From b2ba3d1c14f7e686b36508d9126d6d669dfe5507 Mon Sep 17 00:00:00 2001
From: mark <markm@cs.wisc.edu>
Date: Thu, 8 Oct 2020 15:54:29 -0500
Subject: [PATCH] add assert

---
 ci/linkcheck.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/ci/linkcheck.sh b/ci/linkcheck.sh
index a1cd424f..db6b35a5 100755
--- a/ci/linkcheck.sh
+++ b/ci/linkcheck.sh
@@ -9,6 +9,11 @@ if [ "$TRAVIS_EVENT_TYPE" = "cron" ] ; then # running in cron job
 
   echo "Doing full link check."
 elif [ "$CI" = "true" ] ; then # running in PR CI build
+  if [ -n "$TRAVIS_COMMIT_RANGE" ]; then
+    echo "error: unexpected state: COMMIT_RANGE must be non-empty in CI"
+    exit 1
+  fi
+
   CHANGED_FILES=$(git diff --name-only $TRAVIS_COMMIT_RANGE | tr '\n' ' ')
   FLAGS="-f $CHANGED_FILES"