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https://issues.apache.org/jira/browse/GROOVY-12587?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=18135448#comment-18135448
]
ASF GitHub Bot commented on GROOVY-12587:
-----------------------------------------
codeconsole opened a new pull request, #3112:
URL: https://github.com/apache/groovy/pull/3112
Inside a trait method, reading a static trait property through an explicit
`this` fails static type checking, while the unqualified reference and dynamic
Groovy work:
```groovy
@groovy.transform.CompileStatic
trait T {
static boolean flag = true
static boolean sm() { this.flag }
boolean im() { this.flag }
}
class C implements T {}
assert C.sm() && new C().im()
```
```
[Static type checking] - Cannot find matching method
java.lang.Class#T__flag$get() or static method T#T__flag$get().
[Static type checking] - Cannot find matching method
T$Trait$FieldHelper#T__flag$get().
```
`TraitReceiverTransformer` rewrote `this.<field>` with a placeholder
`FieldNode` that is always non-static, so the accessor was called on the field
helper (instance method; static accessors are on the static field helper) or on
the `Class` receiver (static method), without the `DO_DYNAMIC` marker that
static trait fields get. It now uses the trait's declared field, as the
unqualified reference does: a static property is accessed through the
implementing class, and the read is typed by the field's declared type. This
also covers compound assignments such as `this.count += 1`, and `this.x` inside
closures and lambdas.
## Tests
`TraitASTTransformationTest.testTraitStaticPropertyThroughThis` fails
without the change under `@TypeChecked` and `@CompileStatic`; it covers reads
and writes from static and instance methods, compound assignments, a
non-boolean property, per-implementer copies, and closure and lambda access.
The `org.codehaus.groovy.transform.traitx`, `groovy.transform.stc`,
`org.codehaus.groovy.classgen.asm.sc` and `gls` packages and
`groovy.ThisAndSuperTest` pass. The Checkstyle and CodeNarc gates pass.
Seen in 4.0.33, 5.0.8 and 6.0.0.
> STC rejects reading a static trait property through "this" inside a trait
> method
> --------------------------------------------------------------------------------
>
> Key: GROOVY-12587
> URL: https://issues.apache.org/jira/browse/GROOVY-12587
> Project: Groovy
> Issue Type: Bug
> Affects Versions: 4.0.33, 5.0.8, 6.0.0
> Reporter: Scott Murphy Heiberg
> Priority: Major
>
> {code:groovy}
> @groovy.transform.CompileStatic
> trait T {
> static boolean flag = true
> static boolean sm() { this.flag }
> boolean im() { this.flag }
> }
> class C implements T {}
> assert C.sm() && new C().im()
> {code}
> Actual, under both @CompileStatic and @TypeChecked:
> {noformat}
> [Static type checking] - Cannot find matching method
> java.lang.Class#T__flag$get() or static method T#T__flag$get(). Please check
> if the declared type is correct and if the method exists.
> [Static type checking] - Cannot find matching method
> T$Trait$FieldHelper#T__flag$get(). Please check if the declared type is
> correct and if the method exists.
> {noformat}
> The first error is for the static method, the second for the instance method.
> The same happens for a static trait property or field of any type, for
> compound assignments such as {{this.count += 1}}, and inside closures and
> lambdas.
> Expected: the script compiles and the assertion passes, as it does without
> the annotation and when the property is referenced without {{this.}}.
> Cause: the trait receiver transformer rewrites {{this.flag}} with a
> placeholder non-static field instead of the trait's declared field, so the
> accessor call targets the field helper (instance method) or the Class
> receiver (static method), without the dynamic-dispatch marker that static
> trait fields get.
> Seen in 4.0.33, 5.0.8, 6.0.0 and master.
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