Fix broken module resolution after edits in nodenext

Author: andrewbranch

src/harness/fourslashImpl.ts

@@ -637,7 +637,8 @@ namespace FourSlash {
             ts.forEachKey(this.inputFiles, fileName => {
                 if (!ts.isAnySupportedFileExtension(fileName)
                     || Harness.getConfigNameFromFileName(fileName)
-                    || !ts.getAllowJSCompilerOption(this.getProgram().getCompilerOptions()) && !ts.resolutionExtensionIsTSOrJson(ts.extensionFromPath(fileName))
+                    // Can't get a Program in Server tests
+                    || this.testType !== FourSlashTestType.Server && !ts.getAllowJSCompilerOption(this.getProgram().getCompilerOptions()) && !ts.resolutionExtensionIsTSOrJson(ts.extensionFromPath(fileName))
                     || ts.getBaseFileName(fileName) === "package.json") return;
                 const errors = this.getDiagnostics(fileName).filter(e => e.category !== ts.DiagnosticCategory.Suggestion);
                 if (errors.length) {

src/services/services.ts

@@ -1124,7 +1124,9 @@ namespace ts {
         }
 
         // Otherwise, just create a new source file.
-        return createLanguageServiceSourceFile(sourceFile.fileName, scriptSnapshot, sourceFile.languageVersion, version, /*setNodeParents*/ true, sourceFile.scriptKind);
+        const newSourceFile = createLanguageServiceSourceFile(sourceFile.fileName, scriptSnapshot, sourceFile.languageVersion, version, /*setNodeParents*/ true, sourceFile.scriptKind);
+        newSourceFile.impliedNodeFormat = sourceFile.impliedNodeFormat;
+        return newSourceFile;
     }
 
     const NoopCancellationToken: CancellationToken = {

tests/cases/fourslash/server/impliedNodeFormat.ts

@@ -0,0 +1,20 @@
+/// <reference path="../fourslash.ts" />
+
+// @Filename: /tsconfig.json
+//// { "compilerOptions": { "module": "nodenext" } }
+
+// @Filename: /package.json
+//// { "name": "foo", "type": "module", "exports": { ".": "./main.js" } }
+
+// @Filename: /main.ts
+//// export {};
+
+// @Filename: /index.ts
+//// import {} from "foo";
+
+goTo.file("/index.ts");
+verify.noErrors();
+
+edit.paste(`\n"${"a".repeat(256)}";`);
+
+verify.noErrors();