# Error Handling & API Surface — Checklist Plan

## Summary / Quick Verdict

- [x] **Quick verdict**: core library paths have been migrated off `anyhow::Result`; bounded reads and CI checks are in place.
- [x] **Remediation goal**: typed crate-level errors, bounded IO, CLI edge context, and regression checks landed in this pass.

## Implementation Status (2026-03-28)

- [x] Added `thiserror`, `src/error.rs`, and the central `Result<T>` alias.
- [x] Added `src/io.rs` with bounded `read_to_string_limited` and migrated the scanner to use it.
- [x] Kept `anyhow` in binaries only and added `Context` at the CLI edge.
- [x] Removed the obvious non-test library `unwrap`/`expect` cases identified during planning.
- [x] Added `cargo clippy` unwrap/expect CI enforcement and the grep-based hygiene script.
- [x] Added regression tests and script coverage.
- [x] Added module-specific error fan-in for analysis/config and wired them into the crate-level error type.

## Goals

- [x] **Library errors**: Convert library/public APIs to typed `Error` enums using `thiserror`.
- [x] **Binary ergonomics**: Keep `anyhow` at application edges (`main.rs`, CLI).
- [x] **No panics/unwraps**: Eliminate `panic!` and `.unwrap()` in non-test library code.
- [x] **Bounded IO**: Replace unbounded `fs::read_to_string` with size-limited readers/streaming.
- [x] **CI enforcement**: Add lint/tests to detect regressions.

## Prep / Dependencies

- [x] **Add `thiserror`** to `Cargo.toml` (`thiserror = "1.0"`).
- [x] **Ensure `anyhow`** remains available for binaries (optional feature or workspace dep).

## Top-level API

- [x] **Create `src/error.rs`**: define `pub enum Error` with `#[derive(thiserror::Error, Debug)]` and `pub type Result<T> = std::result::Result<T, Error>`.
- [x] **Export** from `lib.rs`: `pub use crate::error::{Error, Result};`.

## Per-module Errors

- [x] **Add module-level `Error` enums** for large modules (`analysis::parser`, `config`) and fan them into the top-level `Error`.
- [x] **Use `#[from]`** conversions to aggregate into the top-level `Error`.

## Replace `anyhow` in libraries

- [x] **Replace library `anyhow::Result`** with `crate::error::Result<T>` where appropriate.

## Eliminate panics & unwraps

- [x] **Replace `unwrap()`** sites with `ok_or(Error::...)` or `?` and the correct error variants.
- [x] **Replace `panic!()`** in library code with domain errors; reserve `panic!` for unrecoverable internal bugs or use `debug_assert!`.
- [x] **Audit and fix examples** such as `target_segments.last().unwrap()` and explicit `panic!` sites in `src/index/mod.rs`.

## Bounded IO helpers

- [x] **Add `src/io.rs`** with `read_to_string_limited(path, max_bytes)` and `DEFAULT_MAX_BYTES` (e.g., 10 MiB).
- [x] **Replace `fs::read_to_string`** usages with the bounded reader or `Read::take(max)` where streaming sources exist.

## Linting & CI

- [x] **Clippy/CI policy**: run `cargo clippy --all-targets` and consider `-D clippy::unwrap_used -D clippy::expect_used` in CI.
- [x] **Grep-based check**: add a CI step/script to fail on `panic!`, `.unwrap(`, `.expect(`, and `fs::read_to_string` in non-test code.
- [x] **Add test**: a unit/integration test that scans the repo for forbidden patterns (with allow-list support).

## Concrete Migration Checklist (developer tasks)

- [x] Add `thiserror` to `Cargo.toml`.
- [x] Add `src/error.rs` and export `Error` and `Result` from `lib.rs`.
- [x] Implement `read_to_string_limited` and replace easy `fs::read_to_string` calls.
- [x] Fix obvious `unwrap()` occurrences in `index`, `analysis::parser`, and similar modules.
- [x] Add per-module error enums and `#[from]` conversions.
- [x] Convert public functions in library modules to return `Result<T>`.
- [x] Update binaries (`main.rs`, CLI) to convert typed errors into `anyhow` with context for user messages.
- [x] Add CI linting and grep-based checks.
- [x] Write tests for error variants, size limits, and regressions.

## Migration Phases

- [x] **Phase A (low-risk)**: add `thiserror`, top-level `Error`, `read_to_string_limited`, and fix trivial `unwrap()`/panic sites.
- [x] **Phase B (medium-risk)**: add per-module error enums, convert public APIs, and update binaries.
- [x] **Phase C (finish)**: run full compile/tests, add CI enforcement, finalize messages and docs.

## Developer Ergonomics

- [x] **Provide `pub type Result<T>`** centrally for ease of use.
- [x] **Provide small adapters/utilities** for converting IO/parse errors with context where helpful.
- [x] **Add README examples** documenting library vs app boundary and patterns.

## Tests & Benchmarks

- [x] **Unit tests** for error paths (missing files, parse errors, input-too-large).
- [x] **Benchmark/test** to confirm bounded read behavior and memory footprint.

## PR Checklist

- [x] Add `thiserror` to `Cargo.toml`.
- [x] Create `src/error.rs` and export it.
- [x] Implement `src/io.rs` bounded reader and replace call sites.
- [x] Replace `unwrap()`/`panic!` in library code.
- [x] Add per-module error enums and `#[from]` conversions.
- [x] Update binaries to map typed errors to `anyhow` for user-facing messages.
- [x] Add CI checks and tests.
- [x] Run the full test suite and fix fallout.

## Acceptance Criteria

- [x] **Typed public errors**: Library/public APIs return typed `Error` (no `Box`/`anyhow` in public signatures).
- [x] **No unbounded reads**: No lingering `fs::read_to_string` without limits in production code.
- [x] **No unwrap/panic**: No `unwrap()`/`panic!()` in non-test library code.
- [x] **CI enforcement**: CI fails on re-introduction of banned patterns.

## Next Steps / Options

- [x] Implemented Phase A (added `thiserror`, `src/error.rs`, and bounded reader).
- [x] Implemented the focused scanner migration and obvious `unwrap()` cleanup.

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If you want me to proceed with an implementation, tell me which option to start with.
