When postcss-import and postcss-calc with warnWhenCannotResolve enabled are used, postcss-reporter starts to emit warnings saying undefined [undefined] in addition to valid ones ⚠ Could not reduce expression: ....
git cloneyarn installnode index.js
There are separate two issues in postcss-calc and postcss-reporter.
The first undefined is due to postcss-reporter's issue where it doesn't filter out messages that don't have text property. According to the postcss API document, required properties of Message are only type and plugin. postcss-import indeed pushes messages without text property. postcss-reporter, however, assumes each message has text, causing undefined to be shown as a message body.
The second undefined is due to postcss-import's issue where it doesn't set plugin property to their messages. As in the API documentation, the property is mandatory but they don't have it.