ScrollBarAdapter for LazyListState ignores the contentPadding

[m-sasha]

The ScrollBarAdapter for LazyListState doesn't take into account the LazyLists contentPadding.

Reproducer:

import androidx.compose.foundation.VerticalScrollbar
import androidx.compose.foundation.background
import androidx.compose.foundation.layout.Box
import androidx.compose.foundation.layout.PaddingValues
import androidx.compose.foundation.layout.fillMaxHeight
import androidx.compose.foundation.layout.fillMaxSize
import androidx.compose.foundation.layout.fillMaxWidth
import androidx.compose.foundation.layout.height
import androidx.compose.foundation.lazy.LazyColumn
import androidx.compose.foundation.lazy.rememberLazyListState
import androidx.compose.foundation.rememberScrollbarAdapter
import androidx.compose.material.Text
import androidx.compose.runtime.Composable
import androidx.compose.ui.graphics.Color
import androidx.compose.ui.unit.dp
import androidx.compose.ui.window.Window
import androidx.compose.ui.window.application
import androidx.compose.ui.window.rememberWindowState


fun main() = application {
    Window(
        onCloseRequest = ::exitApplication,
        state = rememberWindowState(width = 300.dp, height = 400.dp)
    ) {
        LazyScrollable()
    }
}


@Composable
fun LazyScrollable() {
    Box(
        modifier = Modifier
            .fillMaxSize()
            .background(color = Color.White)
    ) {

        val state = rememberLazyListState()

        LazyColumn(
            modifier = Modifier.fillMaxSize(),
            state = state,
            contentPadding = PaddingValues(vertical = 100.dp)
        ) {
            items(5) { x ->
                TextBox("Item #$x", x)
            }
        }
        VerticalScrollbar(
            modifier = Modifier.align(Alignment.CenterEnd).fillMaxHeight(),
            adapter = rememberScrollbarAdapter(
                scrollState = state,
            )
        )
    }
}


@Composable
fun TextBox(text: String = "Item", index: Int) {
    Box(
        modifier = Modifier
            .height(130.dp)
            .fillMaxWidth()
            .background(
                color = Color(
                    red = (index * 50).mod(255),
                    green = (index * 100).mod(255),
                    blue = (index * 150).mod(255),
                    alpha = 128
                )
            ),
        contentAlignment = Alignment.CenterStart
    ) {
        Text(text = text)
    }
}

Screen.Recording.2023-01-07.at.12.05.56.mp4

As you can see, dragging the scrollbar to the bottom doesn't cause the content to scroll to the bottom.

[m-sasha]

This is part of the problems described by #1211

[okushnikov]

Please check the following ticket on YouTrack for follow-ups to this issue. GitHub issues will be closed in the coming weeks.