When does LineWriter flush?

[8573]

It seems unclear to me from its documentation when exactly
std::io::LineWriter will flush.

The documentation of the struct says that it flushes "whenever a
newline […] is detected", but the existence and documentation of the
constructor with_capacity suggests that LineWriter has an internal
buffer of some set capacity.

What happens if a line written to the LineWriter exceeds the
capacity of the internal buffer? Can LineWriter also flush before
a newline is detected?

[retep998]

Yes, LineWriter will also flush whenever the internal buffer is full (1024 bytes last I checked).