constraints/markers: fix union of multi constraints and thereby union of atomic multi markers resulting in invalid marker strings

[radoering]

Resolves: python-poetry/poetry#10439

• Added tests for changed code.
• Updated documentation for changed code.

Summary by Sourcery

Fix union logic for multi constraints and atomic multi markers to properly return AnyConstraint/AnyMarker when there are no common elements and return a single constraint/marker when there is exactly one common element, accompanied by new tests to verify these behaviors.

Bug Fixes:

• Ensure MultiConstraint.union returns AnyConstraint when there are no shared constraints
• Ensure MultiConstraint.union returns a single Constraint when there is exactly one shared constraint
• Fix atomic marker union to return AnyMarker for disjoint sets and a SingleMarker for a single common element

Tests:

• Add tests for atomic marker union to verify is_any and single marker results
• Update generic constraint tests to expect AnyConstraint for unions with no common constraints

[sourcery-ai]

Reviewer's Guide

Union behavior for multi-constraints has been enhanced to return an AnyConstraint when there are no common elements and a single Constraint when there is exactly one common element, and corresponding tests for both constraint intersection and atomic marker union have been updated or added to reflect the new behavior.

Class diagram for updated MultiConstraint.union behavior

classDiagram
    class BaseConstraint
    class Constraint
    class AnyConstraint
    class MultiConstraint {
        +constraints: List[Constraint]
        +union(other: BaseConstraint) BaseConstraint
    }
    BaseConstraint <|-- Constraint
    BaseConstraint <|-- AnyConstraint
    BaseConstraint <|-- MultiConstraint

    MultiConstraint --> Constraint : contains

    %% Updated union method logic:
    %% - If other is MultiConstraint, find common constraints
    %%   - If no common: return AnyConstraint
    %%   - If one common: return that Constraint
    %%   - Else: return MultiConstraint of common constraints
    %% - If other is not Constraint: (not shown in this diff)

Loading

File-Level Changes

Change	Details	Files
Enhanced MultiConstraint.union to handle no or single common constraint	return AnyConstraint() when no common constraints return single Constraint instance when exactly one common preserve MultiConstraint for multiple common	src/poetry/core/constraints/generic/multi_constraint.py
Added tests for atomic marker union behavior	test_atomic_marker_union_is_any verifies disjoint multi markers yield Any test_atomic_marker_union_is_single verifies overlapping markers yield a SingleMarker	tests/version/test_markers.py
Adjusted generic constraint intersection tests for single and no-common cases	updated expected result to a simple Constraint when one common in intersection added case expecting AnyConstraint for no common in intersection	tests/constraints/generic/test_constraint.py

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[sourcery-ai]

Hey @radoering - I've reviewed your changes - here's some feedback:

• Please update the docstring of MultiConstraint.union to document that it can now return an AnyConstraint or a single Constraint when common constraints count is 0 or 1.
• Consider refactoring the common-length checks in union into early return guard clauses to simplify the control flow.

Prompt for AI Agents

Please address the comments from this code review:
## Overall Comments
- Please update the docstring of MultiConstraint.union to document that it can now return an AnyConstraint or a single Constraint when common constraints count is 0 or 1.
- Consider refactoring the common-length checks in union into early return guard clauses to simplify the control flow.

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