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https://issues.apache.org/jira/browse/GROOVY-10979?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18134401#comment-18134401
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ASF GitHub Bot commented on GROOVY-10979:
-----------------------------------------
codeconsole opened a new pull request, #3089:
URL: https://github.com/apache/groovy/pull/3089
Under `@CompileStatic`, a closure passed for a parameter declared with a
type parameter was passed unconverted when the call binds the type parameter to
a functional interface. The type checker accepted the call, but the writer cast
the argument to the erasure of the parameter type, so the closure itself was
stored and a later call of the interface method failed:
```groovy
@CompileStatic
String f() {
List<Supplier<String>> list = []
list.add { 'x' }
list[0].get() // ClassCastException: _f_closure1 cannot be cast to
java.util.function.Supplier
}
```
The same held for `map.put('k') { ... }` on a `Map<String, Function<String,
String>>`, `set`, `putIfAbsent`, `AtomicReference.set`, a constructor argument
of a parameterized type, `list << { ... }`, the varargs of
`Collections.addAll`, and a variable or conditional expression of type
`Closure`. For `<T extends Function<String, String>> T second(T a, T b)` called
with a `Shout` (a subinterface of `Function`) and a closure, the closure became
a `Function` and the cast of the result to `Shout` failed. The type checker
also did not take the parameter for a functional interface: it inferred no
parameter types for the closure (`it.toUpperCase()` was rejected), compiled a
lambda for it as a closure, and rejected a method reference with "parameter
type 'E' is not a functional interface", which is GROOVY-10979.
The type checker now resolves such a parameter type for the call, as it does
the return type, from the receiver, the type arguments and the other arguments.
When the result is a functional interface, a closure, lambda or method
reference argument is checked against it and records it as its parameter type,
and so does an argument of type `Closure`, for an operator method such as
`leftShift` too. The static writer converts a closure argument for such a
parameter to the recorded interface before the cast to the parameter type.
## Tests
`ClosuresStaticCompileTest.testClosurePassedForATypeParameterIsConvertedToTheInterfaceTheCallBindsItTo`
and `MethodReferenceTest.testNotFunctionalInterface3`, which now runs the
GROOVY-10979 calls and checks the error for a type parameter the call leaves
unbound, fail without the change. 11,625 tests in the `groovy`, `gls`, `bugs`
and STC/SC packages pass, and the Checkstyle and CodeNarc gates pass.
Seen in 4.0.33, 5.0.8 and 6.0.0.
> Cannot provide method reference to a type parameter instantiated with a SAM
> type
> --------------------------------------------------------------------------------
>
> Key: GROOVY-10979
> URL: https://issues.apache.org/jira/browse/GROOVY-10979
> Project: Groovy
> Issue Type: Bug
> Components: Static Type Checker
> Reporter: Thodoris Sotiropoulos
> Priority: Minor
>
> I have the following program
> {code}
> import java.util.function.*;
> import java.util.stream.*;
> public class Test {
> public static void test() {
> Stream<Number> x = null;
> BiFunction<Function<String, Integer>, Number, Function<String,
> Integer>> y = null;
> BinaryOperator<Function<String, Integer>> z = null;
> x.<Function<String, Integer>>reduce(Test::m, y, z); // fails
> x.reduce(Test::m, y, z); // fails
> x.reduce((d) -> 1, y, z); // works
> }
> public static Integer m(String x) { return 1; }
> }
> {code}
> h3. Actual behavior
> {code}
> org.codehaus.groovy.control.MultipleCompilationErrorsException: startup
> failed:
> test.groovy: 12: The argument is a method reference, but the parameter type
> is not a functional interface
> @ line 12, column 43.
> ction<String, Integer>>reduce(Test::m, y
> ^
> test.groovy: 13: The argument is a method reference, but the parameter type
> is not a functional interface
> @ line 13, column 16.
> x.reduce(Test::m, y, z); // fails
> ^
> 2 errors
> {code}
> h3. Expected behavior
> Compile successfully
> Tested against master (commit: 55c6edfd81a64ce759357a3976070c0811bff637)
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