codeconsole opened a new pull request, #3146:
URL: https://github.com/apache/groovy/pull/3146
Static type checking rejected a closure or lambda that returns an int
constant for a byte, short or char SAM return type:
```groovy
interface S { short get() }
interface B { byte get() }
@groovy.transform.CompileStatic
void test() {
S s = () -> 1 // Cannot return value of type int for lambda
expecting short
B b = { -> 2 } // Cannot return value of type int for closure
expecting byte
assert s.get() == (short) 1 && b.get() == (byte) 2
}
```
Java accepts this. A lambda result expression is in an assignment context,
and JLS 5.2 allows narrowing an int constant that fits the target type there.
Groovy already accepts `short x = 1` and `short m() { 1 }`. 4.0.33, 5.0.8 and
6.0.0 reject it the same way.
`StaticTypeCheckingVisitor.checkReturnType` now accepts a return expression
that is an int `ConstantExpression` whose value fits the expected primitive
byte, short or char type. A constant that does not fit (`() -> 70000` for
short, `{ -> -1 }` for char) and a non-constant int are still rejected. Static
compilation already converts the value: a lambda body compiles to `iconst_1;
i2s; ireturn`, and a closure casts the value to the boxed return type.
This and #3142 (GROOVY-12616, widening) each add an `else if` after the
covariance branch of `checkReturnType` and a helper before `isClosureWithType`;
whichever lands second keeps both. No case matches both branches.
## Tests
`CoercionSTCTest.testCoerceNarrowingConstantReturnToFunctionalInterface`
fails without the change, under both `CoercionSTCTest` and
`CoercionStaticCompileTests`. It covers closures and lambdas for byte, short
and char, boundary and negative values, block lambdas with several returns,
method arguments, `as` coercion, static and instance contexts, and the cases
that must stay rejected. `groovy.transform.stc.*`,
`org.codehaus.groovy.classgen.asm.sc.*`, `gls.*` and `groovy.bugs.*` pass. The
Checkstyle and CodeNarc gates pass.
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