pry_instance: factor out command state to be globalcommand-global-state

This change is aimed to simplify #1843 (Rework the Pry config).

Current command state implementation gets in the way. We would like to simplify
the Config class. The current implementation penetrates Pry codebase everywhere,
and during my rework of the config I discovered that `watch` uses global command
state.

It means the state should survive `Pry.new` calls. With my (unpublished yet)
implementation, the `watch` command fails to do so. I realised that we can
refactor command state implementation to be global. It makes sense to me and
also helps with the Config refactoring.

With help of a dedicated class we can easily manage the command
state (resetting).

10 files changed, 98 insertions, 15 deletions

diff --git a/lib/pry.rb b/lib/pry.rb
index 3b4bcfe1..fbbaa2ab 100644
--- a/lib/pry.rb
+++ b/lib/pry.rb
@@ -24,6 +24,7 @@ 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)
 
diff --git a/lib/pry/command.rb b/lib/pry/command.rb
index 81cded01..fa6d2e51 100644
--- a/lib/pry/command.rb
+++ b/lib/pry/command.rb
@@ -196,6 +196,10 @@ class Pry
                   end
         end
       end
+
+      def state
+        Pry::CommandState.default.state_for(match)
+      end
     end
 
     # Properties of one execution of a command (passed by {Pry#run_command} as a hash of
@@ -305,7 +309,7 @@ class Pry
     #   state.my_state = "my state"  # this will not conflict with any
     #                                # `state.my_state` used in another command.
     def state
-      pry_instance.command_state[match] ||= Pry::Config.from_hash({})
+      self.class.state
     end
 
     # Revaluate the string (str) and perform interpolation.
diff --git a/lib/pry/command_state.rb b/lib/pry/command_state.rb
new file mode 100644
index 00000000..263d14d8
--- /dev/null
+++ b/lib/pry/command_state.rb
@@ -0,0 +1,29 @@
+require 'ostruct'
+
+class Pry
+  # CommandState is a data structure to hold per-command state.
+  #
+  # Pry commands can store arbitrary state here. This state persists between
+  # subsequent command invocations. All state saved here is unique to the
+  # command.
+  #
+  # @since ?.?.?
+  # @api private
+  class CommandState
+    def self.default
+      @default ||= new
+    end
+
+    def initialize
+      @command_state = {}
+    end
+
+    def state_for(command_name)
+      @command_state[command_name] ||= OpenStruct.new
+    end
+
+    def reset(command_name)
+      @command_state[command_name] = OpenStruct.new
+    end
+  end
+end
diff --git a/lib/pry/control_d_handler.rb b/lib/pry/control_d_handler.rb
index d02e2110..1021c767 100644
--- a/lib/pry/control_d_handler.rb
+++ b/lib/pry/control_d_handler.rb
@@ -16,8 +16,8 @@ class Pry
       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_instance.command_state['cd'] ||= Pry::Config.from_hash({})
-        pry_instance.command_state['cd'].old_stack = pry_instance.binding_stack.dup
+        cd_state = Pry::CommandState.default.state_for('cd')
+        cd_state.old_stack = pry_instance.binding_stack.dup
         pry_instance.binding_stack.pop
       end
     end
diff --git a/lib/pry/pry_instance.rb b/lib/pry/pry_instance.rb
index 9269ded7..e1309ce9 100644
--- a/lib/pry/pry_instance.rb
+++ b/lib/pry/pry_instance.rb
@@ -34,7 +34,6 @@ class Pry
   attr_accessor :last_dir
 
   attr_reader :last_exception
-  attr_reader :command_state
   attr_reader :exit_value
 
   # @since v0.12.0
@@ -72,7 +71,6 @@ class Pry
   def initialize(options = {})
     @binding_stack = []
     @indent        = Pry::Indent.new
-    @command_state = {}
     @eval_string   = ""
     @backtrace     = options.delete(:backtrace) || caller
     target = options.delete(:target)
diff --git a/spec/command_spec.rb b/spec/command_spec.rb
index f56d92db..5991304f 100644
--- a/spec/command_spec.rb
+++ b/spec/command_spec.rb
@@ -416,6 +416,12 @@ RSpec.describe Pry::Command do
     end
   end
 
