Cannot read property 'substring' of undefined

[elios264]

• Operating System: Mac
• Node Version: 12.4
• NPM Version: 6.10
• webpack Version: 4.35.2
• less-loader Version: 5.0.0

Expected Behavior

Compile without problems

Actual Behavior

Magic error that disappears when recompiling:

Code

  Webpack compilation failed (client)

    ERROR in ./theme/theme.client.less
    Module build failed (from ../node_modules/mini-css-extract-plugin/dist/loader.js):
    ModuleBuildError: Module build failed (from ../node_modules/less-loader/dist/cjs.js):


    Cannot read property 'substring' of undefined
          in undefined (line undefined, column undefined)
        at /Users/elios264/Desktop/alto/promo-panel/node_modules/webpack/lib/NormalModule.js:302:20
        at /Users/elios264/Desktop/alto/promo-panel/node_modules/loader-runner/lib/LoaderRunner.js:367:11
        at /Users/elios264/Desktop/alto/promo-panel/node_modules/loader-runner/lib/LoaderRunner.js:233:18
        at context.callback (/Users/elios264/Desktop/alto/promo-panel/node_modules/loader-runner/lib/LoaderRunner.js:111:13)
     @ ./client/appLoader.js 10:0-33
     @ multi webpack-hot-middleware/client?dynamicPublicPath=true react-hot-loader/patch ./client/appLoader

    ERROR in ./src/theme/theme.client.less (./node_modules/css-loader/dist/cjs.js??ref--5-1!./node_modules/postcss-loader/src??postcss!./node_modules/less-loader/dist/cjs.js??ref--5-3!./src/theme/theme.client.less)
    Module build failed (from ../node_modules/less-loader/dist/cjs.js):
    
    
    Cannot read property 'substring' of undefined
          in undefined (line undefined, column undefined)

How Do We Reproduce?

• Clone: https://github.com/elios264/less-loader-bug
• npm install
• npm start

it happens half the time, probably a race condition because, if I save any file (so webpack recompiles), it will recompile fine, in a larger project I have happens everytime and I have to force webpack to recompile

related:
webpack-contrib/mini-css-extract-plugin#421

[jasonverber]

+1, this has been the bane of my existence the past two or three weeks. Very intermittent, but unfortunately it always seems to rear its head during automated build tests (less often during local development.)

[alexander-akait]

PR welcome

[jasonverber]

Disabling sourcemaps seems to avoid this altogether.

[jasonverber]

I believe this is actually an issue with less itself: less/less.js#3360

[alexander-akait]

Thanks for link

[cap-Bernardito]

Please upgrade less package to the latest version.

[saddampojee]

Thanks. Upgrading less package to the latest version solves the problem.

[ronmi-tr]

hi
am working in a big project with a many developers
and i am the only one getting this error

ERROR in Module build failed (from ./node_modules/less-loader/dist/cjs.js):

Cannot read property 'substring' of undefined
in undefined (line undefined, column undefined)
i updated to latest less loader version and i got some new errors

[alexander-akait]

@ronmi-tr please create reproducible test repo