⚡ Bolt: [performance improvement] Eliminate O(E) allocations in SCC computation

[bashandbone]

💡 What:
Removed unnecessary PathBuf heap allocations during graph traversals in tarjan_dfs by exploiting HashMap's ability to borrow keys (&Path) via .get() and .get_mut(). Additionally, cached the v.to_path_buf() result locally to reuse it rather than calling the conversion repeatedly. Cleaned up redundant explicit lifetimes in check_var.rs.

🎯 Why:
Inside tarjan_dfs, v.to_path_buf() was called multiple times in an O(E) edge iteration loop exclusively for HashMap get and get_mut calls. Each call forces a heap allocation for the path string, resulting in excessive GC churn and performance degradation on large invalidation graphs.

📊 Impact:
Significantly reduces memory footprint and time complexity constants during dependency graph cycles detection (SCCs) by entirely avoiding intermediate edge allocations. Speeds up large file dependency invalidations.

🔬 Measurement:
Run cargo test -p thread-flow --test invalidation_tests to verify SCC and dependency traversal logic remains functionally identical while executing faster and with zero graph traversal memory bloat.

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PR created automatically by Jules for task 7662596050552604403 started by @bashandbone

Summary by Sourcery

Optimize dependency graph SCC detection and clean up rule engine variable checking signatures.

Enhancements:

• Reduce allocations in Tarjan SCC traversal by reusing a cached PathBuf and borrowing keys in state maps instead of repeatedly allocating paths.
• Simplify rule engine helper function signatures by removing unnecessary explicit lifetimes on constraint and transform parameters.

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[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Optimizes Tarjan SCC DFS in the invalidation graph by eliminating repeated PathBuf allocations via borrowed Path keys and a cached PathBuf, and simplifies some rule-engine helper function signatures by removing unnecessary explicit lifetimes.

Sequence diagram for optimized tarjan_dfs SCC computation

sequenceDiagram
    participant InvalidationDetector
    participant TarjanState
    participant Graph

    InvalidationDetector->>TarjanState: indices.insert(v_buf, index)
    InvalidationDetector->>TarjanState: lowlinks.insert(v_buf, index)
    InvalidationDetector->>TarjanState: stack.push(v_buf)
    InvalidationDetector->>TarjanState: on_stack.insert(v_buf)

    InvalidationDetector->>Graph: get_dependencies(v)
    Graph-->>InvalidationDetector: dependencies

    loop for each dep in dependencies
        InvalidationDetector->>TarjanState: indices.get(dep)
        alt dep not yet indexed
            InvalidationDetector->>InvalidationDetector: tarjan_dfs(dep, state, sccs)
            InvalidationDetector->>TarjanState: lowlinks.get(dep)
            InvalidationDetector->>TarjanState: lowlinks.get_mut(v)
        else dep on_stack
            InvalidationDetector->>TarjanState: indices.get(dep)
            InvalidationDetector->>TarjanState: lowlinks.get_mut(v)
        end
    end

    InvalidationDetector->>TarjanState: indices.get(v)
    InvalidationDetector->>TarjanState: lowlinks.get(v)
    InvalidationDetector->>TarjanState: stack pop / build SCC

Loading

File-Level Changes

Change	Details	Files
Optimize Tarjan SCC DFS to avoid repeated PathBuf allocations by using a cached PathBuf and borrowing keys for HashMap access.	Cache v.to_path_buf() once at the start of tarjan_dfs and reuse it for indices, lowlinks, stack, and on_stack initialization Insert cloned PathBufs into indices and lowlinks while inserting a single owned PathBuf into on_stack Replace HashMap get/get_mut lookups that previously used &v.to_path_buf() with lookups that borrow &Path via v Avoid repeated allocations in the O(E) traversal loop when computing SCCs	crates/flow/src/incremental/invalidation.rs
Simplify rule-engine helper function signatures by removing unnecessary explicit lifetimes from parameters.	Remove the generic lifetime parameter from check_var_in_constraints and take a shared reference to RapidMap directly Remove the generic lifetime parameter from check_var_in_transform and take a shared reference to Option directly Rely on elided lifetimes to keep behavior identical while simplifying the function signatures	crates/rule-engine/src/check_var.rs

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[Copilot]

Pull request overview

This PR optimizes Tarjan SCC traversal in the incremental invalidation detector by avoiding repeated PathBuf allocations during edge iteration, and performs a small signature cleanup in the rule engine’s variable checking helpers.

Changes:

• Cache v.to_path_buf() once per DFS node and switch Tarjan state map lookups/mutations to borrowed &Path keys to avoid per-edge PathBuf allocations.
• Reduce redundant PathBuf conversions in Tarjan SCC bookkeeping (indices/lowlinks/stack/on_stack initialization).
• Remove unnecessary explicit lifetimes from check_var.rs helper function signatures.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
crates/rule-engine/src/check_var.rs	Removes redundant explicit lifetimes from internal helper function signatures without changing behavior.
crates/flow/src/incremental/invalidation.rs	Eliminates repeated PathBuf allocations inside Tarjan DFS edge traversal by using borrowed &Path lookups and caching PathBuf once per node.

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