Fix cache types

[chibicode]

With the 2.0.0 update (#1863), each value in cache now holds the current states.

Type changes

• Reuse the existing State type whenever necessary
• Remove null from a list of possible values of the cache
• Update the type of createCacheHelper to be compatible with infinite/index.ts
• Update the default type argument of useSWRConfig.
• Update the type of MutatorOptions['populateCache'] to allow undefined for currentData on function argument.

Non-type changes

• use-swr.ts: isLoading was not being copied over in onStateUpdate. This became obvious as I saw that the State type contained isLoading.

[chibicode]

Reuses the State type, which will add isLoading which was missing in the original type definition.

swr/src/types.ts

Lines 167 to 172 in 09d80c5

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

[chibicode]

Removed null as it seemed like it's no longer being used.

[chibicode]

From release notes:

So you will have to do the following change to your code, get:

- cache.get(key)
+ cache.get(key)?.data

And set:

- cache.set(key, data)
+ cache.set(key, { ...cache.get(key), data })

[chibicode]

isLoading was not being copied over originally, but I believe it should be.

[chibicode]

This was necessary to make ExtendedInfo work:

swr/infinite/index.ts

Lines 67 to 77 in 09d80c5

	const [get, set] = createCacheHelper<
	Data,
	{
	// We use cache to pass extra info (context) to fetcher so it can be globally
	// shared. The key of the context data is based on the first page key.
	$ctx: [boolean] | [boolean, Data[] | undefined]
	// Page size is also cached to share the page data between hooks with the
	// same key.
	$len: number
	}
	>(cache, infiniteKey)

I couldn't figure out a way to do it without type assertion.

---

I did notice that this line below had a type error (Type 'Data' is not assignable to type 'Data[]'), but I couldn't figure out how to resolve this. This line already had a different type error even before this PR.

swr/infinite/index.ts

Line 147 in 09d80c5

!config.compare(originalData[i], pageData))

[codesandbox-ci]

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Latest deployment of this branch, based on commit 1dca126:

Sandbox	Source
SWR-Basic	Configuration
SWR-States	Configuration
SWR-Infinite	Configuration
SWR-SSR	Configuration

[chibicode]

This was a suggested fix for this issue in src/utils/mutate.ts: #1961 (comment)