1 files changed, 55 insertions, 19 deletions

diff --git a/scripts/check_dockerfiles.sh b/scripts/check_dockerfiles.sh
index d225267..95c18cb 100755
--- a/scripts/check_dockerfiles.sh
+++ b/scripts/check_dockerfiles.sh
@@ -1,6 +1,7 @@
 #!/usr/bin/env bash
 
-set -euxo pipefail
+set -euo pipefail
+shopt -s inherit_errexit
 exec 3>&1 # New file descriptor to stdout
 
 BASE_URL="https://dev.azure.com/\
@@ -12,10 +13,18 @@ repositoryType=${BUILD_REPOSITORY_PROVIDER}&\
 repositoryId=${BUILD_REPOSITORY_NAME}&\
 api-version=5.0"
 
-get_build() {
-    set -e # Poor Ubuntu LTS doesn't have Bash 4.4's inherit_errexit
+declare -A build_cache
 
+get_build() {
     local branch="${1:?"get_build: argument 1 'branch' is unset"}"
+
+    # Attempt to use cached value
+    if [[ -v build_cache["${branch}"] ]]; then
+        printf '%s\n' "Retrieving build for ${branch} from cache." >&3
+        printf '%s' "${build_cache[$branch]}"
+        return 0
+    fi
+
     local url="${BASE_URL}&branchName=${branch}"
 
     printf '%s\n' "Retrieving the latest successful build using ${url}" >&3
@@ -29,10 +38,37 @@ get_build() {
     then
         return 1
     else
+        # Cache the response
+        build_cache["${branch}"]="${response}"
         printf '%s' "${response}"
     fi
 }
 
+can_pull() {
+    local image="${1:?"can_pull: argument 1 'image' is unset"}"
+
+    local master_commit
+    if master_commit="$(
+            get_build "refs/heads/master" \
+            | jq -re '.value[0].sourceVersion'
+        )" \
+        && git diff --quiet "${master_commit}" -- "${@:2}"
+    then
+        printf \
+            '%s\n' \
+            "Can pull ${image} image from Docker Hub; no changes since master."
+
+        printf '%s\n' "##vso[task.setvariable variable=${image^^}_PULL]True"
+    else
+        printf \
+            '%s\n' \
+            "Cannot pull ${image} image from Docker Hub due to detected " \
+            "changes; the ${image} image will be built."
+
+        return 1
+    fi
+}
+
 # Get the previous commit
 if [[ "${BUILD_REASON}" = "PullRequest" ]]; then
     if ! prev_commit="$(
@@ -61,31 +97,31 @@ fi
 
 # Compare diffs
 head="$(git rev-parse HEAD)"
-printf \
-    'Comparing HEAD (%s) against %s (%s)\n' \
-    "${head}" \
-    "${prev_commit}" \
-    "$(git rev-parse "${prev_commit}")"
+printf '%s\n' "Comparing HEAD (${head}) against ${prev_commit}."
 
 if git diff --quiet "${prev_commit}" -- docker/base.Dockerfile; then
     echo "No changes detected in docker/base.Dockerfile."
-    echo "##vso[task.setvariable variable=BASE_CHANGED;isOutput=true]False"
+    echo "##vso[task.setvariable variable=BASE_CHANGED]False"
 else
     # Always rebuild the venv if the base changes.
+    echo "Changes detected in docker/base.Dockerfile; all images will be built."
     exit 0
 fi
 
 if git diff --quiet "${prev_commit}" -- docker/venv.Dockerfile Pipfile*; then
     echo "No changes detected in docker/venv.Dockerfile or the Pipfiles."
-    echo "##vso[task.setvariable variable=VENV_CHANGED;isOutput=true]False"
-    if master_commit="$(
-            get_build "refs/heads/master" \
-            | jq -re '.value[0].sourceVersion'
-        )" \
-        && git diff --quiet "${master_commit}" -- docker/base.Dockerfile
-    then
-        # Though base image hasn't changed, it's still needed to build the venv.
-        echo "Can pull base image from Docker Hub; no changes made master."
-        echo "##vso[task.setvariable variable=BASE_PULL;isOutput=true]True"
+    echo "##vso[task.setvariable variable=VENV_CHANGED]False"
+
+    if ! can_pull venv docker/venv.Dockerfile Pipfile*; then
+        # Venv image can't be pulled so it needs to be built.
+        # Therefore, the base image is needed too.
+        can_pull base docker/base.Dockerfile
     fi
+else
+    echo \
+        "Changes detected in docker/venv.Dockerfile or the Pipfiles;" \
+        "the venv image will be built."
+
+    # Though base image hasn't changed, it's still needed to build the venv.
+    can_pull base docker/base.Dockerfile
 fi