How to reduce horizontal space between navigation icon and title in a jetpack compose `TopAppBar`?

I'm making an app bar in jetpack compose but I'm having spacing issues between the navigation icon and the title.

This is my compose function:

@Composable
fun DetailsAppBar(coin: Coin, backAction: () -> Unit) {
    TopAppBar(
        navigationIcon = {
            IconButton(onClick = { backAction() }) {
                Icon(
                    imageVector = Icons.Filled.ArrowBack,
                    contentDescription = null
                )
            }
        },
        title = { Text(text = "${coin.rank}. ${coin.name} (${coin.symbol})") }
    )
}

This is my preview function:

@Composable
@Preview
fun DetailsAppBarPreview() {
    val bitcoin = Coin(
        id = "",
        isActive = true,
        name = "Bitcoin",
        rank = 1,
        symbol = "BTC"
    )
    DetailsAppBar(coin = bitcoin, backAction = {})
}

This is the visual preview of my compose function:

This is the space I want to reduce:

Entering the code of the TopAppBar compose function I can't see any parameters that allow me to do this.

You are right. With the variant of TopAppBar you are using, this is not possible. This is because the width of the NavigationIcon is set to the default (72.dp - 4.dp). You can check the implementation of TopAppBar and see that it uses the below:

private val AppBarHorizontalPadding = 4.dp

// Start inset for the title when there is a navigation icon provided
private val TitleIconModifier = Modifier.fillMaxHeight()
    .width(72.dp - AppBarHorizontalPadding)

What you could do is to use the other variant of the TopAppBar that gives you much more control in placing the title and icon. It could be something like:

@Composable
fun Toolbar(
    @StringRes title: Int,
    onNavigationUp: (() -> Unit)? = null,
) {
    TopAppBar(backgroundColor = MaterialTheme.colors.primary) {
        Row(
            modifier = Modifier
                .fillMaxWidth()
                .height(56.dp)
        ) {
            // Title
            Text(...)
            
            // Navigation Icon
            if (onNavigationUp != null) {
                Icon(
                    painter = painterResource(id = R.drawable.ic_back),
                    contentDescription = stringResource(
                        id = R.string.back
                    ),
                    tint = MaterialTheme.colors.onPrimary,
                    modifier = Modifier
                        .clip(MaterialTheme.shapes.small)
                        .clickable { onNavigationUp() }
                        .padding(16.dp)
                        ...... ,
                )
            }
        }
    }
}