Antigravity PR Reviewer

Problem

A Rust daemon that autonomously reviews pull requests on a production NestJS codebase: it checks each PR out in an isolated git worktree, runs a multi-pass static analysis pipeline, and posts evidence-anchored GitHub review comments — without touching the main branch or waiting for a human to start it.

The central constraint: a reviewer with repository access must not be able to change the repository — and that property is enforced by tests, not by convention.

Architecture

flowchart TB
  Poll[Poll GitHub for review-requested PRs] --> WT[Isolated git worktree at PR head]
  subgraph worktree [Temporary worktree]
    P1[1 · CodeGraph impact analysis]
    P2[2 · Tenant-isolation AST check]
    P3[3 · tsc --noEmit]
    P4[4 · ESLint]
    P5[5 · dependency-cruiser]
    P1 --> P2 --> P3 --> P4 --> P5
  end
  WT --> P1
  P5 --> Gate{Evidence gate<br/>diff-anchored?}
  Gate -- no --> Drop[Dropped]
  Gate -- yes --> Review[GitHub review<br/>REQUEST_CHANGES or APPROVE]
  WT -.->|always removed| Cleanup[Cleanup]

What I Built

Core daemon

A background Rust process that polls the GitHub API for PRs labelled review-requested, filters to those awaiting the bot’s review, and processes them in parallel.
Each PR gets its own git worktree at the PR’s head commit, separate from the main checkout, so reviews can’t contaminate each other or the main branch.

Five-pass review pipeline

CodeGraph impact analysis — maps which modules and functions the diff touches and finds downstream callers outside the diff.
AST-level tenant isolation — verifies every TypeORM repository query in changed files includes an account_id scope clause, catching IDOR vulnerabilities before merge.
TypeScript — tsc --noEmit on the worktree, catching type errors the swc build pipeline passes silently.
ESLint — the project’s full config, including custom tenant-isolation rules.
dependency-cruiser — no new dependency violations, such as infrastructure importing from features, or cycles.

Evidence gate

A finding becomes a comment only if it has diff-anchored evidence: a specific line in a changed file, not a general pattern match.
Comments are pinned to exact diff lines through the GitHub Pull Request Review API.
The bot submits a full review with REQUEST_CHANGES or APPROVE based on aggregate finding severity.

Engineering Decisions

Safety architecture

src/github.rs is architecturally prohibited from containing any git push, git merge or repository-mutation code path. Unit tests parse the source AST and fail if those patterns appear.
Worktrees are created in a temp directory and removed after every review, whether the pipeline succeeds or fails.

→ How I built a PR reviewer that cannot modify the main branch

Technology

Rust · Git worktrees · GitHub REST API · GitHub GraphQL API · Antigravity CLI · CodeGraph

Key results