Allowed parenthesis bodies for one-line promise-function-async functions (#4765)

* Allowed parenthesis bodies for one-line promise-function-async functions

Fixes #4757.

* Used tsutils intead of ts for new parenthesized expression method

Gets me every time...

Author: Josh Goldberg

src/rules/promiseFunctionAsyncRule.ts

@@ -15,7 +15,7 @@
  * limitations under the License.
  */
 
-import { hasModifier, isCallExpression } from "tsutils";
+import * as tsutils from "tsutils";
 import * as ts from "typescript";
 
 import * as Lint from "../index";
@@ -102,34 +102,41 @@ export class Rule extends Lint.Rules.TypedRule {
 function walk(ctx: Lint.WalkContext<EnabledSyntaxKinds>, tc: ts.TypeChecker) {
     const { sourceFile, options } = ctx;
     return ts.forEachChild(sourceFile, function cb(node): void {
-        if (options.has(node.kind)) {
-            const declaration = node as ts.FunctionLikeDeclaration;
-            switch (node.kind) {
-                case ts.SyntaxKind.MethodDeclaration:
-                case ts.SyntaxKind.FunctionDeclaration:
-                    if (declaration.body === undefined) {
-                        break;
-                    }
-                // falls through
-                case ts.SyntaxKind.FunctionExpression:
-                case ts.SyntaxKind.ArrowFunction:
-                    if (
-                        !hasModifier(node.modifiers, ts.SyntaxKind.AsyncKeyword) &&
-                        returnsPromise(declaration, tc) &&
-                        !isCallExpression(declaration.body as ts.Expression)
-                    ) {
-                        ctx.addFailure(
-                            node.getStart(sourceFile),
-                            (node as ts.FunctionLikeDeclaration).body!.pos,
-                            Rule.FAILURE_STRING,
-                        );
-                    }
+        if (options.has(node.kind) && isFunctionLikeWithBody(node)) {
+            if (
+                !tsutils.hasModifier(node.modifiers, ts.SyntaxKind.AsyncKeyword) &&
+                !isCallExpressionBody(node.body) &&
+                returnsPromise(node, tc)
+            ) {
+                ctx.addFailure(node.getStart(sourceFile), node.body.pos, Rule.FAILURE_STRING);
             }
         }
         return ts.forEachChild(node, cb);
     });
 }
 
+function isFunctionLikeWithBody(
+    node: ts.Node,
+): node is ts.FunctionLikeDeclaration & { body: ts.Node } {
+    switch (node.kind) {
+        case ts.SyntaxKind.MethodDeclaration:
+        case ts.SyntaxKind.FunctionDeclaration:
+        case ts.SyntaxKind.FunctionExpression:
+        case ts.SyntaxKind.ArrowFunction:
+            return (node as ts.FunctionLikeDeclaration).body !== undefined;
+    }
+
+    return false;
+}
+
+function isCallExpressionBody(body: ts.Node) {
+    while (tsutils.isParenthesizedExpression(body)) {
+        body = body.expression;
+    }
+
+    return tsutils.isCallExpression(body);
+}
+
 function returnsPromise(node: ts.FunctionLikeDeclaration, tc: ts.TypeChecker): boolean {
     const type = tc.getReturnTypeOfSignature(tc.getTypeAtLocation(node).getCallSignatures()[0]);
     return type.symbol !== undefined && type.symbol.name === "Promise";

test/rules/promise-function-async/test.ts.lint

@@ -38,6 +38,8 @@ const asyncPromiseArrowFunctionB = async () => new Promise<void>();
 
 // non-'async' non-'Promise'-returning arrow functions are allowed
 const nonAsyncNonPromiseArrowFunction = (n: number) => n;
+const nonAsyncNonPromiseArrowFunctionParenthesisOne = (n: number) => (n);
+const nonAsyncNonPromiseArrowFunctionParenthesisTwo = (n: number) => ((n));
 
 class Test {
     public nonAsyncPromiseMethodA(p: Promise<void>) {
@@ -65,6 +67,8 @@ class Test {
 
     // single statement lamda functions that delegate to another promise-returning function are allowed
     public delegatingMethod = () => this.asyncPromiseMethodB(1);
+    public delegatingMethodParenthesisOne = () => (this.asyncPromiseMethodB(1));
+    public delegatingMethodParenthesisTwo = () => ((this.asyncPromiseMethodB(1)));
 }
 
 [0]: functions that return promises must be async