Adds missing peer dependency in @emotion/styled

[arcanis]

What:

@babel/core is added as a peer dependency.

Why:

@emotion/styled-base has a peer dependency on @babel/core, but this package doesn't provide it - which is invalid.

Checklist:

• Documentation - n/a
• Tests - n/a
• Code complete - n/a

[Andarist]

Hm, this is indeed unfortunate. @emotion/styled has a dual purpose - it might be used directly as runtime library or it might be used as babel macro. Only the latter has a peer dep on @babel/core but this cannot be expressed accurately with current package.json metadata.

It would be incorrect (maybe not incorrect, but at least not developer friendly) to warn @emotion/styled users who never intend to use macro flavor about missing peer dep.

I admit this is some problem that ideally would be addressed - but I'm not sure what's the best way to fix it and provide good DX at the same time 🤔

[arcanis]

Yarn supports optional peer dependencies; would that be ok if I was marking @babel/core as optional?

[Andarist]

This will still warn users about missing peer dep when using managers which don't understand the meta property, right?

[arcanis]

@Andarist Yep. I've tried to work with both npm and pnpm on this and while npm didn't make clear whether they would implement it or not (they considered making peer dependencies optional by default), pnpm emitted an intent to implement as well: yarnpkg/rfcs#105 (comment)

[emmatown]

I'm a little confused about this, I can't see a peerDependency in @emotion/styled-base's package.json

emotion/packages/styled-base/package.json

Lines 1 to 43 in ca3ad1c

	{
	"name": "@emotion/styled-base",
	"version": "10.0.10",
	"description": "base styled API for emotion",
	"main": "dist/styled-base.cjs.js",
	"module": "dist/styled-base.esm.js",
	"browser": {
	"./dist/styled-base.cjs.js": "./dist/styled-base.browser.cjs.js",
	"./dist/styled-base.esm.js": "./dist/styled-base.browser.esm.js"
	},
	"types": "types/index.d.ts",
	"license": "MIT",
	"repository": "https://github.com/emotion-js/emotion/tree/master/packages/styled-base",
	"scripts": {
	"test:typescript": "dtslint types"
	},
	"dependencies": {
	"@babel/runtime": "^7.4.3",
	"@emotion/is-prop-valid": "0.7.3",
	"@emotion/serialize": "^0.11.6",
	"@emotion/utils": "0.11.1"
	},
	"devDependencies": {
	"@types/react": "16.3.18",
	"dtslint": "^0.3.0"
	},
	"peerDependencies": {
	"@emotion/core": "^10.0.0",
	"react": ">=16.3.0"
	},
	"publishConfig": {
	"access": "public"
	},
	"files": [
	"src",
	"dist",
	"types"
	],
	"umd:main": "dist/styled-base.umd.min.js",
	"preconstruct": {
	"umdName": "emotionStyledBase"
	}
	}

[Andarist]

This is getting resolved in #1622 with help of optional peer dependencies. Thank you for raising awareness about this issue @arcanis !