Fix two issues in the typescript/vfs module. (#3038)

Co-authored-by: Jake Bailey <5341706+jakebailey@users.noreply.github.com>

Author: xiaoxiyao

.changeset/breezy-gifts-fly.md

@@ -0,0 +1,5 @@
+---
+"@typescript/vfs": patch
+---
+
+Fix the exception when file content is empty

.changeset/gold-pears-flow.md

@@ -0,0 +1,5 @@
+---
+"@typescript/vfs": patch
+---
+
+Fix `moduleDetection` compiler option is not working

packages/typescript-vfs/src/index.ts

@@ -458,7 +458,7 @@ export function createSystem(files: Map<string, string>): System {
     getDirectories: () => [],
     getExecutingFilePath: () => notImplemented("getExecutingFilePath"),
     readDirectory: audit("readDirectory", directory => (directory === "/" ? Array.from(files.keys()) : [])),
-    readFile: audit("readFile", fileName => files.get(fileName) || files.get(libize(fileName))),
+    readFile: audit("readFile", fileName => files.get(fileName) ?? files.get(libize(fileName))),
     resolvePath: path => path,
     newLine: "\n",
     useCaseSensitiveFileNames: true,
@@ -574,14 +574,14 @@ export function createVirtualCompilerHost(sys: System, compilerOptions: Compiler
       // getDefaultLibLocation: () => '/',
       getDirectories: () => [],
       getNewLine: () => sys.newLine,
-      getSourceFile: fileName => {
+      getSourceFile: (fileName, languageVersionOrOptions) => {
         return (
           sourceFiles.get(fileName) ||
           save(
             ts.createSourceFile(
               fileName,
               sys.readFile(fileName)!,
-              compilerOptions.target || defaultCompilerOptions(ts).target!,
+              languageVersionOrOptions ?? compilerOptions.target ?? defaultCompilerOptions(ts).target!,
               false
             )
           )

packages/typescript-vfs/test/index.test.ts

@@ -214,3 +214,34 @@ it("grabs lib dts files from node_modules", async () => {
   const fsMap = createDefaultMapFromNodeModules({})
   expect(fsMap.get("/lib.es2015.collection.d.ts")).toBeDefined()
 })
+
+it("empty file content", async () => {
+  const options = { target: ts.ScriptTarget.ES2020 }
+  const fsMap = createDefaultMapFromNodeModules(options, ts)
+  fsMap.set("index.ts", "")
+  const system = createSystem(fsMap)
+  const host = createVirtualCompilerHost(system, options, ts)
+  ts.createProgram({
+    rootNames: ["index.ts"],
+    options,
+    host: host.compilerHost,
+  })
+})
+
+it("moduleDetection options", async () => {
+  const options: ts.CompilerOptions = {
+    module: ts.ModuleKind.AMD,
+    moduleDetection: ts.ModuleDetectionKind.Force,
+  }
+  const fsMap = createDefaultMapFromNodeModules(options, ts)
+  fsMap.set("index.ts", "let foo = 'foo'")
+  const system = createSystem(fsMap)
+  const host = createVirtualCompilerHost(system, options, ts)
+  const program = ts.createProgram({
+    rootNames: ["index.ts"],
+    options,
+    host: host.compilerHost,
+  })
+  program.emit()
+  expect(fsMap.get("index.js")).toEqual(`define(["require", "exports"], function (require, exports) {\n    "use strict";\n    Object.defineProperty(exports, "__esModule", { value: true });\n    var foo = 'foo';\n});\n`)
+})