`convertFunctionToEs6Class` codefix is never triggered — TS80002 diagnostic not reported

[wizardnet972]

Acknowledgement

• I acknowledge that issues using this template may be closed without further explanation at the maintainer's discretion.

Comment

I'm trying to programmatically use the convertFunctionToEs6Class codefix via the TypeScript LanguageService, based on [its implementation in the TypeScript repo](https://github.com/microsoft/TypeScript/blob/main/src/services/codefixes/convertFunctionToEs6Class.ts).

I expected to get TS80002 as a suggestion diagnostic, but it's never reported, even for very standard constructor + prototype assignments.

---

🔢 Repro

import * as ts from 'typescript';

const fileName = 'virtual.ts';
const fileText = `
function Person(name) {
  this.name = name;
}
Person.prototype.greet = function() {
  console.log("Hello, " + this.name);
};
`;

const files = new Map([[fileName, fileText]]);

const languageService = ts.createLanguageService({
  getScriptFileNames: () => [fileName],
  getScriptVersion: () => '1',
  getScriptSnapshot: (f) => {
    const content = files.get(f);
    return content ? ts.ScriptSnapshot.fromString(content) : undefined;
  },
  getCurrentDirectory: () => process.cwd(),
  getCompilationSettings: () => ({ target: ts.ScriptTarget.ESNext, noImplicitAny: true }),
  getDefaultLibFileName: ts.getDefaultLibFilePath,
  fileExists: ts.sys.fileExists,
  readFile: ts.sys.readFile,
  readDirectory: ts.sys.readDirectory,
});

const diagnostics = languageService.getSuggestionDiagnostics(fileName);
console.log({ diagnostics });
/*
{
  diagnostics: [
    {
      file: [Object ...],
      start: 17,
      length: 4,
      messageText: "Parameter 'name' implicitly has an 'any' type, but a better type may be inferred from usage.",
      category: 2,
      code: 7044,
      reportsUnnecessary: undefined,
      reportsDeprecated: undefined,
    }
  ],
}
*/

---

⚠️ Problem

• I only get TS7044 (Parameter 'name' implicitly has an 'any' type) as a diagnostic.
• TS80002 (May be converted to an ES6 class) is not returned at all, so the codefix cannot be triggered.
• Yet this exact code is handled correctly by the convertFunctionToEs6Class logic in the compiler services source.

---

✅ Expected

TS80002 should be reported, and convertFunctionToEs6Class should be available via getCodeFixesAtPosition.

---

💻 Environment

• TypeScript: ~5.8.3
• Node.js: v22.6.0
• Reproduced via ts-node and plain TS project setup

---

📝 Notes

• Possibly related to file registration or classification of suggestion diagnostics?

[RyanCavanaugh]

This fix intentionally only triggers in JS files, but your sample is using .ts

        if (isJsFile) { <-----
            if (canBeConvertedToClass(node, checker)) {
                diags.push(createDiagnosticForNode(isVariableDeclaration(node.parent) ? node.parent.name : node, Diagnostics.This_constructor_function_may_be_converted_to_a_class_declaration));
            }
        }

[wizardnet972]

Thank you!