TS5071 error fires when using mode="esnext", but builds were fine before 3.0.1

[jpike88]

TypeScript Version: 3.0.1

Search Terms:
TS5071

Code

https://github.com/Microsoft/TypeScript/blob/d8cbe34a051a64d39f55f4e46e18ac404aac922e/src/compiler/diagnosticMessages.json#L2887

Expected behavior:
This should work fine with mode="esnext" just like it always did.

Actual behavior:
I've been using the following tsconfig.json file with zero issues before upgrading to 3.0:

{ "compileOnSave": true, "compilerOptions": { "target": "esnext", "module": "esnext", "sourceMap": true, "declaration": true, "declarationDir": "../decl", "moduleResolution": "node", "allowSyntheticDefaultImports": true, "noUnusedLocals": true, "resolveJsonModule": true, "noUnusedParameters": true, "skipLibCheck":true, "outDir":"../dist/", "typeRoots" : ["../node_modules/@types"] }, "exclude":["../node_modules/@types/"] }
Now this error message is firing, but the resolution and import of json files work fine when module is set to esnext. Switching mode to commonjs breaks my import syntax, modules are missing left right and center.

@sheetalkamat, could you help give insight on this?

[jpike88]

my code originally looked like this and it worked:

import baseConfig from '../../config.json';

The error fired, and if I ignored the error, baseConfig was undefined. so I changed my import syntax to this, and changed mode to "commonjs":

import * as baseConfig from '../../config.json';

baseConfig then was imported correctly.

But it broke import statements for other dependencies, like AWS:

import AWS from 'aws-sdk';

Why was this error introduced to begin with?

[MichalLytek]

I have the same problem - this error is not listed in breaking changes:
https://github.com/Microsoft/TypeScript/wiki/Breaking-Changes

So I think it should be changed as TS 2.9.1 worked well with resolveJsonModule using esnext and webpack.

[sheetalkamat]

This is duplicate of #25755

[sheetalkamat]

--resolveJsonModule is supported only when using nodejs module resolution and emit is commonjs. In other systems json module is not supported natively without any plugins and hence the error. The check for emit was missing earlier rather than intentional allowing it (so your code was always error but we missed on reporting errors on it before)

[MichalLytek]

I get it but I have the same problem as #25755 (comment) - webpack + esnext = tree shaking, so I can't switch to commonjs to satisfy the typescript compiler as webpack handle importing json files very well.

[jpike88]

@sheetalkamat If my code functioned correctly before this error check was implemented, didn't it technically already support it before this error check existed? Theres nothing funky with my code, it's standard syntax (just with allowSyntheticDefaultImports enabled). Why should I be forced to downgrade to commonjs when it was working perfectly fine before?

[wizardnet972]

@sheetalkamat, any idea how to resolve my json file without the extension? i'm using vscode+typescript.
import jsonData from './file'. but I got this error: [ts] Cannot find module './file'.

resolveJsonModule is true in my tsconfig..

[sheetalkamat]

You have to explicitly use .json in the module specifier to be able to resolve to a json module. We have this constraint so that the json files don't get included without intentionally choosing to for those specific module specifiers

[wizardnet972]

I see. @sheetalkamat thank you :)