This line toString should be toJSON

[MXXXXXS]

imports-loader/src/index.js

Line 106 in 1d8f8c3

generator.toString()

babel/babel#14658

It will cause error when using with babel-loader like

Error: .inputSourceMap must be a boolean, object, or undefined
    at assertInputSourceMap (/home/aqua/coding/atri/node_modules/@babel/core/lib/config/validation/option-assertions.js:124:11)

[alexander-akait]

toString and toJSON returns string, don't think you are right here

[MXXXXXS]

@alexander-akait Strange... toJSON actually returns an object

And babel-loader not recognise string, it should be an object

[alexander-akait]

Please create reproducible test repo, babel-loader should handle string source maps (as minimum it worker early)

[MXXXXXS]

@alexander-akait Here is: https://github.com/MXXXXXS/imports-loader-bug

Run npm i && npm run build, and it will output like:

ERROR in ./src/app.js
Module build failed (from ./node_modules/babel-loader/lib/index.js):
Error: .inputSourceMap must be a boolean, object, or undefined
    at assertInputSourceMap (/home/aqua/coding/import-loader-bug/node_modules/@babel/core/lib/config/validation/option-assertions.js:124:11)

[rectalogic]

Confirmed the above patch fixes this issue for us.