Create import helpers for named imports if they contain default imports (microsoft#21550)

Author: weswigham

src/compiler/transformers/module/module.ts

@@ -690,16 +690,36 @@ namespace ts {
             return createCall(createPropertyAccess(promiseResolveCall, "then"), /*typeArguments*/ undefined, [func]);
         }
 
+        function getNamedImportCount(node: ImportDeclaration) {
+            if (!(node.importClause && node.importClause.namedBindings)) return 0;
+            const names = node.importClause.namedBindings;
+            if (!names) return 0;
+            if (!isNamedImports(names)) return 0;
+            return names.elements.length;
+        }
+
+        function containsDefaultReference(node: NamedImportBindings) {
+            if (!node) return false;
+            if (!isNamedImports(node)) return false;
+            return some(node.elements, isNamedDefaultReference);
+        }
+
+        function isNamedDefaultReference(e: ImportSpecifier) {
+            return e.propertyName && e.propertyName.escapedText === InternalSymbolName.Default;
+        }
 
         function getHelperExpressionForImport(node: ImportDeclaration, innerExpr: Expression) {
             if (!compilerOptions.esModuleInterop || getEmitFlags(node) & EmitFlags.NeverApplyImportHelper) {
                 return innerExpr;
             }
-            if (getNamespaceDeclarationNode(node)) {
+            const nameCount = getNamedImportCount(node);
+            const hasDefault = nameCount > 0 ? containsDefaultReference(node.importClause.namedBindings) : undefined;
+
+            if (getNamespaceDeclarationNode(node) || (nameCount > 1 && hasDefault)) {
                 context.requestEmitHelper(importStarHelper);
                 return createCall(getHelperName("__importStar"), /*typeArguments*/ undefined, [innerExpr]);
             }
-            if (isDefaultImport(node)) {
+            if (isDefaultImport(node) || (nameCount === 1 && hasDefault)) {
                 context.requestEmitHelper(importDefaultHelper);
                 return createCall(getHelperName("__importDefault"), /*typeArguments*/ undefined, [innerExpr]);
             }

tests/baselines/reference/esModuleInteropNamedDefaultImports.js

@@ -0,0 +1,49 @@
+//// [tests/cases/compiler/esModuleInteropNamedDefaultImports.ts] ////
+
+//// [mod.ts]
+export default class Foo {}
+export class Bar {}
+//// [idx.ts]
+import Foo from "./mod";
+import { default as Foo2 } from "./mod";
+import { Bar, default as Foo3 } from "./mod";
+new Foo();
+new Foo2();
+new Bar();
+new Foo3();
+
+//// [mod.js]
+"use strict";
+exports.__esModule = true;
+var Foo = /** @class */ (function () {
+    function Foo() {
+    }
+    return Foo;
+}());
+exports["default"] = Foo;
+var Bar = /** @class */ (function () {
+    function Bar() {
+    }
+    return Bar;
+}());
+exports.Bar = Bar;
+//// [idx.js]
+"use strict";
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+}
+var __importStar = (this && this.__importStar) || function (mod) {
+    if (mod && mod.__esModule) return mod;
+    var result = {};
+    if (mod != null) for (var k in mod) if (Object.hasOwnProperty.call(mod, k)) result[k] = mod[k];
+    result["default"] = mod;
+    return result;
+}
+exports.__esModule = true;
+var mod_1 = __importDefault(require("./mod"));
+var mod_2 = __importDefault(require("./mod"));
+var mod_3 = __importStar(require("./mod"));
+new mod_1["default"]();
+new mod_2["default"]();
+new mod_3.Bar();
+new mod_3["default"]();

tests/baselines/reference/esModuleInteropNamedDefaultImports.symbols

@@ -0,0 +1,32 @@
+=== tests/cases/compiler/mod.ts ===
+export default class Foo {}
+>Foo : Symbol(Foo, Decl(mod.ts, 0, 0))
+
+export class Bar {}
+>Bar : Symbol(Bar, Decl(mod.ts, 0, 27))
+
+=== tests/cases/compiler/idx.ts ===
+import Foo from "./mod";
+>Foo : Symbol(Foo, Decl(idx.ts, 0, 6))
+
+import { default as Foo2 } from "./mod";
+>default : Symbol(Foo2, Decl(idx.ts, 1, 8))
+>Foo2 : Symbol(Foo2, Decl(idx.ts, 1, 8))
+
+import { Bar, default as Foo3 } from "./mod";
+>Bar : Symbol(Bar, Decl(idx.ts, 2, 8))
+>default : Symbol(Foo3, Decl(idx.ts, 2, 13))
+>Foo3 : Symbol(Foo3, Decl(idx.ts, 2, 13))
+
+new Foo();
+>Foo : Symbol(Foo, Decl(idx.ts, 0, 6))
+
+new Foo2();
+>Foo2 : Symbol(Foo2, Decl(idx.ts, 1, 8))
+
+new Bar();
+>Bar : Symbol(Bar, Decl(idx.ts, 2, 8))
+
+new Foo3();
+>Foo3 : Symbol(Foo3, Decl(idx.ts, 2, 13))
+

tests/baselines/reference/esModuleInteropNamedDefaultImports.types

@@ -0,0 +1,36 @@
+=== tests/cases/compiler/mod.ts ===
+export default class Foo {}
+>Foo : Foo
+
+export class Bar {}
+>Bar : Bar
+
+=== tests/cases/compiler/idx.ts ===
+import Foo from "./mod";
+>Foo : typeof Foo
+
+import { default as Foo2 } from "./mod";
+>default : typeof Foo
+>Foo2 : typeof Foo
+
+import { Bar, default as Foo3 } from "./mod";
+>Bar : typeof Bar
+>default : typeof Foo
+>Foo3 : typeof Foo
+
+new Foo();
+>new Foo() : Foo
+>Foo : typeof Foo
+
+new Foo2();
+>new Foo2() : Foo
+>Foo2 : typeof Foo
+
+new Bar();
+>new Bar() : Bar
+>Bar : typeof Bar
+
+new Foo3();
+>new Foo3() : Foo
+>Foo3 : typeof Foo
+

tests/cases/compiler/esModuleInteropNamedDefaultImports.ts

@@ -0,0 +1,13 @@
+// @module: commonjs
+// @esModuleInterop: true
+// @filename: mod.ts
+export default class Foo {}
+export class Bar {}
+// @filename: idx.ts
+import Foo from "./mod";
+import { default as Foo2 } from "./mod";
+import { Bar, default as Foo3 } from "./mod";
+new Foo();
+new Foo2();
+new Bar();
+new Foo3();