Write script to check dockerfiles

3 files changed, 88 insertions, 44 deletions

diff --git a/azure-pipelines.yml b/azure-pipelines.yml
index a05fc3b..f9a187a 100644
--- a/azure-pipelines.yml
+++ b/azure-pipelines.yml
@@ -8,47 +8,10 @@ jobs:
     vmImage: 'Ubuntu-16.04'
 
   steps:
-    - script: |
-        set -euo pipefail
-
-        REQUEST_URL="https://dev.azure.com/\
-        python-discord/${SYSTEM_TEAMPROJECTID}/_apis/build/builds?\
-        queryOrder=finishTimeDescending&\
-        resultFilter=succeeded&\
-        \$top=1&\
-        repositoryType=${BUILD_REPOSITORY_PROVIDER}&\
-        repositoryId=${BUILD_REPOSITORY_NAME}&\
-        branchName=${BUILD_SOURCEBRANCH}&\
-        api-version=5.0"
-
-        printf '%s\n' "Retrieving latest successful build using ${REQUEST_URL}"
-        response="$(curl -sSL "${REQUEST_URL}")"
-
-        if [[ "$(printf '%s' "${response}" | jq -re '.count')" = 0 ]]; then
-            (>&2 echo \
-                "No previous build was found." \
-                "Either the previous build is too old and was deleted" \
-                "or the branch was empty before this build."
-            )
-            exit 0
-        fi
-
-        prev_build="$(printf '%s' "${response}" | jq -re '.value[0].id')"
-        printf '%s\n' "Most recent successful build: ${prev_build}"
-        printf '%s\n' "##vso[task.setvariable variable=PREV_BUILD]${prev_build}"
-
-        if [[ "${BUILD_REASON}" = "PullRequest" ]]; then
-            key='triggerInfo."pr.sourceSha"'
-        else
-            key='sourceVersion'
-        fi
-
-        prev_commit="$(printf '%s' "${response}" | jq -re ".value[0].${key}")"
-        printf '%s\n' "Previous commit: ${prev_commit}"
-        printf '%s\n' "##vso[task.setvariable variable=PREV_COMMIT]${prev_commit}"
-      displayName: 'Get Previous Successful Build'
-
-    - script: echo "${BASH_VERSION}"
+    - task: ShellScript@2
+      inputs:
+        scriptPath: scripts/check_dockerfiles.sh
+      displayName: 'Check If Images Need to Be Built'
 
     - task: DownloadPipelineArtifact@2
       inputs:
diff --git a/scripts/check_dockerfiles.sh b/scripts/check_dockerfiles.sh
new file mode 100755
index 0000000..ddc7084
--- /dev/null
+++ b/scripts/check_dockerfiles.sh
@@ -0,0 +1,84 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+exec 3>&1 # New file descriptor to stdout
+
+BASE_URL="https://dev.azure.com/\
+python-discord/${SYSTEM_TEAMPROJECTID}/_apis/build/builds?\
+queryOrder=finishTimeDescending&\
+resultFilter=succeeded&\
+\$top=1&\
+repositoryType=${BUILD_REPOSITORY_PROVIDER}&\
+repositoryId=${BUILD_REPOSITORY_NAME}&\
+api-version=5.0"
+
+get_build() {
+    set -e # Poor Ubuntu LTS doesn't have Bash 4.4's inherit_errexit
+
+    local branch="${1:?"get_build: argument 1 'branch' is unset"}"
+    local url="${BASE_URL}&branchName=${branch}"
+
+    printf '%s\n' "Retrieving the latest successful build using ${url}" >&3
+
+    local response
+    response="$(curl -sSL "${url}")"
+
+    if [[ -z "${response}" ]] \
+        || ! printf '%s' "${response}" | jq -re '.count'
+    then
+        return 1
+    else
+        printf '%s' "${response}"
+    fi
+}
+
+# Get the previous commit
+if [[ "${BUILD_REASON}" = "PullRequest" ]]; then
+    if ! prev_commit="$(
+            get_build "${BUILD_SOURCEBRANCH}" \
+            | jq -re '.value[0].triggerInfo."pr.sourceSha"'
+        )"
+    then
+        echo \
+            "Could not retrieve the previous build's commit." \
+            "Falling back to the head of the target branch."
+
+        prev_commit="origin/${SYSTEM_PULLREQUEST_TARGETBRANCH}"
+    fi
+elif ! prev_commit="$(
+        get_build "${BUILD_SOURCEBRANCH}" \
+        | jq -re '.value[0].sourceVersion'
+    )"
+then
+    echo \
+        "No previous build was found." \
+        "Either the previous build is too old and was deleted" \
+        "or the branch was empty before this build." \
+        "All images will be built."
+    exit 0
+fi
+
+# Compare diffs
+head="$(git rev-parse HEAD)"
+printf '%s\n' "Comparing HEAD (${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"
+else
+    # Always rebuild the venv if the base changes.
+    exit 0
+fi
+
+if git diff --quiet "${prev_commit}" -- docker/venv.Dockerfile Pipfile*; then
+    echo "No changes detected in docker/venv.Dockerfile or the Pipfiles."
+    echo "##vso[task.setvariable variable=VENV_CHANGED;isOutput=true]false"
+elif master_commit="$(
+        get_build "refs/heads/master" \
+        | jq -re '.value[0].sourceVersion'
+    )" \
+    && git diff --quiet "${master_commit}" -- docker/base.Dockerfile
+then
+    echo "Can pull base image from Docker Hub; no changes made since master."
+    echo "##vso[task.setvariable variable=BASE_PULL;isOutput=true]true"
+fi
diff --git a/scripts/test.sh b/scripts/test.sh
deleted file mode 100755
index a267324..0000000
--- a/scripts/test.sh
+++ /dev/null
@@ -1,3 +0,0 @@
-#!/usr/bin/env bash
-
-printf '%s\n' "$1"