#383 — test: first fuzz target on the --pr-diff patch parser by cmbays · Pull Request #385 · breezy-bays-labs/cute-dbt

cmbays · 2026-06-14T00:35:58Z

Summary

Wires cute-dbt's first fuzz target (the org's named "single most valuable Q4 move") over the highest-risk untrusted-input surface: the --pr-diff unified-diff parser (cli::pr_diff::parse_unified_diff). In CI/PR-review mode arbitrary diff text is fed in, so this is the realistic adversarial surface.

Closes #383

Toolchain — bolero on STABLE Rust (no nightly, no libFuzzer)

bolero is chosen over cargo-fuzz because its DefaultEngine mimics libtest and runs under plain cargo test / cargo nextest on the crate's MSRV 1.88 — it replays the committed corpus/ and generates fresh random inputs, with no nightly, no libFuzzer, and no cargo-bolero binary required to exercise the corpus. That lowest-friction property is exactly the AC.

What lands

Fuzz target tests/fuzz_pr_diff_parser/main.rs (harness = false, like bdd) driving bolero::check!().for_each(|bytes: &[u8]| …). It asserts the fail-closed contract ("cute-dbt never panics on a bad diff"): for any byte sequence the parser never panics/hangs, returns Ok(PrDiff)/Err only, emits a structurally well-formed POD on success (no embedded newlines in parsed paths/bodies), and is deterministic.
Seam: parse_unified_diff → pub(crate) + a #[doc(hidden)] cli::fuzz_parse_unified_diff re-export (the pure parser — no @file filesystem I/O on the fuzzed path). Not public API; same internal-reach motive as the bdd target. Does not trip non-mirror-guard (that greps src/lib.rs for pub use crate::…::…; this seam lives in src/cli/mod.rs).
Committed seed corpus (14 inputs) under tests/fuzz_pr_diff_parser/corpus/ per the regression-files-committed rule — valid + adversarial shapes (orphan hunk header, +++ body line, pure rename, CRLF, malformed/huge ranges, prose, empty/whitespace).
Non-blocking CI: a separate .github/workflows/fuzz.yml (workflow_dispatch + weekly cron), NOT a merge gate and not in branch protection. Reuses only actions already in ci.yml (no new org-allowlist entry). The cheap corpus replay rides the normal Test job (cargo test builds the target; the corpus replays there).
testing.md: Fuzz rung aspirational — → in-progress; Q4 WEAK → improving; remaining candidates noted (manifest JSON reader, RFC-4180 CSV parser). The quality-manifest mirror in ops is a follow-up.

Bounded-run result

BOLERO_RANDOM_ITERATIONS=1000000 + the 14-input corpus → zero crashes (~277k iters/s, ~3.6s), no crashes/ or hangs/ produced. The parser was already fail-closed, so no parser fix was needed (including the @@ … +1,99999999999999999999 @@ usize-overflow path, which correctly returns Err, never panics).

Deps + gates

15 new transitive crates, all MIT / MIT-OR-Apache-2.0 — already in deny.toml's allowlist. cargo deny check: advisories ok, bans ok, licenses ok, sources ok (no license change). multiple-versions stays warn per the v0.x policy.
cargo fmt --check, cargo clippy --all-targets --locked -- -D warnings, cargo nextest run (2052 passed), RUSTDOCFLAGS=-D warnings cargo doc --no-deps --locked — all green.
No render change → goldens byte-identical (git status examples/ empty). No .feature change → feature-count mirror untouched.

test: prefix → no version bump.

HELD for founder review — this adds a dev-dep + a fuzz toolchain decision. Do not merge without Christopher's sign-off.

🤖 Generated with Claude Code

Summary by CodeRabbit

Tests
- Added automated fuzzing test suite for the --pr-diff patch parser with validation of edge cases and malformed inputs.
- Expanded test coverage with 14 seed scenarios covering file operations, various diff formats, unusual headers, and whitespace handling.
Documentation
- Updated testing progress documentation to reflect completed fuzzing infrastructure.

