Avoid terminal rendering for non-TTY readline output

lib/reline.rb

@@ -58,14 +58,15 @@ class Core
     attr_accessor :key_stroke
     attr_accessor :line_editor
     attr_accessor :last_incremental_search
-    attr_reader :output
+    attr_reader :input, :output
 
     extend Forwardable
     def_delegators :config,
       :autocompletion,
       :autocompletion=
 
     def initialize
+      self.input = STDIN
       self.output = STDOUT
       @mutex = Mutex.new
       @dialog_proc_list = {}
@@ -175,6 +176,7 @@ def dialog_proc(name_sym)
 
     def input=(val)
       raise TypeError unless val.respond_to?(:getc) or val.nil?
+      @input = val
       if val.respond_to?(:getc) && io_gate.respond_to?(:input=)
         io_gate.input = val
       end
@@ -290,6 +292,10 @@ def readline(_prompt = '', _add_history = false, prompt: _prompt, add_history: _
       end
     end
 
+    private def terminal?
+      input.respond_to?(:tty?) && input.tty? && output.respond_to?(:tty?) && output.tty?
+    end
+
     private def inner_readline(prompt, add_history, multiline, rprompt: nil, &confirm_multiline_termination)
       if ENV['RELINE_STDERR_TTY']
         if io_gate.win?
@@ -333,8 +339,12 @@ def readline(_prompt = '', _add_history = false, prompt: _prompt, add_history: _
         end
       end
 
-      line_editor.update_dialogs
-      line_editor.rerender
+      if terminal?
+        line_editor.update_dialogs
+        line_editor.rerender
+      else
+        output.write(prompt)
+      end
 
       begin
         line_editor.set_signal_handlers
@@ -354,13 +364,18 @@ def readline(_prompt = '', _add_history = false, prompt: _prompt, add_history: _
             end
           }
           if line_editor.finished?
-            line_editor.render_finished
+            if terminal?
+              line_editor.render_finished
+            else
+              line = line_editor.line
+              output.write("#{line}\n") if line
+            end
             break
-          else
+          elsif terminal?
             line_editor.rerender
           end
         end
-        io_gate.move_cursor_column(0)
+        io_gate.move_cursor_column(0) if terminal?
       rescue Errno::EIO
         # Maybe the I/O has been closed.
       ensure

test/reline/test_reline.rb

@@ -420,12 +420,22 @@ def test_dumb_terminal
 
   def test_readline_reads_piped_stdin
     out = readline_from_piped_stdin("input\n")
-    assert_include(out, { result: 'input' }.inspect)
+    assert_equal(">input\n#{ { result: 'input' }.inspect }\n", out)
+  end
+
+  def test_readline_with_dumb_terminal_outputs_plain_piped_stdin
+    out = readline_from_dumb_terminal_piped_stdin("input\n")
+    assert_equal("> input\n#{ { result: 'input' }.inspect }\n", out)
   end
 
   def test_readline_returns_nil_on_piped_stdin_eof
     out = readline_from_piped_stdin("")
-    assert_include(out, { result: nil }.inspect)
+    assert_equal(">#{ { result: nil }.inspect }\n", out)
+  end
+
+  def test_readline_with_dumb_terminal_outputs_plain_piped_stdin_eof
+    out = readline_from_dumb_terminal_piped_stdin("")
+    assert_equal("> #{ { result: nil }.inspect }\n", out)
   end
 
   def test_read_eof_returns_input
@@ -488,6 +498,17 @@ def readline_from_piped_stdin(stdin)
     end
   end
 
+  def readline_from_dumb_terminal_piped_stdin(stdin)
+    lib = File.expand_path("../../lib", __dir__)
+    code = "p result: Reline.readline('> ')"
+
+    IO.popen([{"TERM" => "dumb"}, Reline.test_rubybin, "-I#{lib}", "-rreline", "-e", code], "r+") do |io|
+      io.write stdin
+      io.close_write
+      io.read
+    end
+  end
+
   def test_tty_ambiguous_width
     omit unless defined?(PTY)
     ruby_file = Tempfile.create('rubyfile')