+  describe ".state" do
+    it "returns a command state" do
+      expect(described_class.state).to be_an(OpenStruct)
+    end
+  end
+
   describe "#run" do
     let(:command_set) do
       set = Pry::CommandSet.new
@@ -475,7 +481,7 @@ RSpec.describe Pry::Command do
     subject { Class.new(described_class).new(pry_instance: Pry.new) }
 
     it "returns a state hash" do
-      expect(subject.state).to be_a(Pry::Config)
+      expect(subject.state).to be_an(OpenStruct)
     end
 
     it "remembers the state" do
diff --git a/spec/command_state_spec.rb b/spec/command_state_spec.rb
new file mode 100644
index 00000000..10097b2b
--- /dev/null
+++ b/spec/command_state_spec.rb
@@ -0,0 +1,47 @@
+RSpec.describe Pry::CommandState do
+  describe ".default" do
+    it "returns the default command state" do
+      expect(described_class.default).to be_a(described_class)
+    end
+
+    context "when called multiple times" do
+      it "returns the same command state" do
+        first_state = described_class.default
+        second_state = described_class.default
+        expect(first_state).to eql(second_state)
+      end
+    end
+  end
+
+  describe "#state_for" do
+    it "returns a state for the matching command" do
+      subject.state_for('command').foobar = 1
+      expect(subject.state_for('command').foobar).to eq(1)
+    end
+
+    it "returns new state for new command" do
+      expect(subject.state_for('command'))
+        .not_to equal(subject.state_for('other-command'))
+    end
+
+    it "memoizes state for the same command" do
+      expect(subject.state_for('command')).to equal(subject.state_for('command'))
+    end
+  end
+
+  describe "#reset" do
+    it "resets the command state for the given command" do
+      subject.state_for('command').foobar = 1
+      subject.reset('command')
+      expect(subject.state_for('command').foobar).to be_nil
+    end
+
+    it "doesn't reset command state for other commands" do
+      subject.state_for('command').foobar = 1
+      subject.state_for('other-command').foobar = 1
+      subject.reset('command')
+
+      expect(subject.state_for('other-command').foobar).to eq(1)
+    end
+  end
+end
diff --git a/spec/commands/cd_spec.rb b/spec/commands/cd_spec.rb
index d2120a6e..38830ace 100644
--- a/spec/commands/cd_spec.rb
+++ b/spec/commands/cd_spec.rb
@@ -16,20 +16,16 @@ describe 'cd' do
       end
 
       def command_state
-        pry.command_state["cd"]
+        pry.commands['cd'].state
       end
 
       def old_stack
-        pry.command_state['cd'].old_stack.dup
+        pry.commands['cd'].state.old_stack.dup
       end
     end
   end
 
-  describe 'state' do
-    it 'should not to be set up in fresh instance' do
-      expect(@t.command_state).to equal nil
-    end
-  end
+  after { Pry::CommandState.default.reset('cd') }
 
   describe 'old stack toggling with `cd -`' do
     describe 'in fresh pry instance' do
diff --git a/spec/commands/shell_command_spec.rb b/spec/commands/shell_command_spec.rb
index 4417f0ee..62526b3c 100644
--- a/spec/commands/shell_command_spec.rb
+++ b/spec/commands/shell_command_spec.rb
@@ -5,11 +5,13 @@ describe Pry::Command::ShellCommand do
 
       @t = pry_tester(@o) do
         def command_state
-          pry.command_state[Pry::Command::ShellCommand.match]
+          Pry::CommandState.default.state_for(Pry::Command::ShellCommand.match)
         end
       end
     end
 
+    after { Pry::CommandState.default.reset(Pry::Command::ShellCommand.match) }
+
     describe ".cd" do
       before do
         allow(Dir).to receive(:chdir)
diff --git a/spec/control_d_handler_spec.rb b/spec/control_d_handler_spec.rb
index 2c5a45ae..5e21ccbe 100644
--- a/spec/control_d_handler_spec.rb
+++ b/spec/control_d_handler_spec.rb
@@ -37,7 +37,7 @@ RSpec.describe Pry::ControlDHandler do
 
     it "saves a dup of the current binding stack in the 'cd' command" do
       described_class.default(eval_string, pry_instance)
-      cd_state = pry_instance.command_state['cd']
+      cd_state = pry_instance.commands['cd'].state
       expect(cd_state.old_stack).to eq([binding1, binding2])
     end