Core electron + core backend ESM

[hl662]

Notables:

• Add dual cjs/esm builds for core backend and electron
• Electron needs min range bumped from 23 to 28 BREAKING
• (WIP) Exploring converting DTA's backend code to be ESM, and consume esm version of backend and electron.

Note: tsc does not add .js extensions to extensionless imports (unlike Vite :( ), so had to add .js at the end of our relative import paths in DTA's backend.

[aruniverse]

what happens if we leave the min ver as is?

[GytisCepk]

Electron "properly" supports ESM from version 28. If we're delivering both CJS and ESM, we could leave version 23 as minimum, I think.

[aruniverse]

yourec ompiling core-electron to module esnext, but here es2020?

[aruniverse]

what are we using "backendServer" for?

[aruniverse]

this shouldnt be in the common layer imo

[GytisCepk]

Why deliver both CJS and ESM ? Wouldn't it be less painful to just switch to ESM on 5.0 ?

[hl662]

yeah, I was initially thinking this would go into one of the 4.X versions, but I'm now more certain this should be in 5.x - as I go through with modifying DTA, I'm noticing pain points with delivering dual cjs/esm, both in these packages and our electron-authorization pkg. When running an ESM module, and using named imports (like "@itwin/electron-authorization/Main"), electron complains at run time that it doesn't like electron-auth being CJS. And seems like the only way to solve that is to set 'type': "module" in the respective package.json.

[hl662]

Pausing work on this PR for now, but documenting the work so far:

• Moved display-test-app to all ESM, but having runtime issues.
• When moving core-electron to use export maps, there's one important thing to note: Any ESM-based application that uses a dependency's export maps requires that dependency to be ESM (which is to have "type": "module" in it's package.json). This is relevant to @itwin/electron-authorization, because we have export maps in there. I experimented with making that package to be ESM, pushing my work to a remote branch. I confirmed that electron-authorization's tokenStore was able to run, successfully accessing my OS-based credentials and utilizing 'electron-store' under the hood, so the branch I linked above demonstrates the feasibility of publishing a ESM-based NPM package for backends.
• I haven't dug into the __dirname is not defined error, but it pops up on the frontend side of the electron app, suggesting that our vite.config.js needs to be updated to use electron's ESM version, rather than the CJS version. I suspect that if we are able to solve this particular issue, we'll see more than just the spinner on startup
• I haven't dug into why the preload script is not being able to be loaded - everything does point to the backend being able to find ElectronPreload.mjs though (there was a prior runtime error saying it couldn't find the file). Maybe @GytisCepk could have a better idea on what is going on...
• To reproduce what I see in DTA, go to core/electron/ and run just pnpm build:esm - I'm using the import.meta.url in ElectronHost.ts, so building CJS will throw build errors. Then go to test-apps/display-test-app and run pnpm build followed by pnpm start.
• Have not seen evidence otherwise that we can build dual CJS/ESM for core-electron, solely because of import.meta.url. CJS allows require but ESM doesn't. ESM allows import.meta.url but CJS doesn't. Why is this important? core-electron's ElectronHost requires a path to ElectronPreload.mjs passed into one of it's config, and the 2 ways above are the 2 unique and correct ways to resolve file paths within a module.

Image of the runtime issue:

[GytisCepk]

I haven't dug into why the preload script is not being able to be loaded - everything does point to the backend being able to find ElectronPreload.mjs though (there was a prior runtime error saying it couldn't find the file).

ESM is not supported for preload script if sandbox is enabled (Electron ESM support matrix). If we plan to drop CJS from both backend and frontend code for Electron, we'll still need to transpile preload script to CJS.

[GytisCepk]

I haven't dug into the __dirname is not defined error, but it pops up on the frontend side of the electron app, suggesting that our vite.config.js needs to be updated to use electron's ESM version, rather than the CJS version.

Isn't __dirname only available in CJS ? __dirname Node.js docs