fix: support index modules for dependencies (#123)

CommonJS or ES modules require index modules when a folder is
required, e.g.:

```js
import * from "./schema"
```

will in case of `./schema` is a directory lookup the index module
and require the following:

```js
import * from "./schema/index"
```

under the hood. As the UI5 module loader cannot support this feature
this Babel plugin checks for the existence of the index module and
rewrites the import to the index module so that the UI5 loader also
loads the proper module.

packages/plugin/__test__/__snapshots__/test.js.snap

@@ -1492,7 +1492,7 @@ exports[`mixed mixed-import-export.js 1`] = `
     __esModule: true
   };
   function extendExports(exports, obj) {
-    Object.keys(obj).forEach(function (key) {
+    obj && Object.keys(obj).forEach(function (key) {
       if (key === "default" || key === "__esModule") return;
       Object.defineProperty(exports, key, {
         enumerable: true,
@@ -1875,6 +1875,31 @@ exports[`typescript ts-export-type.ts 1`] = `
 });"
 `;
 
+exports[`typescript ts-export-type-only.ts 1`] = `""`;
+
+exports[`typescript ts-index.ts 1`] = `
+"sap.ui.define(["./_private_/index"], function (____private__index) {
+  "use strict";
+
+  var __exports = {
+    __esModule: true
+  };
+  function extendExports(exports, obj) {
+    obj && Object.keys(obj).forEach(function (key) {
+      if (key === "default" || key === "__esModule") return;
+      Object.defineProperty(exports, key, {
+        enumerable: true,
+        get: function get() {
+          return obj[key];
+        }
+      });
+    });
+  }
+  extendExports(__exports, ____private__index);
+  return __exports;
+});"
+`;
+
 exports[`typescript ts-re-export.ts 1`] = `
 "sap.ui.define(["module", "./having-a-dash", "path/having-a-dash"], function (__module, ___having_a_dash, __path_having_a_dash) {
   "use strict";
@@ -1883,7 +1908,7 @@ exports[`typescript ts-re-export.ts 1`] = `
     __esModule: true
   };
   function extendExports(exports, obj) {
-    Object.keys(obj).forEach(function (key) {
+    obj && Object.keys(obj).forEach(function (key) {
       if (key === "default" || key === "__esModule") return;
       Object.defineProperty(exports, key, {
         enumerable: true,
@@ -1900,6 +1925,29 @@ exports[`typescript ts-re-export.ts 1`] = `
 });"
 `;
 
+exports[`typescript ts-re-export-type-only.ts 1`] = `
+"sap.ui.define(["./ts-export-type-only"], function (___ts_export_type_only) {
+  "use strict";
+
+  var __exports = {
+    __esModule: true
+  };
+  function extendExports(exports, obj) {
+    obj && Object.keys(obj).forEach(function (key) {
+      if (key === "default" || key === "__esModule") return;
+      Object.defineProperty(exports, key, {
+        enumerable: true,
+        get: function get() {
+          return obj[key];
+        }
+      });
+    });
+  }
+  extendExports(__exports, ___ts_export_type_only);
+  return __exports;
+});"
+`;
+
 exports[`typescript-preset-env ts-class-anonymous.ts 1`] = `
 "sap.ui.define(["sap/Class"], function (SAPClass) {
   "use strict";

packages/plugin/__test__/fixtures/typescript/_private_/index.ts

@@ -0,0 +1 @@
+export * from "./type";

packages/plugin/__test__/fixtures/typescript/_private_/type.ts

@@ -0,0 +1 @@
+export type StringOrBoolean = string | boolean;

packages/plugin/__test__/fixtures/typescript/ts-export-type-only.ts

@@ -0,0 +1,4 @@
+/**
+ * any sequence of octets
+ */
+export type Binary = any;

packages/plugin/__test__/fixtures/typescript/ts-index.ts

@@ -0,0 +1 @@
+export * from "./_private_";

packages/plugin/__test__/fixtures/typescript/ts-re-export-type-only.ts

@@ -0,0 +1 @@
+export * from "./ts-export-type-only";

packages/plugin/src/modules/visitor.js

@@ -1,9 +1,30 @@
+import { join, dirname } from "path";
+import { existsSync, statSync } from "fs";
+
 import { types as t, template } from "@babel/core";
 import * as th from "../utils/templates";
 import * as ast from "../utils/ast";
 
 import { hasJsdocGlobalExportFlag } from "../classes/helpers/jsdoc";
 
+const resolveSource = (src, filename) => {
+  src = src.replace(/\\/g, "/");
+  const dir = dirname(filename);
+  const absoluteSrc = join(dir, src);
+  if (existsSync(absoluteSrc) && statSync(absoluteSrc).isDirectory) {
+    if (
+      existsSync(join(absoluteSrc, "index.js")) ||
+      existsSync(join(absoluteSrc, "index.jsx")) ||
+      existsSync(join(absoluteSrc, "index.ts")) ||
+      existsSync(join(absoluteSrc, "index.tsx")) ||
+      existsSync(join(absoluteSrc, "index.mjs")) ||
+      existsSync(join(absoluteSrc, "index.cjs"))
+    ) {
+      src = `${src}/index`;
+    }
+  }
+  return src;
+};
 const cleanImportSource = (src) =>
   src.replace(/(\/)|(-)|(@)/g, "_").replace(/\./g, "");
 const tempModuleName = (name) => `__${name}`;
@@ -23,13 +44,13 @@ export const ModuleTransformVisitor = {
   /*!
    * Removes the ES6 import and adds the details to the import array in our state.
    */
-  ImportDeclaration(path, { opts = {}, ...state }) {
+  ImportDeclaration(path, { filename, opts = {}, ...state }) {
     const { node } = path;
 
     if (node.importKind === "type") return; // flow-type
 
     const { specifiers, source } = node;
-    const src = source.value.replace(/\\/g, "/");
+    const src = resolveSource(source.value, filename);
 
     // When 'libs' are used, only 'libs' will be converted to UI5 imports.
     const { libs = [".*"] } = opts;
@@ -168,14 +189,14 @@ export const ModuleTransformVisitor = {
    * The reason we don't export in place is to handle the situation
    * where a let or var can be defined, and the latest one should be exported.
    */
-  ExportNamedDeclaration(path) {
+  ExportNamedDeclaration(path, { filename }) {
     const { node } = path;
     const { specifiers, declaration, source } = node;
 
     let fromSource = "";
     if (source) {
       // e.g. export { one, two } from 'x'
-      const src = source.value;
+      const src = resolveSource(source.value, filename);
       const name = cleanImportSource(src);
       const tmpName = tempModuleName(name);
       this.imports.push({ src, name, tmpName });
@@ -267,8 +288,8 @@ export const ModuleTransformVisitor = {
     }
   },
 
-  ExportAllDeclaration(path) {
-    const src = path.node.source.value;
+  ExportAllDeclaration(path, { filename }) {
+    const src = resolveSource(path.node.source.value, filename);
     const name = cleanImportSource(src);
     const tmpName = tempModuleName(name);
 

packages/plugin/src/utils/templates.js

@@ -50,7 +50,7 @@ export function buildNamedExport(obj) {
 
 export const buildAllExportHelper = template(`
   function extendExports(exports, obj) {
-    Object.keys(obj).forEach(function (key) {
+    obj && Object.keys(obj).forEach(function (key) {
       if (key === "default" || key === "__esModule") return;
       Object.defineProperty(exports, key, {
         enumerable: true,