rust/chg/src/uihandler.rs

phases: large rewrite on retract boundary

The new code is still pure Python, so we still have room to going significantly
faster. However its complexity of the complex part is `O(|[min_new_draft, tip]|)` instead of
`O(|[min_draft, tip]|` which should help tremendously one repository with old
draft (like mercurial-devel or mozilla-try).

This is especially useful as the most common "retract boundary" operation
happens when we commit/rewrite new drafts or when we push new draft to a
non-publishing server. In this case, the smallest new_revs is very close to the
tip and there is very few work to do.

A few smaller optimisation could be done for these cases and will be introduced in
later changesets.

We still have iterate over large sets of roots, but this is already a great
improvement for a very small amount of work. We gather information on the
affected changeset as we go as we can put it to use in the next changesets.
This extra data collection might slowdown the `register_new` case a bit, however
for register_new, it should not really matters. The set of new nodes is either
small, so the impact is negligible, or the set of new nodes is large, and the
amount of work to do to had them will dominate the overhead the collecting
information in `changed_revs`.

As this new code compute the changes on the fly, it unlock other interesting
improvement to be done in later changeset.

// Copyright 2018 Yuya Nishihara <[e-mail]>
//
// This software may be used and distributed according to the terms of the
// GNU General Public License version 2 or any later version.

use async_trait::async_trait;
use std::io;
use std::os::unix::io::AsRawFd;
use std::os::unix::process::ExitStatusExt;
use std::process::Stdio;
use tokio;
use tokio::process::{Child, ChildStdin, Command};

use crate::message::CommandSpec;
use crate::procutil;

/// Callback to process shell command requests received from server.
#[async_trait]
pub trait SystemHandler {
    type PagerStdin: AsRawFd;

    /// Handles pager command request.
    ///
    /// Returns the pipe to be attached to the server if the pager is spawned.
    async fn spawn_pager(
        &mut self,
        spec: &CommandSpec,
    ) -> io::Result<Self::PagerStdin>;

    /// Handles system command request.
    ///
    /// Returns command exit code (positive) or signal number (negative).
    async fn run_system(&mut self, spec: &CommandSpec) -> io::Result<i32>;
}

/// Default cHg implementation to process requests received from server.
pub struct ChgUiHandler {
    pager: Option<Child>,
}

impl ChgUiHandler {
    pub fn new() -> ChgUiHandler {
        ChgUiHandler { pager: None }
    }

    /// Waits until the pager process exits.
    pub async fn wait_pager(&mut self) -> io::Result<()> {
        if let Some(p) = self.pager.take() {
            p.await?;
        }
        Ok(())
    }
}

#[async_trait]
impl SystemHandler for ChgUiHandler {
    type PagerStdin = ChildStdin;

    async fn spawn_pager(
        &mut self,
        spec: &CommandSpec,
    ) -> io::Result<Self::PagerStdin> {
        let mut pager =
            new_shell_command(&spec).stdin(Stdio::piped()).spawn()?;
        let pin = pager.stdin.take().unwrap();
        procutil::set_blocking_fd(pin.as_raw_fd())?;
        // TODO: if pager exits, notify the server with SIGPIPE immediately.
        // otherwise the server won't get SIGPIPE if it does not write
        // anything. (issue5278)
        // kill(peerpid, SIGPIPE);
        self.pager = Some(pager);
        Ok(pin)
    }

    async fn run_system(&mut self, spec: &CommandSpec) -> io::Result<i32> {
        let status = new_shell_command(&spec).spawn()?.await?;
        let code = status
            .code()
            .or_else(|| status.signal().map(|n| -n))
            .expect("either exit code or signal should be set");
        Ok(code)
    }
}

fn new_shell_command(spec: &CommandSpec) -> Command {
    let mut builder = Command::new("/bin/sh");
    builder
        .arg("-c")
        .arg(&spec.command)
        .current_dir(&spec.current_dir)
        .env_clear()
        .envs(spec.envs.iter().cloned());
    builder
}