jj-vcs/jj · error

SCM-aware Watchman clocks not supported

Error message

SCM-aware Watchman clocks not supported

What it means

In lib/src/fsmonitor.rs, the From impl converting the internal fsmonitor clock into a Watchman clock hits InnerClock::ScmAware and calls unimplemented!(), producing a panic with message 'SCM-aware Watchman clocks not supported'. SCM-aware clocks are a newer Watchman clock flavor (they record source-control state alongside the timestamp) that jj's fsmonitor integration cannot translate into the plain watchman_clock::WatchmanClock representation, so conversion aborts.

Source

Thrown at lib/src/fsmonitor.rs:140

                }
            };
            Self(clock)
        }
    }

    impl From<Clock> for crate::protos::local_working_copy::WatchmanClock {
        fn from(clock: Clock) -> Self {
            use crate::protos::local_working_copy::watchman_clock;
            let Clock(clock) = clock;
            let watchman_clock = match clock {
                InnerClock::Spec(ClockSpec::StringClock(string_clock)) => {
                    watchman_clock::WatchmanClock::StringClock(string_clock)
                }
                InnerClock::Spec(ClockSpec::UnixTimestamp(unix_timestamp)) => {
                    watchman_clock::WatchmanClock::UnixTimestamp(unix_timestamp)
                }
                InnerClock::ScmAware(_) => {
                    unimplemented!("SCM-aware Watchman clocks not supported")
                }
            };
            Self {
                watchman_clock: Some(watchman_clock),
            }
        }
    }

    #[expect(missing_docs)]
    #[derive(Debug, Error)]
    pub enum Error {
        #[error("Could not connect to Watchman")]
        WatchmanConnectError(#[source] watchman_client::Error),

        #[error("Could not canonicalize working copy root path")]
        CanonicalizeRootError(#[source] std::io::Error),

        #[error("Watchman failed to resolve the working copy root path")]

View on GitHub (pinned to 6631dbd4a8)

Solutions

1. Reset/clear the persisted fsmonitor clock state so a fresh plain clock is created instead of converting the SCM-aware one.
2. Use a jj version that supports SCM-aware Watchman clocks (upgrade to match whatever wrote the clock).
3. Avoid constructing InnerClock::ScmAware values in your code; map them to UnixTimestamp before conversion, discarding SCM state.
4. Disable the fsmonitor (Watchman) integration if SCM-aware clocks keep appearing in your environment.

Example fix

// before
let clock = FsmonitorClock::from(inner); // inner is ScmAware(..) -> panic

// after
let inner = match inner {
    InnerClock::ScmAware(_) => InnerClock::Spec(ClockSpec::UnixTimestamp(now)),
    other => other,
};
let clock = FsmonitorClock::from(inner);

// Normalize the clock before conversion:
let inner = if matches!(inner, InnerClock::ScmAware(_)) {
    InnerClock::Spec(ClockSpec::UnixTimestamp(unix_now()))
} else { inner };

fn is_supported_clock(inner: &InnerClock) -> bool {
    !matches!(inner, InnerClock::ScmAware(_))
}

// unimplemented! panics; guard at boundary and fall back to a full scan:
let clock = if is_supported_clock(&inner) {
    FsmonitorClock::from(inner)
} else {
    FsmonitorClock::fresh() // triggers full re-scan instead of incremental
};

When it happens

Trigger: Constructing the fsmonitor clock type (or its From conversion) from an InnerClock::ScmAware(ClockSpec::ScmAware(..)) value — typically when parsing clock state persisted by a newer jj version or supplied via fsmonitor config/API that includes SCM-aware clock data, then converting it for the Watchman query.

Common situations: Downgrading jj after a newer version persisted an SCM-aware clock in repo state; sharing a working copy between jj versions where one writes ScmAware clocks; hand-crafting clock specs for testing with the scm-aware variant; Watchman environments where SCM-aware queries were enabled.

Related errors

• Conflicting factory definitions for '{}' factory
• cannot store git submodules
• Conflict registering revset function '{name}'
• ContentHash cannot be derived for unions.

AI-assisted analysis of jj-vcs/jj@6631dbd4a8 (2026-08-28). Data as JSON: /api/errors/6e5aea0e88fe4f00. Report an issue: GitHub.