Register C globals holding Ruby objects with the GC

CHANGELOG.md

@@ -1,5 +1,7 @@
 ## (unreleased)
 
+* Register the C globals that hold Ruby classes and modules with the GC, so raising `TinyTds::Error` after GC compaction no longer crashes with a segmentation fault. Fixes #608.
+
 ## 3.4.0
 
 * Add Ruby 4.0 to the cross compile list

ext/tiny_tds/client.c

@@ -541,6 +541,7 @@ static VALUE rb_tinytds_connect(VALUE self, VALUE opts)
 void init_tinytds_client()
 {
   cTinyTdsClient = rb_define_class_under(mTinyTds, "Client", rb_cObject);
+  rb_global_variable(&cTinyTdsClient);
   rb_define_alloc_func(cTinyTdsClient, allocate);
   /* Define TinyTds::Client Public Methods */
   rb_define_method(cTinyTdsClient, "tds_version", rb_tinytds_tds_version, 0);

ext/tiny_tds/result.c

@@ -702,9 +702,12 @@ void init_tinytds_result()
 {
   /* Data Classes */
   cKernel = rb_const_get(rb_cObject, rb_intern("Kernel"));
+  rb_global_variable(&cKernel);
   cDate = rb_const_get(rb_cObject, rb_intern("Date"));
+  rb_global_variable(&cDate);
   /* Define TinyTds::Result */
   cTinyTdsResult = rb_define_class_under(mTinyTds, "Result", rb_cObject);
+  rb_global_variable(&cTinyTdsResult);
   rb_undef_alloc_func(cTinyTdsResult);
   /* Define TinyTds::Result Public Methods */
   rb_define_method(cTinyTdsResult, "fields", rb_tinytds_result_fields, 0);

ext/tiny_tds/tiny_tds_ext.c

@@ -8,8 +8,10 @@ VALUE mTinyTds, cTinyTdsError;
 
 void Init_tiny_tds()
 {
-  mTinyTds      = rb_define_module("TinyTds");
+  mTinyTds = rb_define_module("TinyTds");
+  rb_global_variable(&mTinyTds);
   cTinyTdsError = rb_const_get(mTinyTds, rb_intern("Error"));
+  rb_global_variable(&cTinyTdsError);
   init_tinytds_client();
   init_tinytds_result();
 }

test/gc_compaction_test.rb

@@ -0,0 +1,37 @@
+require "test_helper"
+require "open3"
+require "rbconfig"
+
+class GcCompactionTest < Minitest::Spec
+  describe "after GC compaction" do
+    it "raises TinyTds::Error instead of crashing when a connection fails" do
+      skip "GC compaction is not supported on this platform" if !GC.respond_to?(:verify_compaction_references)
+
+      # Ruby 3.2 renamed the double_heap: keyword to expand_heap:
+      heap_keyword =
+        if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("3.2")
+          "expand_heap"
+        else
+          "double_heap"
+        end
+
+      script = <<~RUBY
+        require "tiny_tds"
+
+        GC.verify_compaction_references(#{heap_keyword}: true, toward: :empty)
+
+        begin
+          TinyTds::Client.new(host: "127.0.0.1", port: 1, username: "unused", password: "unused", login_timeout: 1)
+        rescue TinyTds::Error
+          exit 0
+        end
+
+        exit 1
+      RUBY
+
+      output, status = Open3.capture2e(RbConfig.ruby, "-I", File.expand_path("../lib", __dir__), "-e", script)
+
+      assert status.success?, "expected TinyTds::Error to be raised, got #{status.inspect}:\n#{output}"
+    end
+  end
+end