prevent LoadError being raised when using auto completions + Bundler. (#1896)

* Prevent Bundler from raising a LoadError when accessing input completions.

The scenario:

- $ mkdir foogem
- $ cd foogem
- $ echo "source 'https://rubygems.org'" > Gemfile
- $ bundle install
- $ pry -rbundler/setup
- type "foo".<tab> into Pry

Notice that a LoadError is raised when trying to require
"pry/input_completer". This happens because Pry is not in the
Gemfile, so once the sandbox is initialized by Bundler any require
for a Pry file is doomed to file.

Couple that with the fact that '_pry_.config.completer' is not
loaded until a user uses tab completion, and we end up with this
broken situation.

lib/pry.rb

@@ -96,6 +96,7 @@ require 'tempfile'
 require 'pathname'
 
 require 'pry/version'
+require 'pry/input_completer'
 require 'pry/repl'
 require 'pry/code'
 require 'pry/ring'

lib/pry/config/default.rb

@@ -115,7 +115,6 @@ class Pry
           Pry::Config.from_hash(Pry::Command::Ls::DEFAULT_OPTIONS)
         },
         completer: proc {
-          require "pry/input_completer"
           Pry::InputCompleter
         },
         gist: proc {

spec/helper.rb

@@ -1,6 +1,7 @@
 require 'bundler/setup'
 Bundler.require :default, :test
 require 'pry/testable'
+require 'English'
 require_relative 'spec_helpers/mock_pry'
 require_relative 'spec_helpers/repl_tester'
 

spec/integration/bundler_spec.rb

@@ -0,0 +1,19 @@
+RSpec.describe 'Bundler' do
+  let(:ruby) { RbConfig.ruby.shellescape }
+  let(:pry_dir) { File.expand_path(File.join(__FILE__, '../../../lib')).shellescape }
+
+  context "when Pry requires Gemfile, which doesn't specify Pry as a dependency" do
+    it "loads auto-completion correctly" do
+      code = <<-RUBY
+      require "pry"
+      require "bundler/inline"
+      gemfile(true) do
+        source "https://rubygems.org"
+      end
+      exit 42 if Pry.config.completer
+      RUBY
+      `#{ruby} -I#{pry_dir} -e'#{code}'`
+      expect($CHILD_STATUS.exitstatus).to eq(42)
+    end
+  end
+end