call to print!() only executes at the end of the program

[hboutou]

cat /etc/os-release:

NAME="Alpine Linux"
ID=alpine
VERSION_ID=3.12.1
PRETTY_NAME="Alpine Linux v3.12"
HOME_URL="https://alpinelinux.org/"
BUG_REPORT_URL="https://bugs.alpinelinux.org/"

rustc --version --verbose:

rustc 1.47.0 (18bf6b4f0 2020-10-07)
binary: rustc
commit-hash: 18bf6b4f01a6feaf7259ba7cdae58031af1b7b39
commit-date: 2020-10-07
host: x86_64-unknown-linux-musl
release: 1.47.0
LLVM version: 11.0

I tried this code:

use std::io;

fn main() {
    let mut user_input = String::new();
    print!("Enter input: ");
    io::stdin()
        .read_line(&mut user_input)
        .expect("failed to read line");
    println!("Your input: {}", user_input);
}

I expected the program to first print a string to stdout, read a string from stdin, then print again to stdout.

Instead, this happened:
The program reads from stdin first, then prints the two messages.

I noticed this only happens when using print!.
With println! the order is respected.

[ghost]

I think this is #23818?

[jonas-schievink]

Yeah, closing as a duplicate of that