typescript-eslint · bradzacher · Nov 16, 2024 · Nov 9, 2024 · Nov 9, 2024 · Nov 9, 2024
diff --git a/packages/eslint-plugin/src/rules/await-thenable.ts b/packages/eslint-plugin/src/rules/await-thenable.ts
@@ -3,12 +3,13 @@ import type { TSESLint, TSESTree } from '@typescript-eslint/utils';
 import * as tsutils from 'ts-api-utils';
 
 import {
+  Awaitable,
   createRule,
   getFixOrSuggest,
   getParserServices,
   isAwaitKeyword,
   isTypeAnyType,
-  isTypeUnknownType,
+  needsToBeAwaited,
   nullThrows,
   NullThrowsReasons,
 } from '../util';
@@ -51,13 +52,11 @@ export default createRule<[], MessageId>({
     return {
       AwaitExpression(node): void {
         const type = services.getTypeAtLocation(node.argument);
-        if (isTypeAnyType(type) || isTypeUnknownType(type)) {
-          return;
-        }
 
         const originalNode = services.esTreeNodeToTSNodeMap.get(node);
+        const certainty = needsToBeAwaited(checker, originalNode, type);
 
-        if (!tsutils.isThenableType(checker, originalNode.expression, type)) {
+        if (certainty === Awaitable.Never) {
           context.report({
             node,
             messageId: 'await',

diff --git a/packages/eslint-plugin/src/rules/return-await.ts b/packages/eslint-plugin/src/rules/return-await.ts
@@ -1,17 +1,16 @@
 import type { TSESLint, TSESTree } from '@typescript-eslint/utils';
 
 import { AST_NODE_TYPES } from '@typescript-eslint/utils';
-import * as tsutils from 'ts-api-utils';
 import * as ts from 'typescript';
 
 import {
+  Awaitable,
   createRule,
   getFixOrSuggest,
   getParserServices,
   isAwaitExpression,
   isAwaitKeyword,
-  isTypeAnyType,
-  isTypeUnknownType,
+  needsToBeAwaited,
   nullThrows,
 } from '../util';
 import { getOperatorPrecedence } from '../util/getOperatorPrecedence';
@@ -304,14 +303,13 @@ export default createRule({
       }
 
       const type = checker.getTypeAtLocation(child);
-      const isThenable = tsutils.isThenableType(checker, expression, type);
+      const certainty = needsToBeAwaited(checker, expression, type);
 
       // handle awaited _non_thenables
 
-      if (!isThenable) {
+      if (certainty !== Awaitable.Always) {
         if (isAwait) {
-          // any/unknown could be thenable; do not enforce whether they are `await`ed.
-          if (isTypeAnyType(type) || isTypeUnknownType(type)) {
+          if (certainty === Awaitable.May) {
             return;
           }
           context.report({

diff --git a/packages/eslint-plugin/src/util/index.ts b/packages/eslint-plugin/src/util/index.ts
@@ -20,6 +20,7 @@ export * from './isUndefinedIdentifier';
 export * from './misc';
 export * from './needsPrecedingSemiColon';
 export * from './objectIterators';
+export * from './needsToBeAwaited';
 export * from './scopeUtils';
 export * from './types';
 

