Fix bug with storing library model type variable upper bounds

[msridhar]

We can have multiple type variables with modeled upper bounds. Before we used a Map incorrectly, causing issues for types like BiConsumer. Now use a MultiMap.

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of multiple nullable upper bounds in external library models.
  • Fixed nullable upper-bound processing for JSpecify-mode analysis, including BiConsumer declarations.
  • Improved analysis accuracy for code using generic type parameters with multiple nullable constraints.

• Tests

  • Added regression coverage for nullable upper bounds under JSpecify nullness checking.
  • Added validation for JSpecify library models configured with strict null-marked analysis.

[msridhar]

This change is part of the following stack:

• Fix bug with storing library model type variable upper bounds #1687 ◀

_{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 1eb615d and d1d713a.

📒 Files selected for processing (1)

• nullaway/src/test/java/com/uber/nullaway/JSpecifyJDKModelsTest.java

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Walkthrough

Updated upper-bound caches to use SetMultimap<String, Integer>, allowing multiple nullable upper-bound indices per class. Updated cache initialization, accessors, and traversal. Added a JSpecify regression test for a nullable BiConsumer upper bound with OnlyNullMarked=true.

Possibly related PRs

• uber/NullAway#1345: Added related method-level nullable upper-bound library-model support.
• uber/NullAway#1370: Added related method-type-parameter nullable upper-bound support.
• uber/NullAway#1646: Modified the related JSpecify stubx model loading and caching code.

Suggested reviewers: yuxincs

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly and concisely describes the main change: correcting storage of library model type-variable upper bounds.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
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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• Commit unit tests in branch biconsumer-model

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@nullaway/src/main/java/com/uber/nullaway/handlers/LibraryModelsHandler.java`:
- Line 1748: Add Javadoc to
ExternalStubxLibraryModels.typeVariablesWithNullableUpperBounds(), documenting
that the cache maps class-name keys to indexes of type variables with nullable
upper bounds. Keep the documentation focused on the method’s conversion behavior
and its key/value meanings.

🪄 Autofix

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro Plus

Run ID: 7d66f625-c7a7-4c8c-b8b9-d35898940bdd

📥 Commits

Reviewing files that changed from the base of the PR and between 14ac5c1 and 1eb615d.

📒 Files selected for processing (3)

• nullaway/src/main/java/com/uber/nullaway/handlers/LibraryModelsHandler.java
• nullaway/src/main/java/com/uber/nullaway/handlers/StubxCacheUtil.java
• nullaway/src/test/java/com/uber/nullaway/JSpecifyJDKModelsTest.java

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.87%. Comparing base (b61752e) to head (c338eba).

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1687   +/-   ##
=========================================
  Coverage     87.87%   87.87%           
  Complexity     3167     3167           
=========================================
  Files           109      109           
  Lines         10742    10742           
  Branches       2172     2172           
=========================================
  Hits           9440     9440           
  Misses          617      617           
  Partials        685      685           

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