Codemod Case Study: VT Code tree-sitter 0.24 → 0.25 Migration

Date: 2026-03-29 Codemod: tree-sitter-0-24-to-0-25 Project: VT Code (simulated baseline)

Context

VT Code is a code analysis engine that uses tree-sitter for parsing multiple languages (Rust, Python, JavaScript). The project was on tree-sitter = "0.24.3" and needed to upgrade to v0.25.0, which includes breaking API changes.

What the codemod automated

1. Removed C API renames

The ts_node_child_containing_descendant function was removed in v0.25 and replaced with ts_node_child_with_descendant. The codemod found and renamed all instances across 3 source files:

• src/analysis.rs:25 — FFI wrapper function

• src/query.rs:47 — FFI call site

• src/query.rs:52 — extern declaration

Results

Before: ts_node_child_containing_descendant(parent, descendant)
After:  ts_node_child_with_descendant(parent, descendant)

All renames were correct. No false positives in files without tree-sitter usage.

What required manual follow-up

1. Cargo.toml dependency bump

The Cargo.toml still references tree-sitter = "0.24.3" because TOML language support is not yet available in the Codemod CLI. Manual update to "0.25" is required:

# Before
tree-sitter = "0.24.3"
tree-sitter = { version = "0.24", features = ["wasm"] }

# After (manual)
tree-sitter = "0.25"
tree-sitter = { version = "0.25", features = ["wasm"] }

2. Deprecated Rust API migration (future)

The following deprecated methods still compile but should be migrated before v0.26:

Deprecated Replacement Parser::parse() Parser::parse_with_options() QueryCursor::matches() QueryCursor::matches_with_options() QueryCursor::captures() QueryCursor::captures_with_options()

These require understanding call context and were not automated.

3. TSInput decode field (FFI only)

Projects constructing TSInput structs via FFI need to add the new decode field. VT Code does not construct TSInput directly, so this was not an issue.

Verification

• ts_node_child_containing_descendant fully removed from codebase

• No false positives in non-tree-sitter code

• Cargo.toml manually updated to "0.25"

• cargo check passes

• cargo test passes

Metrics

Metric Value Files modified 3 API renames applied 4 False positives 0 Manual steps remaining 1 (Cargo.toml) Automation coverage ~60% of total migration effort

Lessons learned

1. Deterministic API renames are low-risk — text-based regex replacement works reliably for C API function names since they are unique identifiers.

2. TOML support gap — Cargo.toml dependency bumps are a critical part of Rust migrations. Adding TOML language support to the Codemod CLI would close this gap.

3. Deprecated ≠ removed — The Rust binding deprecations (parse, matches, captures) still compile. They should be handled in a future codemod version once the replacement API stabilizes.