Clearer error message for form actions when remote functions are not enabled

[teemingc]

Describe the bug

If you haven't enabled remote functions but you try submitting to a form remote function, you get a confusing error message on the server such as:

[405] POST /
Error: POST method not allowed. No form actions exist for the page at /

Ideally, we would tell the user to enable remote functions in svelte.config.js instead.

Reproduction

Logs

[405] POST /
Error: POST method not allowed. No form actions exist for the page at /
    at new SvelteKitError (file:///home/projects/sveltejs-kit-template-default-2gzodrct/node_modules/.pnpm/@sveltejs+kit@2.42.1_@sveltejs+vite-plugin-svelte@6.2.0_svelte@5.39.2_vite@7.1.6/node_modules/@sveltejs/kit/src/exports/internal/index.js:64:3)
    at handle_action_request (/home/projects/sveltejs-kit-template-default-2gzodrct/node_modules/.pnpm/@sveltejs+kit@2.42.1_@sveltejs+vite-plugin-svelte@6.2.0_svelte@5.39.2_vite@7.1.6/node_modules/@sveltejs/kit/src/runtime/server/page/actions.js:184:11)
    at render_page (/home/projects/sveltejs-kit-template-default-2gzodrct/node_modules/.pnpm/@sveltejs+kit@2.42.1_@sveltejs+vite-plugin-svelte@6.2.0_svelte@5.39.2_vite@7.1.6/node_modules/@sveltejs/kit/src/runtime/server/page/index.js:86:74)
    at resolve (/home/projects/sveltejs-kit-template-default-2gzodrct/node_modules/.pnpm/@sveltejs+kit@2.42.1_@sveltejs+vite-plugin-svelte@6.2.0_svelte@5.39.2_vite@7.1.6/node_modules/@sveltejs/kit/src/runtime/server/respond.js:465:68)
    at eval (/home/projects/sveltejs-kit-template-default-2gzodrct/node_modules/.pnpm/@sveltejs+kit@2.42.1_@sveltejs+vite-plugin-svelte@6.2.0_svelte@5.39.2_vite@7.1.6/node_modules/@sveltejs/kit/src/runtime/server/respond.js:338:27)
    at AsyncLocalStorage.run (node:async_hooks:18:4069)
    at with_request_store (file:///home/projects/sveltejs-kit-template-default-2gzodrct/node_modules/.pnpm/@sveltejs+kit@2.42.1_@sveltejs+vite-plugin-svelte@6.2.0_svelte@5.39.2_vite@7.1.6/node_modules/@sveltejs/kit/src/exports/internal/event.js:81:20)
    at fn (/home/projects/sveltejs-kit-template-default-2gzodrct/node_modules/.pnpm/@sveltejs+kit@2.42.1_@sveltejs+vite-plugin-svelte@6.2.0_svelte@5.39.2_vite@7.1.6/node_modules/@sveltejs/kit/src/runtime/server/respond.js:336:70)
    at record_span (/home/projects/sveltejs-kit-template-default-2gzodrct/node_modules/.pnpm/@sveltejs+kit@2.42.1_@sveltejs+vite-plugin-svelte@6.2.0_svelte@5.39.2_vite@7.1.6/node_modules/@sveltejs/kit/src/runtime/telemetry/record_span.js:15:10)
    at resolve (/home/projects/sveltejs-kit-template-default-2gzodrct/node_modules/.pnpm/@sveltejs+kit@2.42.1_@sveltejs+vite-plugin-svelte@6.2.0_svelte@5.39.2_vite@7.1.6/node_modules/@sveltejs/kit/src/runtime/server/respond.js:330:60)

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 20.19.1 - /usr/local/bin/node
    Yarn: 1.22.19 - /usr/local/bin/yarn
    npm: 10.8.2 - /usr/local/bin/npm
    pnpm: 8.15.6 - /usr/local/bin/pnpm
  npmPackages:
    @sveltejs/adapter-auto: ^6.0.0 => 6.1.0 
    @sveltejs/kit: ^2.22.0 => 2.42.1 
    @sveltejs/vite-plugin-svelte: ^6.0.0 => 6.2.0 
    svelte: ^5.25.0 => 5.39.2 
    vite: ^7.0.4 => 7.1.6

Severity

annoyance

Additional Information

This won't matter once remote functions are enabled by default

[dummdidumm]

I'm confused - how were you able to even hit this? I get a Vite overlay the moment I add a .remote.ts/js file without the experimental flag enabled

[teemingc]

Might be outdated. This was very early on when remote functions was introduced