rust-lang/rust-analyzer · error

Project discovery failed: {error}

Error message

Project discovery failed: {error}

What it means

When the project discovery subsystem (used for non-Cargo workspaces, e.g. the DiscoverWorkspaceConfig command) reports an error, handle_discover_msg formats 'Project discovery failed: {error}', shows it via show_and_log_error (with the optional source detail), and ends the corresponding progress. It means rust-analyzer could not construct a workspace model for the project.

Source

Thrown at crates/rust-analyzer/src/main_loop.rs:1154

        match message {
            DiscoverProjectMessage::Finished { project, buildfile } => {
                self.discover_jobs_active = self.discover_jobs_active.saturating_sub(1);
                if self.discover_jobs_active == 0 {
                    self.report_progress(&title, Progress::End, None, None, None);
                }

                let mut config = Config::clone(&*self.config);
                config.add_discovered_project_from_command(project, buildfile);
                self.update_configuration(config);
            }
            DiscoverProjectMessage::Progress { message } => {
                if self.discover_jobs_active > 0 {
                    self.report_progress(&title, Progress::Report, Some(message), None, None)
                }
            }
            DiscoverProjectMessage::Error { error, source } => {
                let message = format!("Project discovery failed: {error}");
                self.show_and_log_error(message.clone(), source);

                self.discover_jobs_active = self.discover_jobs_active.saturating_sub(1);
                if self.discover_jobs_active == 0 {
                    self.report_progress(&title, Progress::End, Some(message), None, None)
                }
            }
        }
    }

    /// Drop any discover command processes that have exited, due to
    /// finishing or erroring.
    fn cleanup_discover_handles(&mut self) {
        let mut active_handles = vec![];

        for mut discover_handle in self.discover_handles.drain(..) {
            if !discover_handle.handle.has_exited() {
                active_handles.push(discover_handle);
            }

View on GitHub (pinned to e8f7e90aa3)

Solutions

1. Run your discovery command manually and confirm it emits valid `DiscoverProjectData` JSON on stdout.
2. Fix the script/binary path in the DiscoverProjectConfig (check stdout/stderr routing and exit code).
3. Inspect the `source` detail appended to the notification and the rust-analyzer log for the underlying error.
4. Fall back to linkedProjects with a hand-written rust-project.json if custom discovery is unreliable.
5. Update the discovery script after toolchain/layout changes (new subcrates, moved Cargo.toml files).

Example fix

// before (settings.json)
"rust-analyzer.discoverProjectConfig": { "command": ["./discover.py"] } // script exits 1
// after
"rust-analyzer.discoverProjectConfig": { "command": ["python3", "/abs/path/discover.py"] },
// and ensure the script prints rust-project JSON and exits 0

# Validate the discovery command before configuring it:
./your-discover-command | jq -e '.crates' > /dev/null && echo OK || echo BAD_DISCOVERY_OUTPUT

client.onNotification(lsp.ShowMessageNotification.type, (p) => {
  if (p.message.startsWith('Project discovery failed')) {
    // fall back to a static rust-project.json via linkedProjects
  }
});

When it happens

Trigger: DiscoverProjectMessage::Error arriving from a discovery job — the user-configured discovery command exited non-zero, emitted invalid JSON, or failed to describe the workspace; discover_jobs_active is decremented and progress ends with the error message.

Common situations: Misconfigured `rust-analyzer.discoverProjectConfig`/custom discovery command (wrong path, non-JSON output, script errors); monorepo/non-Cargo layouts where the discovery script assumptions break; missing tooling in the environment the script runs in.

Related errors

• Cannot rename builtin type
• cargo check failed to start: {err}
• {message}
• We explicitly do not provide canonicalization API, as that i
• bad kind {other}

AI-assisted analysis of rust-lang/rust-analyzer@e8f7e90aa3 (2026-09-03). Data as JSON: /api/errors/72c234609373c3e1. Report an issue: GitHub.