[Fix] export: False positive for exported overloaded functions in TS

CHANGELOG.md

@@ -12,6 +12,7 @@ This change log adheres to standards from [Keep a CHANGELOG](https://keepachange
 ### Fixed
 - `ExportMap` / flat config: include `languageOptions` in context ([#3052], thanks [@michaelfaith])
 - [`no-named-as-default`]: Allow using an identifier if the export is both a named and a default export ([#3032], thanks [@akwodkiewicz])
+- [`export`]: False positive for exported overloaded functions in TS ([#3065], thanks [@liuxingbaoyu])
 
 ### Changed
 - [Docs] [`no-relative-packages`]: fix typo ([#3066], thanks [@joshuaobrien])
@@ -1140,6 +1141,7 @@ for info on changes for earlier releases.
 [`memo-parser`]: ./memo-parser/README.md
 
 [#3066]: https://github.com/import-js/eslint-plugin-import/pull/3066
+[#3065]: https://github.com/import-js/eslint-plugin-import/pull/3065
 [#3052]: https://github.com/import-js/eslint-plugin-import/pull/3052
 [#3043]: https://github.com/import-js/eslint-plugin-import/pull/3043
 [#3036]: https://github.com/import-js/eslint-plugin-import/pull/3036
@@ -1875,6 +1877,7 @@ for info on changes for earlier releases.
 [@lilling]: https://github.com/lilling
 [@ljharb]: https://github.com/ljharb
 [@ljqx]: https://github.com/ljqx
+[@liuxingbaoyu]: https://github.com/liuxingbaoyu
 [@lo1tuma]: https://github.com/lo1tuma
 [@loganfsmyth]: https://github.com/loganfsmyth
 [@luczsoma]: https://github.com/luczsoma

src/rules/export.js

@@ -2,7 +2,6 @@
 import recursivePatternCapture from '../exportMap/patternCapture';
 import docsUrl from '../docsUrl';
 import includes from 'array-includes';
-import flatMap from 'array.prototype.flatmap';
 
 /*
 Notes on TypeScript namespaces aka TSModuleDeclaration:
@@ -27,42 +26,25 @@
 const tsTypePrefix = 'type:';
 
 /**
- * Detect function overloads like:
+ * remove function overloads like:
  * ```ts
  * export function foo(a: number);
  * export function foo(a: string);
- * export function foo(a: number|string) { return a; }
  * ```
  * @param {Set<Object>} nodes
- * @returns {boolean}
  */
-function isTypescriptFunctionOverloads(nodes) {
-  const nodesArr = Array.from(nodes);
-
-  const idents = flatMap(
-    nodesArr,
-    (node) => node.declaration && (
-      node.declaration.type === 'TSDeclareFunction' // eslint 6+
-      || node.declaration.type === 'TSEmptyBodyFunctionDeclaration' // eslint 4-5
-    )
-      ? node.declaration.id.name
-      : [],
-  );
-  if (new Set(idents).size !== idents.length) {
-    return true;
-  }
-
-  const types = new Set(nodesArr.map((node) => node.parent.type));
-  if (!types.has('TSDeclareFunction')) {
-    return false;
-  }
-  if (types.size === 1) {
-    return true;
-  }
-  if (types.size === 2 && types.has('FunctionDeclaration')) {
-    return true;
-  }
-  return false;
+function removeTypescriptFunctionOverloads(nodes) {
+  nodes.forEach((node) => {
+    const declType = node.type === 'ExportDefaultDeclaration' ? node.declaration.type : node.parent.type;
+    if (
+      // eslint 6+
+      declType === 'TSDeclareFunction'
+      // eslint 4-5
+      || declType === 'TSEmptyBodyFunctionDeclaration'
+    ) {
+      nodes.delete(node);
+    }
+  });
 }
 
 /**
@@ -227,9 +209,11 @@
       'Program:exit'() {
         for (const [, named] of namespace) {
           for (const [name, nodes] of named) {
+            removeTypescriptFunctionOverloads(nodes);
+
             if (nodes.size <= 1) { continue; }
 
-            if (isTypescriptFunctionOverloads(nodes) || isTypescriptNamespaceMerging(nodes)) { continue; }
+            if (isTypescriptNamespaceMerging(nodes)) { continue; }
 
             for (const node of nodes) {
               if (shouldSkipTypescriptNamespace(node, nodes)) { continue; }

tests/src/rules/export.js

@@ -56,6 +56,15 @@ ruleTester.run('export', rule, {
       `,
       parser,
     })),
+    getTSParsers().map((parser) => ({
+      code: `
+        export default function foo(param: string): boolean;
+        export default function foo(param: string, param1?: number): boolean {
+          return param && param1;
+        }
+      `,
+      parser,
+    })),
   ),
 
   invalid: [].concat(
@@ -154,6 +163,19 @@ ruleTester.run('export', rule, {
         ecmaVersion: 2022,
       },
     })),
+
+    getTSParsers().map((parser) => ({
+      code: `
+        export default function a(): void;
+        export default function a() {}
+        export { x as default };
+      `,
+      errors: [
+        'Multiple default exports.',
+        'Multiple default exports.',
+      ],
+      parser,
+    })),
   ),
 });
 
@@ -510,7 +532,7 @@ context('TypeScript', function () {
           }),
           test({
             code: `
-              export function Foo();
+              export function Foo() { };
               export class Foo { }
               export namespace Foo { }
             `,
@@ -529,7 +551,7 @@ context('TypeScript', function () {
           test({
             code: `
               export const Foo = 'bar';
-              export function Foo();
+              export function Foo() { };
               export namespace Foo { }
             `,
             errors: [