implement diff with diffoscope

.github/workflows/test.yml

@@ -9,6 +9,16 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
       - id: test-action
         uses: ./
-      - run: echo "${{ steps.test-action.outputs.diff }}"
+        with:
+          base_ref: 027b33661ae3211230e8cd03d19df49ba620b379
+          head_ref: 182a672418c5bae4d6b7ca1244da5f28bf5ff6f0
+          kustomizations: |-
+            testdata/prod
+            testdata/stage
+      - uses: mshick/add-pr-comment@v2
+        with:
+          message: ${{ steps.test-action.outputs.diff }}

Dockerfile

@@ -1,5 +1,8 @@
-FROM debian:bookworm-slim
+FROM registry.k8s.io/kustomize/kustomize:v5.0.0
 
-COPY entrypoint.sh .
+RUN apk add --no-cache \
+	sed \
+	diffoscope
 
+COPY entrypoint.sh .
 ENTRYPOINT [ "./entrypoint.sh" ]

README.md

@@ -1 +1 @@
-# GitHub Action for Kustomize Build+Diff
+# GitHub Action for Kustomize Build+Diff

action.yml

@@ -2,16 +2,28 @@ name: "kustomize-diff"
 description: "Kustomize build and diff action"
 inputs:
   base_ref:
-    description: "Ref for PR base"
+    description: "Git ref for PR base"
     required: true
     default: ${{ github.base_ref }}
   head_ref:
-    description: "Ref for PR head"
+    description: "Git ref for PR head"
     required: true
     default: ${{ github.head_ref }}
+  kustomizations:
+    description: |-
+      Kustomization directories
+
+      You can specify multiple directories by separating them with a newline:
+      ```yaml
+      kustomizations: |-
+        testdata/prod
+        testdata/stage
+      ```
+    required: true
+    default: ""
 outputs:
   diff:
-    description: "Git diff"
+    description: "Kustomize diff in markdown"
 runs:
   using: "docker"
   image: "Dockerfile"

entrypoint.sh

@@ -1,10 +1,44 @@
 #!/bin/sh
 
-set -x
+set -eux
 
-echo "Hello World"
-echo "head $INPUT_HEAD_REF base $INPUT_BASE_REF"
+build_dir=$(mktemp -d)
 
-echo "diff=foo" >>"$GITHUB_OUTPUT"
+build() {
+	ref="$1"
+	git checkout "$1" --quiet
+
+	for target in $INPUT_KUSTOMIZATIONS; do
+		echo "Building $target" to "$build_dir/$ref/$target"
+		mkdir -p "$build_dir/$ref/$target"
+		kustomize build "$target" -o "$build_dir/$ref/$target/"
+	done
+}
+
+git config --global --add safe.directory "$GITHUB_WORKSPACE"
+
+build "$INPUT_BASE_REF"
+build "$INPUT_HEAD_REF"
+
+base_ref_build_dir="$build_dir/$INPUT_BASE_REF"
+head_ref_build_dir="$build_dir/$INPUT_HEAD_REF"
+
+set +e
+for target in $INPUT_KUSTOMIZATIONS; do
+	diffoscope "$base_ref_build_dir/$target" "$head_ref_build_dir/$target" \
+		--markdown - \
+		--exclude-directory-metadata=yes | tee -a diff.md
+done
+
+set -e
+
+# Formatting hacks
+output=$(cat diff.md | sed "s|$base_ref_build_dir/||" | sed '/Comparing/ s/&.*$//' | sed "s|^#\{2,\} Comparing| Comparing|" | sed "s|^# Comparing|## Comparing|")
+
+{
+	echo 'diff<<EOF'
+	echo "$output"
+	echo 'EOF'
+} >>"$GITHUB_OUTPUT"
 
 exit 0

testdata/base/kustomization.yml

@@ -0,0 +1,4 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - release.yml

testdata/base/release.yml

@@ -0,0 +1,15 @@
+apiVersion: helm.toolkit.fluxcd.io/v2
+kind: HelmRelease
+metadata:
+  name: testapp
+spec:
+  releaseName: testapp
+  chart:
+    spec:
+      chart: charts/internal-service
+      sourceRef:
+        kind: GitRepository
+        name: gitops
+  interval: 1h
+  values:
+    foo: true

testdata/prod/kustomization.yml

@@ -0,0 +1,6 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - ../base
+patches:
+  - path: patch.yml

testdata/prod/patch.yml

@@ -0,0 +1,8 @@
+apiVersion: helm.toolkit.fluxcd.io/v2
+kind: HelmRelease
+metadata:
+  name: testapp
+spec:
+  values:
+    deployment:
+      useServiceAccount: false

testdata/stage/kustomization.yml

@@ -0,0 +1,6 @@
+apiVersion: kustomize.config.k8s.io/v1beta1
+kind: Kustomization
+resources:
+  - ../base
+patches:
+  - path: patch.yml

testdata/stage/patch.yml

@@ -0,0 +1,8 @@
+apiVersion: helm.toolkit.fluxcd.io/v2
+kind: HelmRelease
+metadata:
+  name: testapp
+spec:
+  values:
+    deployment:
+      useServiceAccount: true