there is always at least one potential socket path

Error message

there is always at least one potential socket path

What it means

This is an internal invariant assertion in `existing_socket_path_ctx`: after computing the candidate socket paths, the code calls `.expect("there is always at least one potential socket path")` on the first candidate. The invariant is that `potential_socket_paths_ctx` always yields at least one path (the default). If it ever yields an empty iterator, this panics with that message, indicating a bug in the candidate-generation logic rather than a user-facing problem.

Solutions

Inspect `potential_socket_paths_ctx` and ensure the default socket path is always the first candidate
Verify the SocketCtx passed in resolves a non-empty default path (check XDG_RUNTIME_DIR / home dir resolution)
If you control the caller, fall back to `SocketPath::Default(...).into()` instead of asserting

Example fix

// before
let primary = candidates.next().expect("there is always at least one potential socket path");
// after
let Some(primary) = candidates.next() else {
    return Cow::Owned(ctx.default_socket_path().primary);
};

Defensive patterns

Strategy: type-guard

Validate before calling

// caller-side sanity check
assert!(SocketPath::Default(ctx.default_socket_path().primary).as_path().parent().is_some());

Type guard

fn has_candidates(paths: impl Iterator<Item = PathBuf>) -> bool { paths.count() > 0 }

Try / catch

// expect() panics cannot be caught; verify candidate generation in tests instead
#[test]
fn default_ctx_yields_at_least_one_socket_path() { assert!(paths(ctx).next().is_some()); }

Prevention

Keep the default socket path as the first candidate in potential_socket_paths_ctx
Add a unit test asserting the iterator is non-empty for all SocketCtx variants
Avoid refactoring candidate generation without re-running socket path tests

When it happens

Trigger: Calling `existing_socket_path` (or `existing_socket_path_ctx`) when `potential_socket_paths_ctx` returns an empty iterator — e.g. a refactor or misconfigured SocketCtx that drops the default path from the candidate list.

Common situations: Almost never hit in practice; arises from code changes to candidate generation, or from constructing a settings/SocketCtx state where XDG/home directory resolution produces no paths.

Understand the failure class

Background: "This is a bug, please report it": internal invariant violations, unreachable panics, and SNH errors explained — this error's family across 47 libraries.

Related errors

AI-assisted analysis of atuinsh/atuin@900007c480 (2026-09-19). Data as JSON: /api/errors/d1c02a58e7992440. Report an issue: GitHub.

Appendix: source

Thrown at crates/atuin-client/src/settings/daemon.rs:119

        if let Some(path) = &self.socket_path {
            return SocketPath::UserDefined(path);
        }

        // systemd units typically listen on `%t/atuin.sock`, which is `$XDG_RUNTIME_DIR/atuin.sock`
        // for user units, so we should default to that path when `systemd_socket` is true.
        if self.systemd_socket
            && let Some(path) = ctx.runtime_socket_path()
        {
            return SocketPath::Default(path);
        }

        SocketPath::Default(ctx.default_socket_path().primary)
    }

    fn existing_socket_path_ctx(&self, ctx: impl SocketCtx) -> Cow<'_, Path> {
        let mut candidates = self.potential_socket_paths_ctx(ctx);
        let primary =
            candidates.next().expect("there is always at least one potential socket path");

        if primary.exists() {
            return primary;
        }
        candidates.find(|path| path.exists()).unwrap_or(primary)
    }

    fn potential_socket_paths_ctx(
        &self,
        ctx: impl SocketCtx,
    ) -> impl Iterator<Item = Cow<'_, Path>> {
        let is_user_defined = self.socket_path.is_some();
        let defaults = (!is_user_defined)
            .then(|| self.default_socket_paths(ctx))
            .into_iter()
            .flatten()
            .map(Cow::Owned);
        self.socket_path.as_deref().map(Cow::Borrowed).into_iter().chain(defaults)

View on GitHub (pinned to 900007c480)