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https://issues.apache.org/jira/browse/GROOVY-12154?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18095704#comment-18095704
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ASF GitHub Bot commented on GROOVY-12154:
-----------------------------------------
paulk-asert opened a new pull request, #2697:
URL: https://github.com/apache/groovy/pull/2697
… 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.
> `@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
> Priority: Major
>
> 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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