matrix generator subaction

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

.github/workflows/ci-matrix-gen.yml

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+name: ci-matrix-gen
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: '0 10 * * *'
+  push:
+    branches:
+      - 'master'
+      - 'releases/v*'
+    tags:
+      - 'v*'
+  pull_request:
+
+jobs:
+  group:
+    runs-on: ubuntu-latest
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v4
+      -
+        name: Matrix gen
+        id: gen
+        uses: ./subaction/matrix-gen
+        with:
+          workdir: ./test/group
+      -
+        name: Show matrix
+        run: |
+          echo matrix=${{ steps.gen.outputs.matrix }}

subaction/matrix-gen/action.yml

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+# https://help.github.com/en/articles/metadata-syntax-for-github-actions
+name: 'Bake matrix generator'
+description: 'Generate a matrix to distribute builds in your workflow'
+
+inputs:
+  workdir:
+    description: Working directory
+    default: '.'
+    required: false
+  files:
+    description: Comma separated list of Bake files
+    required: false
+  target:
+    description: Bake target
+    default: 'default'
+    required: false
+
+outputs:
+  matrix:
+    description: Matrix of targets
+    value: ${{ steps.generate.outputs.matrix }}
+
+runs:
+  using: composite
+  steps:
+    -
+      name: Generate matrix
+      id: generate
+      uses: actions/github-script@v6
+      with:
+        script: |
+          let def;
+          const files = `${{ inputs.files }}` ? `${{ inputs.files }}`.split(',') : [];
+          const target = `${{ inputs.target }}` ? `${{ inputs.target }}` : 'default';
+
+          await core.group(`Validating definition`, async () => {
+            let args = ['buildx', 'bake'];
+            for (const file of files) {
+              args.push('--file', file);
+            }
+            args.push(target, '--print');
+
+            const res = await exec.getExecOutput('docker', args, {
+              ignoreReturnCode: true,
+              silent: true,
+              cwd: `${{ inputs.workdir }}`
+            });
+            if (res.stderr.length > 0 && res.exitCode != 0) {
+              throw new Error(res.stderr);
+            }
+            def = JSON.parse(res.stdout.trim());
+            core.info(JSON.stringify(def, null, 2));
+          });
+
+          await core.group(`Set matrix`, async () => {
+            const matrix = def.group[target].targets;
+            core.info(`matrix: ${JSON.stringify(matrix)}`);
+            core.setOutput('matrix', JSON.stringify(matrix));
+          });