Pointer#read_pointer should return a pointer with #type_size 1

* Fixes #3837

Author: eregon

CHANGELOG.md

@@ -17,6 +17,7 @@ Compatibility:
 * Fix explicitly inherited `Struct` subclasses and don't provide `#members` method (#3802, @andrykonchin).
 * Support Digest plugins (#1390, @nirvdrum).
 * Joni has been updated from 2.2.1 to 2.2.6 (@andrykonchin).
+* Return a pointer with `#type_size` of 1 for `Pointer#read_pointer` (@eregon).
 
 Performance:
 

src/main/java/org/truffleruby/extra/ffi/PointerNodes.java

@@ -47,6 +47,7 @@
 import com.oracle.truffle.api.dsl.ImportStatic;
 import com.oracle.truffle.api.dsl.Specialization;
 import org.truffleruby.language.objects.AllocationTracing;
+import org.truffleruby.language.objects.WriteObjectFieldNode;
 
 @CoreModule(value = "Truffle::FFI::Pointer", isClass = true)
 public abstract class PointerNodes {
@@ -503,7 +504,8 @@ public abstract static class PointerReadPointerNode extends PrimitiveArrayArgume
 
         @Specialization
         RubyPointer readPointer(long address,
-                @Cached CheckNullPointerNode checkNullPointerNode) {
+                @Cached CheckNullPointerNode checkNullPointerNode,
+                @Cached WriteObjectFieldNode writeTypeSize) {
             final Pointer ptr = new Pointer(getContext(), address);
             checkNullPointerNode.execute(this, ptr);
             final Pointer readPointer = ptr.readPointer(getContext(), 0);
@@ -512,6 +514,10 @@ RubyPointer readPointer(long address,
                     getLanguage().truffleFFIPointerShape,
                     readPointer);
             AllocationTracing.trace(instance, this);
+
+            // We don't call Truffle::FFI::Pointer#initialize so we manually set it instead
+            writeTypeSize.execute(this, instance, "@type_size", 1);
+
             return instance;
         }