tests: fix false failures and stale skips in official imported suites (parse-errors/grep/jq)

[Haoxincode]

Summary

Three issues were discovered in our imported official test suites that cause false failures or misleading results. These are problems with test infrastructure/test assets themselves, not with MoonBit implementation correctness.

Reproduction Environment

All issues reproduce with the safe test runner parameters:

pnpm exec vitest run --no-cache --pool=forks --maxWorkers=1 --fileParallelism=false --silent <suite>

This matches the execution model of scripts/test-safe.sh (fork + single worker).

Issues

1. parse-errors.comparison — exit code fallback logic is incorrect

• File: tests/comparison/parse-errors.comparison.test.ts:27
• Problem: The original logic uses err.status || 1. Under the fork pool, execSync can throw an error object (e.g. code: "EPERM") that carries status: 0 with normal stdout. The || 1 coercion treats status: 0 as falsy, replacing it with 1, which corrupts the real bash baseline exit code.
• Impact: 11 cases that should pass (for, if, while, until, true, ||, blank commands, etc.) are falsely reported as failures.
• Fix: Change to typeof err.status === "number" ? err.status : 1.
• Verification: After fix, parse-errors.comparison.test.ts passes 24/24. Overall tests/comparison restores to 523/523 under safe parameters.

2. grep spec — stale skip entries cause UNEXPECTED PASS

• File: tests/spec/grep/skips.ts
• Problem: Multiple skipped cases actually pass now, causing the runner to report UNEXPECTED PASS errors. Typical categories:
  • "RE2 doesn't support backreferences" entries (multiple)
  • "RE2 treats grouped *** differently ..."
  • "BRE literal \{,2\} / \{,\} ... not implemented"
• Suggested fix: Remove stale skip entries. Separate remaining skips into "genuine implementation gaps" vs "historical compatibility policy differences" to avoid skip pollution of regression results.

3. jq spec — stale skip entries cause UNEXPECTED PASS

• File: tests/spec/jq/skips.ts
• Problem: Multiple skipped cases now pass, causing UNEXPECTED PASS. Typical entries:
  • Invalid \v escape sequence test
  • String interpolation with complex expression
  • Empty array/object pattern ...
  • Undefined variable $bar behavior differs
  • delpaths with large negative index
  • join error message
  • unique sort order differs
• Suggested fix: Review and remove stale skips. Add "expected removal condition" annotations to remaining skip entries for easier future cleanup.

Scope Clarification

These three items are test asset issues — problems with test infrastructure, baselines, or skip lists. They are distinct from implementation compatibility issues (grep/jq functional gaps), which should be tracked separately.

Checklist

• Fix parse-errors.comparison.test.ts exit code fallback
• Clean up tests/spec/grep/skips.ts stale entries
• Clean up tests/spec/jq/skips.ts stale entries
• Verify 523/523 comparison tests pass after fixes