Redundant bridge methods in nested classes

[Liam Miller-Cushon]

I've been trying to get a better understanding of bridge methods, and
noticed that javac seems to emit different bridge methods depending on the
order of sources passed to the compilation.

As far as I can tell this occurs because TransTypes.translateClass calls
super.visitClassDef before addBridges. The super implementation of
visitClassDef processes all declarations (including nested classes), so
nested classes get translated before their enclosing classes. If a nested
class extends its enclosing class, the enclosing class' bridges won't have
been generated, so the nested class ends up with redundant bridge methods.

I don't think it's a correctness issue, but I found it surprising. Do you
think this is worth fixing?

Here's the repro:

A and B are symmetric: A's nested class extends B, B's nested class extends
A. Depending on the order of compilation a bridge method is generated in
A$Nested or B$Nested, but not both.

$ cat I.java
interface I<T> {
  void f(T t);
}
$ cat A.java
class A implements I<Number> {
  public void f(Number x) {}
  static class Nested extends B {
  }
}
$ cat B.java
class B implements I<Number> {
  public void f(Number x) {}
  static class Nested extends A {
  }
}

# pass A.java to javac first, A$Nested has a bridge method

$ rm -f *.class
$ javac I.java A.java B.java
$ javap -private 'A$Nested'
Compiled from "A.java"
class A$Nested extends B {
  A$Nested();
  public void f(java.lang.Object);
}
$ javap -private 'B$Nested'
Compiled from "B.java"
class B$Nested extends A {
  B$Nested();
}

# pass B.java to javac first, B$Nested has a bridge method

$ rm -f *.class
$ javac I.java B.java A.java
$ javap -private 'A$Nested'
Compiled from "A.java"
class A$Nested extends B {
  A$Nested();
}
$ javap -private 'B$Nested'
Compiled from "B.java"
class B$Nested extends A {
  B$Nested();
  public void f(java.lang.Object);
}
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mail.openjdk.java.net/pipermail/compiler-dev/attachments/20150729/fc741770/attachment.html>