Add initial "composite" action for installing Bashbrew

(Also, fix a few minor bugs in `scripts/github-actions/generate.sh` and update the example appropriately)

action.yml

@@ -0,0 +1,19 @@
+# steps:
+#   - ...
+#   - uses: docker-library/bashbrew
+#   - ...
+
+name: 'Install Bashbrew'
+description: 'Install the "bashbrew" tool in GITHUB_PATH'
+runs:
+  using: 'composite'
+  steps:
+    - uses: actions/setup-go@v3
+      with:
+        go-version-file: '${{ github.action_path }}/go.mod'
+    - run: |
+        '${{ github.action_path }}/bashbrew.sh' --version > /dev/null
+        '${{ github.action_path }}/bin/bashbrew' --version
+        echo '${{ github.action_path }}/bin' >> "$GITHUB_PATH"
+        echo 'BASHBREW_SCRIPTS=${{ github.action_path }}/scripts' >> "$GITHUB_ENV"
+      shell: 'bash -Eeuo pipefail -x {0}'

scripts/github-actions/example-ci.yml

@@ -18,22 +18,22 @@ jobs:
     outputs:
       strategy: ${{ steps.generate-jobs.outputs.strategy }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
+      - uses: docker-library/bashbrew
       - id: generate-jobs
         name: Generate Jobs
         run: |
-          git clone --depth 1 https://github.com/docker-library/bashbrew.git -b master ~/bashbrew
-          strategy="$(~/bashbrew/scripts/github-actions/generate.sh)"
+          strategy="$("$BASHBREW_SCRIPTS/github-actions/generate.sh")"
+          echo "strategy=$strategy" >> "$GITHUB_OUTPUT"
           jq . <<<"$strategy" # sanity check / debugging aid
-          echo "::set-output name=strategy::$strategy"
 
   test:
     needs: generate-jobs
     strategy: ${{ fromJson(needs.generate-jobs.outputs.strategy) }}
     name: ${{ matrix.name }}
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Prepare Environment
         run: ${{ matrix.runs.prepare }}
       - name: Pull Dependencies

scripts/github-actions/generate.sh

@@ -117,8 +117,12 @@ for tag in $tags; do
 		'
 	)"
 
-	parent="$(bashbrew parents "$bashbrewImage" | tail -1)" # if there ever exists an image with TWO parents in the same repo, this will break :)
-	if [ -n "$parent" ]; then
+	if parent="$(bashbrew parents "$bashbrewImage" | grep "^${tag%%:*}:")" && [ -n "$parent" ]; then
+		if [ "$(wc -l <<<"$parent")" -ne 1 ]; then
+			echo >&2 "error: '$tag' has multiple parents in the same repository and this script can't handle that yet!"
+			echo >&2 "$parent"
+			exit 1
+		fi
 		parentBashbrewImage="${parent##*/}" # account for BASHBREW_NAMESPACE being set
 		parent="$(bashbrew list --uniq "$parentBashbrewImage")" # normalize
 		parentMeta="${metas["$parent"]}"