Key arguments (_t) are not part of the State interface (v2)

[piotr-cz]

Bug report

Description / Observed Behavior

I'm using custom cache provider to persist data in IDB.

When implementing garbage collector I'm evaluating given path (as in example).
This works fine for cases when key argument just is simple path.

However for more complex scenarios when key arguments consists of path and query I'd like to have an option to evaluate them.

SWR v2.0 has changed the structure of cached data and added _k property which contains key arguments:

swr/core/use-swr.ts

Lines 97 to 100 in 69105b4

	State<Data, any> & {
	// The original key arguments.
	_k?: Key
	}

However the _k property is not part of the State interface:

swr/_internal/types.ts

Lines 288 to 293 in 69105b4

	export type State<Data = any, Error = any> = {
	data?: Data
	error?: Error
	isValidating?: boolean
	isLoading?: boolean
	}

Assuming the prefix means that accessing this property is not recommended, I cannot rely on it being available in future versions of the library.

Expected Behavior

The _k property is included in the State interface and it's unprefixed:

 export type State<Data = any, Error = any> = {
   data?: Data
   error?: Error
   isValidating?: boolean
   isLoading?: boolean
+  key?: Key
 }

Repro Steps / Code Example

SWR 2.0 branch for the IndexedDB Cache Provider

Additional Context

SWR version: 2.0.0-rc.0

[koba04]

How do you use key in the State?

[piotr-cz]

The simplest case is to not store data in cache for certain paths or query params.

This is easy when key is just a simple string (/api/user/123): than it's possible to check on the stableHash output.

However when it's an array (['/api/user', {userId: 123}]) you have to access the state and it's _k value

[piotr-cz]

@koba04
The key is passed in State to Cache provider, although it's not defined in it's interface.

The result of executing fetcher with key {path: 'items/news/1', query: {...}}, in cache looks like this:

For example imagine I'd want to store items in cache only when path !== items/news/2, or when query.filter.organisation !== null.

To inspect the key (path and query in example above) I can either try to decode stableHash, or access the State#_k property.

• First option doesn't feel right as I assume the stableHash is used by SWR as a checksum.
• Second option involves accessing property that's not part of State interface and is prefixed.