[fix] export: false positive for typescript overloads

src/rules/export.js

@@ -24,6 +24,19 @@ ambient namespaces:
 const rootProgram = 'root'
 const tsTypePrefix = 'type:'
 
+/**
+ * Detect function overloads like:
+ * ```js
+ * export function foo(a: number) {}
+ * export function foo(a: string) {}
+ * ```
+ * @param {Set<Object>} nodes
+ * @returns {boolean}
+ */
+function isTypescriptFunctionOverloads(nodes) {
+  return [...nodes].every(node => node.parent.type === 'FunctionDeclaration')
+}
+
 module.exports = {
   meta: {
     type: 'problem',
@@ -34,6 +47,7 @@ module.exports = {
 
   create: function (context) {
     const namespace = new Map([[rootProgram, new Map()]])
+    const isTypescriptFile = /\.ts|\.tsx$/.test(context.getFilename())
 
     function addNamed(name, node, parent, isType) {
       if (!namespace.has(parent)) {
@@ -123,6 +137,8 @@ module.exports = {
           for (let [name, nodes] of named) {
             if (nodes.size <= 1) continue
 
+            if (isTypescriptFile && isTypescriptFunctionOverloads(nodes)) continue
+
             for (let node of nodes) {
               if (name === 'default') {
                 context.report(node, 'Multiple default exports.')

tests/src/rules/export.js

@@ -147,6 +147,22 @@ context('Typescript', function () {
           `,
         }, parserConfig)),
 
+        test(Object.assign({
+          code: `
+            export function fff(a: string) {};
+            export function fff(a: number) {};
+          `,
+          filename: 'foo.ts',
+        }, parserConfig)),
+
+        test(Object.assign({
+          code: `
+            export function ggg(a: string) {};
+            export function ggg(a: number) {};
+          `,
+          filename: 'foo.tsx',
+        }, parserConfig)),
+
         // namespace
         test(Object.assign({
           code: `