chore: demonstrate ownership bug

Signed-off-by: Norman Meier <norman@berty.tech>

examples/gno.land/r/demo/bugs/mis_ownership/gno.mod

@@ -0,0 +1,5 @@
+module "gno.land/r/demo/bugs/mis_ownership"
+
+require (
+        "gno.land/r/demo/bugs/steal_ownership" v0.0.0-latest
+)

examples/gno.land/r/demo/bugs/mis_ownership/mis_ownership.gno

@@ -0,0 +1,16 @@
+package mis_ownership
+
+import "gno.land/r/demo/bugs/steal_ownership"
+
+var (
+	x   = uint32(42)
+	ptr = &x
+)
+
+func init() {
+	steal_ownership.Steal(ptr)
+}
+
+func Mutate() {
+	*ptr = 21
+}

examples/gno.land/r/demo/bugs/steal_ownership/gno.mod

@@ -0,0 +1 @@
+module "gno.land/r/demo/bugs/steal_ownership"

examples/gno.land/r/demo/bugs/steal_ownership/steal_ownership.gno

@@ -0,0 +1,7 @@
+package steal_ownership
+
+var ptr *uint32
+
+func Steal(xptr *uint32) {
+	ptr = xptr
+}

gnovm/pkg/gnolang/realm.go

@@ -69,8 +69,16 @@ func (pid PkgID) Bytes() []byte {
 	return pid.Hashlet[:]
 }
 
+var pathsFromIds = make(map[string]string)
+
 func PkgIDFromPkgPath(path string) PkgID {
-	return PkgID{HashBytes([]byte(path))}
+	id := PkgID{HashBytes([]byte(path))}
+	pathsFromIds[id.String()] = path
+	return id
+}
+
+func PkgPathFromPkgID(id PkgID) string {
+	return pathsFromIds[id.String()]
 }
 
 func ObjectIDFromPkgPath(path string) ObjectID {
@@ -145,7 +153,12 @@ func (rlm *Realm) DidUpdate(po, xo, co Object) {
 		return // do nothing.
 	}
 	if po.GetObjectID().PkgID != rlm.ID {
-		panic("cannot modify external-realm or non-realm object")
+		opid := po.GetObjectID().PkgID
+		prettyName := PkgPathFromPkgID(opid)
+		if prettyName == "" {
+			prettyName = opid.String()
+		}
+		panic(fmt.Sprintf("cannot modify external-realm or non-realm object: object pkg path: %s, realm: %s", prettyName, rlm.Path))
 	}
 	// From here on, po is real (not new-real).
 	// Updates to .newCreated/.newEscaped /.newDeleted made here. (first gen)