vectordotdev/vector · error

stack was empty during pop

Error message

stack was empty during pop

What it means

`pop_schema_scope` on `OccurrenceVisitor` pops its schema-reference scope stack and asserts a scope existed. The panic fires when pop is called without a matching push, i.e. the visitor's scope stack is empty — a tracking invariant of the scoped traversal (push on entering a $ref, pop on exit) was broken.

Solutions

1. Only drive scoped visitors through `visit_schema_object_scoped` / the standard traversal entry points
2. Verify balanced push/pop pairs if you added custom traversal code
3. Check the schema being visited for unexpected structure and reproduce with a minimal config
4. Report upstream if a stock component config triggers it

Example fix

// before
visitor.pop_schema_scope();
visitor.visit_schema_object(...);
// after
visitor.push_schema_scope("MyDef");
visitor.visit_schema_object(...);
visitor.pop_schema_scope();

if visitor.scope_stack_is_empty() {
    return Err("cannot pop schema scope: stack empty".into());
}

match visitor.try_pop_schema_scope() {
    Ok(scope) => scope,
    Err(e) => { tracing::error!("scope pop failed: {e}"); return Err(e); }
}

When it happens

Trigger: Traversal code calls `pop_schema_scope` more times than `push_schema_scope` was called — e.g. a schema object without a reference still triggers a pop, or the visitor is invoked outside the standard scoped traversal driver (`visit_schema_object_scoped`).

Common situations: Calling visitor methods directly instead of through the scoped traversal entry point; custom schema shapes (e.g. schemas at unexpected nesting) causing unbalanced push/pop in the traversal driver.

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

• stack was empty during pop
• all-of subschemas must be present here
• referenced schema must exist in definitions
• schema definition must exist
• schema definition must exist

AI-assisted analysis of vectordotdev/vector@bdb87aeaa4 (2026-09-16). Data as JSON: /api/errors/9841f7ba2367cf39. Report an issue: GitHub.

Appendix: source

Thrown at lib/vector-config/src/schema/visitors/inline_single.rs:170

        visit_schema_object_scoped(self, definitions, schema);

        if let Some(current_schema_ref) = schema.reference.as_ref() {
            let current_schema_ref = get_cleaned_schema_reference(current_schema_ref);
            *self
                .occurrence_map
                .entry(current_schema_ref.into())
                .or_default() += 1;
        }
    }
}

impl ScopedVisitor for OccurrenceVisitor {
    fn push_schema_scope<S: Into<SchemaReference>>(&mut self, scope: S) {
        self.scope_stack.push(scope.into());
    }

    fn pop_schema_scope(&mut self) {
        self.scope_stack.pop().expect("stack was empty during pop");
    }

    fn get_current_schema_scope(&self) -> &SchemaReference {
        self.scope_stack.current().unwrap_or(&SchemaReference::Root)
    }
}

fn get_schema_metadata_attr<'a>(schema: &'a SchemaObject, key: &str) -> Option<&'a Value> {
    schema
        .extensions
        .get("_metadata")
        .and_then(|metadata| metadata.get(key))
}

#[cfg(test)]
mod tests {
    use serde_json::json;
    use vector_config_common::schema::visit::Visitor;

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