rust-snapshot-review

name	rust-snapshot-review
description	Review and accept/reject insta snapshot changes after cargo nextest runs. Handles the stale .snap.new footgun, shows inline diffs, and does safe bulk or selective acceptance. Use whenever cargo nextest produces .snap.new files.

Rust Snapshot Review

Workflow for reviewing and accepting insta snapshot updates. Guards against the stale-snapshot footgun.

The Footgun

.snap.new files from a PREVIOUS failed run persist until cleaned up. If you accept them instead of the fresh ones, you silently accept stale output. Always check mtime.

Step 1 — Detect snapshots

find . -name "*.snap.new" -not -path "*/target/*" 2>/dev/null

If empty: nothing to do.

Step 2 — Validate freshness

Compare mtime of .snap.new files against the last nextest run:

# Proxy: nextest writes to target/nextest/ on each run
find . -name "*.snap.new" -not -path "*/target/*" \
  -newer target/nextest 2>/dev/null

If no .snap.new files are newer than the last test run: warn before proceeding.

⚠ Snapshot files may be stale (older than last test run).
  Consider deleting them and re-running tests:
    find . -name "*.snap.new" -not -path "*/target/*" -delete
    _DEVLOOP_OP_WRAPPED=1 cargo nextest run -p <crate> <test>

Step 3 — Review diffs

For each .snap.new:

SNAP="${FILE%.new}"
if [ -f "$SNAP" ]; then
    diff "$SNAP" "$FILE"
else
    echo "[NEW SNAPSHOT]"
    cat "$FILE"
fi

Summarize what changed:

• New snapshots: show full content
• Changed: show unified diff, highlight key differences
• If the diff looks like a version bump or timestamp: safe to accept
• If the diff looks like a behavioral change: flag for review

Step 4 — Accept

Bulk accept (after reviewing all):

for f in $(find . -name "*.snap.new" -not -path "*/target/*"); do
  mv "$f" "${f%.new}"
  echo "Accepted: $f"
done

Selective — accept one at a time, asking between each.

Reject — leave .snap.new files in place. The next test run will regenerate them.

Step 5 — Verify acceptance

Re-run only the tests that use these snapshots:

_DEVLOOP_OP_WRAPPED=1 cargo nextest run -p <crate> <test_filter>

Confirm no .snap.new files remain and all tests pass.

Devloop-specific known snapshots

Test	Location	Changes when
cli_snapshot_test__logs_output_format	crates/cli/tests/snapshots/	Session format changes
cli_snapshot_test__bench_output	crates/cli/tests/snapshots/	Bench output format changes
cli_snapshot_test__help_text	crates/cli/tests/snapshots/	CLI help text changes (new commands)

Note: Tests in .worktrees/ paths always fail — do NOT add to nextest exclusions. Run them from the main checkout only.

Quick reference

# Find pending
find . -name "*.snap.new" -not -path "*/target/*"

# Accept all
for f in $(find . -name "*.snap.new" -not -path "*/target/*"); do mv "$f" "${f%.new}"; done

# Delete stale (nuclear option)
find . -name "*.snap.new" -not -path "*/target/*" -delete