Add no-async-in-computed-properties rule (#72)

* Add `no-async-in-computed-properties` rule.

* Remove yield/generator from this rule.

* Remove yield from example code

Author: armano2

docs/rules/no-async-in-computed-properties.md

@@ -0,0 +1,60 @@
+# Check if there are no asynchronous actions inside computed properties (no-async-in-computed-properties)
+
+Computed properties should be synchronous. Asynchronous actions inside them may not work as expected and can lead to an unexpected behaviour, that's why you should avoid them.
+If you need async computed properties you might want to consider using additional plugin [vue-async-computed]
+
+## :book: Rule Details
+
+This rule is aimed at preventing asynchronous methods from being called in computed properties.
+
+:-1: Examples of **incorrect** code for this rule:
+
+```js
+export default {
+  computed: {
+    pro () {
+      return Promise.all([new Promise((resolve, reject) => {})])
+    },
+    foo: async function () {
+      return await someFunc()
+    },
+    bar () {
+      return fetch(url).then(response => {})
+    },
+    tim () {
+      setTimeout(() => { }, 0)
+    },
+    inter () {
+      setInterval(() => { }, 0)
+    },
+    anim () {
+      requestAnimationFrame(() => {})
+    }
+  }
+}
+```
+
+:+1: Examples of **correct** code for this rule:
+
+```js
+export default {
+  computed: {
+    foo () {
+      var bar = 0
+      try {
+        bar = bar / this.a
+      } catch (e) {
+        return 0
+      } finally {
+        return bar
+      }
+    }
+  }
+}
+```
+
+## :wrench: Options
+
+Nothing.
+
+[vue-async-computed]: https://github.com/foxbenjaminfox/vue-async-computed

lib/rules/no-async-in-computed-properties.js

@@ -0,0 +1,157 @@
+/**
+ * @fileoverview Check if there are no asynchronous actions inside computed properties.
+ * @author Armano
+ */
+'use strict'
+
+const utils = require('../utils')
+
+const PROMISE_FUNCTIONS = [
+  'then',
+  'catch',
+  'finally'
+]
+
+const PROMISE_METHODS = [
+  'all',
+  'race',
+  'reject',
+  'resolve'
+]
+
+const TIMED_FUNCTIONS = [
+  'setTimeout',
+  'setInterval',
+  'setImmediate',
+  'requestAnimationFrame'
+]
+
+function isTimedFunction (node) {
+  return (
+    node.type === 'CallExpression' &&
+    node.callee.type === 'Identifier' &&
+    TIMED_FUNCTIONS.indexOf(node.callee.name) !== -1
+  ) || (
+    node.type === 'CallExpression' &&
+    node.callee.type === 'MemberExpression' &&
+    node.callee.object.type === 'Identifier' &&
+    node.callee.object.name === 'window' && (
+      TIMED_FUNCTIONS.indexOf(node.callee.property.name) !== -1
+    )
+  ) && node.arguments.length
+}
+
+function isPromise (node) {
+  if (node.type === 'CallExpression' && node.callee.type === 'MemberExpression') {
+    return ( // hello.PROMISE_FUNCTION()
+      node.callee.property.type === 'Identifier' &&
+      PROMISE_FUNCTIONS.indexOf(node.callee.property.name) !== -1
+    ) || ( // Promise.PROMISE_METHOD()
+      node.callee.object.type === 'Identifier' &&
+      node.callee.object.name === 'Promise' &&
+      PROMISE_METHODS.indexOf(node.callee.property.name) !== -1
+    )
+  }
+  return false
+}
+
+function create (context) {
+  const forbiddenNodes = []
+
+  const expressionTypes = {
+    promise: 'asynchronous action',
+    await: 'await operator',
+    async: 'async function declaration',
+    new: 'Promise object',
+    timed: 'timed function'
+  }
+
+  function onFunctionEnter (node) {
+    if (node.async) {
+      forbiddenNodes.push({
+        node: node,
+        type: 'async'
+      })
+    }
+  }
+
+  return Object.assign({},
+    {
+      FunctionDeclaration: onFunctionEnter,
+
+      FunctionExpression: onFunctionEnter,
+
+      ArrowFunctionExpression: onFunctionEnter,
+
+      NewExpression (node) {
+        if (node.callee.name === 'Promise') {
+          forbiddenNodes.push({
+            node: node,
+            type: 'new'
+          })
+        }
+      },
+
+      CallExpression (node) {
+        if (isPromise(node)) {
+          forbiddenNodes.push({
+            node: node,
+            type: 'promise'
+          })
+        }
+        if (isTimedFunction(node)) {
+          forbiddenNodes.push({
+            node: node,
+            type: 'timed'
+          })
+        }
+      },
+
+      AwaitExpression (node) {
+        forbiddenNodes.push({
+          node: node,
+          type: 'await'
+        })
+      }
+    },
+    utils.executeOnVueComponent(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
+          ) {
+            context.report({
+              node: el.node,
+              message: 'Unexpected {{expressionName}} in "{{propertyName}}" computed property.',
+              data: {
+                expressionName: expressionTypes[el.type],
+                propertyName: cp.key
+              }
+            })
+          }
+        })
+      })
+    })
+  )
+}
+
+// ------------------------------------------------------------------------------
+// Rule Definition
+// ------------------------------------------------------------------------------
+
+module.exports = {
+  create,
+  meta: {
+    docs: {
+      description: 'Check if there are no asynchronous actions inside computed properties.',
+      category: 'Best Practices',
+      recommended: false
+    },
+    fixable: null,
+    schema: []
+  }
+}

lib/rules/no-side-effects-in-computed-properties.js

@@ -39,6 +39,7 @@ function create (context) {
       computedProperties.forEach(cp => {
         forbiddenNodes.forEach(node => {
           if (
+            cp.value &&
             node.loc.start.line >= cp.value.loc.start.line &&
             node.loc.end.line <= cp.value.loc.end.line
           ) {