Type use annotations on instanceof patterns

[Werner Dietl]

Hi all,

Take the following program:

````
import java.lang.annotation.Target;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;

public class InstanceOfPatternVariable {
    public void doSomething(final Object x) {
        if (x instanceof @TA Float) {
        }
        if (x instanceof @TA Boolean b) {
        }
    }

    @Target(ElementType.TYPE_USE)
    @Retention(RetentionPolicy.RUNTIME)
    @interface TA {}
}
````

This successfully compiles with javac (anything >=16 should work, I used
javac 21.0.1).

I think there are two issues:

1) When looking at the bytecode with `javap -v
InstanceOfPatternVariable.class` I only see one use of @TA:

      RuntimeVisibleTypeAnnotations:
        0: #19(): INSTANCEOF, offset=1
          InstanceOfPatternVariable$TA

The JSL 15.20.2 [1] says "An instanceof expression may perform either type
comparison or pattern matching."
The JVMS 4.7.20-B [2] talks about how type annotations on "instanceof
expressions" are stored.
It would therefore seem to me that both occurrences of TA should be stored
in the class file.

2) When looking at the generated ASTs, for the first
InstanceOfTree, getType() returns `@TA Float`.
For the second InstanceOfTree, getType() only returns `Boolean`, without
the type annotation attached.
For the second InstanceOfTree, getPattern() seems to return a
BindingPatternTree that contains a VariableTree which has `@TA Boolean`
type.
It would seem more consistent if getType() for both trees returns an
annotated type.

Thoughts?

I did not find an existing bug report related to type annotations and
binding patterns. Did I miss one?

Thanks,
cu, WMD.

[1]
https://docs.oracle.com/javase/specs/jls/se21/html/jls-15.html#jls-15.20.2
[2]
https://docs.oracle.com/javase/specs/jvms/se21/html/jvms-4.html#jvms-4.7.20-410

-- 
https://ece.uwaterloo.ca/~wdietl/
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