Fix breaking references after GC.compact

ext/rbs_extension/legacy_location.c

@@ -171,10 +171,11 @@ static VALUE location_end_pos(VALUE self) {
 static rbs_constant_id_t rbs_constant_pool_insert_ruby_symbol(VALUE symbol) {
     VALUE name = rb_sym2str(symbol);
 
-    // Constants inserted here will never be freed, but that's acceptable because:
-    // 1. Most symbols passed into here will be the ones already inserted into the constant pool by `parser.c`.
-    // 2. Methods like `add_required_child` and `add_optional_child` will usually only get called with a few different symbols.
-    return rbs_constant_pool_insert_constant(RBS_GLOBAL_CONSTANT_POOL, (const uint8_t *) RSTRING_PTR(name), RSTRING_LEN(name));
+    // To prevent memory compaction from breaking references to strings,
+    // strings are copied and memory managed with an owned type.
+    uint8_t *copied_name = malloc(RSTRING_LEN(name));
+    memcpy((void *) copied_name, RSTRING_PTR(name), RSTRING_LEN(name));
+    return rbs_constant_pool_insert_owned(RBS_GLOBAL_CONSTANT_POOL, copied_name, RSTRING_LEN(name));
 }
 
 static VALUE location_add_required_child(VALUE self, VALUE name, VALUE start, VALUE end) {

test/rbs/location_test.rb

@@ -161,6 +161,34 @@ def test_sub_buffer_local_location
     end
   end
 
+  def test_gc_compaction
+    GC.disable
+    buffer = buffer()
+    locations = 10.times.map do |i|
+      Location.new(buffer, 0, 10).tap do |loc|
+        loc.add_required_child(:static_0, 0...1)
+        loc.add_required_child(:static_1, 1...2)
+        loc.add_required_child(:static_2, 2...3)
+        3.times do |j|
+          loc.add_required_child(:"dynamic_#{i}_#{j}", j...j+1)
+        end
+      end
+    end
+    GC.start
+    GC.start
+    GC.compact
+    locations.each_with_index do |loc, i|
+      assert_instance_of Location, loc[:static_0]
+      assert_instance_of Location, loc[:static_1]
+      assert_instance_of Location, loc[:static_2]
+      3.times do |j|
+        assert_instance_of Location, loc[:"dynamic_#{i}_#{j}"]
+      end
+    end
+  ensure
+    GC.enable
+  end
+
   private
 
   def buffer(content: nil)