Warning "Critical dependency: the request of a dependency is an expression" when used with Serverless & Webpack

[ericbiewener]

Do you want to request a feature or report a bug?
Bug

What is the current behavior?
When using the aws-nodejs-typescript template provided by Serverless, bundling mongoose via Webpack results in the following warnings:

WARNING in ./node_modules/mongoose/lib/index.js 8:26-62
Critical dependency: the request of a dependency is an expression
 @ ./node_modules/mongoose/index.js
 @ ./handler.ts
 @ multi ./source-map-install.js ./handler.ts

WARNING in ./node_modules/require_optional/index.js 82:18-42
Critical dependency: the request of a dependency is an expression
 @ ./node_modules/mongodb-core/index.js
 @ ./node_modules/mongoose/lib/connection.js
 @ ./node_modules/mongoose/lib sync ^.*\/connection$
 @ ./node_modules/mongoose/lib/index.js
 @ ./node_modules/mongoose/index.js
 @ ./handler.ts
 @ multi ./source-map-install.js ./handler.ts

WARNING in ./node_modules/require_optional/index.js 90:20-44
Critical dependency: the request of a dependency is an expression
 @ ./node_modules/mongodb-core/index.js
 @ ./node_modules/mongoose/lib/connection.js
 @ ./node_modules/mongoose/lib sync ^.*\/connection$
 @ ./node_modules/mongoose/lib/index.js
 @ ./node_modules/mongoose/index.js
 @ ./handler.ts
 @ multi ./source-map-install.js ./handler.ts

WARNING in ./node_modules/require_optional/index.js 97:35-67
Critical dependency: the request of a dependency is an expression
 @ ./node_modules/mongodb-core/index.js
 @ ./node_modules/mongoose/lib/connection.js
 @ ./node_modules/mongoose/lib sync ^.*\/connection$
 @ ./node_modules/mongoose/lib/index.js
 @ ./node_modules/mongoose/index.js
 @ ./handler.ts
 @ multi ./source-map-install.js ./handler.ts

If the current behavior is a bug, please provide the steps to reproduce.
You can reproduce it with this example repo. After cloning it, run:

$ yarn install
$ sls package

sls package will bundle it with webpack, and you'll see the error.

Alternatively, if you wish to recreate from scratch, you'll need to install serverless and then run:

sls create -p mongoose-serverless -t AAaws-nodejs-typescript
cd mongoose-serverless
yarn add mongoose

Then, in handler.ts, import mongoose and do something with it (like console.log(mongoose)) so that Webpack's treeshaking doesn't ignore it. Then run sls package.

What is the expected behavior?
No warnings

Please mention your node.js, mongoose and MongoDB version.
node: 10.5.0
mongoose: 5.4.8
mongodb: Warnings occur even if this isn't installed, but using 3.1.13

[vkarpov15]

Unfortunately there's no way to suppress this error with Webpack currently (webpack/webpack#196 (comment)). Most of these warnings come from require_optional, see this issue, which the MongoDB driver requires because it has several optional dependencies (bson-ext, snappy, saslprep). So for now, the only option is to ignore these warnings because there's no way to get rid of them.

There is one place that Mongoose require()s an expression, we'll add a deprecation warning for that.

[ajhoddinott]

For anyone else in the same situation, adding a new ContextReplacementPlugin(/.*/) to webpack, as suggested by the later webpack/webpack#196 (comment), seems to be a convenient way to silence the webpack warnings while waiting for Mongoose v6 (provided you are sure you don’t need any expression requires anywhere at all).

@ajhoddinott Thanks, that did it for me!