From 448a9aac3d6400048ed80b96fb99a3195ce17781 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Mislav=20Marohni=C4=87?= <git@mislav.net>
Date: Thu, 24 Oct 2024 12:33:19 +0200
Subject: [PATCH] Add option to skip downloading shellcheck on every run

With special `version: system` action input value, this will skip downloading
shellcheck from GitHub on every run and instead use the shellcheck version
that comes preinstalled in GitHub Actions runner images.

When shellcheck is downloaded, it is extracted into a temporary directory
(as opposed to `github.action_path`) which is then added to PATH.
---
 README.md   |  4 +++-
 action.yaml | 30 ++++++++++++++++--------------
 2 files changed, 19 insertions(+), 15 deletions(-)

diff --git a/README.md b/README.md
index f1aa462..0e9064e 100644
--- a/README.md
+++ b/README.md
@@ -157,7 +157,7 @@ Shellcheck can print output in these formats: `checkstyle`, `diff`, `gcc`, `json
 
 ## Run a specific version of Shellcheck
 
-If running the latest stable version of Shellcheck is not to your liking, you can specify a concrete version of Shellcheck to be used. When specifying a custom version, please use any of the released versions listed in the [Shellcheck repository](https://github.com/koalaman/shellcheck/tags).
+If downloading the latest stable version of Shellcheck on each run is not to your liking, you can specify a concrete version of Shellcheck to be used, or skip downloading altogether in favor of pre-installed shellcheck in GitHub-hosted runners. When specifying a concrete version, please use any of the released versions listed in the [Shellcheck repository](https://github.com/koalaman/shellcheck/tags).
 
 ```yaml
    ...
@@ -166,3 +166,5 @@ If running the latest stable version of Shellcheck is not to your liking, you ca
      with:
        version: v0.9.0
 ```
+
+To skip downloading shellcheck, use the special value `version: system`. Note that the version of Shellcheck [present in GitHub Actions runner images](https://github.com/actions/runner-images) might be behind the latest released version of Shellcheck.
diff --git a/action.yaml b/action.yaml
index 130781e..aa3dc91 100644
--- a/action.yaml
+++ b/action.yaml
@@ -41,7 +41,7 @@ inputs:
     required: false
     default: "gcc"
   version:
-    description: "Specify a concrete version of ShellCheck to use"
+    description: "The version of ShellCheck to download. Set to 'system' to use pre-installed shellcheck."
     required: false
     default: "stable"
 outputs:
@@ -61,26 +61,30 @@ runs:
       shell: bash
       env:
         INPUT_VERSION: ${{ inputs.version }}
+        OS_NAME: ${{ runner.os }}
       run: |
-        if [[ "${{ runner.os }}" == "macOS" ]]; then
+        if [ "${INPUT_VERSION}" = "system" ]; then
+          echo "Using system shellcheck: $(command -v shellcheck)"
+          exit 0
+        fi
+
+        if [ "${OS_NAME}" = "macOS" ]; then
           osvariant="darwin"
+          download_dir="$(mktemp -d -t shellcheck)"
         else
           osvariant="linux"
+          download_dir="$(mktemp -d --tmpdir shellcheck.XXX)"
         fi
 
-        baseurl="https://github.com/koalaman/shellcheck/releases/download"
-
-        curl -Lso "${{ github.action_path }}/sc.tar.xz" \
-          "${baseurl}/${INPUT_VERSION}/shellcheck-${INPUT_VERSION}.${osvariant}.x86_64.tar.xz"
+        curl -fsSL "https://github.com/koalaman/shellcheck/releases/download/${INPUT_VERSION}/shellcheck-${INPUT_VERSION}.${osvariant}.x86_64.tar.xz" | \
+          tar -xz -C "${download_dir}" --strip-components 1 -- "shellcheck-${INPUT_VERSION}/shellcheck"
 
-        tar -xf "${{ github.action_path }}/sc.tar.xz" -C "${{ github.action_path }}"
-        mv "${{ github.action_path }}/shellcheck-${INPUT_VERSION}/shellcheck" \
-          "${{ github.action_path }}/shellcheck"
+        echo "${download_dir}" >> "$GITHUB_PATH"
 
     - name: Display shellcheck version
       shell: bash
       run: |
-        "${{ github.action_path }}/shellcheck" --version
+        shellcheck --version
 
     - name: Set options
       shell: bash
@@ -204,13 +208,11 @@ runs:
             -print0)
 
         if [[ -n "${INPUT_CHECK_TOGETHER}" ]]; then
-          "${{ github.action_path }}/shellcheck" \
-            ${INPUT_SHELLCHECK_OPTIONS} \
+          shellcheck ${INPUT_SHELLCHECK_OPTIONS} \
             "${filepaths[@]}" || statuscode=$?
         else
           for file in "${filepaths[@]}"; do
-            "${{ github.action_path }}/shellcheck" \
-              ${INPUT_SHELLCHECK_OPTIONS} \
+            shellcheck ${INPUT_SHELLCHECK_OPTIONS} \
               "$file" || statuscode=$?
           done
         fi