From ba19f41873fec98bb24ba709f4b76c3f58ca5aaa Mon Sep 17 00:00:00 2001
From: Nadrieril
Date: Thu, 15 Aug 2019 13:05:23 +0200
Subject: Fix bug in shifting contexts

---
 dhall/src/core/context.rs | 11 ++++++++++-
 1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/dhall/src/core/context.rs b/dhall/src/core/context.rs
index 62affcf..8d14415 100644
--- a/dhall/src/core/context.rs
+++ b/dhall/src/core/context.rs
@@ -97,7 +97,16 @@ impl<T> Context<T> {
     where
         T: Clone + Shift,
     {
-        Some(self.do_with_var(var, |var, i| Ok(i.shift(delta, &var)?))?)
+        if delta < 0 {
+            Some(self.do_with_var(var, |var, i| Ok(i.shift(delta, &var)?))?)
+        } else {
+            Some(Context(Rc::new(
+                self.0
+                    .iter()
+                    .map(|(l, i)| Ok((l.clone(), i.shift(delta, &var)?)))
+                    .collect::<Result<_, _>>()?,
+            )))
+        }
     }
     fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self
     where
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