Enable allowSyntheticDefaultImports if esModuleInterop is enabled

Fixes #26193.

src/compiler/utilities.ts

@@ -7020,9 +7020,8 @@ namespace ts {
         const moduleKind = getEmitModuleKind(compilerOptions);
         return compilerOptions.allowSyntheticDefaultImports !== undefined
             ? compilerOptions.allowSyntheticDefaultImports
-            : compilerOptions.esModuleInterop
-                ? moduleKind !== ModuleKind.None && moduleKind < ModuleKind.ES2015
-                : moduleKind === ModuleKind.System;
+            : compilerOptions.esModuleInterop ||
+            moduleKind === ModuleKind.System;
     }
 
     export function getEmitDeclarations(compilerOptions: CompilerOptions): boolean {

tests/baselines/reference/esModuleInteropEnablesSyntheticDefaultImports.js

@@ -0,0 +1,15 @@
+//// [tests/cases/compiler/esModuleInteropEnablesSyntheticDefaultImports.ts] ////
+
+//// [a.ts]
+import Namespace from "./b";
+export var x = new Namespace.Foo();
+
+//// [b.d.ts]
+export class Foo {
+	member: string;
+}
+
+
+//// [a.js]
+import Namespace from "./b";
+export var x = new Namespace.Foo();

tests/baselines/reference/esModuleInteropEnablesSyntheticDefaultImports.symbols

@@ -0,0 +1,18 @@
+=== tests/cases/compiler/a.ts ===
+import Namespace from "./b";
+>Namespace : Symbol(Namespace, Decl(a.ts, 0, 6))
+
+export var x = new Namespace.Foo();
+>x : Symbol(x, Decl(a.ts, 1, 10))
+>Namespace.Foo : Symbol(Namespace.Foo, Decl(b.d.ts, 0, 0))
+>Namespace : Symbol(Namespace, Decl(a.ts, 0, 6))
+>Foo : Symbol(Namespace.Foo, Decl(b.d.ts, 0, 0))
+
+=== tests/cases/compiler/b.d.ts ===
+export class Foo {
+>Foo : Symbol(Foo, Decl(b.d.ts, 0, 0))
+
+	member: string;
+>member : Symbol(Foo.member, Decl(b.d.ts, 0, 18))
+}
+

tests/baselines/reference/esModuleInteropEnablesSyntheticDefaultImports.types

@@ -0,0 +1,19 @@
+=== tests/cases/compiler/a.ts ===
+import Namespace from "./b";
+>Namespace : typeof Namespace
+
+export var x = new Namespace.Foo();
+>x : Namespace.Foo
+>new Namespace.Foo() : Namespace.Foo
+>Namespace.Foo : typeof Namespace.Foo
+>Namespace : typeof Namespace
+>Foo : typeof Namespace.Foo
+
+=== tests/cases/compiler/b.d.ts ===
+export class Foo {
+>Foo : Foo
+
+	member: string;
+>member : string
+}
+

tests/cases/compiler/esModuleInteropEnablesSyntheticDefaultImports.ts

@@ -0,0 +1,10 @@
+// @esModuleInterop: true
+// @module: es2015
+// @Filename: a.ts
+import Namespace from "./b";
+export var x = new Namespace.Foo();
+
+// @Filename: b.d.ts
+export class Foo {
+	member: string;
+}