[jira] [Closed] (GROOVY-12154) `@CompileStatic` lambda with a primitive-typed parameter targeting a generic functional interface fails at runtime with `LambdaConversionException`

["Paul King (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/GROOVY-12154?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Paul King closed GROOVY-12154.
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> `@CompileStatic` lambda with a primitive-typed parameter targeting a generic functional interface fails at runtime with `LambdaConversionException`
> ---------------------------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: GROOVY-12154
>                 URL: https://issues.apache.org/jira/browse/GROOVY-12154
>             Project: Groovy
>          Issue Type: Bug
>          Components: Static compilation
>    Affects Versions: 6.0.0-alpha-2
>            Reporter: Paul King
>            Assignee: Paul King
>            Priority: Major
>             Fix For: 5.0.8, 6.0.0-beta-1
>
>
> Under {{@CompileStatic}}, a lambda whose parameter is declared with a *primitive* type (e.g. {{int}}) and whose target is a *generic* functional interface (e.g. {{Function<Integer, Integer>}}) compiles without error but throws {{BootstrapMethodError}} / {{LambdaConversionException}} the first time it is invoked. The generated implementation method keeps the primitive parameter type, but the erased/instantiated SAM signature is {{Object}}, and {{LambdaMetafactory}} will not insert the boxing conversion.
> h2. Steps to Reproduce
> {code:groovy}
> import java.util.function.Function
> import groovy.transform.CompileStatic
> @CompileStatic
> class T {
>     Function<Integer, Integer> f = (int a) -> a * 2   // primitive param, generic SAM
>     Integer m() { f.apply(5) }
> }
> new T().m()   // <-- throws
> {code}
> h2. Expected
> Returns {{10}} — the same as the untyped and boxed equivalents (see workarounds). Or, if this form is genuinely unsupported, it should be a *compile-time* error, not a runtime crash.
> h2. Actual
> Compiles clean, then at first invocation:
> {noformat}
> java.lang.BootstrapMethodError: bootstrap method initialization exception
> Caused by: java.lang.invoke.LambdaConversionException:
>     Type mismatch for dynamic parameter 0: int is not a subtype of class java.lang.Object
> {noformat}
> h2. Workarounds
> Declare the parameter untyped or boxed — both return {{10}}:
> {code:groovy}
> Function<Integer, Integer> f = (a) -> a * 2          // untyped   -> OK
> Function<Integer, Integer> f = (Integer a) -> a * 2  // boxed     -> OK
> {code}
> h2. Notes / scope
> * Reproduces with a *single* primitive parameter (above) and with multiple ({{(int a, int b) -> a + b}} on {{BiFunction<Integer,Integer,Integer>}}).
> * *Independent of default parameter values* — {{(int a, int b) -> …}} fails with no default at all; {{(a, b = 10) -> …}} and {{(Integer a, Integer b = 10) -> …}} both work. (Surfaced while checking GEP-27's lambda-default question; defaults themselves are fine.)
> * *Independent of the {{groovy.target.lambda.hoist}} flag* — fails identically with it off and on.
> * The lambda must target a *generic* SAM (type parameter erases to {{Object}}). A non-generic primitive SAM (e.g. {{IntUnaryOperator}}) is unaffected.
> h2. Likely origin
> {{org.codehaus.groovy.classgen.asm.sc.AbstractFunctionalInterfaceWriter#convertParameterType}} (the GROOVY-9790 primitive/boxing reconciliation). For {{inferredType = int}} against {{parameterType = Integer}}, the {{else if (isPrimitiveType(inferredType))}} branch's condition is false, so it falls through to {{type = inferredType…}} ({{int}}) instead of boxing to {{Integer}} — producing an impl method the metafactory cannot link to the {{Object}}-erased SAM.



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