Fix TUnit0023 false positives for disposal through casts

[thomhurst]

Description

TUnit0023 incorrectly reports a disposable field or property when cleanup calls Dispose() or DisposeAsync() through a cast, including the explicit IDisposable implementation in #6804.

Recognize the disposal interface itself as well as types implementing it, and unwrap identity and reference conversions after resolving conditional access. Boxing and unboxing remain excluded because they dispose a copy; user-defined conversions remain excluded because they can return a different object.

Add 70 regression cases covering the reported reproduction, synchronous and asynchronous disposal, fields and properties, this, direct and conditional casts, as, nested casts, matching and mismatched cleanup levels, unrelated receivers, user-defined conversions, and boxing/unboxing of disposable structs.

Related Issue

Fixes #6804

Type of Change

• Bug fix (non-breaking change that fixes an issue)

Checklist

• I have read the contributing guidelines.
• My code follows the project's code style.
• I have written tests that prove the fix is effective.

Testing

• Before the fix: 12 cast regression cases failed with TUnit0023; all 47 existing cases and both negative controls passed.
• After the fix: all 117 cases in DisposableFieldPropertyAnalyzerTests passed on each of .NET 8, 9, and 10 (351 passed, 0 failed).
• All 20 boxing/unboxing regression cases failed before the review fix and pass afterward.
• Built analyzer variants for Roslyn 4.4, 4.7, and 4.14 successfully.
• git diff --check passed.

Command: dotnet test --project tests/TUnit.Analyzers.Tests/TUnit.Analyzers.Tests.csproj --treenode-filter "/*/*/DisposableFieldPropertyAnalyzerTests/*" --no-progress --output Detailed

Additional Notes

This change only affects analyzer behavior. It does not change source generator output, public APIs, runtime discovery, execution, or reflection paths.

Summary by CodeRabbit

Bug Fixes

• Improved disposal diagnostics for disposable struct fields and properties accessed through boxing or unboxing conversions.
• Preserved correct handling for reference, interface, nullable, concrete-type, and object-wrapped casts.
• Improved validation across synchronous and asynchronous cleanup patterns, including explicit interface implementations and conditional access.

Tests

• Added coverage for cast-based disposal scenarios, matching cleanup levels, and cases where members are not actually disposed.

[chatgpt-codex-connector]

Codex Review Summary

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Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-15T19:55:51.401847Z	e150db1	New commits

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Reviewing files that changed from the base of the PR and between 6b02598 and e150db1.

📒 Files selected for processing (2)

• src/TUnit.Analyzers/DisposableFieldPropertyAnalyzer.cs
• tests/TUnit.Analyzers.Tests/DisposableFieldPropertyAnalyzerTests.cs

🚧 Files skipped from review as they are similar to previous changes (1)

• src/TUnit.Analyzers/DisposableFieldPropertyAnalyzer.cs

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📝 Walkthrough

Walkthrough

The analyzer now stops conversion unwrapping at boxing conversions. This preserves TUnit0023 diagnostics for boxed disposable struct members while retaining accepted results for valid reference and interface casts. Tests cover synchronous and asynchronous cleanup paths.

Changes

Disposable cast detection

Layer / File(s)	Summary
Analyzer conversion resolution src/TUnit.Analyzers/DisposableFieldPropertyAnalyzer.cs	The analyzer unwraps only identity and reference conversions when resolving conditional-access instances. Boxing conversions remain wrapped.
Cast disposal validation tests/TUnit.Analyzers.Tests/DisposableFieldPropertyAnalyzerTests.cs	Tests cover boxed and unboxed disposable structs, explicit-interface disposal, valid casts, cleanup hook levels, and invalid disposal targets.

Priority: ⬇️ Low

Estimated code review effort: 2 (Simple) | ~15 minutes

Change: Bug fix · Severity of issue fixed: Low

Merge Risk: ⚪ Minimal · up to e150d

The cast-resolution change preserves diagnostics for boxed struct copies while allowing valid reference casts. No unresolved merge-blocking risk is identified.

🚥 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%. Docstring coverage is scoped to functions touched by this diff. Analyzed 10 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Issue #6804 requires no TUnit0023 warning when a disposable field is disposed through a cast to IDisposable, including explicit IDisposable implementations. The analyzer recognizes IDisposable on the …
Out of Scope Changes check	✅ Passed	The changes remain within cast-based disposal analysis. The analyzer change prevents boxing and unboxing conversions from being treated as disposal of the original member. The added tests verify valid…
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly identifies the primary change: correcting TUnit0023 diagnostics for disposal through casts. It matches the pull request objectives and changed analyzer tests.

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• Create PR with unit tests
• Commit unit tests in branch fix/6804-explicit-dispose

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Boxed structs keep their warning there
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[greptile-apps]

Greptile Summary

This PR corrects TUnit0023 disposal tracking when fields or properties are accessed through casts.

• Recognizes receivers typed directly as IDisposable or IAsyncDisposable.
• Resolves conditional-access receivers before unwrapping safe identity and reference conversions.
• Deliberately excludes boxing, unboxing, and user-defined conversions because they may dispose a copy or different object.
• Adds extensive synchronous, asynchronous, field, property, hook-level, and negative-control regression coverage.

Confidence Score: 5/5

The PR appears safe to merge with no outstanding correctness or security findings.

The analyzer now unwraps only conversions that preserve object identity, directly recognizes disposal interface receiver types, and includes focused negative controls for conversions that must not count as member cleanup.

Important Files Changed

Filename	Overview
src/TUnit.Analyzers/DisposableFieldPropertyAnalyzer.cs	Resolves cast and conditional-access disposal receivers while excluding conversions that can dispose a copy or another object.
tests/TUnit.Analyzers.Tests/DisposableFieldPropertyAnalyzerTests.cs	Adds broad regression coverage for valid cast-based cleanup and negative boxing, unboxing, unrelated-receiver, and hook-level cases.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[Dispose or DisposeAsync invocation] --> B{Conditional access receiver?}
    B -->|Yes| C[Resolve conditional access operation]
    B -->|No| D[Inspect receiver conversion]
    C --> D
    D --> E{Identity or reference conversion?}
    E -->|Yes| F[Unwrap conversion operand]
    F --> D
    E -->|No| G{Field or property reference?}
    G -->|Yes| H[Match member to cleanup scope]
    G -->|No| I[Do not count as member disposal]

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[chatgpt-codex-connector]

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Reviewed commit: 6b02598a36

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Inline comments:
In `@src/TUnit.Analyzers/DisposableFieldPropertyAnalyzer.cs`:
- Line 323: Update the conversion-unwrapping loop in the disposable
field/property analyzer to unwrap only identity and reference conversions,
excluding built-in boxing conversions even when OperatorMethod is null. Add a
regression test covering a disposable struct field cast to IDisposable that
expects a TUnit0023 diagnostic.

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📒 Files selected for processing (2)

• src/TUnit.Analyzers/DisposableFieldPropertyAnalyzer.cs
• tests/TUnit.Analyzers.Tests/DisposableFieldPropertyAnalyzerTests.cs

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