Correct containment algorithm

[smillst]

Fixes #6890.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: fefd25da-eb8b-4b05-8853-bcacf5578a62

📥 Commits

Reviewing files that changed from the base of the PR and between 8c4ec97 and 14e7f2a.

📒 Files selected for processing (2)

• checker/tests/nullness/Issue6890.java
• framework/src/main/java/org/checkerframework/framework/type/DefaultTypeHierarchy.java

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📝 Walkthrough

Walkthrough

This pull request introduces a new nullness-checker test case (Issue6890) that exercises generic type invariance and nullness behavior when assigning a map with nullable-key types to a variable with non-nullable-key types. Concurrently, a modification to DefaultTypeHierarchy.java adjusts the isContainedWithinBounds method for non-covariant wildcard-bounds cases to use the current hierarchy top context for subtype comparisons, affecting how hierarchy-context is applied during containment logic evaluations.

🚥 Pre-merge checks | ✅ 2 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 25.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (2 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	The PR adds a test case and fixes the containment algorithm in DefaultTypeHierarchy to correctly detect invalid assignments with wildcards and nullable keys.
Out of Scope Changes check	✅ Passed	All changes are directly scoped to addressing issue #6890: a test case demonstrating the bug and the core fix to the containment algorithm.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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