fix endless recursion introduced in #821

[radoering]

Related to python-poetry/poetry#9956 (comment)

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

Previously, we have always tried to avoid recursions, which is difficult if you do not want to miss any simplifications. Although, #821 provides significant performance improvements for certain cases, it also introduces the risk of endless recursions due to the symmetry of intersection and union. It might still be possible to avoid this recursion with a more sophisticated fix. However, I decided to detect a recursion early instead of avoiding it.

Summary by Sourcery

Bug Fixes:

• Fix an endless recursion issue in marker intersection and union operations introduced in perf: return least complex marker when building intersection #821.

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request addresses an endless recursion issue introduced in #821. The fix involves adding a decorator to detect recursion in the intersection and union functions, and handling the RecursionError by returning a less complex marker.

Sequence diagram for marker intersection with recursion detection

sequenceDiagram
    participant Client
    participant intersection
    participant detect_recursion
    participant cnf

    Client->>intersection: intersection(*markers)
    activate intersection
    intersection->>detect_recursion: Check recursion
    activate detect_recursion
    alt No recursion detected
        detect_recursion-->>intersection: Continue
        intersection->>cnf: Convert to CNF
        alt CNF successful
            cnf-->>intersection: Return conjunction
            intersection->>intersection: Select min complexity
        else RecursionError
            cnf-->>intersection: Throw RecursionError
            intersection->>intersection: Use limited candidates
        end
    else Recursion detected
        detect_recursion-->>intersection: Throw RecursionError
    end
    intersection-->>Client: Return marker
    deactivate intersection
    deactivate detect_recursion

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Class diagram for marker system with recursion detection

classDiagram
    class BaseMarker {
        +complexity
    }
    class MarkerUnion {
        +markers
    }
    class MultiMarker {
        +markers
    }
    class detect_recursion {
        +call_args: dict
        +decorated(*markers): BaseMarker
    }

    BaseMarker <|-- MarkerUnion
    BaseMarker <|-- MultiMarker

    note for detect_recursion "Decorator to detect recursions
in intersection and union"

    detect_recursion ..> BaseMarker: decorates

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Flow diagram for marker processing with recursion handling

flowchart TD
    A[Start] --> B{Check recursion}
    B -->|No recursion| C[Process markers]
    B -->|Recursion detected| D[Throw RecursionError]
    C --> E{Try normalization}
    E -->|Success| F[Select min complexity]
    E -->|RecursionError| G[Use limited candidates]
    F --> H[Return result]
    G --> H
    D --> I[Handle in caller]
    I --> J[Use unnormalized form]
    J --> H

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File-Level Changes

Change	Details	Files
Added a decorator to detect recursion in intersection and union functions.	Introduced a detect_recursion decorator that uses a thread-local list to track function call arguments. If the same arguments are encountered again, a RecursionError is raised. The intersection and union functions are decorated with detect_recursion.	src/poetry/core/version/markers.py
Modified intersection and union functions to handle RecursionError.	The intersection and union functions now catch RecursionError. If a RecursionError is caught, a less complex marker is returned as a fallback.	src/poetry/core/version/markers.py
Added a test case to verify that the fix prevents endless recursion.	Added a test case test_intersection_no_endless_recursion that uses a complex marker to trigger the recursion. The test asserts that the intersection of the markers does not result in an endless recursion.	tests/version/test_markers.py

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[sourcery-ai]

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

Overall Comments:

• Please update the documentation to mention the recursion detection behavior in intersection/union operations, as indicated in the PR checklist.

Here's what I looked at during the review

• 🟡 General issues: 1 issue found
• 🟡 Security: 1 issue found
• 🟡 Testing: 1 issue found
• 🟢 Complexity: all looks good
• 🟢 Documentation: all looks good

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[sourcery-ai]

issue (bug_risk): Call stack cleanup should be guaranteed even if an exception occurs

Wrap the function call in a try-finally block to ensure call_args.pop() is always executed, even when exceptions occur.