feat(typescript): implement namespace alias (#13528)

support `import alias = Namespace`, reject `import alias = require('foo')`

fix #12345

packages/babel-plugin-transform-typescript/src/index.ts

@@ -465,12 +465,26 @@ export default declare((api, opts) => {
         transpileEnum(path, t);
       },
 
-      TSImportEqualsDeclaration(path) {
+      TSImportEqualsDeclaration(path: NodePath<t.TSImportEqualsDeclaration>) {
-        throw path.buildCodeFrameError(
+        if (t.isTSExternalModuleReference(path.node.moduleReference)) {
-          "`import =` is not supported by @babel/plugin-transform-typescript\n" +
+          // import alias = require('foo');
-            "Please consider using " +
+          throw path.buildCodeFrameError(
-            "`import <moduleName> from '<moduleName>';` alongside " +
+            `\`import ${path.node.id.name} = require('${path.node.moduleReference.expression.value}')\` ` +
-            "Typescript's --allowSyntheticDefaultImports option.",
+              "is not supported by @babel/plugin-transform-typescript\n" +
+              "Please consider using " +
+              `\`import ${path.node.id.name} from '${path.node.moduleReference.expression.value}';\` alongside ` +
+              "Typescript's --allowSyntheticDefaultImports option.",
+          );
+        }
+
+        // import alias = Namespace;
+        path.replaceWith(
+          t.variableDeclaration("var", [
+            t.variableDeclarator(
+              path.node.id,
+              entityNameToExpr(path.node.moduleReference),
+            ),
+          ]),
         );
       },
 
@@ -519,6 +533,14 @@ export default declare((api, opts) => {
     },
   };
 
+  function entityNameToExpr(node: t.TSEntityName): t.Expression {
+    if (t.isTSQualifiedName(node)) {
+      return t.memberExpression(entityNameToExpr(node.left), node.right);
+    }
+
+    return node;
+  }
+
   function visitPattern({ node }) {
     if (node.typeAnnotation) node.typeAnnotation = null;
     if (t.isIdentifier(node) && node.optional) node.optional = null;

packages/babel-plugin-transform-typescript/test/fixtures/imports/import=/options.json

@@ -1,3 +1,3 @@
 {
-  "throws": "`import =` is not supported by @babel/plugin-transform-typescript\nPlease consider using `import <moduleName> from '<moduleName>';` alongside Typescript's --allowSyntheticDefaultImports option."
+  "throws": "`import lib = require('lib')` is not supported by @babel/plugin-transform-typescript\nPlease consider using `import lib from 'lib';` alongside Typescript's --allowSyntheticDefaultImports option."
 }

packages/babel-plugin-transform-typescript/test/fixtures/namespace/alias/input.ts

@@ -0,0 +1,22 @@
+declare module LongNameModule {
+  export type SomeType = number;
+  export const foo: number;
+  module Inner {
+    export type T = string;
+    export const bar: boolean;
+  }
+}
+
+import * as babel from '@babel/core';
+
+/** type only */
+import b = babel;
+import AliasModule = LongNameModule;
+
+const some: AliasModule.SomeType = 3;
+const bar = AliasModule.foo;
+const baz = AliasModule.Inner.bar;
+let str: LongNameModule.Inner.T;
+let node: b.OptionManager;
+
+console.log(some);

packages/babel-plugin-transform-typescript/test/fixtures/namespace/alias/output.mjs

@@ -0,0 +1,11 @@
+import * as babel from '@babel/core';
+/** type only */
+
+var b = babel;
+var AliasModule = LongNameModule;
+const some = 3;
+const bar = AliasModule.foo;
+const baz = AliasModule.Inner.bar;
+let str;
+let node;
+console.log(some);