Migration Problems to Langium 2.0

[bjthehun]

I'm having problems migrating to Langium 2.0 while using npm with Webpack as bundler. When I try to start the example project with npm start, I get five errors of the following kind:

ERROR in ./src/editql/generated/ast.ts 8:18-36
Module not found: Error: Package path . is not exported from package ~/monaco-webpack/node_modules/langium (see exports field in ~/monaco-webpack/node_modules/langium/package.json)
 @ ./src/editql/generated/module.ts 8:17-36
 @ ./src/editql/editql-module.ts 11:20-52
 @ ./src/editql/editql-lsp.ts 7:27-56
 @ ./src/index.tsx 165:14-168:6

Can you tell me what am I doing wrong?

[msujew]

Hey @bjthehun,

assuming you just updated to 2.0 without doing anything else, you probably ran into our ESM change. See this changelog entry. It contains tips on how to migrate to 2.0/ESM. If you're not able to change to ESM in your project, you can use Langium 1.3.0 for now. It contains the same feature set except for the ESM change.

[ballcoach12]

@bjthehun, I had the same issue earlier this week. I recommend running the latest version of the Yeoman generator and creating a new HelloWorld project and compare the 'package.json' file in your project to the one created by the generator.

After a few changes to my 'package.json' file, for me it was a matter of simply adding '.js' to the end of some import statements.

[bjthehun]

@msujew: I'm already using ESM and i've gone through the migration manual linked in the changelog. I've sinced updated Node in package.json to >=16, though that didn't change anything.

@ballcoach12 I've also tried to create a new HelloWorld project with Yeoman 4.3.1. The only change I would say could be significant is esbuild instead of webpack for code bundling. (I don't think I could switch the project I'm working on to use esbuild, for that matter.)

[msujew]

I'm very much confused by the error. Clicking on the file linked in the error shows that we have a perfectly valid "." export defined in langium. I've just tried it with esbuild, which seems to pick this up just fine. TypeScript also doesn't have any issues with the import. I have absolutely no clue why the webpack build fails.

[bjthehun]

Update: I've been trying over the weekend to get Langium 2.0. running with webpack, and eventually figured out that the latter tool doesn't pick up the import conditional exports for .. When I replaced this export with default (chevrotain-allstar also provides an default export), I got this follow-up error:

ERROR in ./node_modules/langium/lib/parser/langium-parser.js 7:0-61
Module not found: Error: Default condition should be last one
 @ ./node_modules/langium/lib/default-module.js 45:0-79 63:50-83
 @ ./node_modules/langium/lib/index.js 6:0-36 6:0-36
 @ ./src/editql/editql-lsp.ts 8:18-36
 @ ./src/index.tsx 165:14-168:6

After swapping the conditional exports in the package.json file for chevrotain-allstar like this:

"exports": {
    ".": {
        "types": "./lib/index.d.ts",
        "default": "./lib/index.js"
    }
},

the webpack build succeeded for me.

So I would ask if the Langium exports could be changed to use default instead of import. I'm not familiar enough with JavaScript bundlers so that I could rule out problems for other Langium users, however.

[davydkov]

Yes, and PR #2 with the fix is waiting 2 weeks ago