[docs] add note about inability to access file system at runtime

Closes #8039

.changeset/polite-stingrays-smell.md

@@ -0,0 +1,8 @@
+---
+'@sveltejs/adapter-cloudflare': patch
+'@sveltejs/adapter-cloudflare-workers': patch
+'@sveltejs/adapter-netlify': patch
+'@sveltejs/adapter-vercel': patch
+---
+
+[docs] add note about inability to access file system at runtime

packages/adapter-cloudflare-workers/README.md

@@ -111,6 +111,12 @@ declare namespace App {
 
 > `platform.env` is only available in the production build. Use [wrangler](https://developers.cloudflare.com/workers/cli-wrangler) to test it locally
 
+## Troubleshooting
+
+### Accessing the file system
+
+You can't access the file system through methods like `fs.readFileSync` in Serverless/Edge environments. If you need to access files that way, do that during building the app through [prerendering](https://kit.svelte.dev/docs/page-options#prerender). If you have a blog for example and don't want to manage your content through a CMS, then you need to prerender the content (or prerender the endpoint from which you get it) and redeploy your blog everytime you add new content.
+
 ## Changelog
 
 [The Changelog for this package is available on GitHub](https://github.com/sveltejs/kit/blob/master/packages/adapter-cloudflare-workers/CHANGELOG.md).

packages/adapter-cloudflare/README.md

@@ -87,6 +87,12 @@ The [`_headers` and `_redirects`](config files) files specific to Cloudflare Pag
 
 However, they will have no effect on responses dynamically rendered by SvelteKit, which should return custom headers or redirect responses from [server endpoints](https://kit.svelte.dev/docs/routing#server) or with the [`handle`](https://kit.svelte.dev/docs/hooks#server-hooks-handle) hook.
 
+## Troubleshooting
+
+### Accessing the file system
+
+You can't access the file system through methods like `fs.readFileSync` in Serverless/Edge environments. If you need to access files that way, do that during building the app through [prerendering](https://kit.svelte.dev/docs/page-options#prerender). If you have a blog for example and don't want to manage your content through a CMS, then you need to prerender the content (or prerender the endpoint from which you get it) and redeploy your blog everytime you add new content.
+
 ## Changelog
 
 [The Changelog for this package is available on GitHub](https://github.com/sveltejs/kit/blob/master/packages/adapter-cloudflare/CHANGELOG.md).

packages/adapter-netlify/README.md

@@ -104,6 +104,12 @@ Additionally, you can add your own Netlify functions by creating a directory for
   directory = "functions"
 ```
 
+## Troubleshooting
+
+### Accessing the file system
+
+You can't access the file system through methods like `fs.readFileSync` in Serverless/Edge environments. If you need to access files that way, do that during building the app through [prerendering](https://kit.svelte.dev/docs/page-options#prerender). If you have a blog for example and don't want to manage your content through a CMS, then you need to prerender the content (or prerender the endpoint from which you get it) and redeploy your blog everytime you add new content.
+
 ## Changelog
 
 [The Changelog for this package is available on GitHub](https://github.com/sveltejs/kit/blob/master/packages/adapter-netlify/CHANGELOG.md).

packages/adapter-vercel/README.md

@@ -74,6 +74,12 @@ Projects created before a certain date will default to using Node 14, while Svel
 
 ![Vercel project settings](settings.png)
 
+## Troubleshooting
+
+### Accessing the file system
+
+You can't access the file system through methods like `fs.readFileSync` in Serverless/Edge environments. If you need to access files that way, do that during building the app through [prerendering](https://kit.svelte.dev/docs/page-options#prerender). If you have a blog for example and don't want to manage your content through a CMS, then you need to prerender the content (or prerender the endpoint from which you get it) and redeploy your blog everytime you add new content.
+
 ## Changelog
 
 [The Changelog for this package is available on GitHub](https://github.com/sveltejs/kit/blob/master/packages/adapter-vercel/CHANGELOG.md).