thirdshift 0.13.1

Turn a GitHub issue into a ready-for-review pull request, unattended
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//! Atomic, per-issue exclusion between Pickup runs on different machines.
//! Label edits and ordinary Issue branch pushes cannot arbitrate that race.
//! A separate origin ref is created only if absent, then held through dispatch.

use anyhow::{Context, Result};

use crate::git::Git;
use crate::issue::IssueUrl;
use crate::progress;

pub(super) struct Reservation {
    launch: Git,
    reference: String,
    token: String,
}

impl Reservation {
    /// Create a unique commit and atomically reserve `issue` with an empty
    /// lease. Existing reservations are never adopted, expired or overwritten.
    /// Errors with an uncertain remote outcome retain the ref for recovery.
    pub(super) fn take(launch: &Git, issue: &IssueUrl) -> Result<Option<Self>> {
        let reference = format!("refs/heads/thirdshift/pickup/{}", issue.number);
        let nonce = tempfile::Builder::new().rand_bytes(32).tempfile()?;
        // A reservation carries no source tree or parent: naming a Base branch
        // permits a Launch directory with unrelated, unpublished local work.
        let tree = launch.run(&["mktree"])?;
        let message = format!(
            "thirdshift Pickup reservation for {}\n\nToken: {}\nLaunch: {}\nProcess: {}\nStarted: {}",
            issue.url,
            nonce.path().display(),
            launch.dir().display(),
            std::process::id(),
            chrono::Utc::now(),
        );
        let token = launch.run(&[
            "-c",
            "commit.gpgSign=false",
            "commit-tree",
            &tree,
            "-m",
            &message,
        ])?;
        let pushed = launch.run(&[
            "push",
            &format!("--force-with-lease={reference}:"),
            "origin",
            &format!("{token}:{reference}"),
        ]);
        if let Err(error) = pushed {
            let remote = launch.run(&["ls-remote", "--refs", "origin", &reference])
                .with_context(|| format!(
                    "{error:#}; could not verify reservation {reference}; check origin by hand (our token {token})"
                ))?;
            if let Some((other, _)) = remote.split_once('\t')
                && other != token
            {
                return Ok(None);
            }
            return Err(error).with_context(|| format!(
                "could not reserve {reference}; check origin by hand before retrying (our token {token})"
            ));
        }
        Ok(Some(Self {
            launch: launch.completion(),
            reference,
            token,
        }))
    }
}

impl Drop for Reservation {
    fn drop(&mut self) {
        // Finish after interruption, and never delete another owner's token.
        if let Err(error) = self.launch.run(&[
            "push",
            &format!("--force-with-lease={}:{}", self.reference, self.token),
            "origin",
            &format!(":{}", self.reference),
        ]) {
            progress::warn(
                &error,
                format_args!(
                    "could not release Pickup reservation {}; check origin by hand (our token {})",
                    self.reference, self.token
                ),
            );
        }
    }
}