config: delete the control_d_handler option

This change is a preparational step for #1824 (Enabling `frozen_string_literal:
true` in `~/.pryc` crashes most operations).

The handler was mutating `eval_string` that we pass, and this behaviour will
stop working in Ruby 3.

I was pondering about keeping this option but couldn't come up with an easy
solution. I made a GitHub search to see if anybody uses it, and it seems like
nobody configures it. I am not sure why anybody would want to do that, so I hope
it won't be missed.

The handler's behaviour wasn't deleted, it is still in place. We just moved the
handler's code to `pry_instance.rb`.

CHANGELOG.md

@@ -72,6 +72,8 @@
   ([#2003](https://github.com/pry/pry/pull/2003))
 * Deleted `Pry.lazy` (use `Pry::Config::LazyValue` instead)
   ([#2024](https://github.com/pry/pry/pull/2024))
+* Deleted `control_d_handler` configuration option
+  ([#2024](https://github.com/pry/pry/pull/2024))
 
 #### Bug fixes
 

lib/pry.rb

@@ -23,7 +23,6 @@
 require 'pry/color_printer'
 require 'pry/exception_handler'
 require 'pry/system_command_handler'
-require 'pry/control_d_handler'
 require 'pry/command_state'
 
 Pry::Commands = Pry::CommandSet.new unless defined?(Pry::Commands)

lib/pry/config.rb

@@ -106,9 +106,6 @@ class Config
     # @return [Integer] how many input/output lines to keep in memory
     attribute :memory_size
 
-    # @return [Proc]
-    attribute :control_d_handler
-
     # @return [Proc] The proc that runs system commands
     attribute :system
 
@@ -199,7 +196,6 @@ def initialize
         should_load_requires: true,
         should_load_plugins: true,
         windows_console_warning: true,
-        control_d_handler: Pry::ControlDHandler.method(:default),
         memory_size: 100,
         extra_sticky_locals: {},
         command_completions: proc { commands.keys },

lib/pry/pry_instance.rb

@@ -276,7 +276,7 @@ def eval(line, options = {})
 
   def handle_line(line, options)
     if line.nil?
-      config.control_d_handler.call(@eval_string, self)
+      handle_control_d_press
       return
     end
 
@@ -697,5 +697,27 @@ def raise_up!(*args)
   def quiet?
     config.quiet
   end
+
+  # 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 ..`.
+  def handle_control_d_press
+    if !@eval_string.empty?
+      # Clear input buffer.
+      @eval_string = ''
+    elsif binding_stack.one?
+      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).
+      cd_state = Pry::CommandState.default.state_for('cd')
+      cd_state.old_stack = binding_stack.dup
+      binding_stack.pop
+    end
+  end
+  private :handle_control_d_press
 end
 # rubocop:enable Metrics/ClassLength

spec/pry_spec.rb

@@ -466,4 +466,57 @@ class Hello
       expect(backtrace.any? { |l| l.include?(location) }).to equal true
     end
   end
+
+  describe "#eval" do
+    context "when line is nil" do
+      let(:line) { nil }
+
+      context "and when eval string is non-empty" do
+        before { subject.eval_string = 'hello' }
+
+        it "clears input buffer" do
+          subject.eval(line)
+          expect(subject.eval_string).to be_empty
+        end
+      end
+
+      context "and when eval string is empty & pry instance has one binding" do
+        before do
+          subject.eval_string = ''
+          subject.binding_stack = [binding]
+        end
+
+        it "catches :breakout" do
+          expect { subject.eval(line) }.not_to throw_symbol(:breakout)
+        end
+
+        it "clears binding stack" do
+          subject.eval(line)
+          expect(subject.binding_stack).to be_empty
+        end
+      end
+
+      context "and when given eval string is empty & pry instance has 2+ bindings" do
+        let(:binding1) { binding }
+        let(:binding2) { binding }
+        let(:binding_stack) { [binding1, binding2] }
+
+        before do
+          subject.eval_string = ''
+          subject.binding_stack = binding_stack
+        end
+
+        it "saves a dup of the current binding stack in the 'cd' command" do
+          subject.eval(line)
+          cd_state = subject.commands['cd'].state
+          expect(cd_state.old_stack).to eq([binding1, binding2])
+        end
+
+        it "pops the binding off the stack" do
+          subject.eval(line)
+          expect(subject.binding_stack).to eq([binding1])
+        end
+      end
+    end
+  end
 end