Various bugs

Whilst developing the latest Partition Manager build, I wasted a lot of time working around bugs/features in the OS. Although I didn’t have time to work out Repros or document them at the time, I’m listing the ones I can remember here:

BASIC bugs/quirks

• DIM var LOCAL size – can cause corruption if not preceded by an explicit LOCAL var

Repro

REM DIM var LOCAL size - can cause stack corruption
REM ======
REM Although this isn't a bug, its by design; I feel an array that is declared
REM LOCAL should be implicitly LOCAL, without the need for LOCAL var%

DIM var% 16
PRINT "var%=&";~var%
PROCtest
PRINT "var% now=&";~var%
END

DEF PROCtest
  REM LOCAL var%    <-- this should be implicit with DIM <var> LOCAL
  DIM var% LOCAL 16
ENDPROC

• DIM var LOCAL errors when used after certain other variable declarations

Repro

REM DIM var LOCAL error when used after certain other variable declarations
REM ======
REM This will report the following error when DIM var% is reached:
REM   Items can only be made local in a function or procedure at line 13
REM
REM The error is misleading at best and shouldn't really be an issue, as the
REM DIM order should not matter

PROCtest
END

DEF PROCtest
  LOCAL var%, array%()

  DIM array%(1)
  REM the next line will error
  DIM var% LOCAL 16
ENDPROC

• ON ERROR LOCAL can corrupt the error stack

REM ON ERROR LOCAL can corrupt the error stack
REM ======
REM Although not a bug, its by design; ON ERROR LOCAL should implicitly store
REM the previous error handler
REM
REM This example will get stuck in an infinite loop

ON ERROR PRINT REPORT$;" at line ";ERL:END
PROCtest
eek
END

DEF PROCtest
  REM LOCAL ERROR  <- this should be implicit by ON ERROR LOCAL
  ON ERROR LOCAL PRINT "LOCAL handler: ";REPORT$;" at line ";ERL:ENDPROC

  eek
ENDPROC

• Passing undimensioned arrays to functions does not return the array if it’s dimensioned inside the function

Repro

REM Passing undimensioned arrays as RETURN parameters
REM ======
REM This is probably by design.  Passing an undimensioned array reference does
REM not return the array if its DIM'd inside the function

PROCtest
END

DEF PROCtest
  LOCAL array%()

  PROCdim(array%())
  PRINT "Array size is now ";DIM(array%(),1)
ENDPROC

DEF PROCdim(a%())
  DIM a%(5)
  PRINT "Array size is currently ";DIM(a%(),1)
ENDPROC

• LOCAL variables can’t be created after LOCAL ERROR

Repro

REM LOCAL variables can't be created after LOCAL ERROR
REM ======

PROCtest
END

DEF PROCtest
  LOCAL ERROR
  LOCAL var%
ENDPROC

• ON ERROR LOCAL appears to corrupt variables and causes hard-locks if an error is trapped and the procedure/function exited. The only workaround appears to be to terminate the program

WIMP bugs

• Wimp_RedrawWindow and/or Wimp_UpdateWindow can return an error about parameters not being correct (possibly when the window has been closed?)
• Wimp_RedrawWindow and/or Wimp_GetRectangle can cause stack corruption
• Wimp_GetRectangle can return an error block instead of R0=0 when there is nothing to return. This behaviour is undocumented

If/when I find time, I’ll code up Repros.

BASIC bugs

Could you be more explicit, please? Perhaps some example code. Thanks.

If/when I find time, I’ll code up Repros.

That would be good.

The various LOCAL statements do interact, but not in ways I can recognise above.