Fix #6868: Move adding annotation constructor after setting classinfo

[noti0na1]

This PR should fix issue #6868. My another PR #6893 is also blocked by this issue.

When parsing an annotation class in ClassfileParser, if some of its paramter types are its inner classes, a CyclicReferenceInvolving is thrown.

Here is a small example:

MyScala.scala:

object MyScala {
  def a(mj: MyJava): Unit = {
    println("MyJava")
  }
}

MyJava.java:

public @interface MyJava {
    public MyClassType type();
    public @interface MyClassType { }
}

The output is:

> javac MyJava.java
> ./bin/dotc -explain MyScala.scala
exception caught when loading class MyClassType: CyclicReferenceInvolving(class MyClassType)
exception caught when loading class MyJava: CyclicReferenceInvolving(class MyClassType)
-- [E046] Cyclic Error: MyScala.scala:2:12 -------------------------------------
2 |  def a(mj: MyJava): Unit = {
  |            ^
  |            Cyclic reference involving class MyClassType

Explanation
===========
class MyClassType is declared as part of a cycle which makes it impossible for the
compiler to decide upon MyClassType's type.
To avoid this error, try giving MyClassType an explicit type.


one error found

The issue is when the parser tries to get the type of a paramter, a cyclic reference will be detected as the parent relationship information has not been set up.

By moving adding annotation constructor after the setting classInfo, the annotation class can be parsed correctly.

[dottybot]

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[smarter]

Thank you for working on this! However, we'll need tests before this can be merged. Just create a subdirectory inside https://github.com/lampepfl/dotty/tree/master/tests/pos-java-interop-separate and drop the java and scala files inside, make sure to call the java file something that ends with _1.java and the scala file something that ends with _2.scala to have the test infrastructure compile them separately and therefore use the ClassfileParser. To check if your test works, you can run it with testCompilation nameOfTheDirectory from sbt, see http://dotty.epfl.ch/docs/contributing/testing.html for more information.

[noti0na1]

@smarter Thanks for your reply! I have add the test files.

[smarter]

While your PR works, I'm not completely comfortable with it since it means the annotation class is in an inconsistent state (no constructor) between the call to setClassInfo and the call to addAnnotationConstructor, usually we avoid cyclic references by creating symbols where the info is a LazyType which will get computed on demand, I was able to apply this technique in this case after some refactoring/simplification of how we handle annotations and made a new PR (which reuses your test case): #6978. Therefore, I'm going to close this PR, but I'd like to thank you for your work on this !