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name ast-grep-runner
description Mechanical rule funnel. Runs all ast-grep YAMLs in rules/ against a target file set, parses findings, groups by Owner agent per rules/index.json. Returns structured JSON findings ready for per-language agent adjudication. Use as Step 1 of /coding:pr-review's dispatcher refactor.
model sonnet
tools Read, Grep, Glob, Bash
color cyan

Purpose

Run every ast-grep YAML in rules/<lang>/*.yml against the target file set, produce structured findings grouped by the rule's Owner: agent. This is the mechanical layer of the doc-driven review pipeline — it gates the much smaller set of findings that LLM-tier per-language agents then adjudicate.

Source of truth: Reads rules/index.json (the deterministic walker output) for rule metadata: id, level, owner, enforcement path. Never reads individual ### RULE blocks — that's the dispatcher's job for judgment-tier rules.

Inputs

Param Source Notes
TARGET_DIR dispatcher arg The PR-review worktree path (e.g. /tmp/pr-review-<repo>-<branch>)
FILE_GLOBS dispatcher arg Optional file include globs, e.g. **/*.go. Default: respect each YAML's ignores.

Output Format

Emit one JSON object to stdout:

{
  "stats": {
    "yamls_run": 15,
    "findings_count": 12,
    "elapsed_ms": 1240
  },
  "findings_by_owner": {
    "go-error-assistant": [
      {
        "rule_id": "go-errors/no-fmt-errorf",
        "rule_level": "MUST",
        "file": "pkg/handler/user.go",
        "line": 47,
        "column": 5,
        "matched_text": "fmt.Errorf(\"fetch failed: %w\", err)",
        "message": "fmt.Errorf must not be used in production code..."
      }
    ],
    "go-time-assistant": [
      { "rule_id": "go-time/no-time-now-direct", ... }
    ]
  },
  "errors": []
}

If ast-grep itself fails on a YAML (syntax error, missing file), include the error in errors[] and continue with remaining YAMLs. Never silently drop findings.

Process

0. Preflight: verify ast-grep binary (fail-fast)

Always run this first, before any scan or inventory step. Without the binary, every subsequent ast-grep scan call returns empty tool_result, the LLM loops on the verification check, and the job hits activeDeadlineSeconds 30 min later with no review posted. Observed end-to-end on #34 (admin-merged after the loop).

if ! command -v ast-grep >/dev/null 2>&1 && ! command -v sg >/dev/null 2>&1; then
  cat <<'EOF' >&2
ERROR: ast-grep / sg binary not found in PATH.
This funnel cannot run without it.

Install (host):     npm install -g @ast-grep/cli
Install (alpine):   apk --no-cache add ast-grep
Install (debian):   curl -fsSL https://github.com/ast-grep/ast-grep/releases/latest/download/ast-grep-linux-x86_64.tar.gz | tar xz -C /usr/local/bin
Container fix:      ensure pr-reviewer image has ast-grep — see
                    bborbe/maintainer agent/pr-reviewer/Dockerfile (commit 1de083f
                    added 'ast-grep' to the alpine apk line).
Runbook:            [[Agent - Debug Missing PR Reviewer Review]] gate 5.
EOF
  printf '{"stats":{"yamls_run":0,"findings_count":0,"elapsed_ms":0},"findings_by_owner":{},"errors":[{"kind":"missing-tool","tool":"ast-grep","detail":"binary not in PATH"}]}\n'
  exit 1
fi

Why exit 1, not "continue with errors": the dispatcher's per-Owner adjudication phase reads from findings_by_owner only. A missing-tool error in errors[] would be invisible to the LLM tier — the review would post as APPROVED with no comments, masking that the mechanical layer never ran. Exit 1 surfaces the gap to the dispatcher (which aborts the review with an actionable error) instead of producing a silently-empty review.

1. Resolve rule inventory

cd $TARGET_DIR
# Build a map of rule_id → (yaml_path, owner, level) from rules/index.json
python3 -c "
import json, sys
idx = json.load(open('rules/index.json'))
for r in idx:
    enf = r.get('enforcement', '')
    if 'rules/' in enf and '.yml' in enf:
        # extract yaml path from enforcement field (may be wrapped in backticks)
        yml = enf.replace('\`', '').strip()
        print(f\"{r['id']}\t{yml}\t{r['owner']}\t{r['level']}\")
"

This yields the active mechanical-rule set. Rules with enforcement: judgment are skipped — the dispatcher's LLM-tier path handles them.

2. Run ast-grep per YAML

For each (rule_id, yml_path, owner, level):

cd $TARGET_DIR && ast-grep scan \
  --rule "$yml_path" \
  --json=stream \
  ${FILE_GLOBS:+--globs "$FILE_GLOBS"} \
  . 2>&1

Why per-YAML and not bulk: ast-grep's --rule rules/ bulk mode is faster but conflates errors — one broken YAML aborts the whole scan. Per-YAML keeps a single broken rule from masking the rest.

Parse the streaming JSON output ({"text": "...", "range": {...}, "file": "...", "metadata": {...}} per match).

3. Group findings by Owner

For each match emitted by ast-grep, look up the rule_id's owner from step 1 and append the finding to findings_by_owner[owner].

Use the rule's message from the YAML (ast-grep echoes it in the match output) as the human-readable description.

4. Emit JSON

Write the structured output to stdout. The dispatcher reads stdout, slices findings_by_owner[<agent>] for each agent dispatch.

Constraints

  • NEVER modify files — read-only scan.
  • NEVER call LLM tools — this agent's whole point is to be the cheap pre-filter. No Task dispatching from inside.
  • NEVER skip a YAML silently — every YAML in rules/<lang>/ MUST appear in either findings_by_owner (with 0+ findings) or errors[].
  • NEVER emit findings for a rule whose enforcement field doesn't point at a YAML — those are judgment-tier; not this agent's concern.

Self-Check Before Returning

  • stats.yamls_run matches wc -l < <inventory> (every active YAML was attempted)
  • Every owner in findings_by_owner exists as an agent file in agents/<owner>.md
  • No finding has a rule_id missing from rules/index.json (impossible if step 1 was followed; sanity check)
  • All findings have non-empty file, line, and matched_text

Failure Modes

Symptom Cause Handling
ast-grep binary missing toolchain gap (e.g. pr-reviewer image regression — see #34) preflight Step 0 catches this BEFORE any scan; emit the missing-tool JSON skeleton, exit 1, dispatcher surfaces actionable error rather than posting an empty review
YAML rejected by ast-grep rule syntax bug (PR #4 / #8 trap) append to errors[], continue
Rule ID not in index stale walker output append to errors[], continue
Owner from index missing in agents/ stale rule entry append to errors[] with kind: missing-owner-agent, drop finding

Smoke Test

Run against the current repo (no changes) to confirm zero findings:

cd $TARGET_DIR && ast-grep scan --rule rules/ . | jq length
# Expect: 0 (the rule-base repo's own code is clean against its own rules)

Run against a known-bad fixture (e.g. an old PR pre-rule):

cd /tmp/pr-review-<repo>-<old-branch>
# Should produce findings for the rules the PR was the first to violate

Verify the findings_by_owner groups match expectations — every finding should land under the agent whose name matches its rule's owner field.