GeezerVison

Union construction and operators now use a shared builder to normalize and deduplicate members. Set helpers and dictionary hash-error contextualization support this path. Union equality and hashing use member partitions recorded at creation.

Changes: Union behavior

Layer / File(s)	Summary
Set and hash support crates/vm/src/builtins/dict.rs, crates/vm/src/builtins/set.rs	Dictionary hash failures can be contextualized with key and container details. Set operations expose helpers for known-hash membership and insertion, and freezing copies stored entries without rehashing or comparing keys.
Union construction and normalization crates/vm/src/builtins/union.rs	UnionBuilder normalizes None, flattens nested unions, and deduplicates hashable and unhashable members. Union operators, class subscription, construction, and generic substitution use the builder.
Union equality and hashing crates/vm/src/builtins/union.rs	Equality compares creation-time hashable and unhashable partitions. Hashing uses the stored hashable frozenset and reports the count of creation-time unhashable members.

Estimated code review effort: 4 (Complex) | ~45 minutes

Change: Bug fix

Sequence Diagram(s)

sequenceDiagram
  participant PyUnion.__or__
  participant UnionBuilder
  participant PySet
  PyUnion.__or__->>UnionBuilder: Add operands with type checking
  UnionBuilder->>PySet: Deduplicate hashable members using set semantics
  UnionBuilder-->>PyUnion.__or__: Return normalized union or lone member

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Possibly related PRs

• RustPython/RustPython#9343: Changes set table ownership and clearing, which connects to the set-table copy in into_frozen.
• RustPython/RustPython#9451: Revalidates dictionary insertion slots used by the insertion path behind insert_known_hash.
• RustPython/RustPython#9700: Changes dictionary unhashable-key message construction in the hash-error path.

Suggested reviewers: youknowone, shaharnaveh, jorge-polanco-roque

Merge Risk: Minimal · up to 4ee5c

No actionable merge-blocking issue is established by the supplied evidence. Merge after normal checks; native execution and the non-threaded build remain unverified.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentat…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly describes the main changes: shared Union construction and callback/error control behavior. It is concise and specific.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 13 functions across 3 files.

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

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