Fix nullability for return and parameter wildcards

[msridhar]

See the new test cases. Use upper and lower bounds to reason about the nullability of accessed values of wildcard type.

Summary by CodeRabbit

• Improvements

  • Enhanced null-checking accuracy for Java generic types with improved wildcard support
  • Better nullness analysis for method parameters, return values, and type-variable bounds in generic declarations
  • Improved handling of complex wildcard scenarios

• Tests

  • Added test coverage for wildcard generic capture behavior across parameters, returns, and local variables

[codecov]

Codecov Report

❌ Patch coverage is 90.00000% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.45%. Comparing base (8f7c7e5) to head (c7a52fd).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...ava/com/uber/nullaway/generics/GenericsChecks.java	90.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1558      +/-   ##
============================================
- Coverage     88.45%   88.45%   -0.01%     
- Complexity     2869     2878       +9     
============================================
  Files           103      103              
  Lines          9587     9603      +16     
  Branches       1930     1935       +5     
============================================
+ Hits           8480     8494      +14     
  Misses          532      532              
- Partials        575      577       +2     

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[msridhar]

This issue was first observed by @wilkinsona in #1528 (comment)

[msridhar]

This change is part of the following stack:

• Initial inference for wildcards #1549
  • Fix wildcard inference bug with method references #1553
    • Fix nullability for return and parameter wildcards #1558 ◀
      • Enable test for issue 1500 and add comment #1560

_{Change managed by git-spice.}

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 8f7c7e5 and c7a52fd.

📒 Files selected for processing (2)

• nullaway/src/main/java/com/uber/nullaway/generics/GenericsChecks.java
• nullaway/src/test/java/com/uber/nullaway/jspecify/WildcardTests.java

---

Walkthrough

This PR updates GenericsChecks.java to enhance generic nullness computation by passing VisitorState to parameter and return nullness helper methods. The changes introduce support for computing nullness from wildcard generics, specifically handling the effective upper bounds in ? super ... cases and optionally following type-variable upper bounds. Four new test methods are added to WildcardTests.java to validate wildcard-capture behavior for parameters, return values, returns via type-variable upper bounds, and captured locals.

Possibly related PRs

• Add more instance fields to GenericsChecks #1256: Modifies the same getGenericMethodReturnTypeNullness and getGenericParameterNullnessAtInvocation code paths with updated method signatures and nullness-computation logic.
• JSpecify: improve inference for generic methods based on method reference arguments #1438: Updates generic nullness computation in GenericsChecks for parameter and return nullness helpers.
• Handle most remaining wildcard subtyping / containment cases #1548: Changes wildcard handling to use effective upper bounds and adjust super/extends capture logic with related wildcard tests.

Suggested labels

jspecify

Suggested reviewers

• lazaroclapp
• yuxincs

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 38.46% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and specifically summarizes the main change: fixing nullability handling for return and parameter wildcards, which is exactly what the changeset implements.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

📝 Generate docstrings

• Create stacked PR
• Commit on current branch

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch wildcard-inference-3

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