Using ESM in external preflight function fails

[skorfmann]

I tried this:

bring cloud;

class Utils {
  init() {}
  extern "./utils.js" toUpperCase(value: str): str;
}

let utils = new Utils();
utils.toUpperCase("world!");

utils.js:

import changecase from 'change-case'

export function toUpperCase(str) {
  return changecase.upperCase(str)
}

This happened:

| [command]/usr/local/bin/wing compile -p /plugins/backend.s3.js -t tf-aws main.w
| Error: ERROR: Cannot use import statement outside a module
|
| target/main.tfaws.166271.tmp/.wing/preflight.js:15
|          }
|           toUpperCase(value)  {
| >>         return (require("/Users/sebastian/projects/monada/wing-github-action/examples/with-dependencies/./utils.js")["toUpperCase"])(value)
|          }
|          static _toInflightType(context) {
|
|     at compile (/usr/local/lib/node_modules/winglang/dist/commands/compile.js:117:19)

I expected this:

It works, as it does for inflight functions (probably due to the esbuild bundling)

Is there a workaround?

use commonjs where possible

Component

Compiler

Wing Version

0.21.5

Wing Console Version

No response

Node.js Version

v18.16.0

Platform(s)

MacOS

Anything else?

Changing the file extension to .mjs or setting "type": "module" doesn't change it either.

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[skyrpex]

I wonder:

• Do you have a package.json in the root of the project with "type": "module"?
• Otherwise, did you try renaming your .js file to .mjs?

If none of the above conditions are met, the .js files are treated as commonjs modules.

[skyrpex]

I tried renaming to .mjs and got this error:

Failed to compile.

ERROR: require() of ES Module /Users/cristian/Code/test/utils.mjs not supported.
Instead change the require of /Users/cristian/Code/test/utils.mjs to a dynamic import() which is available in all CommonJS modules.

target/index.wsim.116480.tmp/.wing/preflight.js:15
         }
         toUpperCase(value) {
>>         return (require("/Users/cristian/Code/test/./utils.mjs")["toUpperCase"])(value)
         }
         static _toInflightType(context) {

[github-actions]

Hi,

This issue hasn't seen activity in 60 days. Therefore, we are marking this issue as stale for now. It will be closed after 7 days.
Feel free to re-open this issue when there's an update or relevant information to be added.
Thanks!

[MarkMcCulloh]

The core issue is that wing runs preflight as CJS modules. So we require in many places, especially when running user-code via platforms. require in node cannot load ESM modules by default. Part of this is for dumb module-specific reasons, but the other part is that we heavily rely on synchronous code in preflight so import can't be used.

This works fine inflight because we upfront bundle everything to CJS.

The two main solution options:

1. All in on Migrate @winglang/sdk to ESM #5416, including using import(). This would require async in a lot more places that we don't currently have it.
2. Use something like https://github.com/unjs/jiti. This provides a mechanism to do synchronous ESM imports in node (unless top-level-await is used).

Both of these things are good ideas regardless, (1) for possible perf and general modernization, (2) to also enable using typescript platforms and preflight externs.

[monadabot]

Congrats! 🚀 This was released in Wing 0.70.2.