Bug with invalid pointers

[John Perry]

There seems to be a bug in internalNameAt that manifests with this code:

MODULE TestPt;
TYPE
  PT = POINTER TO ARRAY 5 OF BOOLEAN;
VAR
  pt: PT;
BEGIN
  pt := NIL;
END TestPt.

The output I get is

$ java -cp $OBERON_BIN oberonc build TestPt.obn 
TestPt.obn:5:37: must point to record
Exception in thread "main" java.lang.NullPointerException
	at OJG.internalNameAt(OJG.Mod:139)
	at OJG.DescriptorR(OJG.Mod:171)
	at OJG.DescriptorAt(OJG.Mod:209)
	at OJG.Descriptor(OJG.Mod:214)
	at OJG.Header(OJG.Mod:2310)
	at OJP.Module(OJP.Mod:1378)
	at OJP.Compile(OJP.Mod:1410)
	at oberonc.Main(oberonc.Mod:40)
	at oberonc.main(oberonc.Mod)

It looks as if it's because type.base.typobj is NIL. If I change it as follows:

      IF type.base.typobj # NIL THEN
        i := Strings.Write(type.base.typobj.name, out, i)
      ELSE
        i := Strings.Write(type.typobj.name, out, i)
      END

...then the compiler doesn't crash. Though maybe it doesn't need the ELSE case anyway; could it be left blank?

[Luca Boasso]

Thanks for reporting this bug.
I have pushed a fix for this, together with another unrelated fix.
Like in other parts of the compiler, when we have a type error, we report it and set the type to a dummy INTEGER so that we resume in stable state.

[John Perry]

Thanks; I merged it to my fork.

Here's a related issue that might not actually be a bug. In the code below, A is never defined, but I can assign NIL to a pointer to A. My impression from reading 6.4 of The Programming Language Oberon is that A should be defined, but perhaps not?

MODULE TestPtr;

TYPE
  PT = POINTER TO A; (* A is undefined *)

VAR
  pt: PT;

BEGIN (* A is still undefined *)
  pt := NIL;
END TestPtr.

[Luca Boasso]

This is a bug, this example should not compile. I'll push a fix soon. Thanks for reporting this issue!

…

On Sun, May 5, 2019, 09:41 John Perry ***@***.***> wrote: Thanks; I merged it to my fork. Here's a related issue that might not actually be a bug. In the code below, A is never defined, but I can assign NIL to a pointer to A. My impression from reading 6.4 of *The Programming Language Oberon* is that A should be defined, but perhaps not? MODULE TestPtr; TYPE PT = POINTER TO A; (* A is undefined *) VAR pt: PT; BEGIN (* A is still undefined *) pt := NIL;END TestPtr. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#12 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAVJAW23KEC7HR4J6NTCYOTPT4E4PANCNFSM4HKZQ7YA> .

[Luca Boasso]

Please try out the new fix in master. Thanks!

[John Perry]

It works!