The stdout.write doesn't print to terminal until new line symbol is sent

[Xkonti]

Description

The stdout.write doesn't actually print out to the terminal window until the \n newline symbol has been "written". Because of that, it's impossible to print something to terminal output without moving the cursor to the new line.

Procs and macros that depend on writing to stdout have the same issue, for example styledWrite in std/terminal.

Nim Version

Nim Compiler Version 2.0.4 [Linux: amd64]
Compiled at 2024-03-28

Operating system

Windows 11 WSL2 Ubuntu 22.04.3 LTS

Current Output

stdout.write("1") # Terminal: ""
sleep(1000)
stdout.write("2") # Terminal: ""
sleep(1000)
stdout.write("3") # Terminal: ""
sleep(1000)
stdout.write("\n4") # Terminal: "123\n"
sleep(1000)
stdout.write("5") # Terminal: "123"
sleep(1000)
stdout.write("6") # Terminal: "123"
sleep(1000)
stdout.write('\n') # Terminal: "123\n456\n"

Expected Output

stdout.write("1") # Terminal: "1"
sleep(1000)
stdout.write("2") # Terminal: "2"
sleep(1000)
stdout.write("3") # Terminal: "3"
sleep(1000)
stdout.write("\n4") # Terminal: "123\n4"
sleep(1000)
stdout.write("5") # Terminal: "123\n45"
sleep(1000)
stdout.write("6") # Terminal: "123\n456"
sleep(1000)
stdout.write('\n') # Terminal: "123\n456\n"

Possible Solution

No response

Additional Information

The equivalent in Zig works properly in the same WSL2 environment:

const std = @import("std");

pub fn main() !void {
    const stdout = std.io.getStdOut().writer();
    try stdout.print("1", .{});
    std.time.sleep(1_000_000_000); // 1 second in nanoseconds
    try stdout.print("2", .{});
    std.time.sleep(1_000_000_000);
    try stdout.print("3", .{});
    std.time.sleep(1_000_000_000);
    try stdout.print("\n4", .{});
    std.time.sleep(1_000_000_000);
    try stdout.print("5", .{});
    std.time.sleep(1_000_000_000);
    try stdout.print("6", .{});
    std.time.sleep(1_000_000_000);
    try stdout.print("\n", .{});
}

The flushFile proc makes it work as intended:

stdout.write("1")
stdout.flushFile()
sleep(1000)
stdout.write("2")
stdout.flushFile()
sleep(1000)
stdout.write("3")
stdout.flushFile()
sleep(1000)
stdout.write("\n4")
stdout.flushFile()
sleep(1000)
stdout.write("5")
stdout.flushFile()
sleep(1000)
stdout.write("6")
stdout.flushFile()
sleep(1000)
stdout.write('\n')
stdout.flushFile()

[Araq]

Use flushFile.

[demotomohiro]

This explains why:
https://stackoverflow.com/questions/1716296/why-does-printf-not-flush-after-the-call-unless-a-newline-is-in-the-format-strin

[Xkonti]

This explains why: https://stackoverflow.com/questions/1716296/why-does-printf-not-flush-after-the-call-unless-a-newline-is-in-the-format-strin

Thank you @demotomohiro !