next/link: legacyBehavior deprecation

[blvdmitry]

With the latest Next.js there is now a runtime error suggesting that legacyBehavior flag is going to be removed and suggesting to use a codemod to migrate. The codemod however just drops this property without any alternative solution.

There were multiple issues / discussions with people asking questions about the alternatives in the past. All solutions I've seen so far recommend either implementing polymorphic rendering implement in the component (as={Link} or asChild) or using next/link inside the component itself.

However, there are no answers about what should be an alternative when these components come from a 3rd party design system that can't have Next.js as a dependency and/or don't support as/asChild. Just ignoring this problem and using the codemod results in the design system button (and other navigation component) to be wrapped with an and either end up having 2 nested tags or end up losing correct focus styles.

I hope we can have this resolved before it gets completely dropped in the next major and would be nice if we can have a way to disable the runtime error meanwhile.

[RossMcMillan92]

Agreed, the legacyBehavior prop is essential for allowing custom components from (non-nextjs) React component libraries.

[Jokinen]

Out of curiosity, what are the component libraries that do not work without legacyBeahvior? In my experience there are many popular frameworks that have never had the API. Shouldn't most 3rd party component libraries have a solution for this problem in one form or another? Otherwise they couldn't be used with a lieu or other often used frameworks?

Not having legacyBehavior means that component libraries have to expect frameworks to provide custom a implementations. There are many frameworks that have never had legacyBehavior and have required this support for a long time already. What are the cases where this support is not provided?

[blvdmitry]

Partially yes, I'm working on https://github.com/reshaped-ui/reshaped and I have to implement render props / asChild just to make sure next/link works after v16. As a library author, that's at least under my control but other library users might not be able to change the behavior of the libraries they're using. All the previously closed threads where people were providing examples of where it won't work for them were just suggesting that those UI libraries should either have an implementation based on what Next.js provides (a bit weird considering that component libraries are usually built for any framework) or just use next/link inside the components (not possible projects also for projects used in multiple frameworks)

[icyJoseph]

A little update:

#76329 (comment)