There is a precedent for this in #6671. That PR added support for undefined directives being passed to withDirectives. This has led to an inconsistency between the handling client-side and server-side, which can be seen in this example:

• Playground - main

It works fine without SSR, but throws an error once SSR is enabled.

This PR does fix that:

• Playground - this PR

Much like with #6671, real use cases would involve resolveDirective, which may return undefined during dev and shouldn't crash SSR.

I have two small concerns about the specifics of the proposed change here:

1. The type of dir. If we're going to handle undefined, shouldn't dir: Directive be updated to reflect that?
2. Ideally this should be tested.

Hey! Thanks for the feedback!

1. The type of dir. If we're going to handle undefined, shouldn't dir: Directive be updated to reflect that?

In this case, is there a reason to update it? This PR is made to handle edge cases, that given the lack of issues reported around it are not that frequent. I think it would be safe to keep dir as is, but I'd like to hear your opinion about this!
I can also keep the original checks and prepend an if dir check beforehand

2. Ideally this should be tested.

When I originally made this PR I wasn't that familiar with testing as the vue ecosystem was pretty new to me, but I believe I could try to make some tests for it

In this case, is there a reason to update it?

I think so, yes.

The similar change in #6671 also updated the types.

The function resolveDirective has return type Directive | undefined, which then gets passed directly into ssrGetDirectiveProps without any further checks. I believe the only reason we aren't getting type errors for this is that nothing is type checking the generated code for the ssrRender function.

If the type of dir had allowed for undefined then this problem would have been caught earlier.

When I originally made this PR I wasn't that familiar with testing as the vue ecosystem was pretty new to me, but I believe I could try to make some tests for it

The test for this should be pretty simple, most likely a small addition to ssrDirectives.spec.ts. There's a test-unit command in package.json to run the unit tests. You may want to merge in main first, to ensure you're using the latest test tooling.