[ruby/reline] Suppress crashing when dynamic_prompt_proc returns a broken prompt list

Co-authored-by: Juanito Fatas <me@juanitofatas.com>

558f7be168

lib/reline/line_editor.rb

@@ -112,6 +112,7 @@ class Reline::LineEditor
           use_cached_prompt_list = true
         end
       end
+      use_cached_prompt_list = false if @rerender_all
       if use_cached_prompt_list
         prompt_list = @cached_prompt_list
       else
@@ -123,6 +124,12 @@ class Reline::LineEditor
       prompt_list = prompt_list.map{ |pr| mode_string + pr } if mode_string
       prompt = prompt_list[@line_index]
       prompt = prompt_list[0] if prompt.nil?
+      prompt = prompt_list.last if prompt.nil?
+      if buffer.size > prompt_list.size
+        (buffer.size - prompt_list.size).times do
+          prompt_list << prompt_list.last
+        end
+      end
       prompt_width = calculate_width(prompt, true)
       [prompt, prompt_width, prompt_list]
     else

test/reline/yamatanooroti/test_rendering.rb

@@ -450,6 +450,18 @@ begin
       EOC
     end
 
+    def test_broken_prompt_list
+      start_terminal(5, 30, %W{ruby -I#{@pwd}/lib #{@pwd}/bin/multiline_repl --broken-dynamic-prompt}, startup_message: 'Multiline REPL.')
+      write("def hoge\n  3\nend")
+      close
+      assert_screen(<<~EOC)
+        Multiline REPL.
+        [0000]> def hoge
+        [0001]>   3
+        [0001]> end
+      EOC
+    end
+
     def test_enable_bracketed_paste
       omit if Reline::IOGate.win?
       write_inputrc <<~LINES