GROOVY-12154: box primitive lambda param when the target SAM param is…

[paulk-asert]

… a reference type

A @CompileStatic lambda declaring a primitive parameter (e.g. (int a) -> ...) against a generic functional interface (e.g. Function<Integer,Integer>) compiled cleanly but threw at runtime:

java.lang.invoke.LambdaConversionException:
int is not a subtype of class java.lang.Object

AbstractFunctionalInterfaceWriter.convertParameterType always emitted a primitive implementation-method parameter when the lambda declared a primitive, ignoring the target (functional-interface) parameter type. But LambdaMetafactory links against the erased SAM signature (Object) and will not unbox to a primitive, so the implementation method must accept the boxed type when the SAM parameter is a reference type. It stays primitive only when the SAM parameter is itself primitive (e.g. IntUnaryOperator), preserving GROOVY-9790.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 69.1047%. Comparing base (c9363db) to head (e27f3d3).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@                Coverage Diff                 @@
##               master      #2697        +/-   ##
==================================================
- Coverage     69.1083%   69.1047%   -0.0036%     
- Complexity      34235      34236         +1     
==================================================
  Files            1537       1537                
  Lines          129310     129311         +1     
  Branches        23478      23479         +1     
==================================================
- Hits            89364      89360         -4     
- Misses          31936      31941         +5     
  Partials         8010       8010                

Files with missing lines	Coverage Δ
...sgen/asm/sc/AbstractFunctionalInterfaceWriter.java	94.1606% <100.0000%> (+1.5135%)	⬆️

... and 7 files with indirect coverage changes

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[testlens-app]

✅ All tests passed ✅

🏷️ Commit: e27f3d3
▶️ Tests: 103577 executed
⚪️ Checks: 31/31 completed

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[Copilot]

Pull request overview

Fixes a @CompileStatic lambda/SAM linkage issue where a lambda declaring a primitive parameter (e.g., int) could target a generic functional interface (erased to Object) and compile, but then fail at runtime with LambdaConversionException due to a primitive implementation-method parameter.

Changes:

• Update AbstractFunctionalInterfaceWriter.convertParameterType to emit a boxed implementation parameter when the target SAM parameter is a reference type, while preserving primitive parameters for primitive-SAM targets (retaining GROOVY-9790 behavior).
• Add a focused regression test suite covering primitive params targeting generic SAMs (single/multiple params, defaults, long) and ensuring primitive-SAM cases remain unaffected.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/main/java/org/codehaus/groovy/classgen/asm/sc/AbstractFunctionalInterfaceWriter.java	Adjusts lambda parameter type reconciliation so impl-method params are boxed when the SAM parameter is a reference type, preventing LambdaMetafactory linkage failures.
src/test/groovy/bugs/Groovy12154.groovy	Adds regression coverage for GROOVY-12154 and verifies GROOVY-9790 behavior is preserved.