From 86f490378f199a7bbe135ba774ee292d296e1476 Mon Sep 17 00:00:00 2001
From: "Pedro D. Garcia Lopez" <lorrydriveloper@gmail.com>
Date: Mon, 27 Nov 2023 22:17:06 +0000
Subject: [PATCH] add the ability to store last eval in variable.

---
 lib/web_console/evaluator.rb       | 14 ++++++++++++--
 lib/web_console/railtie.rb         |  6 ++++++
 test/web_console/evaluator_test.rb | 16 ++++++++++++++++
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/lib/web_console/evaluator.rb b/lib/web_console/evaluator.rb
index dc91d061..4c719bed 100644
--- a/lib/web_console/evaluator.rb
+++ b/lib/web_console/evaluator.rb
@@ -7,6 +7,8 @@ module WebConsole
   # difference of a regular +Binding+ eval is that +Evaluator+ will always
   # return a string and will format exception output.
   class Evaluator
+    # stores last evalutation in this variable for futher use.
+    cattr_accessor :last_evaluation_variable, default: '_'
     # Cleanses exceptions raised inside #eval.
     cattr_reader :cleaner, default: begin
       cleaner = ActiveSupport::BacktraceCleaner.new
@@ -14,6 +16,7 @@ class Evaluator
       cleaner
     end
 
+
     def initialize(binding = TOPLEVEL_BINDING)
       @binding = binding
     end
@@ -21,16 +24,23 @@ def initialize(binding = TOPLEVEL_BINDING)
     def eval(input)
       # Binding#source_location is available since Ruby 2.6.
       if @binding.respond_to? :source_location
-        "=> #{@binding.eval(input, *@binding.source_location).inspect}\n"
+        output = "=> #{@binding.eval(input, *@binding.source_location).inspect}\n"
       else
-        "=> #{@binding.eval(input).inspect}\n"
+        output = "=> #{@binding.eval(input).inspect}\n"
       end
+      set_last_eval(input)
+      output
     rescue Exception => exc
       format_exception(exc)
     end
 
     private
 
+      def set_last_eval(input)
+        return if input.blank?
+        @binding.eval("#{last_evaluation_variable} = #{input}")
+      end
+
       def format_exception(exc)
         backtrace = cleaner.clean(Array(exc.backtrace) - caller)
 
diff --git a/lib/web_console/railtie.rb b/lib/web_console/railtie.rb
index 9bc8fdc6..42a941e3 100644
--- a/lib/web_console/railtie.rb
+++ b/lib/web_console/railtie.rb
@@ -84,5 +84,11 @@ def web_console_permissions
     initializer "i18n.load_path" do
       config.i18n.load_path.concat(Dir[File.expand_path("../locales/*.yml", __FILE__)])
     end
+
+    initializer 'web_console.last_evaluation_variable' do
+      if last_evaluation_variable = config.web_console.last_evaluation_variable
+        Evaluator.last_evaluation_variable = last_evaluation_variable
+      end
+    end
   end
 end
diff --git a/test/web_console/evaluator_test.rb b/test/web_console/evaluator_test.rb
index c5b603c8..b53fec8e 100644
--- a/test/web_console/evaluator_test.rb
+++ b/test/web_console/evaluator_test.rb
@@ -66,6 +66,22 @@ def backtrace
       END
     end
 
+    test "Evaluator preserve the last value in the _ variable" do
+      @repl.class.last_evaluation_variable = "_"
+      assert_equal "=> 42\n", @repl.eval("foo = 42")
+      assert_equal "=> 42\n", @repl.eval("_")
+      assert_equal "=> 50\n", @repl.eval("_ + 8")
+      assert_equal "=> 50\n", @repl.eval("_")
+    end
+
+    test "last evaluation variable can be configured" do
+      assert_equal "=> 42\n", @repl.eval("foo = 42")
+      assert_equal "=> 42\n", @repl.eval("_")
+      @repl.class.last_evaluation_variable = "$_last_value"
+      assert_equal "=> 42\n", @repl.eval("foo = 42")
+      assert_equal "=> 42\n", @repl.eval("$_last_value")
+    end
+
     private
 
       def current_trace