fix: validate preserveSymlinks tsconfig option is not set

[jbedard]

I'm finding this a bit awkward to test because typescript is only fetched from BUILD.typescript which isn't really accessible from tests. But every test out there ensures it at least works with valid config, and I've tested the case this is catching manually. @thesayyn I don't understand how you tested workers with such minimal mocking of typescript?

[thesayyn]

rules_ts/ts/test/ts_project_worker.test.js

Lines 6 to 21 in f6c0dc9

	function mock(name, exports) {
	const p = path.resolve(name);
	require.cache[p] = {
	id: name,
	file: p,
	loaded: true,
	exports: exports
	};
	const realres = mod._resolveFilename;
	mod._resolveFilename = function (request, parent) {
	if (request == name) {
	return p;
	}
	return realres(request, parent);
	};
	}

is the magic function that does it all. I only needed to mock the typescript and worker package partially to test fsTree, not the worker itself. you might wanna bring in a test runner with mocking ability which i didn't want to do in the first place.

[alexeagle]

Yeah I had the same issue in https://github.com/bazelbuild/rules_nodejs/tree/stable/packages/typescript/test/ts_project/validation - it's a challenge to write a negative test case for validation failures.

The logic is so simple to read and understand that I think it's fine to skip automated tests for this one.

[jbedard]

@thesayyn that's what I was looking at, but the number of functions needing to be mocked was just way too high