Enforce alphabetical ordering of element-deps

We've started to require this in reviews, so we should really have
automation in place to catch it right away.

Change-Id: I43fd90647acba400cea11c665fb587856514b0ee

bin/dib-lint

@@ -19,6 +19,8 @@
 # common mistakes and exits with a non-zero status if it finds any.
 
 rc=0
+TMPDIR=$(mktemp -d)
+trap "rm -rf $TMPDIR" EXIT
 for i in $(find elements -type f); do
     # Check that files starting with a shebang are +x
     firstline=$(head -n 1 "$i")
@@ -26,5 +28,18 @@ for i in $(find elements -type f); do
         echo "ERROR: $i is not executable"
         rc=1
     fi
+
+    # Check alphabetical ordering of element-deps
+    if [ $(basename $i) = "element-deps" ]; then
+        UNSORTED=${TMPDIR}/element-deps.unsorted
+        SORTED=${TMPDIR}/element-deps.sorted
+        grep -v '^#' $i > ${UNSORTED}
+        sort ${UNSORTED} > ${SORTED}
+        diff -c ${UNSORTED} ${SORTED}
+        if [ $? -ne 0 ]; then
+            echo "ERROR: $i is not sorted alphabetically"
+            rc=1
+        fi
+    fi
 done
 exit $rc