Throw an error for "main": "something.html" in package.json

[mischnic]

🐛 bug report

It happens way too often that "main": "index.html" is specified in package.json, and the source files are overwritten.

🎛 Configuration (.babelrc, package.json, cli command)

{
    "name": "foo",
    "version": "1.0.0",
    "main": "index.html",
    "license": "MIT",
    "private": true
}

🤔 Expected Behavior

"main" musn't specified a HTML file. Remove this property

😯 Current Behavior

Builds something

💁 Possible Solution

Should be checked in here: https://github.com/parcel-bundler/parcel/blob/v2/packages/core/core/src/requests/TargetRequest.js

[devongovett]

Also if main points to a JS file but the entry is HTML (e.g. auto-generated package.json). Either just ignore that or error too?

[mischnic]

I would say error in that case as well. The possibilites to fix that would be to either remove the property or if you actually need it, add targets: {main: false}

[mischnic]

It should just always error if the type isn't JS. (e.g. "main": "index.ts")