Validate Pr Skill for Claude

validate-pr: Diff-Derived Test Plan

Generate and self-execute a validation plan matched to what actually changed

in a PR. Replaces generic "tests pass" with area-targeted evidence and

revert-test quality checks that prove tests catch regressions.

When To Use

• End of /fix-pr Step 5 (Validate), before Step 6 (Complete)
• Standalone after any PR fix, to generate targeted validation evidence
• When you need proof that revert-tests are genuine guards

When NOT To Use

• --scope minor with only formatting or doc changes (no logic changed)
• No diff available (clean branch, nothing changed)
• --skip-validate passed to /fix-pr

Algorithm

fetch diff -> group by area -> generate steps -> execute -> revert-test -> table

Step 1: Fetch Diff and Detect Areas

# Get changed file list from the PR
PR_NUMBER=<number from invocation or current branch>
CHANGED=$(gh pr diff "$PR_NUMBER" --name-only)
# Fallback when no PR number:
# CHANGED=$(git diff "origin/$(git rev-parse --abbrev-ref HEAD@{upstream})...HEAD" \
#   --name-only 2>/dev/null)

Group changed files into areas using ripgrep (grep if rg unavailable):

RUST_FILES=$(echo "$CHANGED"  | rg '\.rs$|Cargo\.(toml|lock)$' || true)
PY_FILES=$(echo "$CHANGED"    | rg '\.py$|pyproject\.toml$|requirements.*\.txt$' || true)
SH_FILES=$(echo "$CHANGED"    | rg '\.sh$|\.githooks' || true)
GRAMMAR_FILES=$(echo "$CHANGED" | rg '\.(lark|peg|g4)$' || true)

Area routing table:

| Area | File patterns | Verification type |

|------|---------------|-------------------|

| Rust | *.rs, Cargo.toml, Cargo.lock | cargo build + per-crate test |

| Python | *.py, pyproject.toml | pytest per changed module |

| Shell | *.sh, .githooks/* | shellcheck |

| Grammar | *.lark, *.peg, *.g4 | language-specific lint |

| Build/config | *.yaml, *.json, *.toml | parse check |

Step 2: Generate and Execute Steps per Area

For each non-empty area, generate and run at least one verification step.

Assign [E1], [E2], ... labels to each captured output.

Rust

# Build with default features
cargo build --workspace 2>&1
# Evidence: [En] → "0 errors, 0 warnings"

# Build with --all-features
cargo build --workspace --all-features 2>&1
# Evidence: [En+1]

# Per-crate test for each changed crate
# Extract crate directory from changed path, e.g. crates/token-types/src/lib.rs
CHANGED_CRATES=$(echo "$RUST_FILES" \
  | rg -o '(?:crates|src)/[^/]+' \
  | sort -u \
  | xargs -I{} basename {})
for CRATE in $CHANGED_CRATES; do
  cargo test -p "$CRATE" 2>&1
done

Python

# Targeted test per changed module
for PY_FILE in $PY_FILES; do
  MODULE=$(basename "${PY_FILE%.py}")
  TEST_FILE="tests/test_${MODULE}.py"
  if [[ -f "$TEST_FILE" ]]; then
    uv run pytest "$TEST_FILE" -v 2>&1
  fi
done

# Or project-specific runner if Makefile target exists
make test 2>&1 || uv run pytest tests/ -v 2>&1

Shell

for SH_FILE in $SH_FILES; do
  [[ -f "$SH_FILE" ]] && shellcheck "$SH_FILE" 2>&1
done

Build/config parse check

# YAML files
for YML in $(echo "$CHANGED" | rg '\.ya?ml$' || true); do
  [[ -f "$YML" ]] && python3 -c "import yaml; yaml.safe_load(open('$YML'))" \
    && echo "PASS: $YML" || echo "FAIL: $YML"
done

# JSON files
for JSON_F in $(echo "$CHANGED" | rg '\.json$' || true); do
  [[ -f "$JSON_F" ]] && python3 -m json.tool "$JSON_F" > /dev/null \
    && echo "PASS: $JSON_F" || echo "FAIL: $JSON_F"
done

Step 3: Revert-Test Quality Check

Prove at least one test is a genuine guard, not a dead assertion.

