perf: skip ImmutableMetadata allocation when builder has no entries

[tobias-ibounig-dt]

This PR

• ImmutableMetadata.build() returns EMPTY singleton when the builder's metadata map is empty
• ImmutableMetadata.asUnmodifiableMap() returns Collections.emptyMap() singleton when metadata is empty

Related Issues

None

Notes

ImmutableMetadata.builder().build() is the @Builder.Default for ProviderEvaluation.flagMetadata, so every flag evaluation without explicit metadata allocated a throwaway ImmutableMetadata backed by an empty HashMap. Returning EMPTY is safe — ImmutableMetadata has no mutation methods.

asUnmodifiableMap() now returns the JDK Collections.emptyMap() singleton for empty metadata, avoiding the UnmodifiableMap wrapper allocation.

Metric	Baseline	This PR	Delta
run:+totalAllocatedInstances	2,239,379	2,145,282	−94,097 (−4.2%)
run:+totalAllocatedBytes	106,304,128	102,105,728	−4,198,400 (−3.9%)

Follow-up Tasks

• More PRs with memory improvements
• Update benchmark.txt after all are applied

Summary by CodeRabbit

• Bug Fixes

  • Optimized empty metadata handling to improve performance and ensure consistent behavior across metadata operations.

• Tests

  • Enhanced test coverage for empty metadata scenarios, including validation of immutability guarantees.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro Plus

Run ID: 6b74093e-23bb-4991-978e-ef8eeec1ea7a

📥 Commits

Reviewing files that changed from the base of the PR and between cc837b1 and d8d3088.

📒 Files selected for processing (2)

• src/main/java/dev/openfeature/sdk/ImmutableMetadata.java
• src/test/java/dev/openfeature/sdk/ImmutableMetadataTest.java

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📝 Walkthrough

Walkthrough

ImmutableMetadata.asUnmodifiableMap() now returns Collections.emptyMap() for empty metadata, and ImmutableMetadataBuilder.build() short-circuits to the ImmutableMetadata.EMPTY singleton when the builder holds no entries. Two new tests verify singleton identity and that the empty map rejects mutation.

Changes

ImmutableMetadata empty-singleton optimization

Layer / File(s)	Summary
Empty singleton short-circuit src/main/java/dev/openfeature/sdk/ImmutableMetadata.java	build() returns the EMPTY singleton when the builder's metadata is empty; asUnmodifiableMap() returns Collections.emptyMap() instead of an unmodifiable view of an empty map.
Empty metadata test coverage src/test/java/dev/openfeature/sdk/ImmutableMetadataTest.java	Imports updated to use AssertJ and @DisplayName; new tests assert the empty builder returns the EMPTY singleton and that asUnmodifiableMap() on EMPTY yields an empty unmodifiable map that throws on put.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 28.57% 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 accurately summarizes the main optimization: skipping ImmutableMetadata allocation when the builder is empty, which is the core performance improvement.
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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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.11%. Comparing base (cc837b1) to head (d8d3088).

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1971      +/-   ##
============================================
+ Coverage     92.11%   93.11%   +0.99%     
- Complexity      660      664       +4     
============================================
  Files            59       59              
  Lines          1624     1626       +2     
  Branches        182      183       +1     
============================================
+ Hits           1496     1514      +18     
+ Misses           80       66      -14     
+ Partials         48       46       -2     

Flag	Coverage Δ
unittests	93.11% <100.00%> (+0.99%)	⬆️

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[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud