Preserve selection direction and improve entering line editing

https://asciinema.org/a/zdNDOTO0LLJzvJjX4pYYm5IZV

src/normal.cc

@@ -2221,7 +2221,7 @@ static const HashMap<Key, NormalCmd, MemoryDomain::Undefined, KeymapBackend> key
     { shift(Key::Home), {"extend to line begin", repeated<select<SelectMode::Extend, select_to_line_begin<false>>>} },
 
     { {'x'}, {"select line", repeated<select<SelectMode::Replace, select_line>>} },
-    { {'X'}, {"extend line", repeated<select<SelectMode::Extend, select_line>>} },
+    { {'X'}, {"extend line", repeated<select<SelectMode::Extend, select_line_extend>>} },
     { {alt('x')}, {"extend selections to whole lines", select<SelectMode::Replace, select_lines>} },
     { {alt('X')}, {"crop selections to whole lines", select<SelectMode::Replace, trim_partial_lines>} },
 

src/selectors.cc

@@ -174,7 +174,9 @@ Optional<Selection>
 select_line(const Context& context, const Selection& selection)
 {
     auto& buffer = context.buffer();
-    auto line = selection.cursor().line;
+    bool forward = selection.anchor() < selection.cursor();
+    auto line = forward ? std::max(selection.cursor().line, selection.anchor().line)
+        : std::min(selection.cursor().line, selection.anchor().line);
 
     if (context.is_line_editing()) {
         ++line;
@@ -185,7 +187,35 @@ select_line(const Context& context, const Selection& selection)
     if (line >= buffer.line_count()) {
         return Optional<Selection>();
     }
-    return target_eol({{line, 0_byte}, {line, buffer[line].length() - 1}});
+    if (forward) {
+        return target_eol({{line, 0_byte}, {line, buffer[line].length() - 1}});
+    } else {
+       return target_eol({{line, buffer[line].length() - 1}, {line, 0_byte}});
+    }
+}
+
+Optional<Selection>
+select_line_extend(const Context& context, const Selection& selection)
+{
+    auto& buffer = context.buffer();
+    bool forward = selection.anchor() < selection.cursor();
+    auto line = std::max(selection.cursor().line, selection.anchor().line);
+    auto starting_line = std::min(selection.cursor().line, selection.anchor().line);
+
+    if (context.is_line_editing()) {
+        ++line;
+    }
+
+    context.enter_or_keep_line_editing();
+
+    if (line >= buffer.line_count()) {
+        return Optional<Selection>();
+    }
+    if (forward) {
+        return target_eol({{starting_line, 0_byte}, {line, buffer[line].length() - 1}});
+    } else {
+       return target_eol({{line, buffer[line].length() - 1}, {starting_line, 0_byte}});
+    }
 }
 
 template<bool only_move>

src/selectors.hh

@@ -31,6 +31,9 @@ select_to_previous_word(const Context& context, const Selection& selection);
 Optional<Selection>
 select_line(const Context& context, const Selection& selection);
 
+Optional<Selection>
+select_line_extend(const Context& context, const Selection& selection);
+
 template<bool forward>
 Optional<Selection>
 select_matching(const Context& context, const Selection& selection);