Fixes #89

Overview

This PR adds support for caching Astro's build artifacts (optimized images and other assets) between workflow runs, significantly improving build performance for subsequent runs.

Problem

As discussed in #89, Astro maintains its own cache directory (default: node_modules/.astro) that stores optimized images and other build artifacts. Without caching this directory, every workflow run needs to re-optimize the same images, which can add significant time to builds - especially for sites with many images.

While actions/setup-node caches the npm package store, it does not cache Astro's build artifacts, which live in node_modules/.astro.

Solution

This PR implements automatic caching of Astro's build directory using actions/cache:

• Cache Restore: Before the build step, the action attempts to restore the Astro cache from previous runs
• Cache Save: After a successful build, the action saves the Astro cache for future runs
• Smart Cache Keys: Uses astro-cache-${runner.os}-${github.sha} with fallback to astro-cache-${runner.os}- to allow reusing caches across commits while maintaining OS-specific caches

Changes

New Inputs

1. cache (optional, default: "true")

   • Enable or disable Astro build caching
   • Set to "false" to disable caching (useful for debugging)

2. cache-dir (optional, default: "node_modules/.astro")

   • Path to the Astro cache directory (relative to path input)
   • Allows customization if users have configured a custom cacheDir in their Astro config

Implementation Details

• Uses actions/cache/[email protected] to restore cache before build
• Uses actions/cache/[email protected] to save cache after build (only if cache wasn't hit)
• Cache is OS-specific to ensure compatibility
• Works with all supported package managers (npm, yarn, pnpm, bun, deno)

Testing

Test Methodology

1. Created a test Astro project with images requiring optimization
2. Set up a deployment workflow using this action with cache: "true"
3. Made multiple commits to trigger sequential workflow runs
4. Observed that:
   • First run: All images were optimized from scratch
   • Subsequent runs: Previously optimized images show "(reused cache entry)"
   • Build times improved for subsequent runs

Test Results

Evidence of caching working: Workflow Run #58564230627

Key log lines showing cache reuse:

  generating optimized images 
18:24:11   ▶ /_astro/300_Z1muf00.webp (reused cache entry) (+3ms) (1/3)
18:24:11   ▶ /_astro/300_Z1ESw9V.webp (reused cache entry) (+3ms) (2/3)
18:24:12   ▶ /_astro/300_Z1XhNjR.webp (before: 12kB, after: 12kB) (+889ms) (3/3)
18:24:12 ✓ Completed in 890ms.

Cache Behavior Verified

• ✅ Cache is created on first build
• ✅ Cache is restored on subsequent builds
• ✅ Previously optimized images are reused (not re-optimized)
• ✅ New/modified images are optimized and added to cache
• ✅ Cache works across commits (using restore-keys fallback)

Backwards Compatibility

This change is fully backwards compatible:

• Caching is enabled by default but can be disabled with cache: "false"
• All existing workflows will continue to work without modifications
• Users automatically benefit from improved build performance
• No breaking changes to any inputs or outputs

Usage Examples

Default (caching enabled)

- uses: withastro/action@v6
  # Caching is enabled by default, no changes needed!

Explicitly enable caching

- uses: withastro/action@v6
  with:
    cache: "true"

Disable caching (for debugging)

- uses: withastro/action@v6
  with:
    cache: "false"

Custom cache directory

- uses: withastro/action@v6
  with:
    cache: "true"
    cache-dir: "custom-cache-dir"