IssueTracker

• Jetpack Compose version: 1.2.0-alpha07
• Kotlin version: 1.6.10

The conditions to trigger this bug seem to be very specific, so bear with me:

1. When there is a remembered movableContentOf that calls another composable lambda,
2. where the inner lambda comes from a MutableState,
3. and the movable content is moved from outside the lazy layout (e.g. LazyColumn or LazyVerticalGrid) to inside it,
4. and the MutableState holding the inner lambda is assigned a new lambda from inside the lazy layout immediately after the content is moved
5. and the inner lambda reads a snapshot state object,
6. various exceptions will be thrown.

However,

• When the inner lambda state is not updated, no exception is thrown.
• If there is no lazy layout, no exception is thrown.
• If the inner function doesn't read a state, no exception is thrown.

Simple repro

This is the smallest repro case I could come up with. To reproduce the bug, check the box and then uncheck it. The crash should happen as soon as you uncheck it.

Code:

@Composable
fun MinimalRepro() {
    var extractContent by remember { mutableStateOf(false) }
    val innerState by remember { mutableStateOf(false) }
    var content: (@Composable () -> Unit)? by remember { mutableStateOf(null) }
    val movableContent = remember {
        movableContentOf {
            content?.invoke()
        }
    }

    Column {
        Row(verticalAlignment = CenterVertically) {
            Text("Text in lazy? ")
            Checkbox(extractContent, onCheckedChange = {
                extractContent = it
            })
        }

        LazyColumn {
            item {
                if (!extractContent) {
                    content = {
                        Text("Movable text: innerState=$innerState")
                    }
                    movableContent()
                }
            }
        }

        if (extractContent) {
            movableContent()
        }
    }
}

Exception (full trace attached as simple-repro-stacktrace.txt):

java.lang.IllegalStateException: CompositionLocal LocalDensity not present

Complex repro

However, in other cases the exception is very different. If you check out this github repo at the movable-in-lazy-repro branch, run the galaxyapp, tap on a grid item and then navigate back, you should get a crash after the animation with this exception (stack trace also attached as galaxyapp-stacktrace.txt):

java.lang.IllegalStateException: Compose Runtime internal error. Unexpected or incorrect use of the Compose internal runtime API (Cannot seek outside the current group (288-626)). Please report to Google or use https://goo.gle/compose-feedback