Add vue/require-explicit-emits rule (#1124)

* Add `vue/require-explicit-emits` rule

* Refactor

Author: ota-meshi

Diff for: docs/rules/README.md

@@ -287,6 +287,7 @@ For example:
 | [vue/object-curly-spacing](./object-curly-spacing.md) | enforce consistent spacing inside braces | :wrench: |
 | [vue/padding-line-between-blocks](./padding-line-between-blocks.md) | require or disallow padding lines between blocks | :wrench: |
 | [vue/require-direct-export](./require-direct-export.md) | require the component to be directly exported |  |
+| [vue/require-explicit-emits](./require-explicit-emits.md) | require `emits` option with name triggered by `$emit()` |  |
 | [vue/require-name-property](./require-name-property.md) | require a name property in Vue components |  |
 | [vue/script-indent](./script-indent.md) | enforce consistent indentation in `<script>` | :wrench: |
 | [vue/sort-keys](./sort-keys.md) | enforce sort-keys in a manner that is compatible with order-in-components |  |

Diff for: docs/rules/no-deprecated-vue-config-keycodes.md

@@ -13,7 +13,7 @@ description: disallow using deprecated `Vue.config.keyCodes` (in Vue.js 3.0.0+)
 
 This rule reports use of deprecated `Vue.config.keyCodes` (in Vue.js 3.0.0+)
 
