feat: support scalar qjson.decode roots

[membphis]

Summary

• Allow qjson.decode() to return top-level scalar JSON roots via the existing cursor decode path.
• Add Lua regression coverage for number, string, boolean, null, and invalid/empty decode inputs.

Fixes #120

Test Plan

• DYLD_LIBRARY_PATH=./target/release LUA_PATH='./lua/?.lua;;' LUA_CPATH='./vendor/lua-cjson/?.so;./target/release/lib?.dylib;./target/release/lib?.so;./?.so;;' /opt/homebrew/bin/luajit -e 'local qjson=require("qjson"); assert(qjson.decode("42") == 42); assert(qjson.decode("3.14") == 3.14); assert(qjson.decode("true") == true); assert(qjson.decode("false") == false); assert(qjson.decode("null") == qjson.null); assert(qjson.decode("\"hello\"") == "hello"); local ok = pcall(qjson.decode, ""); assert(not ok); print("focused-ok")'
• PATH=/Users/yuanshengwang/.luarocks/bin:$PATH make test
• make lint
• cargo test --release --no-default-features
• cargo test --features test-panic --release

Summary by CodeRabbit

• New Features

  • decode() now supports top-level JSON scalar values (numbers, strings, booleans, and null) in addition to objects and arrays.

• Tests

  • Added comprehensive tests for top-level scalar value decoding scenarios.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: 1660cf09-f7d1-45a6-953a-0f8465657a09

📥 Commits

Reviewing files that changed from the base of the PR and between f4a4f70 and 899014e.

📒 Files selected for processing (2)

• lua/qjson/table.lua
• tests/lua/lazy_table_spec.lua

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📝 Walkthrough

Walkthrough

The PR extends qjson.decode() to accept top-level JSON scalar values (numbers, strings, booleans, null) instead of raising an error. The implementation reuses the existing lazy cursor and view infrastructure to wrap scalar roots, while comprehensive test coverage validates the new decode behavior for all primitive types and error conditions.

Changes

Top-level scalar decode support

Layer / File(s)	Summary
Scalar decode implementation and tests lua/qjson/table.lua, tests/lua/lazy_table_spec.lua	_M.decode() now returns top-level scalar values via decode_cursor(view, root_box) instead of raising an error. Test suite validates correct decoding of numbers, strings (with escapes), booleans, and null, plus error behavior on invalid/empty input.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely summarizes the main change: enabling qjson.decode() to support scalar (non-object/array) JSON roots.
Linked Issues check	✅ Passed	The PR implements all core requirements from issue #120: modified qjson.decode() to accept top-level scalars (numbers, strings, booleans, null), preserve existing behavior for objects/arrays and errors, and added comprehensive test coverage.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to the stated objectives: one-line modification in lua/qjson/table.lua to handle scalar roots and new test cases in lazy_table_spec.lua for validation.
E2e Test Quality Review	✅ Passed	PR correctly implements scalar decode support and tests comprehensively cover all required types, edge cases, and error conditions with proper error handling.
Security Check	✅ Passed	Change reuses safe decode_cursor() for top-level scalars. No sensitive data exposure, logging, database, authorization, or crypto concerns. Library scope makes categories 2-7 inapplicable.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch codex/120-top-level-scalar-decode

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