[Fix] export: false positive for typescript namespace merging

Fixes #1964.

Author: magarcia

CHANGELOG.md

@@ -10,6 +10,9 @@ This change log adheres to standards from [Keep a CHANGELOG](https://keepachange
 - [`no-named-default`, `no-default-export`, `prefer-default-export`, `no-named-export`, `export`, `named`, `namespace`, `no-unused-modules`]: support arbitrary module namespace names ([#2358], thanks [@sosukesuzuki])
 - [`no-dynamic-require`]: support dynamic import with espree ([#2371], thanks [@sosukesuzuki])
 
+### Fixed
+- [`export`]/TypeScript: false positive for typescript namespace merging ([#2375], thanks [@magarcia])
+
 ### Changed
 - [Tests] `no-nodejs-modules`: add tests for node protocol URL ([#2367], thanks [@sosukesuzuki])
 - [Tests] `default`, `no-anonymous-default-export`, `no-mutable-exports`, `no-named-as-default-member`, `no-named-as-default`: add tests for arbitrary module namespace names ([#2358], thanks [@sosukesuzuki])
@@ -964,6 +967,7 @@ for info on changes for earlier releases.
 
 [`memo-parser`]: ./memo-parser/README.md
 
+[#2375]: https://github.com/import-js/eslint-plugin-import/pull/2375
 [#2371]: https://github.com/import-js/eslint-plugin-import/pull/2371
 [#2367]: https://github.com/import-js/eslint-plugin-import/pull/2367
 [#2332]: https://github.com/import-js/eslint-plugin-import/pull/2332
@@ -1571,6 +1575,7 @@ for info on changes for earlier releases.
 [@ludofischer]: https://github.com/ludofischer
 [@lukeapage]: https://github.com/lukeapage
 [@lydell]: https://github.com/lydell
+[@magarcia]: https://github.com/magarcia
 [@Mairu]: https://github.com/Mairu
 [@malykhinvi]: https://github.com/malykhinvi
 [@manovotny]: https://github.com/manovotny
@@ -1661,4 +1666,4 @@ for info on changes for earlier releases.
 [@wtgtybhertgeghgtwtg]: https://github.com/wtgtybhertgeghgtwtg
 [@xpl]: https://github.com/xpl
 [@yordis]: https://github.com/yordis
-[@zloirock]: https://github.com/zloirock
+[@zloirock]: https://github.com/zloirock

src/rules/export.js

@@ -45,6 +45,27 @@ function isTypescriptFunctionOverloads(nodes) {
   );
 }
 
+/**
+ * Detect merging Namespaces with Classes, Functions, or Enums like:
+ * ```ts
+ * export class Foo { }
+ * export namespace Foo { }
+ * ```
+ * @param {Set<Object>} nodes
+ * @returns {boolean}
+ */
+function isTypescriptNamespaceMerging(nodes) {
+  const types = new Set(Array.from(nodes, (node) => node.parent.type));
+  return (
+    types.has('TSModuleDeclaration') &&
+    (types.size === 1 ||
+      (types.size === 2 && (
+        types.has('ClassDeclaration') || types.has('FunctionDeclaration') || types.has('TSEnumDeclaration')
+      ))
+    )
+  );
+}
+
 module.exports = {
   meta: {
     type: 'problem',
@@ -156,7 +177,7 @@ module.exports = {
           for (const [name, nodes] of named) {
             if (nodes.size <= 1) continue;
 
-            if (isTypescriptFunctionOverloads(nodes)) continue;
+            if (isTypescriptFunctionOverloads(nodes) || isTypescriptNamespaceMerging(nodes)) continue;
 
             for (const node of nodes) {
               if (name === 'default') {

tests/src/rules/export.js

@@ -219,6 +219,27 @@ context('TypeScript', function () {
             }
           `,
         }, parserConfig)),
+        test(Object.assign({
+          code: `
+            export class Foo { }
+            export namespace Foo { }
+            export namespace Foo {
+              export class Bar {}
+            }
+          `,
+        }, parserConfig)),
+        test(Object.assign({
+          code: `
+            export function Foo() { }
+            export namespace Foo { }
+          `,
+        }, parserConfig)),
+        test(Object.assign({
+          code: `
+            export enum Foo { }
+            export namespace Foo { }
+          `,
+        }, parserConfig)),
         test(Object.assign({
           code: 'export * from "./file1.ts"',
           filename: testFilePath('typescript-d-ts/file-2.ts'),