Paul King created GROOVY-12481:
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Summary: SC: `this::method` in a static context fails to compile
with "Failed to find method ... for the type: java.lang.Class<A>"
Key: GROOVY-12481
URL: https://issues.apache.org/jira/browse/GROOVY-12481
Project: Groovy
Issue Type: Improvement
Components: Static compilation
Affects Versions: 6.0.0, 5.1.2
Reporter: Paul King
h2. Description:
In a static context, `this` is the class itself (a `Class<A>` value). Under
{{@CompileStatic}}, a method reference with a {{this}} receiver in a static
method, static initializer or static script method looks for the method on
{{java.lang.Class}} only, not as a static method of the class. So {{this::foo}}
fails to compile, although {{A::foo}}, {{this.foo()}} and {{this.&foo}} all
work. With {{@TypeChecked}} or dynamic compilation, {{this::foo}} works.
{code:groovy}
import groovy.transform.CompileStatic
import java.util.function.Supplier
@CompileStatic
class A {
static foo() { 42 }
static m() {
Supplier s = this::foo
s.get()
}
}
assert A.m() == 42
{code}
{noformat}
Failed to find method 'foo()' for the type: java.lang.Class<A>
{noformat}
||Form, in a static method||{{@CompileStatic}}||{{@TypeChecked}}||dynamic||
|{{this::foo}} (static {{foo()}})|*compile error*|42|42|
|{{this::bar}} (static {{bar(int)}}, {{Function<Integer,Object>}})|*compile
error*|works|works|
|{{this::foo}} in a {{static \{ \}}} initializer|*compile error*|works|works|
|{{this::foo}} in a static method of a script|*compile error*|works|works|
|{{this::getSimpleName}} (method of {{java.lang.Class}})|"A"|"A"|"A"|
|{{A::foo}}|42|42|42|
|{{this.foo()}}|42|42|42|
|{{this.&foo}}|42|42|42|
|{{this::inst}} (instance method {{inst()}})|compile error (same wrong
message)|{{MissingMethodException}} at runtime|{{MissingMethodException}} at
runtime|
Expected: in a static context, {{this::name}} resolves the way {{this.name()}}
already does under {{@CompileStatic}}: first as a static method of the
enclosing class, otherwise as a method of {{java.lang.Class}}, so that
{{this::getSimpleName}} keeps working. When neither exists, the error should
name the enclosing class, not only {{Class<A>}}.
Cause:
{{StaticTypesMethodReferenceExpressionWriter.resolveMethodReferenceTarget}}
treats only a {{ClassExpression}} receiver as a type reference. For any other
receiver it takes the type from the type chooser, which for {{this}} in a
static context is {{Class<A>}}. So the lookup runs against {{java.lang.Class}}
and fails in {{validate}}. Because the error is raised during class generation,
the type checker has already accepted the code, which is why {{@TypeChecked}}
compiles it.
Workaround: use {{A::foo}} or {{this.&foo}}.
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