diff --git a/packages/eslint-plugin/src/util/needsToBeAwaited.ts b/packages/eslint-plugin/src/util/needsToBeAwaited.ts
@@ -0,0 +1,43 @@
+import type * as ts from 'typescript';
+
+import {
+  isTypeAnyType,
+  isTypeUnknownType,
+} from '@typescript-eslint/type-utils';
+import * as tsutils from 'ts-api-utils';
+
+export enum Awaitable {
+  Always,
+  Never,
+  May,
+}
+
+export function needsToBeAwaited(
+  checker: ts.TypeChecker,
+  node: ts.Node,
+  type: ts.Type,
+): Awaitable {
+  // can't use `getConstrainedTypeAtLocation` directly since it's bugged for
+  // unconstrained generics.
+  const constrainedType = !tsutils.isTypeParameter(type)
+    ? type
+    : checker.getBaseConstraintOfType(type);
+
+  // unconstrained generic types should be treated as unknown
+  if (constrainedType == null) {
+    return Awaitable.May;
+  }
+
+  // `any` and `unknown` types may need to be awaited
+  if (isTypeAnyType(constrainedType) || isTypeUnknownType(constrainedType)) {
+    return Awaitable.May;
+  }
+
+  // 'thenable' values should always be be awaited
+  if (tsutils.isThenableType(checker, node, constrainedType)) {
+    return Awaitable.Always;
+  }
+
+  // anything else should not be awaited
+  return Awaitable.Never;
+}
diff --git a/packages/eslint-plugin/tests/rules/await-thenable.test.ts b/packages/eslint-plugin/tests/rules/await-thenable.test.ts
@@ -275,6 +275,68 @@ async function foo() {
 async function iterateUsing(arr: Array<AsyncDisposable>) {
   for (await using foo of arr) {
   }
+}
+      `,
+    },
+    {
+      code: `
+async function wrapper<T>(value: T) {
+  return await value;
+}
+      `,
+    },
+    {
+      code: `
+async function wrapper<T extends unknown>(value: T) {
+  return await value;
+}
+      `,
+    },
+    {
+      code: `
+async function wrapper<T extends any>(value: T) {
+  return await value;
+}
+      `,
+    },
+    {
+      code: `
+async function wrapper<T extends Promise<unknown>>(value: T) {
+  return await value;
+}
+      `,
+    },
+    {
+      code: `
+async function wrapper<T extends number | Promise<unknown>>(value: T) {
+  return await value;
+}
+      `,
+    },
+    {
+      code: `
+class C<T> {
+  async wrapper<T>(value: T) {
+    return await value;
+  }
+}
+      `,
+    },
+    {
+      code: `
+class C<R> {
+  async wrapper<T extends R>(value: T) {
+    return await value;
+  }
+}
+      `,
+    },
+    {
+      code: `
+class C<R extends unknown> {
+  async wrapper<T extends R>(value: T) {
+    return await value;
+  }
 }
       `,
     },
@@ -639,5 +701,91 @@ async function foo() {
         },
       ],
     },
+    {
+      code: `
+async function wrapper<T extends number>(value: T) {
+  return await value;
+}
+      `,
+      errors: [
+        {
+          column: 10,
+          endColumn: 21,
+          endLine: 3,
+          line: 3,
+          messageId: 'await',
+          suggestions: [
+            {
+              messageId: 'removeAwait',
+              output: `
+async function wrapper<T extends number>(value: T) {
+  return  value;
+}
+      `,
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: `
+class C<T> {
+  async wrapper<T extends string>(value: T) {
+    return await value;
+  }
+}
+      `,
+      errors: [
+        {
+          column: 12,
+          endColumn: 23,
+          endLine: 4,
+          line: 4,
+          messageId: 'await',
+          suggestions: [
+            {
+              messageId: 'removeAwait',
+              output: `
+class C<T> {
+  async wrapper<T extends string>(value: T) {
+    return  value;
+  }
+}
+      `,
+            },
+          ],
+        },
+      ],
+    },
+    {
+      code: `
+class C<R extends number> {
+  async wrapper<T extends R>(value: T) {
+    return await value;
+  }
+}
+      `,
+      errors: [
+        {
+          column: 12,
+          endColumn: 23,
+          endLine: 4,
+          line: 4,
+          messageId: 'await',
+          suggestions: [
+            {
+              messageId: 'removeAwait',
+              output: `
+class C<R extends number> {
+  async wrapper<T extends R>(value: T) {
+    return  value;
+  }
+}
+      `,
+            },
+          ],
+        },
+      ],
+    },
   ],
 });