From b2b5dc5779bf836f46789e913dc006c5699adef6 Mon Sep 17 00:00:00 2001
From: Scott Wittenburg <scott.wittenburg@kitware.com>
Date: Wed, 13 Sep 2023 16:29:20 -0600
Subject: [PATCH] Only rebuild, tag, and push the images that actually changed.

---
 .github/workflows/custom_docker_builds.yml | 23 +++++++++++++++++
 scripts/get-changed-files.sh               | 29 ++++++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100755 scripts/get-changed-files.sh

diff --git a/.github/workflows/custom_docker_builds.yml b/.github/workflows/custom_docker_builds.yml
index cee5f9219..b41acc659 100644
--- a/.github/workflows/custom_docker_builds.yml
+++ b/.github/workflows/custom_docker_builds.yml
@@ -6,8 +6,22 @@ on:
       - main
     paths:
       - images/**
+      - .github/workflows/custom_docker_builds.yml
+      - scripts/get-changed-files.sh
 
 jobs:
+  getchanges:
+    runs-on: ubuntu-latest
+    outputs:
+      changelist: ${{ steps.changes.outputs.diff }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
+        with:
+          fetch-depth: 0
+      - name: Get changed files
+        id: changes
+        run: ./scripts/get-changed-files.sh
   publish:
     runs-on: ubuntu-latest
     strategy:
@@ -50,11 +64,18 @@ jobs:
       - name: Checkout
         uses: actions/checkout@c85c95e3d7251135ab7dc9ce3241c5835cc595a9 # v3.5.3
 
+      - name: Matrix element to relative path
+        run: |
+          REL_PATH=$(realpath --relative-to $(git rev-parse --show-toplevel) ${{ matrix.docker-image }})
+          echo "REL_PATH=$REL_PATH" >> $GITHUB_ENV
+
       - name: Set up QEMU
         uses: docker/setup-qemu-action@2b82ce82d56a2a04d2637cd93a637ae1b359c0a7 # v2.2.0
+        if: contains(needs.getchanges.outputs.changelist, env.REL_PATH)
 
       - name: Log in to the Container registry
         uses: docker/login-action@465a07811f14bebb1938fbed4728c6a1ff8901fc # v2.2.0
+        if: contains(needs.getchanges.outputs.changelist, env.REL_PATH)
         with:
           registry: ghcr.io
           username: ${{ github.actor }}
@@ -63,6 +84,7 @@ jobs:
       - name: Build and push ${{ matrix.docker-image }}
         id: docker-build-push
         uses: docker/build-push-action@2eb1c1961a95fc15694676618e422e8ba1d63825 # v4.1.1
+        if: contains(needs.getchanges.outputs.changelist, env.REL_PATH)
         with:
           context: ${{ matrix.docker-image }}
           file: ${{ matrix.docker-image }}/Dockerfile
@@ -71,4 +93,5 @@ jobs:
           platforms: linux/amd64,linux/arm64
 
       - name: Image digest
+        if: contains(needs.getchanges.outputs.changelist, env.REL_PATH)
         run: echo ${{ steps.docker-build-push.outputs.digest }}
diff --git a/scripts/get-changed-files.sh b/scripts/get-changed-files.sh
new file mode 100755
index 000000000..25473e6c3
--- /dev/null
+++ b/scripts/get-changed-files.sh
@@ -0,0 +1,29 @@
+#!/bin/bash
+
+case "${GITHUB_EVENT_NAME}"
+in
+  pull_request)
+    BASE_SHA=$(jq -r .pull_request.base.sha ${GITHUB_EVENT_PATH})
+    HEAD_SHA=$(jq -r .pull_request.head.sha ${GITHUB_EVENT_PATH})
+    ;;
+  push)
+    BASE_SHA=$(jq -r .before ${GITHUB_EVENT_PATH})
+    HEAD_SHA=$(jq -r .after ${GITHUB_EVENT_PATH})
+    ;;
+  *)
+    echo "Unable to get changed files from '${GITHUB_EVENT_NAME}' event"
+    exit 1
+esac
+
+echo "Event: ${GITHUB_EVENT_NAME}"
+echo "Base: ${BASE_SHA}"
+echo "Head: ${HEAD_SHA}"
+echo ""
+
+git fetch origin ${BASE_SHA}
+git fetch origin ${HEAD_SHA}
+
+echo ""
+echo "::group::All changed files"
+git diff --name-only ${BASE_SHA}...${HEAD_SHA} | xargs
+echo "diff=$(git diff --name-only ${BASE_SHA}...${HEAD_SHA} | xargs dirname | xargs)" >> $GITHUB_OUTPUT