From 6b1bfd123f172d6bc75042adc192a703bb4bdee6 Mon Sep 17 00:00:00 2001
From: Lars Kanis <lars@greiz-reinsdorf.de>
Date: Thu, 20 Apr 2023 13:14:25 +0200
Subject: Add some tests to verify that GC.compact works

---
 spec/ffi/gc_compact_spec.rb | 66 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 66 insertions(+)
 create mode 100644 spec/ffi/gc_compact_spec.rb

diff --git a/spec/ffi/gc_compact_spec.rb b/spec/ffi/gc_compact_spec.rb
new file mode 100644
index 0000000..974d7f8
--- /dev/null
+++ b/spec/ffi/gc_compact_spec.rb
@@ -0,0 +1,66 @@
+# -*- rspec -*-
+# encoding: utf-8
+#
+# Tests to verify correct implementation of compaction callbacks in rb_data_type_t definitions.
+#
+# Compaction callbacks update moved VALUEs.
+# In ruby-2.7 they are invoked only while GC.compact or GC.verify_compaction_references.
+# Ruby constants are usually moved, but local variables are not.
+#
+# Effectiveness of the tests below should be verified by commenting the compact callback out like so:
+#
+#   const rb_data_type_t rbffi_struct_layout_data_type = {
+#     .wrap_struct_name = "FFI::StructLayout",
+#     .function = {
+#         .dmark = struct_layout_mark,
+#         .dfree = struct_layout_free,
+#         .dsize = struct_layout_memsize,
+#        # ffi_compact_callback( struct_layout_compact )
+#     },
+#     .parent = &rbffi_type_data_type,
+#     .flags = RUBY_TYPED_FREE_IMMEDIATELY | RUBY_TYPED_WB_PROTECTED
+#   };
+#
+# This should result in a segmentation fault aborting the whole process.
+# Therefore the effectiveness of only one test can be verified per rspec run.
+
+require File.expand_path(File.join(File.dirname(__FILE__), "spec_helper"))
+
+describe "GC.compact", if: GC.respond_to?(:compact) do
+	before :all do
+
+		class St1 < FFI::Struct
+			layout  :i, :int
+		end
+		ST1 = St1.new
+
+		class St2 < FFI::Struct
+			layout  :i, :int
+		end
+		ST2 = St2.new
+		ST2[:i] = 6789
+
+		begin
+			# Use GC.verify_compaction_references instead of GC.compact .
+			# This has the advantage that all movable objects are actually moved.
+			# The downside is that it doubles the heap space of the Ruby process.
+			# Therefore we call it only once and do several tests afterwards.
+			GC.verify_compaction_references(toward: :empty, double_heap: true)
+		rescue NotImplementedError, NoMethodError => err
+			skip("GC.compact skipped: #{err}")
+		end
+	end
+
+	it "should compact FFI::StructLayout without field cache" do
+		expect( ST1[:i] ).to eq( 0 )
+	end
+
+	it "should compact FFI::StructLayout with field cache" do
+		expect( ST2[:i] ).to eq( 6789 )
+	end
+
+	it "should compact FFI::StructLayout::Field" do
+		l = St1.layout
+		expect( l.fields.first.type ).to eq( FFI::Type::Builtin::INT32 )
+	end
+end
-- 
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