codeconsole opened a new pull request, #3143:
URL: https://github.com/apache/groovy/pull/3143
Under `@CompileStatic`, a method reference whose method's return value must
be converted by Groovy to the functional interface's primitive return type
compiled, but failed at bootstrap:
```groovy
import java.util.function.Predicate
@groovy.transform.CompileStatic
class C {
static String str(String s) { s }
static void main(args) {
Predicate<String> p = C::str // LambdaConversionException: class
java.lang.String is not convertible to boolean
assert !p.test('') && p.test('x')
}
}
```
Dynamic Groovy, `@TypeChecked` and the method pointer `C.&str` apply Groovy
truth and give `[false, true]`. 4.0.33, 5.0.8 and 6.0.0 fail the same way. The
same failure affected the other primitive returns the type checker accepts but
`LambdaMetafactory` cannot convert, for example `ToDoubleFunction` from a
`BigDecimal` method and `ToIntFunction` from a `long` or `Long` method.
`LambdaMetafactory` converts a return value to a primitive type only by
unboxing and widening primitive conversion.
`StaticTypesMethodReferenceExpressionWriter` already routes some method
references through a synthetic static adapter to convert `GString` parameters.
That adapter is now also used when the return value needs a conversion the
metafactory does not perform. The adapter then returns the SAM's primitive
type, and its statically compiled `return` converts the value like a cast:
Groovy truth for `boolean`, Number conversion for the numeric types. Method
references whose return value the metafactory can convert still bind the method
directly.
## Tests
`MethodReferenceTest` adds three tests that fail without the change:
`testPrimitiveBooleanSAMFromNonBooleanReturnType` (dynamic, `@TypeChecked` and
`@CompileStatic`, with static, instance, bound, extension, constructor and
variadic references),
`testPrimitiveBooleanSAMFromNonBooleanReturnTypeSerializable` and
`testPrimitiveNumberSAMFromNonWideningReturnType`. The `groovy.transform.stc`,
`org.codehaus.groovy.classgen.asm.sc`, `bugs` and `groovy.bugs` tests and
`LambdasTest` pass. The Checkstyle and CodeNarc gates pass.
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