[labs/testing] WTR plugin for SSR does not work in Windows

[augustjk]

Which package(s) are affected?

Other/unknown (please mention in description)

Description

For @lit-labs/testing, when utilizing ssrFixture, the server command registered by the WTR plugin resolves the provided relative module paths before sending to the worker thread to be imported before rendering.

lit/packages/labs/testing/src/lib/lit-ssr-plugin.ts

Lines 32 to 34 in 1ac5805

	const resolvedModules = modules.map((module) =>
	pathlib.join(process.cwd(), module)
	);

In windows, this creates module paths that begin with "drive:" like c:, causing an error like

Only file and data URLs are supported by the default ESM loader. On Windows, absolute paths must be valid file:// URLs. Received protocol 'c:' 

We should fix it so it's always a proper file URL for all platforms.

Reproduction

TODO

Workaround

Manually patch the plugin code.

Is this a regression?

No or unsure. This never worked, or I haven't tried before.

Affected versions

latest

Browser/OS/Node environment

OS: Windows