refactor: move decorators into their own package

packages/decorators/.npmignore

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+__tests__/
+__mocks__/
+dist/packages

packages/decorators/README.md

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+# @vue/decorators

packages/decorators/__tests__/prop.spec.ts

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+import { prop } from '../src/prop'
+import { Component, createInstance } from '@vue/runtime-test'
+
+test('without options', () => {
+  let capturedThisValue
+  let capturedPropsValue
+
+  class Foo extends Component<{ p: number }> {
+    @prop
+    p: number
+
+    created() {
+      capturedThisValue = this.p
+      capturedPropsValue = this.$props.p
+    }
+  }
+
+  createInstance(Foo, {
+    p: 1
+  })
+  expect(capturedThisValue).toBe(1)
+  expect(capturedPropsValue).toBe(1)
+
+  // explicit override
+  createInstance(Foo, {
+    p: 2
+  })
+  expect(capturedThisValue).toBe(2)
+  expect(capturedPropsValue).toBe(2)
+})
+
+test('with options', () => {
+  let capturedThisValue
+  let capturedPropsValue
+  let capturedDataValue
+
+  class Foo extends Component<{ p: number }> {
+    @prop({
+      default: 1
+    })
+    p: number
+    // data property should be able to make use of prop
+    d: number = this.p + 1
+
+    created() {
+      capturedThisValue = this.p
+      capturedPropsValue = this.$props.p
+      capturedDataValue = this.d
+    }
+  }
+
+  // default value
+  createInstance(Foo)
+  expect(capturedThisValue).toBe(1)
+  expect(capturedPropsValue).toBe(1)
+  expect(capturedDataValue).toBe(2)
+
+  // explicit override
+  createInstance(Foo, {
+    p: 2
+  })
+  expect(capturedThisValue).toBe(2)
+  expect(capturedPropsValue).toBe(2)
+  expect(capturedDataValue).toBe(3)
+})

packages/decorators/index.js

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+'use strict'
+
+if (process.env.NODE_ENV === 'production') {
+  module.exports = require('./dist/decorators.cjs.prod.js')
+} else {
+  module.exports = require('./dist/decorators.cjs.js')
+}

packages/decorators/package.json

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+{
+  "name": "@vue/decorators",
+  "version": "3.0.0-alpha.1",
+  "description": "@vue/decorators",
+  "main": "index.js",
+  "module": "dist/decorators.esm-bundler.js",
+  "types": "dist/index.d.ts",
+  "repository": {
+    "type": "git",
+    "url": "git+https://github.com/vuejs/vue.git"
+  },
+  "keywords": [
+    "vue"
+  ],
+  "author": "Evan You",
+  "license": "MIT",
+  "bugs": {
+    "url": "https://github.com/vuejs/vue/issues"
+  },
+  "homepage": "https://github.com/vuejs/vue/tree/dev/packages/decorators#readme"
+}

packages/decorators/src/index.ts

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+export { prop } from './prop'
+export { inject } from './inject'

packages/decorators/src/inject.ts

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+export function inject() {}

packages/decorators/src/prop.ts

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+import { Component, PropValidator } from '@vue/runtime-core'
+import { camelize } from '@vue/shared'
+
+export function prop(
+  target: Component | PropValidator<any>,
+  key?: string
+): any {
+  if (key) {
+    applyProp(target, key)
+  } else {
+    const options = target as PropValidator<any>
+    return (target: any, key: string) => {
+      applyProp(target, key, options)
+    }
+  }
+}
+
+function applyProp(target: any, key: string, options: PropValidator<any> = {}) {
+  // here `target` is the prototype of the component class
+  Object.defineProperty(target, `__prop_${camelize(key)}`, {
+    value: options
+  })
+}