⚡ Bolt: [performance improvement] Optimize Tarjan DFS allocations

[bashandbone]

💡 What: Cached v.to_path_buf() to a local variable v_buf and reused it, while replacing map lookups to use the borrowed reference v. Also cleaned up explicit lifetimes in check_var.rs as identified by clippy.
🎯 Why: Repeated calls to v.to_path_buf() caused excessive O(E) heap allocations during SCC DAG traversal within tarjan_dfs, degrading incremental build performance.
📊 Impact: Significantly reduces memory churn and O(E) heap allocations to O(V) during graph invalidation computations by utilizing zero-cost Borrow traits for Map lookups.
🔬 Measurement: Observe memory allocations and execution time of cargo test -p thread-flow --test invalidation_tests.

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PR created automatically by Jules for task 15864650468603263492 started by @bashandbone

Summary by Sourcery

Optimize incremental invalidation Tarjan DFS to reduce path allocation overhead and apply minor code cleanups across AST and rule engine modules.

Enhancements:

• Reduce heap allocations in Tarjan DFS by caching path conversions and using borrowed keys for map lookups.
• Simplify function signatures in the rule engine by removing unnecessary explicit lifetimes.
• Apply minor readability and formatting improvements in AST and rule engine utilities.

[google-labs-jules]

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[sourcery-ai]

Reviewer's Guide

Optimizes Tarjan DFS by reusing a cached PathBuf and switching map lookups to borrow-based access, while also applying minor Clippy-driven cleanup and formatting changes across AST and rule-engine modules.

File-Level Changes

Change	Details	Files
Reduce allocations and leverage borrowed keys in Tarjan DFS implementation used for invalidation.	Cache v.to_path_buf() into a local v_buf and reuse it instead of recomputing for each map/stack operation. Change indices/lowlinks/stack/on_stack insertions to use cloned v_buf rather than new PathBuf allocations per call. Switch hash map lookups in lowlinks/indices from using &v.to_path_buf() to borrowing &Path (v) to take advantage of the map’s Borrow implementation. Use borrowed v in indices/lowlinks lookups when computing v_index and v_lowlink to avoid extra allocations.	crates/flow/src/incremental/invalidation.rs
Apply minor refactors and style cleanups suggested by Clippy and rustfmt in AST and rule-engine code.	Reformat a FromUtf8 error-handling expression into a single chained call for readability. Reformat an assert_eq! call in tests over multiple lines for clarity. Remove unnecessary explicit lifetime parameter from check_var_in_constraints and accept a simple shared reference instead. Remove unnecessary explicit lifetime parameter from check_var_in_transform and accept a simple shared reference instead. Format Rule::Pattern branch to break the iterator chain across multiple lines. Inline the read lock unwrap_or_else call in Registration::read into a single expression.	crates/ast-engine/src/tree_sitter/mod.rs crates/rule-engine/src/check_var.rs crates/rule-engine/src/rule/mod.rs crates/rule-engine/src/rule/referent_rule.rs

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[sourcery-ai]

Hey - I've found 1 issue

Prompt for AI Agents

Please address the comments from this code review:

## Individual Comments

### Comment 1
<location path="crates/flow/src/incremental/invalidation.rs" line_range="348-350" />
<code_context>

     /// DFS helper for Tarjan's algorithm
     fn tarjan_dfs(&self, v: &Path, state: &mut TarjanState, sccs: &mut Vec<Vec<PathBuf>>) {
+        let v_buf = v.to_path_buf();
         // Initialize node
         let index = state.index_counter;
-        state.indices.insert(v.to_path_buf(), index);
-        state.lowlinks.insert(v.to_path_buf(), index);
+        state.indices.insert(v_buf.clone(), index);
+        state.lowlinks.insert(v_buf.clone(), index);
         state.index_counter += 1;
-        state.stack.push(v.to_path_buf());
-        state.on_stack.insert(v.to_path_buf());
+        state.stack.push(v_buf.clone());
+        state.on_stack.insert(v_buf.clone());

         // Visit all successors (dependencies)
</code_context>
<issue_to_address>
**suggestion (performance):** Reduce redundant cloning of `v_buf` when initializing Tarjan state for a node.

`v_buf` is now allocated once, which is good, but it’s still cloned four times (for `indices`, `lowlinks`, `stack`, and `on_stack`). You can avoid one clone by moving `v_buf` into the last insertion:

```rust
let v_buf = v.to_path_buf();
state.indices.insert(v_buf.clone(), index);
state.lowlinks.insert(v_buf.clone(), index);
state.stack.push(v_buf.clone());
state.on_stack.insert(v_buf);
```

```suggestion
        state.index_counter += 1;
        state.stack.push(v_buf.clone());
        state.on_stack.insert(v_buf);
```
</issue_to_address>

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[sourcery-ai]

suggestion (performance): Reduce redundant cloning of v_buf when initializing Tarjan state for a node.

v_buf is now allocated once, which is good, but it’s still cloned four times (for indices, lowlinks, stack, and on_stack). You can avoid one clone by moving v_buf into the last insertion:

let v_buf = v.to_path_buf();
state.indices.insert(v_buf.clone(), index);
state.lowlinks.insert(v_buf.clone(), index);
state.stack.push(v_buf.clone());
state.on_stack.insert(v_buf);

Suggested change

	state.index_counter += 1;
	state.stack.push(v.to_path_buf());
	state.on_stack.insert(v.to_path_buf());
	state.stack.push(v_buf.clone());
	state.on_stack.insert(v_buf.clone());
	state.index_counter += 1;
	state.stack.push(v_buf.clone());
	state.on_stack.insert(v_buf);

[Copilot]

Pull request overview

This PR reduces unnecessary heap allocations during Tarjan SCC traversal in the incremental invalidation detector by caching PathBuf conversions and leaning on borrowed lookups, plus applies small clippy/rustfmt cleanups in the rule engine and tree-sitter utilities.

Changes:

• Optimize tarjan_dfs by caching v.to_path_buf() and switching map/set lookups to use borrowed &Path.
• Remove redundant explicit lifetimes in check_var.rs per clippy.
• Apply formatting-only refactors in rule engine and tree-sitter tests/utility code.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
crates/flow/src/incremental/invalidation.rs	Reduces PathBuf allocations in Tarjan DFS and uses borrowed lookups for RapidMap/RapidSet.
crates/rule-engine/src/check_var.rs	Simplifies function signatures by removing unnecessary explicit lifetimes.
crates/rule-engine/src/rule/referent_rule.rs	Minor refactor (single-expression chain) in Registration::read.
crates/rule-engine/src/rule/mod.rs	Formatting-only change to defined_vars for Rule::Pattern.
crates/ast-engine/src/tree_sitter/mod.rs	Minor formatting refactors in UTF-8 conversion and a test assertion.

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