FEATURE: JavaScript evaluation tool (#630)

This is similar to code interpreter by ChatGPT, except that it uses
JavaScript as the execution engine.

Safeguards were added to ensure memory is constrained and evaluation
times out.

config/locales/server.en.yml

@@ -234,6 +234,7 @@ en:
         search_settings: "Searching site settings"
         dall_e: "Generate image"
         search_meta_discourse: "Search Meta Discourse"
+        javascript_evaluator: "Evaluate JavaScript"
       command_help:
         web_browser: "Browse web page using the AI Bot"
         github_search_code: "Search for code in a GitHub repository"
@@ -253,6 +254,7 @@ en:
         search_settings: "Search site settings"
         dall_e: "Generate image using DALL-E 3"
         search_meta_discourse: "Search Meta Discourse"
+        javascript_evaluator: "Evaluate JavaScript"
       command_description:
         web_browser: "Reading <a href='%{url}'>%{url}</a>"
         github_search_code: "Searched for '%{query}' in %{repo}"

lib/ai_bot/personas/persona.rb

@@ -88,6 +88,7 @@ def all_available_tools
               Tools::GithubFileContent,
               Tools::GithubPullRequestDiff,
               Tools::WebBrowser,
+              Tools::JavascriptEvaluator,
             ]
 
             tools << Tools::GithubSearchCode if SiteSetting.ai_bot_github_access_token.present?

lib/ai_bot/tools/javascript_evaluator.rb

@@ -0,0 +1,106 @@
+# frozen_string_literal: true
+
+require "mini_racer"
+require "json"
+
+module DiscourseAi
+  module AiBot
+    module Tools
+      class JavascriptEvaluator < Tool
+        TIMEOUT = 500
+        MAX_MEMORY = 10_000_000
+        MARSHAL_STACK_DEPTH = 20
+
+        def self.signature
+          {
+            name: name,
+            description: "Evaluates JavaScript code using MiniRacer",
+            parameters: [
+              {
+                name: "script",
+                description: "The JavaScript code to evaluate",
+                type: "string",
+                required: true,
+              },
+            ],
+          }
+        end
+
+        def self.name
+          "javascript_evaluator"
+        end
+
+        def script
+          parameters[:script].to_s
+        end
+
+        def timeout
+          @timeout || TIMEOUT
+        end
+
+        def timeout=(value)
+          @timeout = value
+        end
+
+        def max_memory
+          @max_memory || MAX_MEMORY
+        end
+
+        def max_memory=(value)
+          @max_memory = value
+        end
+
+        def invoke
+          context =
+            MiniRacer::Context.new(
+              timeout: timeout,
+              max_memory: MAX_MEMORY,
+              marshal_stack_depth: MARSHAL_STACK_DEPTH,
+            )
+
+          # works around llms like anthropic loving console.log
+          eval_script = <<~JS
+            let console = {};
+            console.log = function(val) {
+              return val;
+            };
+
+            #{script}
+          JS
+
+          result = context.eval(eval_script)
+
+          # only do special handling and truncating for long strings
+          if result.to_s.length > 1000
+            result = truncate(result.to_s, max_length: 10_000, percent_length: 0.3, llm: llm)
+          end
+
+          { result: result }
+        rescue MiniRacer::ScriptTerminatedError => e
+          { error: "JavaScript execution timed out: #{e.message}" }
+        rescue MiniRacer::V8OutOfMemoryError => e
+          { error: "JavaScript execution exceeded memory limit: #{e.message}" }
+        rescue MiniRacer::Error => e
+          { error: "JavaScript execution error: #{e.message}" }
+        end
+
+        def details
+          <<~MD
+
+
+            ```
+            #{script}
+            ```
+
+          MD
+        end
+
+        private
+
+        def description_args
+          { script: script }
+        end
+      end
+    end
+  end
+end

spec/lib/modules/ai_bot/tools/javascript_evaluator_spec.rb

@@ -0,0 +1,71 @@
+# frozen_string_literal: true
+
+RSpec.describe DiscourseAi::AiBot::Tools::JavascriptEvaluator do
+  let(:bot_user) { User.find(DiscourseAi::AiBot::EntryPoint::GPT3_5_TURBO_ID) }
+  let(:llm) { DiscourseAi::Completions::Llm.proxy("open_ai:gpt-3.5-turbo") }
+  let(:progress_blk) { Proc.new {} }
+
+  before { SiteSetting.ai_bot_enabled = true }
+
+  describe "#invoke" do
+    it "successfully evaluates a simple JavaScript expression" do
+      evaluator = described_class.new({ script: "2 + 2" }, bot_user: bot_user, llm: llm)
+
+      result = evaluator.invoke(&progress_blk)
+      expect(result[:result]).to eq(4)
+    end
+
+    it "handles JavaScript execution timeout" do
+      evaluator = described_class.new({ script: "while(true){}" }, bot_user: bot_user, llm: llm)
+
+      evaluator.timeout = 5
+
+      result = evaluator.invoke(&progress_blk)
+      expect(result[:error]).to include("JavaScript execution timed out")
+    end
+
+    it "handles JavaScript memory limit exceeded" do
+      evaluator =
+        described_class.new(
+          { script: "var a = new Array(10000); while(true) { a = a.concat(new Array(10000)) }" },
+          bot_user: bot_user,
+          llm: llm,
+        )
+
+      evaluator.max_memory = 10_000
+      result = evaluator.invoke(&progress_blk)
+      expect(result[:error]).to include("JavaScript execution exceeded memory limit")
+    end
+
+    it "returns error for invalid JavaScript syntax" do
+      evaluator = described_class.new({ script: "const x =;" }, bot_user: bot_user, llm: llm)
+
+      result = evaluator.invoke(&progress_blk)
+      expect(result[:error]).to include("JavaScript execution error: ")
+    end
+
+    it "truncates long results" do
+      evaluator =
+        described_class.new(
+          { script: "const x = 'zxn'.repeat(10000); x + 'Z';" },
+          bot_user: bot_user,
+          llm: llm,
+        )
+
+      result = evaluator.invoke(&progress_blk)
+      expect(result[:result]).not_to include("Z")
+    end
+
+    it "returns result for more complex JavaScript" do
+      evaluator =
+        described_class.new(
+          { script: "const x = [1, 2, 3, 4].map(n => n * 2); x.reduce((a, b) => a + b, 0);" },
+          bot_user: bot_user,
+          llm: llm,
+        )
+
+      result = evaluator.invoke(&progress_blk)
+      expect(result[:result]).to eq(20)
+    end
+  end
+end