From: Mark Thom <markjordanthom@gmail.com>
Date: Wed, 4 Dec 2019 05:01:38 +0000 (-0700)
Subject: fix copy_term/3 infinite looping on cyclic terms
X-Git-Tag: v0.8.118~36^2~5
X-Git-Url: https://git.sagredo.dev/?a=commitdiff_plain;h=738ea59e2367b1f24233fa1897554fecbbbcf185;p=scryer-prolog.git

fix copy_term/3 infinite looping on cyclic terms
---

diff --git a/src/prolog/machine/copier.rs b/src/prolog/machine/copier.rs
index 51a56dd2..13e21ee3 100644
--- a/src/prolog/machine/copier.rs
+++ b/src/prolog/machine/copier.rs
@@ -90,6 +90,11 @@ impl<T: CopierTarget> CopyTermState<T> {
             ra @ Addr::AttrVar(_) | ra @ Addr::HeapCell(..) | ra @ Addr::StackCell(..) => {
                 if ra == rd {
                     self.reinstantiate_var(ra, threshold);
+
+                    if let AttrVarPolicy::StripAttributes = self.attr_var_policy {
+                        self.trail.push((Ref::HeapCell(addr), self.target[addr].clone()));
+                        self.target[addr] = HeapCellValue::Addr(Addr::HeapCell(threshold));
+                    }
                 } else {
                     self.target[threshold] = HeapCellValue::Addr(ra);
                 }