codeconsole opened a new pull request, #3142:
URL: https://github.com/apache/groovy/pull/3142
Static type checking rejects a closure or lambda whose return value needs a
widening primitive conversion to the SAM's primitive return type:
```groovy
import java.util.function.ToLongFunction
@groovy.transform.CompileStatic
class C {
static void main(args) {
ToLongFunction<String> f = (String s) -> s.length() // Cannot return
value of type int for lambda expecting long
assert f.applyAsLong('abc') == 3L
}
}
```
Java accepts this, and so do `C::len` and `C.&len`. 4.0.33, 5.0.8 and 6.0.0
reject it the same way. `StaticTypeCheckingVisitor.checkReturnType` compared
the wrapped types only, so `int` to `long`, `int`/`long`/`float` to `double`,
`char` to `int`, and `Integer` to `long` were all reported as incompatible.
`checkReturnType` now accepts a return value whose type, after unboxing,
widens to the primitive SAM return type under JLS 5.1.2. In that case the SAM
return type is recorded as the closure's return type, so static compilation
emits the conversion (`i2l`, `l2d`, ...). These are still rejected:
- narrowing, for example long to int and char to short;
- boxing into a different wrapper, for example int for `Supplier<Long>`
(GROOVY-11414).
## Tests
`CoercionSTCTest.testCoerceToFunctionalInterface22` covers lambdas and
closures, assigned, coerced with `as` and passed as method arguments;
`ToLongFunction`, `ToDoubleFunction`, `LongSupplier`, `DoubleUnaryOperator` and
`IntSupplier`; char/byte widening, unboxing then widening, an instance-property
capture and mixed returns; and rejection of long, double and Long returns for
an int SAM, and of char for a short SAM. It fails without the change both
type-checked and in `CoercionStaticCompileTests`. `groovy.transform.stc.*` and
`org.codehaus.groovy.classgen.asm.sc.*` pass. The Checkstyle and CodeNarc gates
pass.
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