fix(scripts/cache-olean): only run the post-checkout hook if we actually changed branches

Author: Scott Morrison

scripts/post-checkout

@@ -1,10 +1,17 @@
 #!/bin/sh
 export PATH=$HOME/.mathlib/bin:$PATH
-# hooks are sometimes run from git GUIs with a limited environment
-# if python3 isn't available, we don't generate an error; just a message
-if /usr/bin/env python3 -c ""; then
+
+OLD_HEAD=$1
+NEW_HEAD=$2
+CHANGED_BRANCH=$3
+
+if [ "$CHANGED_BRANCH" -eq "1" ]; then
+    # hooks are sometimes run from git GUIs with a limited environment
+    # if python3 isn't available, we don't generate an error; just a message
+    if /usr/bin/env python3 -c ""; then
 	echo "Trying to fetch cached olean"
 	cache-olean --fetch
-else
-    echo "'env python3' failed; not running post-checkout hook"
+    else
+        echo "'env python3' failed; not running post-checkout hook"
+    fi
 fi