Restore support for parsing Variant::NIL and handling related cases in VariantParser

[Arctis-Fireblight]

Fixes #1275

• Implemented parsing logic for Variant::NIL and error handling for invalid constants.
• Added tests to validate Variant::NIL, null, and nil parsing, including regression cases.
• Improved security gating for object parsing with p_allow_objects.
• Enhanced str_to_var to support Variant::NIL.

Summary by CodeRabbit

• New Features
  • Added parsing support for Variant::NIL using Variant::NIL syntax.
  • Accepts alternative nil representations (null and nil) as valid inputs.
  • Ensures Variant::NIL parsing still succeeds even when object parsing is disabled.
• Bug Fixes
  • Improved parse errors for unknown variant constants and incomplete Variant::... expressions.
• Tests
  • Added coverage for successful Variant::NIL parsing and expected failure scenarios, plus a regression check via string-to-variant conversion.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: d6c7d9af-94ae-4293-8fa7-70316b23e4a2

📥 Commits

Reviewing files that changed from the base of the PR and between d98b24c and aadd319.

📒 Files selected for processing (2)

• core/variant/variant_parser.cpp
• tests/core/variant/test_variant.h

🚧 Files skipped from review as they are similar to previous changes (2)

• core/variant/variant_parser.cpp
• tests/core/variant/test_variant.h

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Walkthrough

VariantParser::parse_value gains a new branch that recognizes the identifier "Variant", then parses a :: token pair and an identifier constant, mapping "NIL" to Variant() and raising a parse error for any other constant. Tests are added covering success paths, error paths, the p_allow_objects security gate, and a str_to_var regression.

Changes

Variant::NIL parsing support

Layer / File(s)	Summary
Parser branch and test coverage core/variant/variant_parser.cpp, tests/core/variant/test_variant.h	Adds the "Variant" identifier branch in parse_value that expects :: followed by an identifier and maps "NIL" to Variant(), raising parse errors otherwise. Tests cover "Variant::NIL", "null", "nil" success paths; "Variant::INVALID" and bare "Variant" error paths; the p_allow_objects flag behaviour; and a VariantUtilityFunctions::str_to_var("Variant::NIL") regression.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The PR title accurately summarizes the main change: restoring support for parsing Variant::NIL in VariantParser, which aligns with the core code modifications and objectives.
Linked Issues check	✅ Passed	The PR addresses issue #1275 by restoring Variant::NIL parsing in VariantParser and str_to_var(), implementing error handling for invalid constants, and adding comprehensive test coverage to prevent regression.
Out of Scope Changes check	✅ Passed	All changes are scoped to restoring Variant::NIL parsing support and related test coverage; no unrelated modifications are present in the changeset.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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[VictorSohier]

It's moments like this that make me wish for or_return in C and C++

[Arctis-Fireblight]

That would be really nice ;-;