feat(eslint-plugin): [no-floating-promises] add suggestion fixer to add an 'await'

packages/eslint-plugin/src/rules/no-floating-promises.ts

@@ -1,7 +1,7 @@
 import type { TSESLint, TSESTree } from '@typescript-eslint/utils';
 import { AST_NODE_TYPES } from '@typescript-eslint/utils';
 import * as tsutils from 'tsutils';
-import type * as ts from 'typescript';
+import * as ts from 'typescript';
 
 import * as util from '../util';
 
@@ -12,7 +12,11 @@ type Options = [
   },
 ];
 
-type MessageId = 'floating' | 'floatingVoid' | 'floatingFixVoid';
+type MessageId =
+  | 'floating'
+  | 'floatingVoid'
+  | 'floatingFixVoid'
+  | 'floatingFixAwait';
 
 export default util.createRule<Options, MessageId>({
   name: 'no-floating-promises',
@@ -27,6 +31,7 @@ export default util.createRule<Options, MessageId>({
     messages: {
       floating:
         'Promises must be awaited, end with a call to .catch, or end with a call to .then with a rejection handler.',
+      floatingFixAwait: 'Add await operator.',
       floatingVoid:
         'Promises must be awaited, end with a call to .catch, end with a call to .then with a rejection handler' +
         ' or be explicitly marked as ignored with the `void` operator.',
@@ -95,12 +100,54 @@ export default util.createRule<Options, MessageId>({
             context.report({
               node,
               messageId: 'floating',
+              suggest: [
+                {
+                  messageId: 'floatingFixAwait',
+                  fix(fixer): TSESLint.RuleFix | TSESLint.RuleFix[] {
+                    if (
+                      expression.type === AST_NODE_TYPES.UnaryExpression &&
+                      expression.operator === 'void'
+                    ) {
+                      return fixer.replaceTextRange(
+                        [expression.range[0], expression.range[0] + 4],
+                        'await',
+                      );
+                    }
+                    const tsNode = parserServices.esTreeNodeToTSNodeMap.get(
+                      node.expression,
+                    );
+                    if (isHigherPrecedenceThanAwait(tsNode)) {
+                      return fixer.insertTextBefore(node, 'await ');
+                    } else {
+                      return [
+                        fixer.insertTextBefore(node, 'await ('),
+                        fixer.insertTextAfterRange(
+                          [expression.range[1], expression.range[1]],
+                          ')',
+                        ),
+                      ];
+                    }
+                  },
+                },
+              ],
             });
           }
         }
       },
     };
 
+    function isHigherPrecedenceThanAwait(node: ts.Node): boolean {
+      const operator = tsutils.isBinaryExpression(node)
+        ? node.operatorToken.kind
+        : ts.SyntaxKind.Unknown;
+      const nodePrecedence = util.getOperatorPrecedence(node.kind, operator);
+      const awaitPrecedence = util.getOperatorPrecedence(
+        ts.SyntaxKind.AwaitExpression,
+        ts.SyntaxKind.Unknown,
+      );
+      return nodePrecedence > awaitPrecedence;
+    }
+
     function isAsyncIife(node: TSESTree.ExpressionStatement): boolean {
       if (node.expression.type !== AST_NODE_TYPES.CallExpression) {
         return false;

packages/eslint-plugin/tests/rules/no-floating-promises.test.ts

@@ -656,6 +656,147 @@ async function test() {
         {
           line: 3,
           messageId: 'floating',
+          suggestions: [
+            {
+              messageId: 'floatingFixAwait',
+              output: `
+async function test() {
+  await Promise.resolve();
+}
+      `,
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: `
+async function test() {
+  const promise = new Promise((resolve, reject) => resolve('value'));
+  promise;
+}
+      `,
+      options: [{ ignoreVoid: false }],
+      errors: [
+        {
+          line: 4,
+          messageId: 'floating',
+          suggestions: [
+            {
+              messageId: 'floatingFixAwait',
+              output: `
+async function test() {
+  const promise = new Promise((resolve, reject) => resolve('value'));
+  await promise;
+}
+      `,
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: `
+async function returnsPromise() {
+  return 'value';
+}
+void returnsPromise();
+      `,
+      options: [{ ignoreVoid: false }],
+      errors: [
+        {
+          line: 5,
+          messageId: 'floating',
+          suggestions: [
+            {
+              messageId: 'floatingFixAwait',
+              output: `
+async function returnsPromise() {
+  return 'value';
+}
+await returnsPromise();
+      `,
+            },
+          ],
+        },
+      ],
+    },
+    {
+      // eslint-disable-next-line @typescript-eslint/internal/plugin-test-formatting
+      code: `
+async function returnsPromise() {
+  return 'value';
+}
+void /* ... */ returnsPromise();
+      `,
+      options: [{ ignoreVoid: false }],
+      errors: [
+        {
+          line: 5,
+          messageId: 'floating',
+          suggestions: [
+            {
+              messageId: 'floatingFixAwait',
+              output: `
+async function returnsPromise() {
+  return 'value';
+}
+await /* ... */ returnsPromise();
+      `,
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: `
+async function returnsPromise() {
+  return 'value';
+}
+1, returnsPromise();
+      `,
+      options: [{ ignoreVoid: false }],
+      errors: [
+        {
+          line: 5,
+          messageId: 'floating',
+          suggestions: [
+            {
+              messageId: 'floatingFixAwait',
+              output: `
+async function returnsPromise() {
+  return 'value';
+}
+await (1, returnsPromise());
+      `,
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: `
+async function returnsPromise() {
+  return 'value';
+}
+bool ? returnsPromise() : null;
+      `,
+      options: [{ ignoreVoid: false }],
+      errors: [
+        {
+          line: 5,
+          messageId: 'floating',
+          suggestions: [
+            {
+              messageId: 'floatingFixAwait',
+              output: `
+async function returnsPromise() {
+  return 'value';
+}
+await (bool ? returnsPromise() : null);
+      `,
+            },
+          ],
         },
       ],
     },