Typescript in script with context="module" Sapper server side rendering

[dionysiusmarquis]

Describe the bug

If you the <script context="module"> docs in Sapper environment and add lang="typescript" to both <script> elements the page/component will not be rendererd server side. Instead of the page/component render the server will response an 500 error.

To Reproduce

Here is a repo to reproduce. It is a fork of sapper-template-rollup. With only the preprocessor and some simple typescript declarations and lang="typescript" added (see diff). If you go to http://localhost:3000/blog you will get an 500 error. If you go to the blog via navigation link it will render correctly.

https://github.com/dionysiusmarquis/sapper-template-rollup/tree/bug/typescript-context-module

Expected behavior

Preprocessor to be able to handle typescript in Svelte module context for preload functionality.

Stacktraces

Inside the page/component as server response

500
Cannot read property 'length' of undefined

TypeError: Cannot read property 'length' of undefined
    at each (/…/__sapper__/dev/server/server.js:200:31)
    at create_ssr_component (/…/__sapper__/dev/server/server.js:305:35)
    at Object.$$render (/…/__sapper__/dev/server/server.js:230:22)
    at Object.default (/…/__sapper__/dev/server/server.js:548:86)
    at create_ssr_component (/…/__sapper__/dev/server/server.js:375:70)
    at Object.$$render (/…/__sapper__/dev/server/server.js:230:22)
    at create_ssr_component (/…/__sapper__/dev/server/server.js:545:40)
    at $$render (/…/__sapper__/dev/server/server.js:230:22)
    at Object.render (/…/__sapper__/dev/server/server.js:238:26)
    at handle_page (/…/__sapper__/dev/server/server.js:3021:36)

Information about your project:

• Your browser and the version: Chromium Version 80.0.3987.122 (Official Build) (64-bit)
• Your operating system: OS X 10.13.6
• svelte version 3.22.3
• sapper version 0.27.13
• svelte-preprocess version 3.7.4
• Rollup

[dionysiusmarquis]

I just realized that the Rollup warnings are always pressend as soon as you add a function which returns a Promise. Even without context="module". Could this be related anyhow 🤔. Otherwise the warnings might be another "issue"

Edit: I edited the issue and removed the Rollup part. I changed the tsconfig.json to:

{
    "compilerOptions": {
        "target": "ESNext",
        "module": "ESNext" 
    },
    "include": ["src/**/*"],
    "exclude": ["node_modules", "**/*.spec.ts"]
}

This will prevent typescript recompiling async functions

[dionysiusmarquis]

This is a sapper issue see: sveltejs/sapper#1241