Wrong data passed to custom compare function in version 2.0.x

[fscali]

Bug report

Description / Observed Behavior

When I configure a custom compare function, the parameters that are passed to my function at runtime are booleans instead of the expected custom type

Expected Behavior

The expected behaviour is that my custom compare functions receives the expected type returned by the fetcher.

Repro Steps / Code Example

compare(a, b) {
        if (typeof a === 'undefined' || typeof b === 'undefined') {
          return false;
        } else if (typeof a === 'object' && typeof b === 'object') {
          const mappedA = a.results.map((r) => r.id);
          const mappedB = a.results.map((r) => r.id);
          return isEqual(mappedA, mappedB);
        } else {
          return a == b;
        }
      },

Additional Context

SWR version: 2.0.1
Framework: Next.js 12.3.1

[koba04]

@fscali Could you provide a CodeSandbox project to reproduce this?

[fscali]

@koba04 here it is:
https://codesandbox.io/p/sandbox/confident-pine-yxt8l1?file=%2Fpages%2Findex.tsx&selection=%5B%7B%22endColumn%22%3A19%2C%22endLineNumber%22%3A22%2C%22startColumn%22%3A18%2C%22startLineNumber%22%3A22%7D%5D

[koba04]

@fscali Thank you!

[promer94]

Compare fn is now not only used for comparing data but also other state field (error, isLoading, isValidating).

swr/core/use-swr.ts

Lines 110 to 125 in ad7bb15

	const isEqual = (prev: State<Data, any>, current: State<Data, any>) => {
	let equal = true
	for (const _ in stateDependencies) {
	const t = _ as keyof StateDependencies
	if (!compare(current[t], prev[t])) {
	if (t === 'data' && isUndefined(prev[t])) {
	if (!compare(current[t], returnedData)) {
	equal = false
	}
	} else {
	equal = false
	}
	}
	}
	return equal
	}

[Retrospection]

I'd like try solve this~

[fscali]

Hi, If I undersand well this bug should have been fixed by 2.0.3 but I still get the error in the sandbox I provided..

[promer94]

try {
          return _.isEqual(
            a!.map((val) => val.id),
            b!.map((val) => val.id)
          );
        } catch (_) {
          return false;
        }

Your compare fn is buggy, it does not have the correct behaviour as

undefined,udefined => true 
undefined, Data => false
Data,undefined => false
Data, Data => boolean

[fscali]

Thank you @promer94 ...I tried but same error (see same codesandbox). In version 1.3 it works..