Add docs and tests for plugins setup

Signed-off-by: Matheus Pimenta <matheuscscp@gmail.com>

.github/workflows/action.yaml

@@ -27,3 +27,41 @@ jobs:
         uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
       - name: Setup flux
         uses: ./action
+
+  plugins:
+    runs-on: ubuntu-latest
+    name: action plugins on ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
+      - name: Setup Go
+        uses: actions/setup-go@44694675825211faa026b3c33043df3e48a5fa00 # v6.0.0
+        with:
+          go-version-file: go.mod
+          cache-dependency-path: go.sum
+      - name: Build flux
+        shell: bash
+        run: |
+          set -euo pipefail
+          mkdir -p cmd/flux/manifests "$RUNNER_TEMP/flux-bin"
+          printf "apiVersion: v1\nkind: List\nitems: []\n" > cmd/flux/manifests/dummy.yaml
+          CGO_ENABLED=0 go build -ldflags="-s -w -X main.VERSION=0.0.0-pr" -o "$RUNNER_TEMP/flux-bin/flux" ./cmd/flux
+      - name: Setup flux with plugin
+        id: setup
+        uses: ./action
+        with:
+          version: 0.0.0-pr
+          bindir: ${{ runner.temp }}/flux-bin
+          plugins: |
+            mirror@sha256:91a1e04c2015ee66b1633e362cdb6d4550891b91bf3391a83414b9e9912e53f1
+      - name: Assert plugin installation
+        shell: bash
+        env:
+          ACTION_PLUGIN_DIR: ${{ steps.setup.outputs['plugin-dir'] }}
+        run: |
+          set -euo pipefail
+          test -n "${FLUXCD_PLUGINS:-}"
+          test "$ACTION_PLUGIN_DIR" = "$FLUXCD_PLUGINS"
+          test -x "$FLUXCD_PLUGINS/flux-mirror"
+          flux plugin list
+          flux mirror --help

action/README.md

@@ -12,6 +12,25 @@ steps:
     run: flux version --client
 ```
 
+To install Flux plugins alongside the CLI:
+
+```yaml
+steps:
+  - name: Setup Flux CLI
+    uses: fluxcd/flux2/action@main
+    with:
+      plugins: |
+        mirror@0.0.1
+  - name: Run Flux plugin
+    run: flux mirror --help
+```
+
+Installing plugins requires a Flux version with plugin support (v2.9.0 or later).
+The `plugins` input accepts one plugin per line in `<name>@<version|digest>`
+format. The `plugin-dir` input is only used when `plugins` is set; when
+plugins are installed, the action exports `FLUXCD_PLUGINS` for subsequent
+steps.
+
 The Flux GitHub Action can be used to automate various tasks in CI, such as:
 
 - [Automate Flux upgrades on clusters via Pull Requests](https://fluxcd.io/flux/flux-gh-action/#automate-flux-updates)

action/action.yml

@@ -18,9 +18,10 @@ inputs:
     required: false
   plugin-dir:
     description: >
-      Directory where requested plugins are installed. When plugins are installed,
-      the action exports `FLUXCD_PLUGINS` for subsequent steps. Defaults to a
-      `plugins` directory alongside the Flux binary in $RUNNER_TOOL_CACHE.
+      Directory where requested plugins are installed. This input is only used when
+      `plugins` is set. When plugins are installed, the action exports
+      `FLUXCD_PLUGINS` for subsequent steps. Defaults to a `plugins` directory
+      alongside the Flux binary in $RUNNER_TOOL_CACHE.
     required: false
   bindir:
     description: "Alternative location for the Flux binary, defaults to path relative to $RUNNER_TOOL_CACHE."
@@ -58,13 +59,13 @@ runs:
         if [[ $VERSION = v* ]]; then
           VERSION="${VERSION:1}"
         fi
-        echo installed-flux-version="$VERSION" >> $GITHUB_OUTPUT
+        echo "installed-flux-version=$VERSION" >> "$GITHUB_OUTPUT"
 
         OS=$(echo "${RUNNER_OS}" | tr '[:upper:]' '[:lower:]')
         if [[ "$OS" == "macos" ]]; then
           OS="darwin"
         fi
-        echo os="$OS" >> $GITHUB_OUTPUT
+        echo "os=$OS" >> "$GITHUB_OUTPUT"
 
         ARCH=$(echo "${RUNNER_ARCH}" | tr '[:upper:]' '[:lower:]')
         if [[ "$ARCH" == "x64" ]]; then
@@ -72,7 +73,7 @@ runs:
         elif [[ "$ARCH" == "x86" ]]; then
           ARCH="386"
         fi
-        echo arch="$ARCH" >> $GITHUB_OUTPUT
+        echo "arch=$ARCH" >> "$GITHUB_OUTPUT"
 
         FLUX_EXEC_FILE="flux"
         if [[ "$OS" == "windows" ]]; then
@@ -82,7 +83,7 @@ runs:
         if [[ -z "$FLUX_TOOL_DIR" ]]; then
           FLUX_TOOL_DIR="${RUNNER_TOOL_CACHE}/flux2/${VERSION}/${OS}/${ARCH}"
         fi
-        if [[ ! -x "$FLUX_TOOL_DIR/FLUX_EXEC_FILE" ]]; then
+        if [[ ! -x "$FLUX_TOOL_DIR/$FLUX_EXEC_FILE" ]]; then
           DL_DIR="$(mktemp -dt flux2-XXXXXX)"
           trap 'rm -rf $DL_DIR' EXIT
 
@@ -173,10 +174,10 @@ runs:
       run: |
         flux_version="$(flux -v 2>/dev/null | awk '{print $3}')"
         if flux plugin --help >/dev/null 2>&1; then
-          echo plugin-support="yes" >> $GITHUB_OUTPUT
+          echo "plugin-support=yes" >> "$GITHUB_OUTPUT"
           exit 0
         else
-          echo plugin-support="no" >> $GITHUB_OUTPUT
+          echo "plugin-support=no" >> "$GITHUB_OUTPUT"
           msg="Installed Flux version ${flux_version:-unknown} does not support plugins; need >= 2.9.0. Requested plugins cannot be installed."
           echo "::error title=Unsupported Flux version::$msg"
           echo "> [!CAUTION]" >> $GITHUB_STEP_SUMMARY
@@ -224,4 +225,4 @@ runs:
       if: steps.plugin-support-gate.outputs.plugin-support == 'yes'
       shell: bash
       run: |
-        echo "plugin-dir=$FLUXCD_PLUGINS" >> $GITHUB_OUTPUT
+        echo "plugin-dir=$FLUXCD_PLUGINS" >> "$GITHUB_OUTPUT"