1);
     DisplayBuffer display_buffer;
@@ -267,8 +267,8 @@ ByteCoord Window::offset_coord(ByteCoord coord, LineCount offset)
     m_highlighters(hook_handler.context(), HighlightFlags::MoveOnly, display_buffer);
     m_builtin_highlighters(hook_handler.context(), HighlightFlags::MoveOnly, display_buffer);
 
-    CharCount column = find_display_column(lines[0], buffer(), coord);
+    CharCount column = coord.target == -1 ? find_display_column(lines[0], buffer(), coord) : coord.target;
-    return find_buffer_coord(lines[1], buffer(), column);
+    return { find_buffer_coord(lines[1], buffer(), column), column };
 }
 
 void Window::on_option_changed(const Option& option)

src/window.hh

@@ -51,7 +51,7 @@ public:
     void   forget_timestamp() { m_timestamp = -1; }
 
     ByteCoord offset_coord(ByteCoord coord, CharCount offset);
-    ByteCoord offset_coord(ByteCoord coord, LineCount offset);
+    ByteCoordAndTarget offset_coord(ByteCoordAndTarget coord, LineCount offset);
 private:
     Window(const Window&) = delete;