Add section in docs for child read functions with @client fields

[jerelmiller]

Closes #12930

[changeset-bot]

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[pkg-pr-new]

npm i https://pkg.pr.new/apollographql/apollo-client/@apollo/client@12931

commit: bad9fbd

[github-actions]

size-limit report 📦

Path	Size
import { ApolloClient, InMemoryCache, HttpLink } from "@apollo/client" (CJS)	42.84 KB (0%)
import { ApolloClient, InMemoryCache, HttpLink } from "@apollo/client" (production) (CJS)	37.8 KB (0%)
import { ApolloClient, InMemoryCache, HttpLink } from "@apollo/client"	32.65 KB (0%)
import { ApolloClient, InMemoryCache, HttpLink } from "@apollo/client" (production)	26.81 KB (0%)
import { ApolloProvider } from "@apollo/client/react"	5.91 KB (0%)
import { ApolloProvider } from "@apollo/client/react" (production)	994 B (0%)
import { useQuery } from "@apollo/client/react"	7.35 KB (0%)
import { useQuery } from "@apollo/client/react" (production)	2.38 KB (0%)
import { useLazyQuery } from "@apollo/client/react"	7.11 KB (0%)
import { useLazyQuery } from "@apollo/client/react" (production)	2.16 KB (0%)
import { useMutation } from "@apollo/client/react"	6.47 KB (0%)
import { useMutation } from "@apollo/client/react" (production)	1.52 KB (0%)
import { useSubscription } from "@apollo/client/react"	6.79 KB (0%)
import { useSubscription } from "@apollo/client/react" (production)	1.82 KB (0%)
import { useSuspenseQuery } from "@apollo/client/react"	8.55 KB (0%)
import { useSuspenseQuery } from "@apollo/client/react" (production)	3.63 KB (0%)
import { useBackgroundQuery } from "@apollo/client/react"	8.34 KB (0%)
import { useBackgroundQuery } from "@apollo/client/react" (production)	3.4 KB (0%)
import { useLoadableQuery } from "@apollo/client/react"	8.29 KB (0%)
import { useLoadableQuery } from "@apollo/client/react" (production)	3.39 KB (0%)
import { useReadQuery } from "@apollo/client/react"	6.6 KB (0%)
import { useReadQuery } from "@apollo/client/react" (production)	1.65 KB (0%)
import { useFragment } from "@apollo/client/react"	6.66 KB (0%)
import { useFragment } from "@apollo/client/react" (production)	1.71 KB (0%)

[apollo-librarian]

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* (developer-tools)/react/(latest)/local-state/managing-state-with-field-policies.mdx

Build ID: 52ce29ebfe3b38191b5a0288
Build Logs: View logs

URL: https://www.apollographql.com/docs/deploy-preview/52ce29ebfe3b38191b5a0288

[phryneas]

Definitely something we need documented, let's get this in

[phryneas]

Is this something we can help with by providing a dev-only warning?

It's a bit tricky, but this should catch most cases:

const no_args_or_spread_function = /^(function\s+)?([\p{ID_Start}$_][\p{ID_Continue}$]*\s*)?\(\s*([)]|\.\.\.[\p{ID_Start}$_][\p{ID_Continue}$]*)/u
if (readPolicyFn.length === 0 && !readPolicyFn.toString().match(no_args_or_spread_function)) {
  // warn about using default arguments
}

• length is defined as the number or arguments before the first optional argument, so length == 0 means either spread arguments, no arguments or default arguments
• JS identifiers are specified here https://tc39.es/ecma262/multipage/ecmascript-language-lexical-grammar.html#prod-IdentifierName and if we ignore identifiers with a UnicodeEscapeSequence,[\p{ID_Start}$_][\p{ID_Continue}$]* should match all of them

I think this should eliminate all weird one-offs, but an additional check for a general function shape of the string might make it even more solid so it doesn't warn on engine builtins (but why would one pass those in there?)

[jerelmiller]

Going a different direction with #12934