Safety: abort if the working tree has uncommitted changes.

if ! git diff --exit-code > /dev/null 2>&1; then
  echo "[RT] SKIP: working tree dirty: revert-test unsafe"
  # Mark INCONCLUSIVE and continue
fi

Algorithm (one representative fix):

• From the changed source files, find one that has a corresponding test.
• Rust: a #[test] in the same crate that exercises a changed function.
• Python: tests/test_<module>.py for a changed <module>.py.
• Shell: a test harness that invokes the changed script.
• Identify the specific changed line or block from the diff.
• Edit that line to revert the fix to its broken state.
• Run the targeted test: confirm it FAILS with exit code 1

specifically. A pytest usage error (4) or an empty collection (5)

is also non-zero, so a harness that only checks "not zero" reports a

dead assertion as a genuine guard.

• Restore: git checkout -- <file> (git-based restore, safe on interrupt).
• Run the targeted test again: confirm it PASSES.
• If any step cannot complete, mark INCONCLUSIVE with the reason.

Revert-test output format:

[RT-1] Target: <file>:<line>: <description of fix>
[RT-2] Broke fix: <edit description>
[RT-3] Ran: <test command> → <test name> FAILED (expected)
[RT-4] Restored: git checkout -- <file>
[RT-5] Ran: <test command> → <test name> PASSED
Result: PASS: test is a genuine guard

Reverting a test that guards document content:

Content tests assert on prose, and this repo wraps prose at 80 columns,

so any anchor phrase long enough to be meaningful eventually straddles a

line break. Collapse whitespace before matching. Otherwise a pure reflow

turns the test red and tempts an author to "fix" it by unwrapping the

line.

Normalizing reintroduces the hazard the revert test exists to catch: a

rejoined anchor can also appear elsewhere in the file, so deleting the

paragraph the test guards leaves it green. Anchor on a full clause that

is unique to that paragraph, then delete the paragraph and confirm the

test goes red. A DDD paradigm test passed its revert check this way in

PR #612 while guarding nothing.

When no covering test exists:

Revert-test: INCONCLUSIVE: no covering test for <changed area>
Recommendation: add a test for <changed function or behaviour>

Step 4: Final Full-Suite Run

After all area checks and the revert-test:

# Rust workspace
cargo test --workspace 2>&1

# Python project
uv run pytest tests/ -v 2>&1

# Mixed project: run both
cargo test --workspace 2>&1 && uv run pytest tests/ -v 2>&1

Capture full output as final evidence [En].

Step 5: Produce Summary Table

### validate-pr: <PR title or number>

| Area | Step | Evidence | Result |
|------|------|----------|--------|
| Rust: token-types | cargo build --workspace | [E1] 0 errors | PASS |
| Rust: token-types | cargo test -p token-types | [E2] 12 passed | PASS |
| Rust: token-types | cargo build --all-features | [E3] 0 errors | PASS |
| Shell: hooks/pre-commit | shellcheck | [E4] 0 issues | PASS |
| Revert-test: lib.rs:45 | break/fail/restore | [RT-1..5] genuine guard | PASS |
| Final: cargo test --workspace | full suite | [E5] 694 passed, 0 failed | PASS |

**Totals**: 6 steps: 6 PASS, 0 FAIL, 0 INCONCLUSIVE

Step 6: Posting (--post flag only)

When --post is given, post the summary table as a PR comment:

gh pr comment "$PR_NUMBER" --body "$(cat /tmp/validate-pr-summary.md)"

Skip posting when invoked from /fix-pr: results feed into the Gate 3

summary comment instead.

Failure Behaviour

When any step produces FAIL:

• Surface the failures in the summary table with the evidence reference.
• When called from /fix-pr: halt before Step 6 (Complete). The user must

fix the failures or pass --skip-validate to /fix-pr to bypass.

• When called standalone: report failures and exit with non-zero status.

INCONCLUSIVE results are reported but do not halt the workflow.

Exit Criteria

• [ ] gh pr diff --name-only returned a non-empty file list (diff fetched)
• [ ] Every detected area has at least one row in the summary table
• [ ] Every row shows an Evidence reference ([E1], [E2], etc.) with the

actual command output, not fabricated

• [ ] Revert-test attempted for at least one area with a covering test, or

documented as INCONCLUSIVE with reason

• [ ] Final full-suite run appears in the summary table
• [ ] Summary table is present with columns: Area, Step, Evidence, Result
• [ ] Any FAIL result halts /fix-pr before Step 6 when called from fix-pr
• [ ] Working tree is clean after skill completes (git checkout restore

confirmed successful for any revert-test mutation)