Astro build ignores cacheDir if outDir is outside project folder

[EkaanshArora]

Astro Info

Astro                    v3.6.5
Node                     v18.17.0
System                   Linux (x64)
Package Manager          bun
Output                   static
Adapter                  none
Integrations             @astrojs/mdx
                         @astrojs/tailwind
                         @astrojs/react

If this issue only occurs in one browser, which browser is a problem?

No response

Describe the Bug

I'm trying to use Astro inside an AWS Lambda as a build service tool. I'm using the JS API:

import { build } from "astro";
...
          await build({
            root: path.resolve("/tmp", uniqueDestination),
            outDir: path.resolve("/tmp", "dist", uniqueDestination),
            mode: "production",
            cacheDir: path.resolve("/tmp", "cache", uniqueDestination),
            vite: {
              cacheDir: path.resolve("/tmp", "cache", uniqueDestination),
            },
          });

Since a lambda only has read-only access the build fails as Astro tries to create a .astro directory inside the project folder instead of the specified /tmp dir. Is this a supported use-case? Can I avoid creating the .astro directory in my project folder?

I tried to read through the source and find getOutDirWithinCwd states:

/**
 * Ensures the `outDir` is within `process.cwd()`. If not it will fallback to `<cwd>/.astro`.
 * This is used for static `ssrBuild` so the output can access node_modules when we import
 * the output files. A hardcoded fallback dir is fine as it would be cleaned up after build.
 */

I think this makes sense for most use-cases but fails for being able to use astro inside a read-only directory.

What's the expected result?

Astro uses the specified folder for build cache

Link to Minimal Reproducible Example

https://github.com/EkaanshArora/astro-build-api-cache-repro

Participation

• I am willing to submit a pull request for this issue.

[github-actions]

Hello @EkaanshArora. Please provide a minimal reproduction using a GitHub repository or StackBlitz. Issues marked with needs repro will be closed if they have no activity within 3 days.

[EkaanshArora]

Added a repro here: https://github.com/EkaanshArora/astro-build-api-cache-repro