crypto/hmac: panics

[Mr-Leshiy]

Hello I have found a weird behaviour of the sha256 Reset() method with the hmac. So I have the following question.
Why does this example produce panics ?

sha256Hash := sha256.New()

salt := []byte{1, 2, 3}

hmac.New(func() hash.Hash {
	sha256Hash.Reset()
	return sha256Hash
}, salt)

panic: crypto/hmac: hash generation function does not produce unique values

But this example does not produce panics

salt := []byte{1, 2, 3}

hmac.New(func() hash.Hash {
	return sha256.New()
}, salt)

What is the difference between these examples.

[ericlagergren]

This on purpose. See: #41089

cc: @FiloSottile

[FiloSottile]

An HMAC instance needs two independent hash instances simultaneously. Your first example used to produce incorrect results if you tried to call hmac.Reset.