Created attachment 176747 [details]
Screenshots showing the results

There's definitely a problem here. I ran Andrew's code and got many issues, however a bit different than originally reported.

For instance, in "otherExampleCreateNewType" (the sub with PersonType objects), I got weird results in a piece of the code before the one with the comment. It seems the error started earlier. See in the attached file (Page 1) that the values being watched do not match the values being printed (Person(1) and Person(2) have the same values).

Now about the "otherExampleCreateAWTPoint" (the sub with Point objects), on Page 2 the values watched do make sense, but the ones printed are wrong (as pointed out by Andrew). However, note that there is a difference with how the watch behaved in each example.

Still on "otherExampleCreateAWTPoint" I got a different behavior than originally reported. I got the correct outputs in the last 2 prints, instead of a Correct and a Wrong one. Notice that the watched values are also correct (see Page 3).

System info:
Version: 7.2.3.2 / LibreOffice Community
Build ID: 20(Build:2)
CPU threads: 16; OS: Linux 5.13; UI render: default; VCL: kf5 (cairo+xcb)
Locale: pt-BR (pt_BR.UTF-8); UI: en-US
Ubuntu package version: 1:7.2.3~rc2-0ubuntu0.21.10.1~lo1
Calc: threaded

Andreas, maybe this bug would interest you.

I have added an attachment which shows 1 aspect of this bug in much simpler code.      
2 simple integer classes and a collector class.  
Both the simple integer classes look like this: 

private _a as integer 

private sub class_initialize() 
end sub 
private sub class_terminate() 
end sub 

And the collector like this: 

public _a() as object 'ClassA
public _c() as ClassC
private _upperBound as integer

private sub class_initialize() 
   _upperBound = -1
end sub 
private sub class_terminate() 
end sub 
public sub AddElements(byref elementA as ClassA, byref elementC as ClassC)
   _upperBound = _upperBound + 1
   redim preserve _a(0 to _upperBound)
   set _a(_upperBound) = elementA
   redim preserve _c(0 to _upperBound)
   set _c(_upperBound) = elementC
   msgbox(_a(0)._a) 
   msgbox(_c(0)._c)
end sub
 
And then a test to see what happens: 
public sub test() 
   dim n as integer 
   dim a as ClassA, b as ClassB, c as ClassC, d as ClassD

   set a = new ClassA 
   a._a = 10
   set c = new ClassC 
   c._c = 12
		
   set b = new ClassB
   b.AddElements(a,c)
end sub 

When in the above code _a() is defined as ClassA the message box will always show 0. 
When it is defined as object it will show the expected result 10.

Created attachment 177076 [details]
Simple code showing 1 aspect of bug

Mike: thought you might be interested in this one or at least have some opinion here.

(In reply to Julien Nabet from comment #5)

We have some utter mess with by-reference handling of array elements in general (and not only in array - but it needs case-by-case analysis). We already were hit several time in different forms (including some strange behavior with ReDim); but first of all, I would love to see (or develop) some formal specification where the ByRef semantics are needed - which array operations? Assignment of array to another variable - do they become pointers to the same array? or are different arrays with pointers to same elements? or different arrays with independent elements? Passing to ByVal function argument? ReDim? Here I suppose Andrew is the greatest expert who could at least suggest a list of cases to consider, with suggested expected semantics ... and then test all variations of element types -s strings, numbers, UNO and user types, VBA-specific like enums... and then see the matrix of problems - and then try to revise the implementation to fix that. Because now I feel that trying to fix this thing would not help, only resulting in regression because of not seeing the whole picture.

(Anyway, my opinion with this bug is that whenever the author of the bug is Andrew, we must just automatically confirm :D - there's no one more knowledgeable in this matter on this planet.)

Let's first look at issues related to arrays of UNO structures.

If the function PrintPoint is written like this:

Sub PrintPoint(s, Byval x)
  Print "Expect " & s & " Found (" & x.X & ", " & x.Y & ")"
End Sub

then everything is displayed correctly in function otherExampleCreateAWTPoint.


Another problematic macro on the same topic.

Sub TestAWTPoint
  Dim p(0) As New com.sun.star.awt.Point
  Dim h As New com.sun.star.awt.Point
  h.X=1
  p(0) = h
  Msgbox p(0).X   ' 0 : Wrong
  h=Nothing
  h=p(0)
  Msgbox h.X      ' 1 : Correct
End Sub

Maybe this code will be useful for making a diagnosis.