Android Jetpack Compose Scroll to Top

Question

In Jetpack Compose, where is ScrollToTopButton coming from? It is mentioned in Google's documentation. Annoyingly, they neglect to mention the package. I have imports of foundation version 1.2.0-alpha08 ; also tried with 1.2.0-beta02 as well as ui and material (1.1.1). Not found. (yes did do an internet search on the term, came back empty handed).

implementation "androidx.compose.foundation:foundation:${version}"
implementation "androidx.compose.foundation:foundation-layout:${version}"
implementation "androidx.compose.ui:ui:$compose_version"
implementation "androidx.compose.material:material:$compose_version"

    @Composable
    fun MessageList(messages: List<Message>) {
        val listState = rememberLazyListState()
        // Remember a CoroutineScope to be able to launch
        val coroutineScope = rememberCoroutineScope()
    
        LazyColumn(state = listState) {
            // ...
        }
    
        ScrollToTopButton(
            onClick = {
                coroutineScope.launch {
                    // Animate scroll to the first item
                    listState.animateScrollToItem(index = 0)
                }
            }
        )
    }

Google documentation

Edit: If this is NOT a function they offer, but rather a suggestion to create your own, shame on whoever wrote the documentation, it literally suggests being a function offered by Compose.

Edit 2: Turns out it is a custom function (see the answer). What moved the author of the documentation to write it like this? Why not just put Button? Sigh.

Answer 1

It's not clear from the documentation but you actually have to make your own. For example you can use this:

    @Composable
fun ScrollToTopButton(onClick: () -> Unit) {
    Box(
        Modifier
            .fillMaxSize()
            .padding(bottom = 50.dp), Alignment.BottomCenter
    ) {
        Button(
            onClick = { onClick() }, modifier = Modifier
                .shadow(10.dp, shape = CircleShape)
                .clip(shape = CircleShape)
                .size(65.dp),
            colors = ButtonDefaults.buttonColors(
                backgroundColor = Color.White,
                contentColor = Color.Green
            )
        ) {
            Icon(Icons.Filled.KeyboardArrowUp, "arrow up")
        }
    }
}

And then:

  val showButton by remember{
    derivedStateOf {
    listState.firstVisibleItemIndex > 0
   }
}
            AnimatedVisibility(
                visible = showButton,
                enter = fadeIn(),
                exit = fadeOut(),
            ) {
                ScrollToTopButton(onClick = {
                    scope.launch {
                        listState.animateScrollToItem(0)
                    }
                })
            }