no-useless-undefined: Flag return undefined for explicit undefined return types (#2876)

sindresorhus · web-flow · commit 41fc9c27ebe5 · 2026-02-14T00:44:07.000+07:00
diff --git a/rules/no-useless-undefined.js b/rules/no-useless-undefined.js
@@ -77,6 +77,9 @@ const getFunction = scope => {
 	}
 };
 
+const isUndefinedReturnType = functionNode =>
+	functionNode.returnType?.typeAnnotation?.type === 'TSUndefinedKeyword';
+
 const isFunctionBindCall = node =>
 	!node.optional
 	&& node.callee.type === 'MemberExpression'
@@ -118,10 +121,14 @@ const create = context => {
 			&& node.parent.type === 'ReturnStatement'
 			&& node.parent.argument === node
 		) {
+			const functionNode = getFunction(sourceCode.getScope(node));
+			if (functionNode?.returnType && !isUndefinedReturnType(functionNode)) {
+				return;
+			}
+
 			return getProblem(
 				node,
 				fixer => removeNodeAndLeadingSpace(node, fixer),
-				/* CheckFunctionReturnType */ true,
 			);
 		}
 	});
diff --git a/test/no-useless-undefined.js b/test/no-useless-undefined.js
@@ -274,71 +274,163 @@ test.typescript({
 				return undefined;
 			}
 		`,
-		'const foo = (): undefined => {return undefined;}',
 		'const foo = (): undefined => undefined;',
 		'const foo = (): string => undefined;',
-		'const foo = function (): undefined {return undefined}',
-		'export function foo(): undefined {return undefined}',
-		outdent`
-			const object = {
-				method(): undefined {
-					return undefined;
+		'createContext<T>(undefined);',
+		'React.createContext<T>(undefined);',
+	],
+	invalid: [
+		{
+			code: 'function shouldBeFlagged(): undefined {return undefined;}',
+			output: 'function shouldBeFlagged(): undefined {return;}',
+			errors,
+		},
+		{
+			code: 'const foo = function (): undefined {return undefined};',
+			output: 'const foo = function (): undefined {return};',
+			errors,
+		},
+		{
+			code: outdent`
+				class A {
+					method(): undefined {
+						return undefined;
+					}
 				}
-			}
-		`,
-		outdent`
-			class A {
-				method(): undefined {
-					return undefined;
+			`,
+			output: outdent`
+				class A {
+					method(): undefined {
+						return;
+					}
 				}
-			}
-		`,
-		outdent`
-			const A = class A {
-				method(): undefined {
-					return undefined
+			`,
+			errors,
+		},
+		{
+			code: 'export function foo(): undefined {return undefined}',
+			output: 'export function foo(): undefined {return}',
+			errors,
+		},
+		{
+			code: outdent`
+				const object = {
+					method(): undefined {
+						return undefined;
+					}
 				}
-			};
-		`,
-		outdent`
-			class A {
-				static method(): undefined {
-					return undefined
+			`,
+			output: outdent`
+				const object = {
+					method(): undefined {
+						return;
+					}
 				}
-			}
-		`,
-		outdent`
-			class A {
-				get method(): undefined {
-					return undefined;
+			`,
+			errors,
+		},
+		{
+			code: outdent`
+				const A = class A {
+					method(): undefined {
+						return undefined
+					}
+				};
+			`,
+			output: outdent`
+				const A = class A {
+					method(): undefined {
+						return
+					}
+				};
+			`,
+			errors,
+		},
+		{
+			code: outdent`
+				class A {
+					static method(): undefined {
+						return undefined
+					}
 				}
-			}
-		`,
-		outdent`
-			class A {
-				static get method(): undefined {
-					return undefined;
+			`,
+			output: outdent`
+				class A {
+					static method(): undefined {
+						return
+					}
 				}
-			}
-		`,
-		outdent`
-			class A {
-				#method(): undefined {
-					return undefined;
+			`,
+			errors,
+		},
+		{
+			code: outdent`
+				class A {
+					get method(): undefined {
+						return undefined;
+					}
 				}
-			}
-		`,
-		outdent`
-			class A {
-				private method(): undefined {
-					return undefined;
+			`,
+			output: outdent`
+				class A {
+					get method(): undefined {
+						return;
+					}
 				}
-			}
-		`,
-		'createContext<T>(undefined);',
-		'React.createContext<T>(undefined);',
-	],
-	invalid: [
+			`,
+			errors,
+		},
+		{
+			code: outdent`
+				class A {
+					static get method(): undefined {
+						return undefined;
+					}
+				}
+			`,
+			output: outdent`
+				class A {
+					static get method(): undefined {
+						return;
+					}
+				}
+			`,
+			errors,
+		},
+		{
+			code: outdent`
+				class A {
+					#method(): undefined {
+						return undefined;
+					}
+				}
+			`,
+			output: outdent`
+				class A {
+					#method(): undefined {
+						return;
+					}
+				}
+			`,
+			errors,
+		},
+		{
+			code: outdent`
+				class A {
+					private method(): undefined {
+						return undefined;
+					}
+				}
+			`,
+			output: outdent`
+				class A {
+					private method(): undefined {
+						return;
+					}
+				}
+			`,
+			errors,
+		},
 		{
 			code: outdent`
 				function foo():undefined {
