[ruby-core:75449] [Ruby trunk Bug#12367] [PATCH] Declaring an already defined class with Object as the new superclass does not raise an error

Issue #12367 has been updated by Nobuyoshi Nakada.

Backport changed from 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN to 2.1: REQUIRED, 2.2: REQUIRED, 2.3: REQUIRED

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Bug #12367: [PATCH] Declaring an already defined class with Object as the new superclass does not raise an error
https://bugs.ruby-lang.org/issues/12367#change-58567

* Author: Benoit Daloze
* Status: Assigned
* Priority: Normal
* Assignee: Benoit Daloze
* ruby -v: 
* Backport: 2.1: REQUIRED, 2.2: REQUIRED, 2.3: REQUIRED
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For example:

~~~ ruby
class SuperclassIgnoresObject < A
end
SuperclassIgnoresObject.superclass # A

class SuperclassIgnoresObject < Object # Should raise a superclass mismatch but it doesn't.
end
SuperclassIgnoresObject.superclass # A
~~~

This seems an unintended side-effect of using Object as the default superclass in the code and not differentiating given/non-given superclass.
In insns.def defineclass:

~~~ c
if (super == Qnil) {
    super = rb_cObject;
}
...
if (super != rb_cObject) {
    // check is superclass mismatch
}
~~~

Proposed patch:

~~~ diff
diff --git a/insns.def b/insns.def
index d34a663..ae7f98f 100644
--- a/insns.def
+++ b/insns.def
@@ -865,10 +865,6 @@ defineclass
 		     rb_obj_class(super));
 	}
 
-	if (super == Qnil) {
-	    super = rb_cObject;
-	}
-
 	vm_check_if_namespace(cbase);
 
 	/* find klass */
@@ -881,7 +877,7 @@ defineclass
 		rb_raise(rb_eTypeError, "%"PRIsVALUE" is not a class", rb_id2str(id));
 	    }
 
-	    if (super != rb_cObject) {
+	    if (VM_DEFINECLASS_HAS_SUPERCLASS_P(flags)) {
 		VALUE tmp;
 		tmp = rb_class_real(RCLASS_SUPER(klass));
 
@@ -892,6 +888,9 @@ defineclass
 	    }
 	}
 	else {
+	    if (!VM_DEFINECLASS_HAS_SUPERCLASS_P(flags)) {
+		super = rb_cObject;
+	    }
 	    /* new class declaration */
 	    klass = rb_define_class_id(id, super);
 	    rb_set_class_path_string(klass, cbase, rb_id2str(id));
~~~

Can I commit?



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