Expose method to get list of routes associated with cache tag

[dsosborn]

Goals

1. Trigger subsequent actions for a route when it is revalidated, even if revalidated by tag.

Non-Goals

No response

Background

The cache tag revalidation system is brilliant, but sometimes there are actions that need to be taken when a route is updated that do not come out of the box with Next. For instance, if using Next behind a CDN, when a tag is revalidated, we also need a way to invalidate the affected routes on the CDN.

To my knowledge there is currently no way to do this—I have asked on Discord and help forum and got no responses.

Thus, we need a method to get all routes associated with a tag, in order to perform these actions.

Proposal

I propose exposing a method to get routes associated with a tag. There are a couple ways I could see doing this.

1a.) A new getRoutesByTag function that we could use in API endpoints:

// app/api/revalidate/route.ts 
revalidateTag(“myTag”);
const revalidatedRoutes = getRoutesByTag(“myTag”);
revalidatedRoutes.forEach( route => {
    invalidateCdnRoute(route);
}

1b.) Or, it would be nifty if the revalidateTag function returned the affected routes.

// app/api/revalidate/route.ts
const revalidatedRoutes = revalidateTag(“myTag”);
revalidatedRoutes.forEach( route => {
    invalidateCdnRoute(route);
}

2.) Another approach would be to expose an “onRevalidate” callback on page files. This would be give us control of what happens when the route(s) generated by this file are revalidated.

// app/[slug]/page.tsx 
export const onRevalidate = (route) => {
    invalidateCdnRoute(route);
}

Method 1 would be a more global solution, and could cover off on things like the unstable_cache function. Method 2 would give you more granular control over what happens for particular route segments.