view rust/rhg/src/ui.rs @ 45049:513b3ef277a3

rhg: add RootCommand using hg-core FindRoot operation to prepare `hg root`

The println macro is not used to avoid string usage.
Dealing only with bytes allows us to be compatible with any encoding
and not just UTF8.

Later on, format macro will be made to have more readable code.

Differential Revision: https://phab.mercurial-scm.org/D8612

use std::io;
use std::io::Write;

pub struct Ui {}

/// The kind of user interface error
pub enum UiError {
    /// The standard output stream cannot be written to
    StdoutError(io::Error),
    /// The standard error stream cannot be written to
    StderrError(io::Error),
}

/// The commandline user interface
impl Ui {
    pub fn new() -> Self {
        Ui {}
    }

    /// Write bytes to stdout
    pub fn write_stdout(&self, bytes: &[u8]) -> Result<(), UiError> {
        let mut stdout = io::stdout();

        self.write_stream(&mut stdout, bytes)
            .or_else(|e| self.into_stdout_error(e))?;

        stdout.flush().or_else(|e| self.into_stdout_error(e))
    }

    fn into_stdout_error(&self, error: io::Error) -> Result<(), UiError> {
        self.write_stderr(
            &[b"abort: ", error.to_string().as_bytes(), b"\n"].concat(),
        )?;
        Err(UiError::StdoutError(error))
    }

    /// Write bytes to stderr
    pub fn write_stderr(&self, bytes: &[u8]) -> Result<(), UiError> {
        let mut stderr = io::stderr();

        self.write_stream(&mut stderr, bytes)
            .or_else(|e| Err(UiError::StderrError(e)))?;

        stderr.flush().or_else(|e| Err(UiError::StderrError(e)))
    }

    fn write_stream(
        &self,
        stream: &mut impl Write,
        bytes: &[u8],
    ) -> Result<(), io::Error> {
        stream.write_all(bytes)
    }
}