feat: add hover for global variables

lib/ruby_lsp/listeners/hover.rb

@@ -13,6 +13,7 @@ class Hover
           Prism::ConstantReadNode,
           Prism::ConstantWriteNode,
           Prism::ConstantPathNode,
+          Prism::GlobalVariableReadNode,
           Prism::InstanceVariableReadNode,
           Prism::InstanceVariableAndWriteNode,
           Prism::InstanceVariableOperatorWriteNode,
@@ -62,6 +63,7 @@ def initialize(response_builder, global_state, uri, node_context, dispatcher, so
           :on_constant_write_node_enter,
           :on_constant_path_node_enter,
           :on_call_node_enter,
+          :on_global_variable_read_node_enter,
           :on_instance_variable_read_node_enter,
           :on_instance_variable_write_node_enter,
           :on_instance_variable_and_write_node_enter,
@@ -128,6 +130,18 @@ def on_call_node_enter(node)
         handle_method_hover(message)
       end
 
+      sig { params(node: Prism::GlobalVariableReadNode).void }
+      def on_global_variable_read_node_enter(node)
+        global_variable = node.name.to_s
+        entries = @index[global_variable]
+
+        return unless entries
+
+        categorized_markdown_from_index_entries(global_variable, entries).each do |category, content|
+          @response_builder.push(content, category: category)
+        end
+      end
+
       sig { params(node: Prism::InstanceVariableReadNode).void }
       def on_instance_variable_read_node_enter(node)
         handle_instance_variable_hover(node.name.to_s)

test/requests/hover_expectations_test.rb

@@ -60,6 +60,25 @@ def test_hovering_on_erb
     end
   end
 
+  def test_hovering_for_global_variables
+    source = <<~RUBY
+      $DEBUG
+    RUBY
+
+    with_server(source) do |server, uri|
+      index = server.instance_variable_get(:@global_state).index
+      RubyIndexer::RBSIndexer.new(index).index_ruby_core
+
+      server.process_message(
+        id: 1,
+        method: "textDocument/hover",
+        params: { textDocument: { uri: uri }, position: { line: 0, character: 1 } },
+      )
+
+      assert_match("The debug flag", server.pop_response.response.contents.value)
+    end
+  end
+
   def test_hovering_precision
     source = <<~RUBY
       module Foo