System module format - fixes function hoisting failure case (#8820)

* failing test case

* fix function hoist bug

packages/babel-plugin-transform-modules-systemjs/src/index.js

@@ -332,8 +332,23 @@ export default declare((api, options) => {
                     const nodes = [];
 
                     for (const specifier of specifiers) {
-                      // only globals exported this way
+                      const binding = path.scope.getBinding(
-                      if (!path.scope.getBinding(specifier.local.name)) {
+                        specifier.local.name,
+                      );
+                      // hoisted function export
+                      if (
+                        binding &&
+                        t.isFunctionDeclaration(binding.path.node)
+                      ) {
+                        beforeBody.push(
+                          buildExportCall(
+                            specifier.exported.name,
+                            t.cloneNode(specifier.local),
+                          ),
+                        );
+                      }
+                      // only globals also exported this way
+                      else if (!binding) {
                         nodes.push(
                           buildExportCall(
                             specifier.exported.name,

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-fn-decl/input.mjs

@@ -0,0 +1,10 @@
+var testProp = 'test property';
+
+function testFunc() {
+  return 'test function';
+}
+
+export {
+  testFunc,
+  testProp
+};

packages/babel-plugin-transform-modules-systemjs/test/fixtures/systemjs/export-fn-decl/output.mjs

@@ -0,0 +1,18 @@
+System.register([], function (_export, _context) {
+  "use strict";
+
+  var testProp;
+
+  function testFunc() {
+    return 'test function';
+  }
+
+  _export("testFunc", testFunc);
+
+  return {
+    setters: [],
+    execute: function () {
+      _export("testProp", testProp = 'test property');
+    }
+  };
+});