CRA 3 fails to handle a trailing comma in tsconfig.json - TSC has no problem

[TomasHubelbauer]

This is a bug report. To reproduce it, run npx create-react-app . --typescript and change the "jsx": "preserve" line to "jsx": "preserve",. This is with CRA3 and I don't think this happened in CRA2 because I kept my tsconfig.json the same while upgrading CRA from 2 to 3 and only now got the error. I think this is a CRA issue because running tsc -p . in the directory goes through with no problem.

[ianschmitz]

Yeah you're definitely right that tsconfig.json supports it. We'll have to investigate this. Likely a JSON.parse() somewhere.

[iansu]

TypeScript also allows you to put comments in tsconfig.json which makes it not actually JSON. As far as I know they strip them before parsing the file so it's possible they are doing something similar with trailing commas.

[TomasHubelbauer]

I think as long as a JSONC parser is used it should all go through because that's what TS is using I'd assume.

[heyimalex]

Unfortunately it looks like typescript uses a hand-written parser. I traced it down to parseJsonText which is defined in src/compiler/parser.ts. Ahahaha.

If we're allowed to hook into the typescript package, it looks like they provide public access to their parse function.

[ianschmitz]

For whomever investigates this, I recommend taking a look at https://github.com/Realytics/fork-ts-checker-webpack-plugin for similar logic. I did a few PRs there related to parsing tsconfig using the TypeScript API that may be helpful.

However be careful as some of their functions will actually mutate the config. May not be worth using TS API potentially.

[TomasHubelbauer]

This might have been fixed by #7248? In which case can be closed. I see it deals with comments, not sure if it fixed the commas as well?

[heyimalex]

@TomasHubelbauer You're absolutely right!