[gnome-shell] ci: Cache eslint results

[verdre <jonasd src gnome org>]

commit 9232cbf8a7654d84001e4016a7fc5ada2482bb4c
Author: Florian Müllner <fmuellner gnome org>
Date:   Sat Mar 14 16:15:45 2020 +0100

    ci: Cache eslint results
    
    While this isn't useful during CI, it can provide a massive speed-up
    when used locally.
    
    https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1094

 .gitlab-ci/run-eslint.sh | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)
---
diff --git a/.gitlab-ci/run-eslint.sh b/.gitlab-ci/run-eslint.sh
index accbbecb0a..411c9d45b7 100755
--- a/.gitlab-ci/run-eslint.sh
+++ b/.gitlab-ci/run-eslint.sh
@@ -18,12 +18,14 @@ run_eslint() {
   local extra_args=ARGS_$1
   local output_var=OUTPUT_$1
   local output=${!output_var}
+  local cache=.eslintcache-${1,,}
 
   # ensure output exists even if eslint doesn't report any errors
   mkdir -p $(dirname $output)
   touch $output
 
-  eslint -f unix ${!extra_args} -o $output js subprojects/extensions-app/js
+  eslint -f unix --cache --cache-location $cache ${!extra_args} -o $output \
+    js subprojects/extensions-app/js
 }
 
 list_commit_range_additions() {