Turn off semantic highlighting on files with more than 100k chars

lib/ruby_lsp/requests/semantic_highlighting.rb

@@ -23,6 +23,10 @@ module Requests
     class SemanticHighlighting < Request
       extend T::Sig
 
+      # This maximum number of characters for providing highlighting is the same limit imposed by the VS Code TypeScript
+      # extension. Even with delta requests, anything above this number lags the editor significantly
+      MAXIMUM_CHARACTERS_FOR_HIGHLIGHT = 100_000
+
       class << self
         extend T::Sig
 

lib/ruby_lsp/server.rb

@@ -307,13 +307,25 @@ def text_document_did_open(message)
           Document::LanguageId::Ruby
         end
 
-        @store.set(
+        document = @store.set(
           uri: text_document[:uri],
           source: text_document[:text],
           version: text_document[:version],
           encoding: @global_state.encoding,
           language_id: language_id,
         )
+
+        if document.source.length > Requests::SemanticHighlighting::MAXIMUM_CHARACTERS_FOR_HIGHLIGHT
+          send_message(
+            Notification.new(
+              method: "window/showMessage",
+              params: Interface::ShowMessageParams.new(
+                type: Constant::MessageType::WARNING,
+                message: "This file is too long. For performance reasons, semantic highlighting will be disabled",
+              ),
+            ),
+          )
+        end
       end
     end
 
@@ -415,6 +427,11 @@ def run_combined_requests(message)
     def text_document_semantic_tokens_full(message)
       document = @store.get(message.dig(:params, :textDocument, :uri))
 
+      if document.source.length > Requests::SemanticHighlighting::MAXIMUM_CHARACTERS_FOR_HIGHLIGHT
+        send_empty_response(message[:id])
+        return
+      end
+
       unless document.is_a?(RubyDocument) || document.is_a?(ERBDocument)
         send_empty_response(message[:id])
         return
@@ -431,6 +448,11 @@ def text_document_semantic_tokens_full(message)
     def text_document_semantic_tokens_delta(message)
       document = @store.get(message.dig(:params, :textDocument, :uri))
 
+      if document.source.length > Requests::SemanticHighlighting::MAXIMUM_CHARACTERS_FOR_HIGHLIGHT
+        send_empty_response(message[:id])
+        return
+      end
+
       unless document.is_a?(RubyDocument) || document.is_a?(ERBDocument)
         send_empty_response(message[:id])
         return
@@ -454,6 +476,11 @@ def text_document_semantic_tokens_range(message)
       uri = params.dig(:textDocument, :uri)
       document = @store.get(uri)
 
+      if document.source.length > Requests::SemanticHighlighting::MAXIMUM_CHARACTERS_FOR_HIGHLIGHT
+        send_empty_response(message[:id])
+        return
+      end
+
       unless document.is_a?(RubyDocument) || document.is_a?(ERBDocument)
         send_empty_response(message[:id])
         return

lib/ruby_lsp/store.rb

@@ -66,7 +66,7 @@ def get(uri)
         version: Integer,
         language_id: Document::LanguageId,
         encoding: Encoding,
-      ).void
+      ).returns(Document[T.untyped])
     end
     def set(uri:, source:, version:, language_id:, encoding: Encoding::UTF_8)
       @state[uri.to_s] = case language_id

test/server_test.rb

@@ -544,6 +544,55 @@ def test_closing_document_before_computing_features_does_not_error
     end
   end
 
+  def test_semantic_highlighting_support_is_disabled_at_100k_characters
+    path_to_large_file = Gem.find_files("prism/**/node.rb").first
+    uri = URI::Generic.from_path(path: path_to_large_file)
+
+    capture_io do
+      @server.process_message({
+        method: "textDocument/didOpen",
+        params: {
+          textDocument: {
+            uri: uri,
+            text: File.read(path_to_large_file),
+            version: 1,
+            languageId: "ruby",
+          },
+        },
+      })
+
+      @server.process_message({
+        id: 1,
+        method: "textDocument/semanticTokens/full",
+        params: { textDocument: { uri: uri } },
+      })
+
+      result = find_message(RubyLsp::Result, id: 1)
+      assert_nil(result.response)
+
+      @server.process_message({
+        id: 2,
+        method: "textDocument/semanticTokens/full/delta",
+        params: { textDocument: { uri: uri } },
+      })
+
+      result = find_message(RubyLsp::Result, id: 2)
+      assert_nil(result.response)
+
+      @server.process_message({
+        id: 3,
+        method: "textDocument/semanticTokens/range",
+        params: {
+          textDocument: { uri: uri },
+          range: { start: { line: 0, character: 0 }, end: { line: 15, character: 0 } },
+        },
+      })
+
+      result = find_message(RubyLsp::Result, id: 3)
+      assert_nil(result.response)
+    end
+  end
+
   private
 
   def with_uninstalled_rubocop(&block)