Wire cute-dbt's first fuzz target (the Q4 bring-into-shape move) over the highest-risk untrusted-input surface: the `--pr-diff` unified-diff parser (`cli::pr_diff::parse_unified_diff`). In CI/PR-review mode arbitrary diff text is fed in, so this is the realistic adversarial surface. Harness: bolero on STABLE Rust (MSRV 1.88) — its DefaultEngine mimics libtest and runs under plain `cargo test`/`cargo nextest`, replaying the committed corpus AND generating fresh random inputs, with no nightly, no libFuzzer, and no `cargo-bolero` binary required. Chosen over cargo-fuzz for exactly that lowest-friction property. The target asserts the fail-closed contract ("cute-dbt never panics on a bad diff"): for any byte sequence the parser never panics/hangs, returns Ok(PrDiff) or Err only, emits a structurally well-formed POD on success (no embedded newlines in parsed paths/bodies), and is deterministic. A bounded in-session run of 1,000,000 random iterations + the 14-input seed corpus surfaced zero crashes — the parser was already fail-closed, so no parser fix was needed. - Expose `parse_unified_diff` as `pub(crate)` + a `#[doc(hidden)]` `cli::fuzz_parse_unified_diff` seam (the pure parser, no `@file` I/O on the fuzzed path). Not public API; same internal-reach motive as `bdd`. - Seed corpus committed (regression-files-committed rule) under tests/fuzz_pr_diff_parser/corpus/ — valid + adversarial shapes (orphan hunk header, `+++` body line, pure rename, CRLF, malformed/huge ranges, prose, empty/whitespace). - All 15 new transitive crates are MIT / MIT-OR-Apache-2.0 (already in deny.toml's allowlist) — `cargo deny check` stays green, no license change. multiple-versions stays "warn" per the v0.x policy. - Non-blocking CI: a separate `fuzz.yml` (workflow_dispatch + weekly cron), NOT a merge gate and not in branch protection; reuses only actions already in ci.yml. The cheap corpus replay rides the normal Test job. - testing.md: Fuzz rung aspirational -> in-progress; Q4 WEAK -> improving; remaining candidates noted (manifest JSON reader, RFC-4180 CSV parser). The quality-manifest mirror in ops is a follow-up. Closes #383 Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

gemini-code-assist · 2026-06-14T00:36:01Z

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coderabbitai · 2026-06-14T00:36:11Z

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: fdc255ce-96aa-4572-8f52-124ca0d27669

📥 Commits

Reviewing files that changed from the base of the PR and between f67a393 and e2a2907.

⛔ Files ignored due to path filters (1)

Cargo.lock is excluded by !**/*.lock

📒 Files selected for processing (20)

.claude/rules/testing.md
.github/workflows/fuzz.yml
Cargo.toml
src/cli/mod.rs
src/cli/pr_diff.rs
tests/fuzz_pr_diff_parser/corpus/seed_bad_hunk_header
tests/fuzz_pr_diff_parser/corpus/seed_bad_old_range
tests/fuzz_pr_diff_parser/corpus/seed_bare_at
tests/fuzz_pr_diff_parser/corpus/seed_crlf
tests/fuzz_pr_diff_parser/corpus/seed_deleted_file
tests/fuzz_pr_diff_parser/corpus/seed_empty
tests/fuzz_pr_diff_parser/corpus/seed_huge_range
tests/fuzz_pr_diff_parser/corpus/seed_new_file
tests/fuzz_pr_diff_parser/corpus/seed_orphan_hunk
tests/fuzz_pr_diff_parser/corpus/seed_plus_body
tests/fuzz_pr_diff_parser/corpus/seed_prose
tests/fuzz_pr_diff_parser/corpus/seed_pure_rename
tests/fuzz_pr_diff_parser/corpus/seed_simple_edit
tests/fuzz_pr_diff_parser/corpus/seed_whitespace
tests/fuzz_pr_diff_parser/main.rs

📝 Walkthrough

Walkthrough

A Bolero-based fuzz harness is wired for the --pr-diff unified-diff parser. parse_unified_diff gains pub(crate) visibility and a public fuzz_parse_unified_diff seam; Cargo.toml registers the bolero dependency, a harness = false test target, and a [profile.fuzz] build profile. Thirteen seed corpus files are committed, and a GitHub Actions workflow runs bounded fuzz campaigns on schedule and manual dispatch.

