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https://issues.apache.org/jira/browse/GROOVY-12600?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18135574#comment-18135574
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ASF GitHub Bot commented on GROOVY-12600:
-----------------------------------------
codeconsole opened a new pull request, #3127:
URL: https://github.com/apache/groovy/pull/3127
A statically compiled static nested subclass that refers to a private field
of its outer (and super) class by bare name fails verification:
```groovy
class Base {
private String z = 'x'
@groovy.transform.CompileStatic
static class Sub extends Base {
def m() { z }
}
}
new Base.Sub().m() // java.lang.VerifyError: ... Type 'Base$Sub' ... is not
assignable to 'groovy/lang/Closure'
```
The same happens for writes, compound assignments and `z++`, in closures and
lambdas, in an anonymous class inside the subclass, and for a non-static inner
subclass of a static nested class. 5.0.8 and 6.0.0 fail the same way. `this.z`
and `super.z` already return the field.
The type checker resolves `z` as `this.z` and marks it as a nestmate private
field access. `VariableExpressionTransformer` then always rewrote such an
instance field to `DeclaringClass.this.@z`. The subclass has no enclosing
instance of the declaring class, so `AsmClassGenerator` took its closure branch
and called `Closure.getThisObject()` on a non-closure. The transformer now
walks the `this$0` chain from the current class. If it reaches the declaring
class, `DeclaringClass.this.@z` is kept unchanged, so a non-static inner
subclass still uses the enclosing instance's field, as dynamic Groovy and
`@TypeChecked` do. Otherwise it uses the innermost instance in that chain that
is a subclass of the declaring class: `this`, or `Sub.this` from an anonymous
class.
## Tests
`testPrivateFieldOfOuterClassInStaticNestedSubclass` and
`testPrivateFieldOfOuterClassInInnerSubclassOfStaticNestedClass` in
`FieldsAndPropertiesStaticCompileTest` fail without the change with the
VerifyError. `testPrivateFieldOfOuterClassInInnerSubclass` checks that an inner
subclass keeps using the enclosing instance. `groovy.transform.stc.*`,
`org.codehaus.groovy.classgen.asm.sc.*`, `bugs.*`, `groovy.bugs.*`, `gls.*`,
`groovy.ThisAndSuperTest` and `org.codehaus.groovy.transform.traitx.*` pass.
The Checkstyle and CodeNarc gates pass.
> SC: a private field of the outer class referenced by its bare name in a
> static nested subclass throws VerifyError ("not assignable to
> groovy/lang/Closure")
> -----------------------------------------------------------------------------------------------------------------------------------------------------------
>
> Key: GROOVY-12600
> URL: https://issues.apache.org/jira/browse/GROOVY-12600
> Project: Groovy
> Issue Type: Bug
> Affects Versions: 5.0.8, 6.0.0
> Reporter: Scott Murphy Heiberg
> Priority: Major
>
> {code:groovy}
> class Base {
> private String z = 'x'
> @groovy.transform.CompileStatic
> static class Sub extends Base {
> def m() { z }
> }
> }
> assert new Base.Sub().m() == 'x'
> {code}
> Actual: the class fails verification when loaded:
> {noformat}
> java.lang.VerifyError: Bad type on operand stack
> Location: Base$Sub.m()Ljava/lang/Object; @1: invokevirtual
> Reason: Type 'Base$Sub' (current frame, stack[0]) is not assignable to
> 'groovy/lang/Closure'
> {noformat}
> The same happens for assignment, compound assignment and increment of the
> bare name, inside closures and lambdas, in an anonymous class within the
> subclass, and for a non-static inner subclass of a static nested class.
> Expected: {{m()}} returns 'x', the field the subclass inherits, as {{this.z}}
> and {{super.z}} already do under static compilation.
> Cause: the type checker resolves the name to the inherited field as a
> nestmate private access, but the static compilation transformer always
> rewrites it to {{Base.this.@z}}. The subclass has no enclosing Base instance,
> so the class generator falls back to the closure path and emits
> {{Closure.getThisObject()}} on a non-closure.
> Seen in 5.0.8 and 6.0.0. 4.0.33 compiles it to a dynamic access that throws
> MissingPropertyException.
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