Jetpack Compose: `derivedStateOf` that depends on a composable function parameter

So, here is an interesting situation I am in:

ComposableA (CA) calls ComposableB (CB) with a parameter email. In ComposableB, I want to have an emailError state that depends on email. Everytime the email changes (or some other event like FocusChange), I want to recompute the emailError state and force a recomposition of the Composable.

In CB, If I use derivedStateOf or mutableStateOf without remember, I get a linter error like this:

I can suppress that by adding @SuppressLint("UnrememberedMutableState") annotation but that doesn't force the state to be recomputed even when the focus or email changes. If I just use a variable, the compose engine wouldn't know that the composable UI depends on that value and would not recompose it even if there is a change in value.

Here is the code:

ComposableB

fun CB(
  emailValue: TextFieldValue = TextFieldValue("", TextRange.Zero),
  onEmailChanged: (emailValue: TextFieldValue) -> Unit = {},
  focusedTextField: FeatTextField = FeatTextField.Email,
  onFocusedTextField: (textField: FeatTextField) -> Unit = {}
) {
  // Error is derived from emailAddress
  val emailError by derivedStateOf {
    Timber.tag("StateTest").i("EmailValue: ${emailValue.text}")
    focusedTextField != SignInTextField.Email && !Validator.validateEmail(emailValue.text)
  }

  ... Rest of the code that renders the composable using focusedTextField, email and emailError values

ComposableA

.... Maintains the state and calls CB

fun CA(
  emailValue = emailValue,
  onEmailChanged = { vm.newUiState(copy(emailValue = it)) },
  focusedTextField = focusedTextField,
  onFocusedTextField = { focusedTextField = it }
)

I can make error as one of the parameters and hoist the state in CA but I am trying to avoid that because I want to keep CB as independent as possible.

Any pointers is appreciated.

Thank you!

1. I have tried several options: using mutableStateOf, derivedStateOf and rememberUpdateState.
2. I am expecting a directional help. Suggestions around which is the right Class/Function to use

The short answer is that you shouldn't be using derivedStateOf and probably don't even need remember.

derivedStateOf should only be used if the expression reads mutable state values. If no mutable state values are read, then the derivedStateOf is providing no value and is overhead you don't need. Also, derivedStateOf is only really useful if the value produced will change less frequently than the data it reads.

If the parameter values are not changing frequently then the normal skipping of a composable function might be all you need here. CB will only execute when one of its parameters change (assuming they are all stable).

If, however, one of the parameters is changing a lot and is not part of the expensive calculation, consider using remember for the expensive calculation. Be sure to pass in the values that are changing as parameters to remember so Compose knows when to re-evaluate the remembered expression. For example,

val emailError by remember(emailValue.text, focusedTextField) {
    Timber.tag("StateTest").i("EmailValue: ${emailValue.text}")
    focusedTextField != SignInTextField.Email && !Validator.validateEmail(emailValue.text)
  }

However, as noted above, since these two parameter are the only ones likely to be changing, the skipping Compose is already doing might be enough.

The article https://stefma.medium.com/jetpack-compose-remember-mutablestateof-derivedstateof-and-remembersaveable-explained-270dbaa61b8 goes into this in more detail.