Build fails with `adapter-cloudflare` when `config.kit.paths.base` is used

[adriansaelen]

Describe the bug

I have a few projects that make use of the config.kit.paths.base setting, and after updating adapter-cloudflare to v7.0.2, our build breaks/fails on the sites that use that setting.

Error message:

✓ built in 958ms

Run npm run preview to preview your production build locally.

> Using @sveltejs/adapter-cloudflare
error during build:
Error: ENOENT: no such file or directory, open '---/.svelte-kit/cloudflare/base/404.html

Reproduction

https://github.com/adriansaelen/sveltekit-base-adapter-cloudflare-bug

Logs

System Info

System:
    OS: macOS 15.4.1
    CPU: (10) arm64 Apple M2 Pro
    Memory: 113.58 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.15.1 - ~/.nvm/versions/node/v20.15.1/bin/node
    npm: 10.9.0 - ~/.nvm/versions/node/v20.15.1/bin/npm
    pnpm: 10.9.0 - ~/.nvm/versions/node/v20.15.1/bin/pnpm
  Browsers:
    Chrome: 135.0.7049.116
    Safari: 18.4
  npmPackages:
    @sveltejs/adapter-auto: ^6.0.0 => 6.0.0 
    @sveltejs/adapter-cloudflare: ^7.0.2 => 7.0.2 
    @sveltejs/kit: ^2.16.0 => 2.20.8 
    @sveltejs/vite-plugin-svelte: ^5.0.0 => 5.0.3 
    svelte: ^5.0.0 => 5.28.2 
    vite: ^6.2.6 => 6.3.5

Severity

serious, but I can work around it

Additional Information

I believe the issue is that the "base" folder isn't available when it's trying to write the 404.html file:

kit/packages/adapter-cloudflare/index.js

Line 74 in 7bb41aa

writeFileSync(fallback, 'Not Found');

Below the following:

kit/packages/adapter-cloudflare/index.js

Line 64 in 7bb41aa

const assets_dest = `${dest}${builder.config.kit.paths.base}`;

I added this code:

if (!existsSync(assets_dest)) {
  builder.mkdirp(assets_dest);
}

and that did the trick for me.