Errors when using `resolveJsonModule` through tools (due to missing `JSON` in the list of supported extensions?)

[mbenadda]

TypeScript Version: 2.9.1, 3.0.0-dev.20180609 with resolveJsonModule: true

Search Terms: JSON, resolveJsonModule, import JSON, getOptionsDiagnostics

Code

This only happens when using a tool that uses the API and not through tsc CLI, but I tracked it down through to code in TypeScript itself (see repo & explanations below).

Expected behavior:

Compiles, parses settings.json (whatever JSON file) properly.

Actual behavior:

Gets ts-loader to throw TypeError: Cannot read property 'getOptionsDiagnostics' of undefined due to missing program (undefined) in instance.

Digging deeper, I can get to this error emitted in TypeScript: Debug Failure. File /path/to/repo/settings.json has unknown extension.

See TypeStrong/ts-loader#793 for the full discussion until now and mostly this comment for the most TypeScript-related bit and a more complete explanation.

The issue can be solved by manually adding ".json" to the supportedTypescriptExtensionsForExtractExtension list (in https://github.com/Microsoft/TypeScript/blob/master/src/parser/utilities.ts#L7812): compilation goes through and we actually get an output file that contains the JSON data as it should.

NB: we've come to suspect this bug might originate in TypeScript, but even if it is in ts-loader, any pointers as to a cause and/or possible fix would be very welcome.

Playground Link:

Here is a very minimal GitHub repository that reproduces this behavior: https://github.com/mbenadda/ts-loader-issue-793-example-repo

Related Issues:

N/A

[mhegazy]

@sheetalkamat can you take a look.

[rdsedmundo]

I can confirm the same problem here.

Same options being used. Removing resolveJsonModules make it to work here again as well.

[johnnyreilly]

Good work!

[mbenadda]

Thank you very much 👌