# Regression Review Report

**Branch**: feat/rskim-search-foundation -> main
**Date**: 2026-05-11

## Issues in Your Changes (BLOCKING)

### CRITICAL

(none)

### HIGH

(none)

## Issues in Code You Touched (Should Fix)

(none)

## Pre-existing Issues (Not Blocking)

(none)

## Suggestions (Lower Confidence)

(none)

## Summary

| Category | CRITICAL | HIGH | MEDIUM | LOW |
|----------|----------|------|--------|-----|
| Blocking | 0 | 0 | 0 | - |
| Should Fix | - | 0 | 0 | - |
| Pre-existing | - | - | 0 | 0 |

**Regression Score**: 9/10
**Recommendation**: APPROVED

## Analysis Notes

### Changes Reviewed

This PR introduces 3 major cross-cutting changes with regression potential:

1. **thiserror 1.0 to 2.0 workspace upgrade**
2. **Rust edition 2021 to 2024 migration**
3. **52 `collapsible_if` refactorings** (clippy auto-fix via edition 2024 if-let chaining)
4. **New `rskim-search` crate** (additive, no existing code modified for it)
5. **New `search` CLI subcommand** (additive stub)

### Detailed Regression Assessment

**thiserror 2.0 upgrade**: thiserror 2.0 is a drop-in replacement for 1.0 for all derive patterns used in this workspace (`#[error("...")]`, `#[from]`, `#[source]`). The only breaking change in thiserror 2.0 is that it now requires `core::error::Error` trait (Rust 1.81+) rather than `std::error::Error`, which is forward-compatible. All error types (`SkimError`, `SearchError`) use standard patterns and compile correctly. No behavioral regression.

**Edition 2024 migration**: Two semantic changes applied:
- `if let Some(ref d) = dir` changed to `if let Some(d) = dir` in `metrics.rs` — correct because the iterator already produces `&Option<String>`, making `ref` redundant under edition 2024 binding rules. No behavioral change.
- `std::env::set_var`/`remove_var` wrapped in `unsafe` blocks in test code (`cursor.rs`) — required by edition 2024 which made these functions unsafe. The operations were already test-only and single-threaded. No behavioral change.

**Collapsible if-let chain refactoring (52 instances)**: Every instance was verified to be a purely structural transformation that preserves semantics:
- Nested `if A { if B { ... } }` becomes `if A && B { ... }` — identical behavior.
- Nested `if let X = expr { if let Y = expr2 { ... } }` becomes `if let X = expr && let Y = expr2 { ... }` — short-circuit evaluation is identical.
- Side effects in conditions (e.g., `HashSet::insert()`) are preserved because the side effect occurs during expression evaluation, not after the `&&` check.
- Critical paths verified: `render_changed_only`, `parse_impl_with_auto_detect`, `three_tier_parse`, `split_compound`, `run_hook_mode`, `try_parse_nextest`, `collect_hunks` — all confirmed semantically equivalent.

**New `rskim-search` crate**: Purely additive. Added as workspace member and dev-dependency of `rskim`. Does not affect any existing runtime paths. The compile-time canary pattern (dev-dep only) ensures API surface is validated without runtime coupling.

**New `search` subcommand**: Registered in `KNOWN_SUBCOMMANDS` and dispatch table. Existing subcommands are unaffected. The sync-guard test validates no routing conflicts.

### Regression Checklist

- [x] No exports removed without deprecation
- [x] Return types backward compatible
- [x] Default values unchanged
- [x] Side effects preserved (events, logging)
- [x] All consumers of changed code updated
- [x] Migration complete across codebase (all 52 collapsible_if sites)
- [x] CLI options preserved
- [x] Commit messages match implementation
- [x] 3333 tests passing (up from baseline)
