[K/JS] test: add @file:JsExport tests for each @JsExport test + auto-generate TypeScript export tests.

js/js.tests/build.gradle.kts

@@ -156,6 +156,41 @@ val unzipJsShell by task<Copy> {
 val testDataDir = project(":js:js.translator").projectDir.resolve("testData")
 val typescriptTestsDir = testDataDir.resolve("typescript-export")
 
+val generateJsExportOnFileTestFilesForTS by task<Copy> {
+    val exportFileDirPostfix = "-in-exported-file"
+
+    from(typescriptTestsDir) {
+        include("**/*.kt")
+        include("**/*.ts")
+        include("**/tsconfig.json")
+        exclude("selective-export/*")
+        exclude("implicit-export/*")
+        exclude("inheritance/*")
+        exclude("strict-implicit-export/*")
+        exclude("*$exportFileDirPostfix")
+
+        eachFile {
+            path = "${relativePath.parent}$exportFileDirPostfix/$name"
+
+            var isFirstLine = true
+            filter {
+                when {
+                    isFirstLine && name.endsWith(".kt") -> "/** This file is generated by {@link :js:js.test:generateJsExportOnFileTestFilesForTS} task. DO NOT MODIFY MANUALLY */\n\n$it"
+                        .also { isFirstLine = false }
+
+                    it.contains("// FILE") -> "$it\n\n@file:JsExport"
+                    else -> it.replace("@JsExport", "")
+                }
+            }
+
+        }
+
+    }
+
+    into(typescriptTestsDir)
+}
+
+
 val installTsDependencies = task<NpmTask>("installTsDependencies") {
     workingDir.set(testDataDir)
     args.set(listOf("install"))
@@ -314,6 +349,7 @@ testsJar {}
 
 val generateTests by generator("org.jetbrains.kotlin.generators.tests.GenerateJsTestsKt") {
     dependsOn(":compiler:generateTestData")
+    dependsOn(generateJsExportOnFileTestFilesForTS)
 }
 
 val prepareMochaTestData by tasks.registering(Copy::class) {