Changes

--pr-diff fuzz pilot

Layer / File(s)	Summary
Cargo wiring and parser fuzz seam `src/cli/pr_diff.rs`, `src/cli/mod.rs`, `Cargo.toml`	`parse_unified_diff` is made `pub(crate)`; a `#[doc(hidden)]` `fuzz_parse_unified_diff` public wrapper is added to `src/cli/mod.rs`; `bolero = "0.13.4"` is added as a dependency; a `fuzz_pr_diff_parser` test target with `harness = false` and a `[profile.fuzz]` are registered.
Bolero harness and committed seed corpus `tests/fuzz_pr_diff_parser/main.rs`, `tests/fuzz_pr_diff_parser/corpus/*`	The harness converts fuzzed bytes to lossy UTF-8, calls `fuzz_parse_unified_diff`, and on `Ok` asserts no embedded `\n` in file paths/hunk lines/rename fields, plus parse idempotence. Thirteen seed files cover simple edits, new/deleted files, pure rename, CRLF, orphan hunk, bad hunk headers, malformed ranges, huge ranges, bare `@@`, whitespace, and prose.
CI workflow and testing docs `.github/workflows/fuzz.yml`, `.claude/rules/testing.md`	New `fuzz.yml` runs `cargo test --test fuzz_pr_diff_parser --locked` with `BOLERO_RANDOM_ITERATIONS` validated from input, on weekly schedule and `workflow_dispatch`. `testing.md` marks the `--pr-diff` bolero target as Done, upgrades Q4 status from WEAK to improving, and identifies CSV and manifest JSON parsers as next fuzz targets.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

Possibly related PRs

breezy-bays-labs/cute-dbt#184: Extends parse_unified_diff in src/cli/pr_diff.rs to record rename from/rename to pairs into PrDiff::renames, the same parser function now exposed as a fuzz seam and exercised by the new seed_pure_rename corpus entry.

Poem

🐇 Hop hop, I throw garbage bytes at the diff,
The parser stays steady — no panic, no cliff.
Seeds of bad hunks and bare @@ I toss,
Bolero counts millions, I'm never at loss.
✨ Fuzzing is done (well, the first bit at least),
Next up: the CSV parser, a quite different beast!

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: introducing the first fuzz target for the --pr-diff patch parser, which aligns with the primary objective of the PR.
Linked Issues check	✅ Passed	All acceptance criteria from issue `#383` are met: fuzz target created over --pr-diff parser with bolero on stable Rust, fail-closed verification passed, corpus committed, testing.md updated, and CI workflow documented as non-blocking.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to implementing the fuzz target infrastructure and documentation: no unrelated refactoring, cleanup, or feature creep is present.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

📝 Generate docstrings

Create stacked PR
Commit on current branch

🧪 Generate unit tests (beta)

Create PR with unit tests
Commit unit tests in branch test-383-fuzz-prdiff-parser

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ghost · 2026-06-14T00:36:20Z

Ready to review this PR? Stage has broken it down into 7 individual chapters for you:

	Title
1	Add bolero dependency and fuzzing profile
2	Expose internal parser via fuzzing seam
3	Implement the pr-diff parser fuzz target
4	Add initial seed corpus for fuzzing
5	Configure scheduled fuzzing workflow
6	Update testing documentation and status
7	Other changes

_{Chapters generated by Stage for commit e5ac304 on Jun 14, 2026 1:09am UTC.}

github-actions · 2026-06-14T00:37:28Z

📄 Rendered report preview

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Alternative: GitHub CLI

# gh CLI >= 2.63 extracts into ./report-preview-playground/.
gh run download 27484340693 -R breezy-bays-labs/cute-dbt -n report-preview-playground
open report-preview-playground/playground-report.html

_{Posted by report-preview.yml for e5ac3049fb373e418dfcdd3fc0286ca89ef61117. Affordance only — never blocks merge.}

Merge branch 'main' into test-383-fuzz-prdiff-parser

e5ac304

cmbays merged commit 468d3f0 into main Jun 14, 2026
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cmbays deleted the test-383-fuzz-prdiff-parser branch June 14, 2026 01:19

github-actions Bot added a commit that referenced this pull request Jun 14, 2026

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#383 — test: first fuzz target on the --pr-diff patch parser - #385

#383 — test: first fuzz target on the --pr-diff patch parser#385
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Summary

Toolchain — bolero on STABLE Rust (no nightly, no libFuzzer)

What lands

Bounded-run result

Deps + gates

Summary by CodeRabbit

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