Netlify Adapter: Custom redirects not working

Describe the bug Custom Netlify redirects don’t work. Neither using netlify.toml nor static/_redirects.

To Reproduce

1. Setup a minimal SvelteKit app using the Netlify adapter
2. Specify a redirection rule, e.g. put /old /new in static/_redirects
3. Deploy the build output on Netlify (or test it locally using Netlify Dev)
4. Navigate to https://YOUR-TEST-PAGE.example/old
5. Now you’ll get a Svelte 404 error

Expected behavior

• Instead of the 404, my website should actually redirect to https://YOUR-TEST-PAGE.example/new
• Document that redirections in netlify.toml aren’t supported (for now?) because the adapter itself defines a “catch all” in _redirects making all in netlify.toml unusable

Information about your SvelteKit Installation:

• @sveltejs/kit: next => 1.0.0-next.64
• @sveltejs/adapter-netlify => 1.0.0-next.4
• svelte: ^3.29.0 => 3.36.0
• vite: ^2.1.0 => 2.1.4

Severity For me personally? High, as I’m planning to replace an old website with SvelteKit and have to gracefully deal with old URLs. At least the _redirects definitions should work.

Additional context

• I already noticed that the adapter is simply overwriting my own _redirects file with its own content because writeFileSync() is used.
• When investigating the issue locally I tried to change it to appendFileSync() (which makes more sense in my opinion).
• Then however I’m getting the following:

  Must use import to load ES Module: MY-PROJECT/functions/render/index.js
  require() of ES modules is not supported.
  require() of MY-PROJECT/functions/render/index.js from /npm/node_modules/netlify-cli/node_modules/lambda-local/build/lambdalocal.js is an ES module file as it is a .js file whose nearest parent package.json contains "type": "module" which defines all .js files in that package scope as ES modules.
  Instead rename index.js to end in .cjs, change the requiring code to use import(), or remove "type": "module" from MY-PROJECT/package.json.
  

• Renaming index.js to index.cjs as suggested leads to another error.

Here I had to stop because I don’t know what that error above exactly means. I hope my report is helping though. Nice project btw!

[kvn-shn]

Thought about it even more. 😉 We should try to make it even smarter:

1. Check if the adapter-specific redirection is in the TOML:
   • Yes: nothing to do here anymore, proceed normally.
   • No: continue.
2. Check if there are any other [[redirects]] in the TOML:
   • Yes: fail with an error, e.g. “Netlify adapter’s redirection rule is missing. Please add […] at the end of your netlify.toml”
   • No: continue.
3. Do the appendFileSync(publish + '/_redirects', '\n\n/* /.netlify/functions/render 200') thing. It should automatically create the file if it doesn’t already exist. Else, \n ensures that it’s added in a proper new line.

Additionally we should point out in the readme that no (other) custom “catch all” redirects are allowed, neither in netlify.toml nor in _redirects.

[caesar]

@benmccann true, but it will require several lines of code to do what you could do with one line in _redirects or with a simple netlify.toml config. It’s probably faster too. For the same reasons, on my own server I do redirects in nginx config instead of in application code.

I guess it comes down to personal preference, but either way, I think in principle the adapter shouldn’t break Netlify’s built-in functionality unless it really has to.