fix: ignore top-level awaits in prefer-await-to-then (#126)

Resolves #122

Author: macklinu

__tests__/prefer-await-to-then.js

@@ -14,20 +14,22 @@ ruleTester.run('prefer-await-to-then', rule, {
   valid: [
     'async function hi() { await thing() }',
     'async function hi() { await thing().then() }',
-    'async function hi() { await thing().catch() }'
+    'async function hi() { await thing().catch() }',
+    'a = async () => (await something())',
+    'something().then(async () => await somethingElse())'
   ],
 
   invalid: [
     {
-      code: 'hey.then(x => {})',
+      code: 'function foo() { hey.then(x => {}) }',
       errors: [{ message }]
     },
     {
-      code: 'hey.then(function() { }).then()',
+      code: 'function foo() { hey.then(function() { }).then() }',
       errors: [{ message }, { message }]
     },
     {
-      code: 'hey.then(function() { }).then(x).catch()',
+      code: 'function foo() { hey.then(function() { }).then(x).catch() }',
       errors: [{ message }, { message }]
     },
     {

rules/prefer-await-to-then.js

@@ -14,17 +14,27 @@ module.exports = {
     }
   },
   create: function(context) {
+    /** Returns true if node is inside yield or await expression. */
+    function isInsideYieldOrAwait() {
+      return context.getAncestors().some(parent => {
+        return (
+          parent.type === 'AwaitExpression' || parent.type === 'YieldExpression'
+        )
+      })
+    }
+
+    /**
+     * Returns true if node is created at the top-level scope.
+     * Await statements are not allowed at the top level,
+     * only within function declarations.
+     */
+    function isTopLevelScoped() {
+      return context.getScope().block.type === 'Program'
+    }
+
     return {
       MemberExpression: function(node) {
-        // you can then() if you are inside of a yield or await
-        if (
-          context.getAncestors().some(function(parent) {
-            return (
-              parent.type === 'AwaitExpression' ||
-              parent.type === 'YieldExpression'
-            )
-          })
-        ) {
+        if (isTopLevelScoped() || isInsideYieldOrAwait()) {
           return
         }