Include RBS paths when indexing workspace

lib/rubydex/graph.rb

@@ -45,6 +45,7 @@ def workspace_paths
       end
 
       add_workspace_dependency_paths(paths)
+      add_core_rbs_definition_paths(paths)
       paths.uniq!
       paths
     end
@@ -71,5 +72,21 @@ def add_workspace_dependency_paths(paths)
         nil
       end
     end
+
+    # Searches for the latest installation of the `rbs` gem and adds the paths for the core and stdlib RBS definitions
+    # to the list of paths. This method does not require `rbs` to be a part of the bundle. It searches for whatever
+    # latest installation of `rbs` exists in the system and fails silently if we can't find one
+    #
+    #: (Array[String]) -> void
+    def add_core_rbs_definition_paths(paths)
+      rbs_gem_path = Gem.path
+        .flat_map { |path| Dir.glob(File.join(path, "gems", "rbs-[0-9]*/")) }
+        .max_by { |path| Gem::Version.new(File.basename(path).delete_prefix("rbs-")) }
+
+      return unless rbs_gem_path
+
+      paths << File.join(rbs_gem_path, "core")
+      paths << File.join(rbs_gem_path, "stdlib")
+    end
   end
 end

test/graph_test.rb

@@ -560,6 +560,23 @@ def test_workspace_paths
     end
   end
 
+  def test_index_workspace_includes_rbs_core_definitions
+    # Ensure the `rbs` gem is installed on CI
+    Gem.install("rbs") if ENV["CI"]
+
+    graph = Rubydex::Graph.new
+    graph.index_workspace
+    graph.resolve
+
+    ["Kernel", "Object", "BasicObject", "Integer"].each do |core_namespace|
+      rbs_kernel = graph[core_namespace].definitions.find do |definition|
+        uri = URI(definition.location.uri)
+        File.extname(uri.path) == ".rbs"
+      end
+      assert(rbs_kernel, "Expected to find RBS definition for `#{core_namespace}` in the graph")
+    end
+  end
+
   private
 
   def assert_diagnostics(expected, actual)