From a3bb288f015b52ad23e0ad1cbbdc76bef8701e3e Mon Sep 17 00:00:00 2001
From: Mark Thom <markjordanthom@gmail.com>
Date: Tue, 28 Apr 2020 19:22:20 -0600
Subject: [PATCH] check that lower bound on term expansion drain is below the
 len of the term expansion vector, queue (#416)

---
 src/prolog/machine/code_repo.rs      | 21 ++++++++++++++++-----
 src/prolog/machine/term_expansion.rs |  1 +
 2 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/src/prolog/machine/code_repo.rs b/src/prolog/machine/code_repo.rs
index eba8c5c9..78f3a548 100644
--- a/src/prolog/machine/code_repo.rs
+++ b/src/prolog/machine/code_repo.rs
@@ -53,12 +53,23 @@ impl CodeRepo {
         self.term_dir
             .get_mut(&key)
             .map(|entry| {
-                (
-                    Predicate((entry.0).0.drain(len..).collect()),
-                    entry.1.drain(queue_len..).collect(),
-                )
+                let terms =
+                    if len < (entry.0).0.len() {
+                        (entry.0).0.drain(len ..).collect()
+                    } else {
+                        vec![]
+                    };
+
+                let queue =
+                    if queue_len < entry.1.len() {
+                        entry.1.drain(queue_len ..).collect()
+                    } else {
+                        VecDeque::new()
+                    };
+
+                (Predicate(terms), queue)
             })
-            .unwrap_or((Predicate::new(), VecDeque::from(vec![])))
+            .unwrap_or((Predicate::new(), VecDeque::new()))
     }
 
     pub(crate)
diff --git a/src/prolog/machine/term_expansion.rs b/src/prolog/machine/term_expansion.rs
index 06d7b3be..d2b6419c 100644
--- a/src/prolog/machine/term_expansion.rs
+++ b/src/prolog/machine/term_expansion.rs
@@ -181,6 +181,7 @@ impl<'a> TermStream<'a> {
             te_len,
             te_queue_len,
         );
+
         let goal_expansion_additions = self.wam.code_repo.truncate_terms(
             (clause_name!("goal_expansion"), 2),
             ge_len,
-- 
2.54.0