Fix 11.1.2 regression on ruby 2.7.0 on Windows

By default ruby 2.7.0 on Windows comes with rb-readline, which doesn't
like `nil` completion procs, and with a version of `irb` that installs
its own completion proc.

That combination causes `byebug` to crash.

Installing a dummy "nil proc" seems like the most compatible thing to
do.

.github/workflows/windows.yml

@@ -15,7 +15,7 @@ jobs:
 
     strategy:
       matrix:
-        version: [2.4.9, 2.5.7, 2.6.5, head]
+        version: [2.4.9, 2.5.7, 2.6.5, 2.7.0, head]
 
     steps:
       - uses: actions/checkout@v2
@@ -33,8 +33,7 @@ jobs:
         run: |
           git clone -q --depth=5  --no-tags --branch=byebug https://github.com/deivid-rodriguez/rb-readline.git C:\rb-readline
           $n_dir = $(ruby -e "print RbConfig::CONFIG['sitelibdir']")
-          Copy-Item -Path C:\rb-readline\lib\readline.rb -Destination $n_dir\readline.rb
-          Copy-Item -Path C:\rb-readline\lib\rbreadline.rb -Destination $n_dir\rbreadline.rb
+          Copy-Item -Path C:\rb-readline\lib\* -Destination $n_dir -Recurse
 
       - name: Setup dependencies
         shell: bash

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [Unreleased]
 
+### Fixed
+
+* [#674](https://github.com/deivid-rodriguez/byebug/pull/674): crash when using byebug on ruby 2.7.0 on Windows.
+
 ## [11.1.2] - 2020-04-17
 
 ### Fixed

lib/byebug/interfaces/local_interface.rb

@@ -53,7 +53,7 @@ def without_readline_completion
       return yield unless orig_completion
 
       begin
-        Readline.completion_proc = nil
+        Readline.completion_proc = ->(_) { nil }
         yield
       ensure
         Readline.completion_proc = orig_completion