Fix crash on TAB under ruby 2.7

When IRB from ruby 2.7 is loaded, it installs a Readline completion proc
that assumes IRB is running (and crashes otherwise). Workaround this by
clearing the Readline completion when using it directly.

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+* [#657](https://github.com/deivid-rodriguez/byebug/pull/657): crash when hitting \<TAB\> due to IRB completion mechanism included in the default ruby 2.7 version of the `irb` gem ([@terceiro]).
+
 ## [11.1.1] - 2020-01-24
 
 ### Fixed
@@ -911,6 +915,7 @@
 [@sethk]: https://github.com/sethk
 [@shuky19]: https://github.com/shuky19
 [@tacnoman]: https://github.com/tacnoman
+[@terceiro]: https://github.com/terceiro
 [@tzmfreedom]: https://github.com/tzmfreedom
 [@wallace]: https://github.com/wallace
 [@windwiny]: https://github.com/windwiny

lib/byebug/interfaces/local_interface.rb

@@ -21,7 +21,7 @@ def initialize
     # @param prompt Prompt to be displayed.
     #
     def readline(prompt)
-      with_repl_like_sigint { Readline.readline(prompt) || EOF_ALIAS }
+      with_repl_like_sigint { without_readline_completion { Readline.readline(prompt) || EOF_ALIAS } }
     end
 
     #
@@ -40,5 +40,24 @@ def with_repl_like_sigint
     ensure
       trap("INT", orig_handler)
     end
+
+    #
+    # Disable any Readline completion procs.
+    #
+    # Other gems, for example, IRB could've installed completion procs that are
+    # dependent on them being loaded. Disable those while byebug is the REPL
+    # making use of Readline.
+    #
+    def without_readline_completion
+      orig_completion = Readline.completion_proc
+      return yield unless orig_completion
+
+      begin
+        Readline.completion_proc = nil
+        yield
+      ensure
+        Readline.completion_proc = orig_completion
+      end
+    end
   end
 end

test/runner_against_valid_program_test.rb

@@ -118,6 +118,15 @@ def test_run_with_debug_flag
       assert_match(/Debug flag is true/, stdout)
     end
 
+    def test_run_and_press_tab_doesnt_make_byebug_crash
+      stdout = run_byebug(
+        example_path,
+        input: "\tputs 'Reached here'"
+      )
+
+      assert_match(/Reached here/, stdout)
+    end
+
     def test_run_stops_at_the_first_line_by_default
       stdout = run_byebug(example_path)