[Fix] export: do not error on TS export overloads

Fixes #1590

CHANGELOG.md

@@ -21,6 +21,7 @@ This change log adheres to standards from [Keep a CHANGELOG](https://keepachange
 - [`order`]: leave more space in rankings for consecutive path groups ([#2506], thanks [@Pearce-Ropion])
 - [`no-cycle`]: add ExportNamedDeclaration statements to dependencies ([#2511], thanks [@BenoitZugmeyer])
 - [`dynamic-import-chunkname`]: prevent false report on a valid webpack magic comment ([#2330], thanks [@mhmadhamster])
+- [`export`]: do not error on TS export overloads ([#1590], thanks [@ljharb])
 
 ### Changed
 - [Tests] [`named`]: Run all TypeScript test ([#2427], thanks [@ProdigySim])
@@ -1341,6 +1342,7 @@ for info on changes for earlier releases.
 [#1631]: https://github.com/import-js/eslint-plugin-import/issues/1631
 [#1616]: https://github.com/import-js/eslint-plugin-import/issues/1616
 [#1613]: https://github.com/import-js/eslint-plugin-import/issues/1613
+[#1590]: https://github.com/import-js/eslint-plugin-import/issues/1590
 [#1589]: https://github.com/import-js/eslint-plugin-import/issues/1589
 [#1565]: https://github.com/import-js/eslint-plugin-import/issues/1565
 [#1366]: https://github.com/import-js/eslint-plugin-import/issues/1366

src/rules/export.js

@@ -1,6 +1,7 @@
 import ExportMap, { recursivePatternCapture } from '../ExportMap';
 import docsUrl from '../docsUrl';
 import includes from 'array-includes';
+import flatMap from 'array.prototype.flatmap';
 
 /*
 Notes on TypeScript namespaces aka TSModuleDeclaration:
@@ -35,12 +36,31 @@ const tsTypePrefix = 'type:';
  * @returns {boolean}
  */
 function isTypescriptFunctionOverloads(nodes) {
-  const types = new Set(Array.from(nodes, node => node.parent.type));
-  return types.has('TSDeclareFunction')
-    && (
-      types.size === 1
-      || (types.size === 2 && types.has('FunctionDeclaration'))
-    );
+  const nodesArr = Array.from(nodes);
+  const types = new Set(nodesArr.map(node => node.parent.type));
+
+  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;
+  }
+
+  if (!types.has('TSDeclareFunction')) {
+    return false;
+  }
+  if (types.size === 1) {
+    return true;
+  }
+  if (types.size === 2 && types.has('FunctionDeclaration')) {
+    return true;
+  }
+  return false;
 }
 
 /**

tests/src/rules/export.js

@@ -45,6 +45,17 @@ ruleTester.run('export', rule, {
         ecmaVersion: 2020,
       },
     })) || [],
+
+    getTSParsers().map((parser) => ({
+      code: `
+        export default function foo(param: string): boolean;
+        export default function foo(param: string, param1: number): boolean;
+        export default function foo(param: string, param1?: number): boolean {
+          return param && param1;
+        }
+      `,
+      parser,
+    })),
   ),
 
   invalid: [].concat(