[ruby/reline] Use appropriate dialog height and reduce screen pushup

problem
(https://github.com/ruby/reline/pull/542)

* Provide preferred_dialog_height for dialog positioning

* Fix rendering test

lib/reline.rb

@@ -260,7 +260,7 @@ module Reline
         pos: cursor_pos_to_render,
         contents: result,
         scrollbar: true,
-        height: 15,
+        height: [15, preferred_dialog_height].min,
         bg_color: 46,
         pointer_bg_color: 45,
         fg_color: 37,

lib/reline/line_editor.rb

@@ -562,6 +562,16 @@ class Reline::LineEditor
       @line_editor.instance_variable_get(:@screen_size).last
     end
 
+    def screen_height
+      @line_editor.instance_variable_get(:@screen_size).first
+    end
+
+    def preferred_dialog_height
+      rest_height = @line_editor.instance_variable_get(:@rest_height)
+      scroll_partial_screen = @line_editor.instance_variable_get(:@scroll_partial_screen) || 0
+      [cursor_pos.y - scroll_partial_screen, rest_height, (screen_height + 6) / 5].max
+    end
+
     def completion_journey_data
       @line_editor.instance_variable_get(:@completion_journey_data)
     end

test/reline/yamatanooroti/test_rendering.rb

@@ -1365,21 +1365,21 @@ begin
 
     def test_scroll_at_bottom_for_dialog
       start_terminal(10, 40, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl --autocomplete}, startup_message: 'Multiline REPL.')
-      write("\n\n\n\n\n\n")
-      write("def hoge\n\n\n\n\n\n\nend\C-p\C-p\C-p\C-e")
+      write("\n\n\n\n\n\n\n\n\n\n\n")
+      write("def hoge\n\nend\C-p\C-e")
       write("  S")
       close
       assert_screen(<<~'EOC')
+        prompt>
+        prompt>
+        prompt>
+        prompt>
+        prompt>
         prompt> def hoge
-        prompt>
-        prompt>
-        prompt>
         prompt>   S
-        prompt>   String
-        prompt>   Struct
-        prompt> enSymbol
-                  ScriptError
-                  SyntaxError
+        prompt> enString     █
+                  Struct     ▀
+                  Symbol
       EOC
     end
 
@@ -1433,30 +1433,35 @@ begin
 
     def test_clear_dialog_when_just_move_cursor_at_last_line
       start_terminal(10, 30, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl --autocomplete}, startup_message: 'Multiline REPL.')
-      write("class A\n  3\nend\n")
-      write("\C-p\C-p\C-p\C-e\C-hS")
+      write("class A\n  3\nend\n\n\n")
+      write("\C-p\C-p\C-e; S")
       write("\C-n")
-      write("1")
+      write(";")
       close
       assert_screen(<<~'EOC')
         prompt>   3
         prompt> end
         => 3
-        prompt> class S
-        prompt>   31
-        prompt> end
+        prompt>
+        prompt>
+        prompt> class A
+        prompt>   3; S
+        prompt> end;
       EOC
     end
 
     def test_clear_dialog_when_adding_new_line_to_end_of_buffer
       start_terminal(10, 30, %W{ruby -I#{@pwd}/lib #{@pwd}/test/reline/yamatanooroti/multiline_repl --autocomplete}, startup_message: 'Multiline REPL.')
-      write("class A\n  def a\n    3\n  end\nend")
+      write("class A\n  def a\n    3\n    3\n  end\nend")
       write("\n")
       write("class S")
       write("\n")
       write("  3")
       close
       assert_screen(<<~'EOC')
+        prompt>   def a
+        prompt>     3
+        prompt>     3
         prompt>   end
         prompt> end
         => :a
@@ -1474,6 +1479,7 @@ begin
       write("  3")
       close
       assert_screen(<<~'EOC')
+        prompt>     3
         prompt>   end
         prompt> end
         => :a