Align completion menu items like Readline in noautocomplete mode

lib/reline/line_editor.rb

@@ -49,7 +49,29 @@ module CompletionState
   RenderedScreen = Struct.new(:base_y, :lines, :cursor_y, keyword_init: true)
 
   CompletionJourneyData = Struct.new(:preposing, :postposing, :list, :pointer)
-  MenuInfo = Struct.new(:target, :list)
+
+  class MenuInfo
+    attr_reader :list
+
+    def initialize(list)
+      @list = list
+    end
+
+    def lines(screen_width)
+      return [] if @list.empty?
+
+      list = @list.sort
+      sizes = list.map { |item| Reline::Unicode.calculate_width(item) }
+      item_width = sizes.max + 2
+      num_cols = [screen_width / item_width, 1].max
+      num_rows = list.size.fdiv(num_cols).ceil
+      list_with_padding = list.zip(sizes).map { |item, size| item + ' ' * (item_width - size) }
+      aligned = (list_with_padding + [nil] * (num_rows * num_cols - list_with_padding.size)).each_slice(num_rows).to_a.transpose
+      aligned.map do |row|
+        row.join.rstrip
+      end
+    end
+  end
 
   MINIMUM_SCROLLBAR_HEIGHT = 1
 
@@ -460,7 +482,7 @@ def render_differential
       [[0, Reline::Unicode.calculate_width(l, true), l]]
     end
     if @menu_info
-      @menu_info.list.sort!.each do |item|
+      @menu_info.lines(screen_width).each do |item|
         new_lines << [[0, Reline::Unicode.calculate_width(item), item]]
       end
       @menu_info = nil # TODO: do not change state here
@@ -781,8 +803,8 @@ def editing_mode
     @config.editing_mode
   end
 
-  private def menu(target, list)
-    @menu_info = MenuInfo.new(target, list)
+  private def menu(_target, list)
+    @menu_info = MenuInfo.new(list)
   end
 
   private def complete_internal_proc(list, is_menu)

test/reline/test_line_editor.rb

@@ -121,4 +121,29 @@ def test_complicated
       end
     end
   end
+
+  def test_menu_info_format
+    list = %w[aa b c d e f g hhh i j k]
+    col3 = [
+      'aa   e    i',
+      'b    f    j',
+      'c    g    k',
+      'd    hhh'
+    ]
+    col2 = [
+      'aa   g',
+      'b    hhh',
+      'c    i',
+      'd    j',
+      'e    k',
+      'f'
+    ]
+    assert_equal(col3, Reline::LineEditor::MenuInfo.new(list).lines(19))
+    assert_equal(col3, Reline::LineEditor::MenuInfo.new(list).lines(15))
+    assert_equal(col2, Reline::LineEditor::MenuInfo.new(list).lines(14))
+    assert_equal(col2, Reline::LineEditor::MenuInfo.new(list).lines(10))
+    assert_equal(list, Reline::LineEditor::MenuInfo.new(list).lines(9))
+    assert_equal(list, Reline::LineEditor::MenuInfo.new(list).lines(0))
+    assert_equal([], Reline::LineEditor::MenuInfo.new([]).lines(10))
+  end
 end