feat(`diagnostic`): add missing error codes

[tommy-mitchell]

Fixes #170. Fixes #143.

Adds missing diagnostic codes:

• ts2375, ts2379, and ts2412, which occur when exactOptionalPropertyTypes is set to true in tsconfig.json.
• ts2542, which occurs when attempting to modify a readonly key in an object.

---

Related, I think it's worth improving the error reporting when expectError fails. Currently, it reports

Expected an error, but found none.

even if another error is reported for the same invocation (i.e., tsd doesn't support that diagnostic code). We could change it to:

Expected an error, but found none. tsd may not currently support this error code, consider creating an issue on GitHub.

I used the following snippet in compiler.ts to confirm which DiagnosticCode to add[^1]:

if (ignoreDiagnosticResult === 'preserve') {
  console.log(diagnostic.code);
}

I think it would be worthwhile to either report the codes of all diagnostics (potentionally in a --verbose mode?), or at the very least in the expectError message:

let message = 'Expected an error, but found none.';

if (diagnostic.code) {
  message += ` tsd may not currently support \`ts${diagnostic.code}\`, consider creating an issue on GitHub.`;
}

[^1]: Full list here.

[tommy-mitchell]

Perhaps users could set additional diagnostic codes in their tsd config, to let their tests still pass if that code isn't in our list.

[tommy-mitchell]

Added ts2542 to fix #143.

[sindresorhus]

or at the very least in the expectError message:

👍

[sindresorhus]

or at the very least in the expectError message:

Do you plan to work on this? No pressure, but I need to know whether or not to release a new version after merging this.

[tommy-mitchell]

I did start attempting to add the updated error message, but it‘s a little more involved because the diagnostic object at that location doesn’t have access to the error code.

Should we just update the error message and add the code there, or report the code on all diagnostics?

[sindresorhus]

It would be too noisy to have the code on all diagnostics.