🐛 Catch Python-equal numeric duplicate keys under OPT_DUPLICATE_KEYS_ERROR

[frenck]

Breaking change

None by default (last-wins is unchanged). With OPT_DUPLICATE_KEYS_ERROR set, a mapping that repeats a key under two Python-equal spellings (1 and 1.0, True and 1, 0 and False) now raises YAMLRocksDuplicateKeyError instead of silently keeping the last value, matching ruamel.

Proposed change

Keys distinct in YAML but equal as Python dict keys collapse to one entry once the mapping becomes a dict, so one silently overwrote the other even with the strict option set. Detection used a type-distinct signature (merge's key_sig), which kept 1 and 1.0 apart.

This adds a Python-equality signature that collapses a bool/int/bigint/integral-float to the same integer signature, used in both duplicate-key paths (the fast decoder and the round-trip composer). Numerically distinct keys (1 vs 2, 1 vs 1.5) and cross-type keys (1 vs "1") are still allowed. The now-unused key_sig import is dropped.

Type of change

• Dependency or tooling upgrade
• Bugfix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Deprecation (replaces or removes a feature, with a migration path)
• Breaking change (a fix or feature that changes existing behavior)
• Code quality, refactor, or test-only change
• Documentation only

Additional information

• This PR fixes or closes issue: None
• This PR is related to: None
• Link to a separate documentation pull request: None

Checklist

• I have read the AI Policy, and this pull request was not created by an autonomous agent.
• I fully understand the code in this pull request and can explain every line, including any AI-assisted changes.
• The change is covered by tests, and uv run pytest passes locally. A pull request cannot be merged unless CI is green.
• uv run ruff check . and uv run ruff format --check . pass.
• cargo fmt --check and cargo clippy --all-targets -- -D warnings pass.
• Round-trip fidelity is preserved: an unmodified document still re-emits byte-for-byte.
• No commented-out or dead code is left in the pull request.

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Review details

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Run ID: 152a07e2-35a0-4802-af1e-0e61aa27942f

📥 Commits

Reviewing files that changed from the base of the PR and between 19c5a83 and f33fc0c.

📒 Files selected for processing (3)

• src/decode/mod.rs
• src/roundtrip/composer.rs
• tests/features/test_options.py

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[codspeed-hq]

Merging this PR will not alter performance

✅ 16 untouched benchmarks

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_{Comparing frenck/dup-keys-python-equal (f33fc0c) with main (19c5a83)}

[codecov-commenter]

Codecov Report

❌ Patch coverage is 53.65854% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 92.29%. Comparing base (19c5a83) to head (f33fc0c).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/decode/mod.rs	46.87%	17 Missing ⚠️
src/roundtrip/composer.rs	77.77%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #182      +/-   ##
==========================================
- Coverage   92.42%   92.29%   -0.13%     
==========================================
  Files          40       40              
  Lines       11242    11278      +36     
==========================================
+ Hits        10390    10409      +19     
- Misses        852      869      +17     

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[Copilot]

Pull request overview

This PR fixes duplicate-key detection under the opt-in OPT_DUPLICATE_KEYS_ERROR (and OPT_DUPLICATE_KEYS_WARN) mode so that keys which are distinct in YAML but equal as Python dict keys (1/1.0/True, 0/False, integral floats vs ints) are now flagged instead of silently collapsing to the last value once the mapping becomes a dict. Previously detection used merge's type-distinct key_sig, which kept these apart. Default last-wins behavior is unchanged. The change is applied consistently across the fast decoder and the round-trip/annotated AST composer, matching ruamel's behavior.

Changes:

• Add a Python-equality key signature that collapses bool/int/bigint/integral-float to a shared n: signature in the fast decode path (python_dup_key_sig + float_dup_sig) and drop the now-unused key_sig import.
• Mirror the same numeric-collapsing logic in the round-trip/annotated AST composer's key_signature, preserving the s:<< merge-key exemption.
• Add tests covering Python-equal numeric duplicate keys (fast + annotated paths) and confirming numerically distinct keys remain allowed.

Reviewed changes

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

File	Description
src/decode/mod.rs	Adds python_dup_key_sig/float_dup_sig and switches check_duplicate_key to use it; removes the unused key_sig import (verified no remaining references).
src/roundtrip/composer.rs	Updates key_signature numeric branches to collapse bool/int/bigint/integral-float per Python dict semantics; doc comment updated accordingly.
tests/features/test_options.py	Adds parametrized tests for Python-equal numeric duplicate keys and for numerically distinct keys remaining allowed.

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