Fix ^D press in nested REPLs

The interesting moment is that `cd -` is still a bit dorky.

  [1] pry(main)> _pry_.repl :a
  [2] pry(:a):1> _pry_.repl :b
  [3] pry(:b):2> cd -
  [4] pry(:b):2> cd -
  [5] pry(:b):2>

The problem is that `_pry_.repl` pushes a new binding onto
`binding_stack`, however, it knows nothing about `old_stack`.

Well, there is a workaround for this.

  [1] pry(main)> _pry_.repl :a
  [2] pry(:a):1> ^D
  [3] pry(main)> cd -
  [4] pry(:a):1> cd -
  [5] pry(main)>

Fix "undefined method `old_stack=' for nil:NilClass" error in this
commit, when you press ^D in a nested REPL. Add a test case for this.
Rewrite some comments and old Control-D units tests (so they use newer
test API).

Signed-off-by: Kyrylo Silin <kyrylosilin@gmail.com>

lib/pry.rb

@@ -104,23 +104,22 @@ class Pry
                 end,
                ]
 
-  # Deal with the ^D key being pressed, different behaviour in
-  # different cases:
-  # 1) In an expression     - behave like `!` command   (clear input buffer)
-  # 2) At top-level session - behave like `exit command (break out of repl loop)
-  # 3) In a nested session  - behave like `cd ..`       (pop a binding)
+  # Deal with the ^D key being pressed. Different behaviour in different cases:
+  #   1. In an expression behave like `!` command.
+  #   2. At top-level session behave like `exit` command.
+  #   3. In a nested session behave like `cd ..`.
   DEFAULT_CONTROL_D_HANDLER = proc do |eval_string, _pry_|
     if !eval_string.empty?
-      # Clear input buffer.
-      eval_string.replace("")
+      eval_string.replace('') # Clear input buffer.
     elsif _pry_.binding_stack.one?
-      # ^D at top-level breaks out of a REPL loop.
       _pry_.binding_stack.clear
       throw(:breakout)
     else
-      # Otherwise, saves current binding stack as old stack and pops last
-      # binding out of binding stack (the old stack still has that binding).
-      _pry_.command_state["cd"].old_stack = _pry_.binding_stack.dup
+      # Store the entire binding stack before popping. Useful for `cd -`.
+      if _pry_.command_state['cd'].nil?
+        _pry_.command_state['cd'] = OpenStruct.new
+      end
+      _pry_.command_state['cd'].old_stack = _pry_.binding_stack.dup
       _pry_.binding_stack.pop
     end
   end

spec/control_d_handler_spec.rb

@@ -1,45 +1,58 @@
 require 'helper'
 
 describe Pry::DEFAULT_CONTROL_D_HANDLER do
-  describe 'control-d press' do
+
+  describe "control-d press" do
+
     before do
+      # Simulates a ^D press.
       @control_d = "Pry::DEFAULT_CONTROL_D_HANDLER.call('', _pry_)"
-      @binding_stack = "self.binding_stack = _pry_.binding_stack.dup"
     end
 
-   describe 'in an expression' do
-      it 'should clear out passed string' do
-        str = "hello world"
+    describe "in an expression" do
+      it "should clear out passed string" do
+        str = 'hello world'
         Pry::DEFAULT_CONTROL_D_HANDLER.call(str, nil)
-        str.should == ""
+        str.should == ''
       end
     end
 
-    describe 'at top-level session' do
-      it 'should break out of a REPL loop' do
-        instance = nil
-        redirect_pry_io(InputTester.new(@control_d)) do
-          instance = Pry.new
-          instance.repl
+
+    describe "at top-level session" do
+      it "breaks out of a REPL" do
+        pry_tester(0).simulate_repl do |t|
+          t.eval @control_d
+        end.should == nil
+      end
+    end
+
+    describe "in a nested session" do
+      it "pops last binding from the binding stack" do
+        pry_tester(0).simulate_repl { |t|
+          t.eval 'cd :foo'
+          t.eval('_pry_.binding_stack.size').should == 2
+          t.eval(@control_d)
+          t.eval('_pry_.binding_stack.size').should == 1
+          t.eval 'exit-all'
+        }
+      end
+
+      it "breaks out of the parent session" do
+        pry_tester(:outer).simulate_repl do |o|
+          o.context = :inner
+          o.simulate_repl { |i|
+            i.eval('_pry_.current_context.eval("self")').should == :inner
+            i.eval('_pry_.binding_stack.size').should == 2
+            i.eval @control_d
+            i.eval('_pry_.binding_stack.size').should == 1
+            i.eval('_pry_.current_context.eval("self")').should == :outer
+            i.eval 'throw :breakout'
+          }
+          o.eval 'exit-all'
         end
-
-        instance.binding_stack.should.be.empty
       end
     end
 
-    describe 'in a nested session' do
-      it 'should pop last binding from the binding stack' do
-        base = OpenStruct.new
-        base.obj = OpenStruct.new
-
-        redirect_pry_io(InputTester.new("cd obj", "self.stack_size = _pry_.binding_stack.size",
-                                        @control_d, "self.stack_size = _pry_.binding_stack.size", "exit-all")) do
-          Pry.start(base)
-        end
-
-        base.obj.stack_size.should == 2
-        base.stack_size.should == 1
-      end
-    end
   end
+
 end