Add MCP support

Signed-off-by: Stan Lo <stan.lo@shopify.com>

Author: st0012

.cursor/mcp.json

@@ -0,0 +1,7 @@
+{
+  "mcpServers": {
+    "rubyMcp": {
+      "command": "./.ruby-lsp/ruby-mcp-bridge"
+    }
+  }
+}

.vscode/mcp.json

@@ -0,0 +1,9 @@
+{
+  "inputs": [],
+  "servers": {
+    "rubyMcp": {
+      "type": "stdio",
+      "command": "${workspaceFolder}/.ruby-lsp/ruby-mcp-bridge"
+    }
+  }
+}

Gemfile.lock

@@ -2,10 +2,12 @@ PATH
   remote: .
   specs:
     ruby-lsp (0.23.24)
+      json_rpc_handler (~> 0.1.1)
       language_server-protocol (~> 3.17.0)
       prism (>= 1.2, < 2.0)
       rbs (>= 3, < 5)
       sorbet-runtime (>= 0.5.10782)
+      webrick (>= 1.8)
 
 GEM
   remote: https://rubygems.org/
@@ -23,6 +25,7 @@ GEM
       rdoc (>= 4.0.0)
       reline (>= 0.4.2)
     json (2.10.2)
+    json_rpc_handler (0.1.1)
     language_server-protocol (3.17.0.4)
     lint_roller (1.1.0)
     logger (1.7.0)
@@ -117,6 +120,7 @@ GEM
     unicode-display_width (3.1.4)
       unicode-emoji (~> 4.0, >= 4.0.4)
     unicode-emoji (4.0.4)
+    webrick (1.9.1)
     yard (0.9.37)
     yard-sorbet (0.9.0)
       sorbet-runtime

lib/ruby_lsp/global_state.rb

@@ -33,6 +33,9 @@ class GlobalState
     #: String?
     attr_reader :telemetry_machine_id
 
+    #: bool
+    attr_reader :uses_ruby_mcp
+
     #: -> void
     def initialize
       @workspace_uri = URI::Generic.from_path(path: Dir.pwd) #: URI::Generic
@@ -56,6 +59,7 @@ def initialize
       @enabled_feature_flags = {} #: Hash[Symbol, bool]
       @mutex = Mutex.new #: Mutex
       @telemetry_machine_id = nil #: String?
+      @uses_ruby_mcp = false #: bool
     end
 
     #: [T] { -> T } -> T
@@ -151,6 +155,9 @@ def apply_options(options)
         )
       end
 
+      @uses_ruby_mcp = detects_ruby_mcp
+      notifications << Notification.window_log_message("Uses Ruby MCP: #{@uses_ruby_mcp}")
+
       encodings = options.dig(:capabilities, :general, :positionEncodings)
       @encoding = if !encodings || encodings.empty?
         Encoding::UTF_16LE
@@ -205,8 +212,30 @@ def supports_watching_files
       @client_capabilities.supports_watching_files
     end
 
+    #: -> bool
+    def detects_ruby_mcp
+      check_mcp_file(".vscode/mcp.json", ["servers", "rubyMcp"]) ||
+        check_mcp_file(".cursor/mcp.json", ["mcpServers", "rubyMcp"])
+    end
+
     private
 
+    # Helper method to check for rubyMcp configuration in a specific file
+    #: (String relative_path, Array[String] keys_to_check) -> bool
+    def check_mcp_file(relative_path, keys_to_check)
+      file_path = File.join(workspace_path, relative_path)
+      return false unless File.exist?(file_path)
+
+      begin
+        config = JSON.parse(File.read(file_path))
+        # Check if the nested keys exist
+        !!config.dig(*keys_to_check)
+      rescue JSON::ParserError
+        # If JSON parsing fails, consider it not configured
+        false
+      end
+    end
+
     #: (Array[String] direct_dependencies, Array[String] all_dependencies) -> String
     def detect_formatter(direct_dependencies, all_dependencies)
       # NOTE: Intentionally no $ at end, since we want to match rubocop-shopify, etc.

lib/ruby_lsp/internal.rb

@@ -31,6 +31,8 @@
 require "securerandom"
 require "shellwords"
 require "set"
+require "webrick"
+require "json_rpc_handler"
 
 require "ruby-lsp"
 require "ruby_lsp/base_server"
@@ -41,6 +43,7 @@
 require "ruby_lsp/client_capabilities"
 require "ruby_lsp/global_state"
 require "ruby_lsp/server"
+require "ruby_lsp/mcp_server"
 require "ruby_lsp/type_inferrer"
 require "ruby_lsp/node_context"
 require "ruby_lsp/document"