fix(hql): handle TraversalValue::Empty in DROP operations

[xav-db]

Summary

This PR integrates the fix from #670 into the arena-implementation branch. It resolves runtime errors when attempting to DROP non-existent nodes, edges, or vectors.

Problem

Queries attempting to drop non-existent items failed with:

Conversion error: Incorrect Type: Empty

This occurred because drop_traversal did not handle TraversalValue::Empty returned when querying for non-existent items.

Solution

Added TraversalValue::Empty => Ok(()) case in the match statement of drop_traversal in helix-db/src/helix_engine/traversal_core/ops/util/drop.rs:51.

This treats empty traversals as successful no-ops, making DROP operations idempotent.

Testing

• ✅ cargo check passes with no errors
• ✅ All 109 helix_engine tests pass, including all DROP-related tests

Related

• Integrates fix from PR fix(hql): DROP operation on empty traversals #670
• No changes needed to helixc generator - the fix automatically applies to generated code

Co-Authored-By: ishaksebsib

Greptile Overview

Updated On: 2025-10-29 11:44:54 UTC

Greptile Summary

Added handling for TraversalValue::Empty in DROP operations to prevent runtime errors when attempting to drop non-existent nodes, edges, or vectors.

• Fixed "Conversion error: Incorrect Type: Empty" by treating empty traversals as successful no-ops
• Implementation is consistent with how TraversalValue::Empty is handled elsewhere in the codebase (returns default/neutral values)
• Makes DROP operations idempotent, which is expected behavior for deletion operations

Important Files Changed

File Analysis

Filename	Score	Overview
helix-db/src/helix_engine/traversal_core/ops/util/drop.rs	5/5	Added TraversalValue::Empty handling to gracefully treat empty traversals as no-ops in DROP operations

Sequence Diagram

sequenceDiagram
    participant Client
    participant HQL
    participant drop_traversal
    participant collect_to_obj
    participant Storage

    Client->>HQL: DROP N<NodeType>(non_existent_id)
    HQL->>collect_to_obj: Query for node by ID
    collect_to_obj->>Storage: Fetch node
    Storage-->>collect_to_obj: No results found
    collect_to_obj-->>HQL: TraversalValue::Empty
    HQL->>drop_traversal: Process traversal items
    alt Empty traversal (after fix)
        drop_traversal-->>HQL: Ok(()) - no-op
        HQL-->>Client: Success
    else Empty traversal (before fix)
        drop_traversal-->>HQL: ConversionError
        HQL-->>Client: Error: "Incorrect Type: Empty"
    end

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