fix: mark decoded arrays with cjson array metatable

[jarvis9443]

Decoded JSON arrays now carry cjson.array_mt, matching cjson.decode_array_with_array_mt(true). This lets callers decode with simdjson and then encode with cjson without turning [] into {}.

This only changes simdjson decode output metadata. The simdjson encoder behavior is unchanged. The test workflow also moves from ubuntu-20.04 to ubuntu-latest because the old runner is no longer usable in this repo.

Tests run:

• make build
• PATH=/usr/local/openresty/nginx/sbin:$PATH prove -r t/02-decode.t t/09-empty_array.t
• make test

CI:

• Lua Check passed
• Tests (1.21.4.3) passed
• Tests (1.25.3.2) passed

[coderabbitai]

📝 Walkthrough

Walkthrough

Decoder applies cjson.array_mt to arrays constructed during SIMDJSON decoding. Tests were added/updated to assert arrays (including nested and empty) carry cjson.array_mt while objects do not; empty-array round-trip via cjson.encode is verified. CI workflow runner updated to ubuntu-latest.

Changes

cjson Array Metatable Alignment

Layer / File(s)	Summary
Decoder array metatable application lib/resty/simdjson/decoder.lua	Import cjson.array_mt and apply it to tables constructed in _build_array via setmetatable, so decoded arrays carry the same metatable as cjson arrays.
Array metatable verification tests t/02-decode.t, t/09-empty_array.t	Extended array tests assert cjson.array_mt on outer and nested arrays; object tests assert objects do not use the array metatable. New tests verify empty-array decoding and cjson.encode round-trip.

CI runner update

Layer / File(s)	Summary
GitHub Actions runner update .github/workflows/tests.yml	Change the tests job runner platform from ubuntu-20.04 to ubuntu-latest.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~20 minutes

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: marking decoded arrays with cjson's array metatable to ensure proper behavior when re-encoding with cjson.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
E2e Test Quality Review	✅ Passed	E2E tests verify arrays are marked with cjson.array_mt. Tests cover nested arrays, empty arrays, round-trip encoding in real OpenResty HTTP environment with proper assertions.
Security Check	✅ Passed	No security vulnerabilities across 7 categories. PR applies cjson.array_mt metatable to arrays—a standard Lua pattern with no credential exposure, auth issues, or data leakage.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch fix-array-mt-20260520123607

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[Copilot]

Pull request overview

This PR updates the decoder so JSON arrays decoded via resty.simdjson are tagged with cjson.array_mt, making them round-trip correctly through cjson.encode (so [] doesn’t become {}), consistent with cjson.decode_array_with_array_mt(true) behavior.

Changes:

• Set cjson.array_mt on all decoded arrays in the Lua decoder.
• Extend decode/empty-array tests to assert array metatables (including nested/empty arrays) and validate cjson.encode output.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
lib/resty/simdjson/decoder.lua	Marks decoded arrays with cjson.array_mt during table construction.
t/02-decode.t	Adds assertions that decoded arrays (including nested arrays) have cjson.array_mt; asserts objects do not.
t/09-empty_array.t	Adds a regression test that cjson.encode preserves decoded empty arrays as [].

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[github-actions]

Luacheck Report

1 tests   1 ✅  0s ⏱️
1 suites  0 💤
1 files    0 ❌

Results for commit aa3816e.

♻️ This comment has been updated with latest results.

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.