feat(always-return): add ignoreLastCallback option (#365)

* feat(always-return): add `ignoreLastCallback` option

* docs: format

Author: ota-meshi

__tests__/always-return.js

@@ -4,7 +4,7 @@ const rule = require('../rules/always-return')
 const RuleTester = require('eslint').RuleTester
 const ruleTester = new RuleTester({
   parserOptions: {
-    ecmaVersion: 6,
+    ecmaVersion: 11,
   },
 })
 
@@ -48,6 +48,59 @@ ruleTester.run('always-return', rule, {
         }
         return x
       })`,
+    {
+      code: 'hey.then(x => { console.log(x) })',
+      options: [{ ignoreLastCallback: true }],
+    },
+    {
+      code: 'if(foo) { hey.then(x => { console.log(x) }) }',
+      options: [{ ignoreLastCallback: true }],
+    },
+    {
+      code: 'void hey.then(x => { console.log(x) })',
+      options: [{ ignoreLastCallback: true }],
+    },
+    {
+      code: `
+      async function foo() {
+        await hey.then(x => { console.log(x) })
+      }`,
+      options: [{ ignoreLastCallback: true }],
+    },
+    {
+      code: `hey?.then(x => { console.log(x) })`,
+      options: [{ ignoreLastCallback: true }],
+    },
+    {
+      code: `foo = (hey.then(x => { console.log(x) }), 42)`,
+      options: [{ ignoreLastCallback: true }],
+    },
+    {
+      code: `(42, hey.then(x => { console.log(x) }))`,
+      options: [{ ignoreLastCallback: true }],
+    },
+    {
+      code: `
+      hey
+        .then(x => { console.log(x) })
+        .catch(e => console.error(e))`,
+      options: [{ ignoreLastCallback: true }],
+    },
+    {
+      code: `
+      hey
+        .then(x => { console.log(x) })
+        .catch(e => console.error(e))
+        .finally(() => console.error('end'))`,
+      options: [{ ignoreLastCallback: true }],
+    },
+    {
+      code: `
+      hey
+        .then(x => { console.log(x) })
+        .finally(() => console.error('end'))`,
+      options: [{ ignoreLastCallback: true }],
+    },
   ],
 
   invalid: [
@@ -130,5 +183,44 @@ ruleTester.run('always-return', rule, {
       })`,
       errors: [{ message }],
     },
+    {
+      code: `
+      hey
+        .then(function(x) { console.log(x) /* missing return here */ })
+        .then(function(y) { console.log(y) /* no error here */ })`,
+      options: [{ ignoreLastCallback: true }],
+      errors: [{ message, line: 3 }],
+    },
+    {
+      code: `const foo = hey.then(function(x) {});`,
+      options: [{ ignoreLastCallback: true }],
+      errors: [{ message }],
+    },
+    {
+      code: `
+      function foo() {
+        return hey.then(function(x) {});
+      }`,
+      options: [{ ignoreLastCallback: true }],
+      errors: [{ message }],
+    },
+    {
+      code: `
+      async function foo() {
+        return await hey.then(x => { console.log(x) })
+      }`,
+      options: [{ ignoreLastCallback: true }],
+      errors: [{ message }],
+    },
+    {
+      code: `const foo = hey?.then(x => { console.log(x) })`,
+      options: [{ ignoreLastCallback: true }],
+      errors: [{ message }],
+    },
+    {
+      code: `const foo = (42, hey.then(x => { console.log(x) }))`,
+      options: [{ ignoreLastCallback: true }],
+      errors: [{ message }],
+    },
   ],
 })

docs/rules/always-return.md

@@ -10,10 +10,18 @@ as `return Promise.reject()`.
 #### Valid
 
 ```js
-myPromise.then((val) => val * 2));
-myPromise.then(function(val) { return val * 2; });
-myPromise.then(doSomething); // could be either
-myPromise.then((b) => { if (b) { return "yes" } else { return "no" } });
+myPromise.then((val) => val * 2)
+myPromise.then(function (val) {
+  return val * 2
+})
+myPromise.then(doSomething) // could be either
+myPromise.then((b) => {
+  if (b) {
+    return 'yes'
+  } else {
+    return 'no'
+  }
+})
 ```
 
 #### Invalid
@@ -31,3 +39,51 @@ myPromise.then((b) => {
   }
 })
 ```
+
+#### Options
+
+##### `ignoreLastCallback`
+
+You can pass an `{ ignoreLastCallback: true }` as an option to this rule to the
+last `then()` callback in a promise chain does not warn if it does not have a
+`return`. Default is `false`.
+
+```js
+// OK
+promise.then((x) => {
+  console.log(x)
+})
+// OK
+void promise.then((x) => {
+  console.log(x)
+})
+// OK
+await promise.then((x) => {
+  console.log(x)
+})
+
+promise
+  // NG
+  .then((x) => {
+    console.log(x)
+  })
+  // OK
+  .then((x) => {
+    console.log(x)
+  })
+
+// NG
+var v = promise.then((x) => {
+  console.log(x)
+})
+// NG
+var v = await promise.then((x) => {
+  console.log(x)
+})
+function foo() {
+  // NG
+  return promise.then((x) => {
+    console.log(x)
+  })
+}
+```