JSpecify: assume NONNULL in generic method inference for unconstrained type variables

[msridhar]

Fixes #1453

I think a change in 0.13.0 made it more important that we have some solution for all type variables of a method.

Summary by CodeRabbit

• Bug Fixes

  • Improved handling of generic methods so unconstrained type parameters are treated as non-null, enhancing nullability inference for generics.

• Tests

  • Added a new test validating helper usage and nullability inference in generic method scenarios.

[msridhar]

@agrieve is there any way you could test this fixes the issue for Chromium using a snapshot build?

[coderabbitai]

Walkthrough

The PR changes generic type-variable inference in GenericsChecks.java to copy the solver result into a mutable HashMap, then iterates the method's type parameters and inserts a NONNULL mapping for any unconstrained type variables (with comments explaining the choice). It also adds a new test issue1453 in GenericMethodTests.java that exercises an assumeNonNull helper in a foreach scenario to validate the updated inference behavior.

Possibly related PRs

• Add a case in our inference for generic method calls #1240: Modifies GenericsChecks.java to explicitly populate type-variable substitutions and add fallback handling for unconstrained variables.
• Record when generic method inference fails #1280: Alters generic inference and caching in GenericsChecks.java, including how solver results and inference outcomes are stored and applied.
• Invoke generic method inference in more places #1286: Changes inference collection and caching flow in GenericsChecks.java, overlapping with how solver results are recorded and used.

Suggested labels

jspecify

Suggested reviewers

• yuxincs
• lazaroclapp

🚥 Pre-merge checks | ✅ 5 | ❌ 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 (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: treating unconstrained type variables as NONNULL in generic method inference for JSpecify processing.
Linked Issues check	✅ Passed	The code changes address issue #1453 by modifying type inference to treat unconstrained generic method type variables as NONNULL, enabling helpers like assumeNonNull() to work without explicit @NonNull annotations.
Out of Scope Changes check	✅ Passed	All changes are scoped to addressing the regression: GenericsChecks.java modifications handle type variable inference, and GenericMethodTests.java adds a test case validating the fix.
Merge Conflict Detection	✅ Passed	✅ No merge conflicts detected when merging into master

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch issue-1453

---

No actionable comments were generated in the recent review. 🎉

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[coderabbitai]

Actionable comments posted: 1

🤖 Fix all issues with AI agents

In `@nullaway/src/test/java/com/uber/nullaway/jspecify/GenericMethodTests.java`:
- Around line 1536-1547: Remove the unused import of
org.jetbrains.annotations.Contract from the test source where the NullUtil class
and assumeNonNull method are defined; locate the import line in the
NullUtil.java test snippet and delete the Contract import so only the necessary
imports (org.jspecify.annotations.NullMarked and
org.jspecify.annotations.Nullable) remain.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.49%. Comparing base (bd25690) to head (84d5fa3).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1471      +/-   ##
============================================
+ Coverage     88.48%   88.49%   +0.01%     
- Complexity     2723     2725       +2     
============================================
  Files            99       99              
  Lines          9073     9076       +3     
  Branches       1812     1813       +1     
============================================
+ Hits           8028     8032       +4     
  Misses          518      518              
+ Partials        527      526       -1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.