From 02f4ef7cde5ab7b69545791f3750ae03d251e8ae Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jakub=20Ber=C3=A1nek?= <berykubik@gmail.com>
Date: Fri, 3 May 2024 15:52:00 +0200
Subject: [PATCH] Allow reusing CI Docker cache when running CI images locally

---
 src/ci/docker/run.sh | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/src/ci/docker/run.sh b/src/ci/docker/run.sh
index acd88870b16..22dcb808c74 100755
--- a/src/ci/docker/run.sh
+++ b/src/ci/docker/run.sh
@@ -101,10 +101,18 @@ if [ -f "$docker_dir/$image/Dockerfile" ]; then
     # It seems that it cannot be the same as $IMAGE_TAG, otherwise it overwrites the cache
     CACHE_IMAGE_TAG=${REGISTRY}/${REGISTRY_USERNAME}/rust-ci-cache:${cksum}
 
-    # On non-CI jobs, we don't do any caching.
+    # On non-CI jobs, we try to download a pre-built image from the rust-lang-ci
+    # ghcr.io registry. If it is not possible, we fall back to building the image
+    # locally.
     if ! isCI;
     then
-        retry docker build --rm -t rust-ci -f "$dockerfile" "$context"
+        if docker pull "${IMAGE_TAG}"; then
+            echo "Downloaded Docker image from CI"
+            docker tag "${IMAGE_TAG}" rust-ci
+        else
+            echo "Building local Docker image"
+            retry docker build --rm -t rust-ci -f "$dockerfile" "$context"
+        fi
     # On PR CI jobs, we don't have permissions to write to the registry cache,
     # but we can still read from it.
     elif [[ "$PR_CI_JOB" == "1" ]];