Flag default imports with named imports as needing importStar (microsoft#23795)

* Flag default imports with named imports as needing importStar

* Restructure helpers a bit, add double-default testcase

Author: weswigham

src/compiler/transformers/utilities.ts

@@ -15,14 +15,6 @@ namespace ts {
         hasExportStarsToExportValues: boolean; // whether this module contains export*
     }
 
-    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;
@@ -34,11 +26,27 @@ namespace ts {
     }
 
     export function getImportNeedsImportStarHelper(node: ImportDeclaration) {
-        return !!getNamespaceDeclarationNode(node) || (getNamedImportCount(node) > 1 && containsDefaultReference(node.importClause.namedBindings));
+        if (!!getNamespaceDeclarationNode(node)) {
+            return true;
+        }
+        const bindings = node.importClause && node.importClause.namedBindings;
+        if (!bindings) {
+            return false;
+        }
+        if (!isNamedImports(bindings)) return false;
+        let defaultRefCount = 0;
+        for (const binding of bindings.elements) {
+            if (isNamedDefaultReference(binding)) {
+                defaultRefCount++;
+            }
+        }
+        // Import star is required if there's default named refs mixed with non-default refs, or if theres non-default refs and it has a default import
+        return (defaultRefCount > 0 && defaultRefCount !== bindings.elements.length) || (!!(bindings.elements.length - defaultRefCount) && isDefaultImport(node));
     }
 
     export function getImportNeedsImportDefaultHelper(node: ImportDeclaration) {
-        return isDefaultImport(node) || (getNamedImportCount(node) === 1 && containsDefaultReference(node.importClause.namedBindings));
+        // Import default is needed if there's a default import or a default ref and no other refs (meaning an import star helper wasn't requested)
+        return !getImportNeedsImportStarHelper(node) && (isDefaultImport(node) || (node.importClause && isNamedImports(node.importClause.namedBindings) && containsDefaultReference(node.importClause.namedBindings)));
     }
 
     export function collectExternalModuleInfo(sourceFile: SourceFile, resolver: EmitResolver, compilerOptions: CompilerOptions): ExternalModuleInfo {

tests/baselines/reference/esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.errors.txt

@@ -0,0 +1,9 @@
+tests/cases/compiler/esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts(1,42): error TS2307: Cannot find module 'm'.
+
+
+==== tests/cases/compiler/esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts (1 errors) ====
+    import {default as a, default as b} from "m";
+                                             ~~~
+!!! error TS2307: Cannot find module 'm'.
+    void a;
+    void b;

tests/baselines/reference/esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.js

@@ -0,0 +1,14 @@
+//// [esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts]
+import {default as a, default as b} from "m";
+void a;
+void b;
+
+//// [esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.js]
+"use strict";
+var __importDefault = (this && this.__importDefault) || function (mod) {
+    return (mod && mod.__esModule) ? mod : { "default": mod };
+};
+exports.__esModule = true;
+var m_1 = __importDefault(require("m"));
+void m_1["default"];
+void m_1["default"];

tests/baselines/reference/esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.symbols

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts ===
+import {default as a, default as b} from "m";
+>default : Symbol(a, Decl(esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts, 0, 8))
+>a : Symbol(a, Decl(esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts, 0, 8))
+>default : Symbol(b, Decl(esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts, 0, 21))
+>b : Symbol(b, Decl(esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts, 0, 21))
+
+void a;
+>a : Symbol(a, Decl(esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts, 0, 8))
+
+void b;
+>b : Symbol(b, Decl(esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts, 0, 21))
+

tests/baselines/reference/esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.types

@@ -0,0 +1,15 @@
+=== tests/cases/compiler/esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts ===
+import {default as a, default as b} from "m";
+>default : any
+>a : any
+>default : any
+>b : any
+
+void a;
+>void a : undefined
+>a : any
+
+void b;
+>void b : undefined
+>b : any
+

tests/baselines/reference/esModuleInteropUsesExportStarWhenDefaultPlusNames.errors.txt

@@ -0,0 +1,9 @@
+tests/cases/compiler/esModuleInteropUsesExportStarWhenDefaultPlusNames.ts(1,28): error TS2307: Cannot find module './dep'.
+
+
+==== tests/cases/compiler/esModuleInteropUsesExportStarWhenDefaultPlusNames.ts (1 errors) ====
+    import Deps, { var2 } from './dep';
+                               ~~~~~~~
+!!! error TS2307: Cannot find module './dep'.
+    void Deps;
+    void var2;

tests/baselines/reference/esModuleInteropUsesExportStarWhenDefaultPlusNames.js

@@ -0,0 +1,18 @@
+//// [esModuleInteropUsesExportStarWhenDefaultPlusNames.ts]
+import Deps, { var2 } from './dep';
+void Deps;
+void var2;
+
+//// [esModuleInteropUsesExportStarWhenDefaultPlusNames.js]
+"use strict";
+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 dep_1 = __importStar(require("./dep"));
+void dep_1["default"];
+void dep_1.var2;

tests/baselines/reference/esModuleInteropUsesExportStarWhenDefaultPlusNames.symbols

@@ -0,0 +1,11 @@
+=== tests/cases/compiler/esModuleInteropUsesExportStarWhenDefaultPlusNames.ts ===
+import Deps, { var2 } from './dep';
+>Deps : Symbol(Deps, Decl(esModuleInteropUsesExportStarWhenDefaultPlusNames.ts, 0, 6))
+>var2 : Symbol(var2, Decl(esModuleInteropUsesExportStarWhenDefaultPlusNames.ts, 0, 14))
+
+void Deps;
+>Deps : Symbol(Deps, Decl(esModuleInteropUsesExportStarWhenDefaultPlusNames.ts, 0, 6))
+
+void var2;
+>var2 : Symbol(var2, Decl(esModuleInteropUsesExportStarWhenDefaultPlusNames.ts, 0, 14))
+

tests/baselines/reference/esModuleInteropUsesExportStarWhenDefaultPlusNames.types

@@ -0,0 +1,13 @@
+=== tests/cases/compiler/esModuleInteropUsesExportStarWhenDefaultPlusNames.ts ===
+import Deps, { var2 } from './dep';
+>Deps : any
+>var2 : any
+
+void Deps;
+>void Deps : undefined
+>Deps : any
+
+void var2;
+>void var2 : undefined
+>var2 : any
+

tests/cases/compiler/esModuleInteropImportDefaultWhenAllNamedAreDefaultAlias.ts

@@ -0,0 +1,4 @@
+// @esModuleInterop: true
+import {default as a, default as b} from "m";
+void a;
+void b;