Add test demonstrating interop for esbuild and webpack

src/compiler/checker.ts

@@ -4047,9 +4047,9 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
 
     function canHaveSyntheticDefault(file: SourceFile | undefined, moduleSymbol: Symbol, dontResolveAlias: boolean, usage: Expression) {
         const usageMode = file && getModuleFormatInteropKind(compilerOptions) !== ModuleFormatInteropKind.Babel && getUsageModeForExpression(usage);
+        // fallthrough on cjs usages so we imply defaults for interop'd imports, too
         if (usageMode === ModuleKind.ESNext) {
             return isESMFormatImportImportingCommonjsFormatFile(usageMode, file!.impliedNodeFormat);
-            // fallthrough on cjs usages so we imply defaults for interop'd imports, too
         }
         if (!allowSyntheticDefaultImports) {
             return false;

tests/baselines/reference/esbuildInterop.errors.txt

@@ -0,0 +1,26 @@
+/index.ts(2,5): error TS2339: Property 'toLowerCase' does not exist on type 'typeof import("/node_modules/dep/index")'.
+
+
+==== /node_modules/dep/package.json (0 errors) ====
+    {
+        "name": "dep",
+        "version": "1.0.0",
+        "main": "index.js"
+    }
+    
+==== /node_modules/dep/index.d.ts (0 errors) ====
+    declare const _default: string;
+    export default _default;
+    
+==== /package.json (0 errors) ====
+    {
+      "type": "module"
+    }
+    
+==== /index.ts (1 errors) ====
+    import dep from "dep";
+    dep.toLowerCase(); // Error
+        ~~~~~~~~~~~
+!!! error TS2339: Property 'toLowerCase' does not exist on type 'typeof import("/node_modules/dep/index")'.
+    dep.default.toLowerCase(); // Ok
+    

tests/baselines/reference/esbuildInterop.js

@@ -0,0 +1,28 @@
+//// [tests/cases/conformance/module/esbuildInterop.ts] ////
+
+//// [package.json]
+{
+    "name": "dep",
+    "version": "1.0.0",
+    "main": "index.js"
+}
+
+//// [index.d.ts]
+declare const _default: string;
+export default _default;
+
+//// [package.json]
+{
+  "type": "module"
+}
+
+//// [index.ts]
+import dep from "dep";
+dep.toLowerCase(); // Error
+dep.default.toLowerCase(); // Ok
+
+
+//// [index.js]
+import dep from "dep";
+dep.toLowerCase(); // Error
+dep.default.toLowerCase(); // Ok

tests/baselines/reference/esbuildInterop.symbols

@@ -0,0 +1,23 @@
+//// [tests/cases/conformance/module/esbuildInterop.ts] ////
+
+=== /node_modules/dep/index.d.ts ===
+declare const _default: string;
+>_default : Symbol(_default, Decl(index.d.ts, 0, 13))
+
+export default _default;
+>_default : Symbol(_default, Decl(index.d.ts, 0, 13))
+
+=== /index.ts ===
+import dep from "dep";
+>dep : Symbol(dep, Decl(index.ts, 0, 6))
+
+dep.toLowerCase(); // Error
+>dep : Symbol(dep, Decl(index.ts, 0, 6))
+
+dep.default.toLowerCase(); // Ok
+>dep.default.toLowerCase : Symbol(String.toLowerCase, Decl(lib.es5.d.ts, --, --))
+>dep.default : Symbol(dep.default, Decl(index.d.ts, 0, 31))
+>dep : Symbol(dep, Decl(index.ts, 0, 6))
+>default : Symbol(dep.default, Decl(index.d.ts, 0, 31))
+>toLowerCase : Symbol(String.toLowerCase, Decl(lib.es5.d.ts, --, --))
+

tests/baselines/reference/esbuildInterop.types

@@ -0,0 +1,27 @@
+//// [tests/cases/conformance/module/esbuildInterop.ts] ////
+
+=== /node_modules/dep/index.d.ts ===
+declare const _default: string;
+>_default : string
+
+export default _default;
+>_default : string
+
+=== /index.ts ===
+import dep from "dep";
+>dep : typeof dep
+
+dep.toLowerCase(); // Error
+>dep.toLowerCase() : any
+>dep.toLowerCase : any
+>dep : typeof dep
+>toLowerCase : any
+
+dep.default.toLowerCase(); // Ok
+>dep.default.toLowerCase() : string
+>dep.default.toLowerCase : () => string
+>dep.default : string
+>dep : typeof dep
+>default : string
+>toLowerCase : () => string
+

tests/cases/conformance/module/esbuildInterop.ts

@@ -0,0 +1,25 @@
+// @module: esnext
+// @moduleResolution: bundler
+// @moduleFormatDetection: bundler
+// @moduleFormatInterop: bundlernode
+
+// @Filename: /node_modules/dep/package.json
+{
+    "name": "dep",
+    "version": "1.0.0",
+    "main": "index.js"
+}
+
+// @Filename: /node_modules/dep/index.d.ts
+declare const _default: string;
+export default _default;
+
+// @Filename: /package.json
+{
+  "type": "module"
+}
+
+// @Filename: /index.ts
+import dep from "dep";
+dep.toLowerCase(); // Error
+dep.default.toLowerCase(); // Ok