RFR: 8368966: Remove spurious VMStructs friends

[Francesco Andreuzzi]

On Wed, 1 Oct 2025 07:34:00 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

> Was this done because you removed the one in the parent class?

Yeah that's the reasoning.

> the exposed _data field is inside GrowableArrayView, so maybe it would work to put the friend declaration there instead?

Actually I'm a bit confused. What you suggest _should not_ work, but it compiles happily. Friendship is not inherited, so we should not be able to access `GrowableArray::_data` if we move `friend class VMStructs` to `GrowableArrayView`.

I thought maybe that was a quirk of `offsetof`, but that does not seem to be the case:

#include <cstddef>

class X {
 protected:
  int field;
};

class Y : public X {};

class Z {
  friend X;

  void doStuff() {
    Y y;
    // both these are illegal
    // int foo = y.field;
    // int foo = offsetof(Y, field);
  }
};

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PR Review Comment: https://git.openjdk.org/jdk/pull/27583#discussion_r2394806258