Provide a way to configure targets outside package.json

[jogold]

🙋 feature request

Parcel should provide a way to configure targets outside the package.json, either via the CLI (with v1 it was possible to pass all the configuration) or in another file.

🤔 Expected Behavior

Be able to fully configure a build without "touching" the package.json

😯 Current Behavior

Currently not possible

🔦 Context

Parcel is currently being used in the AWS CDK (AWS Cloud Development Kit) library to bundle Lambda functions written in JavaScript or Typesript.

The module @aws-cdk/aws-lambda-nodejs offers this feature.

It works by extracting/finding entries of Lambda functions defined in a stack and then automatically bundles them for the user when the AWS CDK app gets synthesized. Unfortunately, in order to offer this "it just works" experience we have to temporarily update the user's package.json with some Parcel configuration, run a Parcel build and then revert the file to its original content. This is not clean.

💻 Examples

$ parcel build /my/entry/file.ts --target-config target.json

OR (bring back CLI parameters when the entry file is specified)

$ parcel build /my/entry/file.ts --context node ...

[mischnic]

targets outside the package.json,

This is possible from the API:

parcel/packages/core/types/index.js

Line 255 in 803ec97

+targets?: ?(Array<string> | {+[string]: TargetDescriptor, ...}),

CLI parameters when the entry file is specified

You can specify entries on the CLI, you mean --context?

[jogold]

Ideally I would like to fully configure a target from the CLI (context, includeNodeModules, engines).

Also when developing with the API in TypeScript where can I find the definition files (.d.ts) for @parcel/core?

[mischnic]

We use Flow for Parcel itself, so there are no TS definitons yet.

The plan is to create proper Flow libdefs and then convert them to TS at some point (#3912, #3720)