-<eslint-code-block filename="a.js" language="javascript ":rules="{'vue/no-deprecated-vue-config-keycodes': ['error']}">
+<eslint-code-block filename="a.js" language="javascript" :rules="{'vue/no-deprecated-vue-config-keycodes': ['error']}">
 
 ```js
 /* ✗ BAD */
@@ -31,14 +31,16 @@ Nothing.
 ## :couple: Related rules
 
 - [vue/no-deprecated-v-on-number-modifiers]
-- [API - Global Config - keyCodes]
 
 [vue/no-deprecated-v-on-number-modifiers]: ./no-deprecated-v-on-number-modifiers.md
-[API - Global Config - keyCodes]: https://vuejs.org/v2/api/#keyCodes
 
 ## :books: Further reading
 
-- [Vue RFCs - 0014-drop-keycode-support](https://github.com/vuejs/rfcs/blob/master/active-rfcs/0014-drop-keycode-support.md)
+- [Vue RFCs - 0014-drop-keycode-support]
+- [API - Global Config - keyCodes]
+
+[Vue RFCs - 0014-drop-keycode-support]: https://github.com/vuejs/rfcs/blob/master/active-rfcs/0014-drop-keycode-support.md
+[API - Global Config - keyCodes]: https://vuejs.org/v2/api/#keyCodes
 
 ## :mag: Implementation
 

Diff for: docs/rules/require-explicit-emits.md

@@ -0,0 +1,84 @@
+---
+pageClass: rule-details
+sidebarDepth: 0
+title: vue/require-explicit-emits
+description: require `emits` option with name triggered by `$emit()`
+---
+# vue/require-explicit-emits
+> require `emits` option with name triggered by `$emit()`
+
+## :book: Rule Details
+
+This rule reports event triggers not declared with the `emits` option. (The `emits` option is a new in Vue.js 3.0.0+)
+
+Explicit `emits` declaration serves as self-documenting code. This can be useful for other developers to instantly understand what events the component is supposed to emit.
+Also,  with attribute fallthrough changes in Vue.js 3.0.0+, `v-on` listeners on components will fallthrough as native listeners by default. Declare it as a component-only event in `emits` to avoid unnecessary registration of native listeners.
+
+<eslint-code-block :rules="{'vue/require-explicit-emits': ['error']}">
+
+```vue
+<template>
+  <!-- ✓ GOOD -->
+  <div @click="$emit('good')"/>
+  <!-- ✗ BAD -->
+  <div @click="$emit('bad')"/>
+</template>
+<script>
+export default {
+  emits: ['good']
+}
+</script>
+```
+
+</eslint-code-block>
+
+<eslint-code-block :rules="{'vue/require-explicit-emits': ['error']}">
+
+```vue
+<script>
+export default {
+  emits: ['good'],
+  methods: {
+    foo () {
+      // ✓ GOOD
+      this.$emit('good')
+      // ✗ BAD
+      this.$emit('bad')
+    }
+  }
+}
+</script>
+```
+
+</eslint-code-block>
+
+<eslint-code-block :rules="{'vue/require-explicit-emits': ['error']}">
+
+```vue
+<script>
+export default {
+  emits: ['good'],
+  setup (props, context) {
+    // ✓ GOOD
+    context.emit('good')
+    // ✗ BAD
+    context.emit('bad')
+  }
+}
+</script>
+```
+
+</eslint-code-block>
+
+## :wrench: Options
+
+Nothing.
+
+## :books: Further reading
+
+- [Vue RFCs - 0030-emits-option](https://github.com/vuejs/rfcs/blob/master/active-rfcs/0030-emits-option.md)
+
+## :mag: Implementation
+
+- [Rule source](https://github.com/vuejs/eslint-plugin-vue/blob/master/lib/rules/require-explicit-emits.js)
+- [Test source](https://github.com/vuejs/eslint-plugin-vue/blob/master/tests/lib/rules/require-explicit-emits.js)

Diff for: lib/index.js

@@ -88,6 +88,7 @@ module.exports = {
     'require-component-is': require('./rules/require-component-is'),
     'require-default-prop': require('./rules/require-default-prop'),
     'require-direct-export': require('./rules/require-direct-export'),
+    'require-explicit-emits': require('./rules/require-explicit-emits'),
     'require-name-property': require('./rules/require-name-property'),
     'require-prop-type-constructor': require('./rules/require-prop-type-constructor'),
     'require-prop-types': require('./rules/require-prop-types'),

Diff for: lib/rules/no-async-in-computed-properties.js

@@ -72,7 +72,7 @@ module.exports = {
   },
 
   create (context) {
-    const forbiddenNodes = []
+    const computedPropertiesMap = new Map()
     let scopeStack = { upper: null, body: null }
 
     const expressionTypes = {
@@ -83,13 +83,9 @@ module.exports = {
       timed: 'timed function'
     }
 
-    function onFunctionEnter (node) {
+    function onFunctionEnter (node, { node: vueNode }) {
       if (node.async) {
-        forbiddenNodes.push({
-          node: node,
-          type: 'async',
-          targetBody: node.body
-        })
+        verify(node, node.body, 'async', computedPropertiesMap.get(vueNode))
       }
 
       scopeStack = { upper: scopeStack, body: node.body }
@@ -98,68 +94,53 @@ module.exports = {
     function onFunctionExit () {
       scopeStack = scopeStack.upper
     }
-    return Object.assign({},
-      {
-        ':function': onFunctionEnter,
-        ':function:exit': onFunctionExit,
-
-        NewExpression (node) {
-          if (node.callee.name === 'Promise') {
-            forbiddenNodes.push({
-              node: node,
-              type: 'new',
-              targetBody: scopeStack.body
-            })
-          }
-        },
-
-        CallExpression (node) {
-          if (isPromise(node)) {
-            forbiddenNodes.push({
-              node: node,
-              type: 'promise',
-              targetBody: scopeStack.body
-            })
-          } else if (isTimedFunction(node)) {
-            forbiddenNodes.push({
-              node: node,
-              type: 'timed',
-              targetBody: scopeStack.body
-            })
-          }
-        },
-
-        AwaitExpression (node) {
-          forbiddenNodes.push({
+
+    function verify (node, targetBody, type, computedProperties) {
+      computedProperties.forEach(cp => {
+        if (
+          cp.value &&
+          node.loc.start.line >= cp.value.loc.start.line &&
+          node.loc.end.line <= cp.value.loc.end.line &&
+          targetBody === cp.value
+        ) {
+          context.report({
             node: node,
-            type: 'await',
-            targetBody: scopeStack.body
-          })
-        }
-      },
-      utils.executeOnVue(context, (obj) => {
-        const computedProperties = utils.getComputedProperties(obj)
-
-        computedProperties.forEach(cp => {
-          forbiddenNodes.forEach(el => {
-            if (
-              cp.value &&
-              el.node.loc.start.line >= cp.value.loc.start.line &&
-              el.node.loc.end.line <= cp.value.loc.end.line &&
-              el.targetBody === cp.value
-            ) {
-              context.report({
-                node: el.node,
-                message: 'Unexpected {{expressionName}} in "{{propertyName}}" computed property.',
-                data: {
-                  expressionName: expressionTypes[el.type],
-                  propertyName: cp.key
-                }
-              })
+            message: 'Unexpected {{expressionName}} in "{{propertyName}}" computed property.',
+            data: {
+              expressionName: expressionTypes[type],
+              propertyName: cp.key
             }
           })
-        })
+        }
       })
-    )
+    }
+    return utils.defineVueVisitor(context, {
+      ObjectExpression (node, { node: vueNode }) {
+        if (node !== vueNode) {
+          return
+        }
+        computedPropertiesMap.set(node, utils.getComputedProperties(node))
+      },
+      ':function': onFunctionEnter,
+      ':function:exit': onFunctionExit,
+
+      NewExpression (node, { node: vueNode }) {
+        if (node.callee.name === 'Promise') {
+          verify(node, scopeStack.body, 'new', computedPropertiesMap.get(vueNode))
+        }
+      },
+
+      CallExpression (node, { node: vueNode }) {
+        if (isPromise(node)) {
+          verify(node, scopeStack.body, 'promise', computedPropertiesMap.get(vueNode))
+        } else if (isTimedFunction(node)) {
+          verify(node, scopeStack.body, 'timed', computedPropertiesMap.get(vueNode))
+        }
+      },
+
+      AwaitExpression (node, { node: vueNode }) {
+        verify(node, scopeStack.body, 'await', computedPropertiesMap.get(vueNode))
+      }
+    })
   }
 }

Diff for: lib/rules/no-deprecated-events-api.js

@@ -30,28 +30,17 @@ module.exports = {
   },
 
   create (context) {
-    const forbiddenNodes = []
-
-    return Object.assign(
+    return utils.defineVueVisitor(context,
       {
         'CallExpression > MemberExpression > ThisExpression' (node) {
           if (!['$on', '$off', '$once'].includes(node.parent.property.name)) return
-          forbiddenNodes.push(node.parent.parent)
+
+          context.report({
+            node: node.parent.parent,
+            messageId: 'noDeprecatedEventsApi'
+          })
         }
-      },
-      utils.executeOnVue(context, (obj) => {
-        forbiddenNodes.forEach(node => {
-          if (
-            node.loc.start.line >= obj.loc.start.line &&
-            node.loc.end.line <= obj.loc.end.line
-          ) {
-            context.report({
-              node,
-              messageId: 'noDeprecatedEventsApi'
-            })
-          }
-        })
-      })
+      }
     )
   }
 }