M2compiler-V3/docs/wip/nested-array-field-bug.mod

MODULE NestedArrayFieldBug;
(* Repro: a RECORD field that is a nested ARRAY OF ARRAY OF CHAR, accessed
   as `arr[i].field[j][k]`, is miscompiled by V3 -> segfault (rc 139).
   Observed 2026-10-05.  Expected exit 42; observed 139.

   Found while adding Lower's procedure-formal name table (a module-level
   ARRAY OF RECORD with a `pname : ARRAY [0..31] OF ARRAY [0..63] OF
   CHAR` field): the V3-built compiler crashed (SIGABRT) on every input.
   Flattening the field to `ARRAY [0..2047] OF CHAR` fixed that crash.

   STATUS (2026-10-05):
     - The *stride* half is FIXED (commit v3-fix-arrayrec-stride):
       QbeGen.ArrBodyItems now uses SymTab.TypeSize for record/class/set
       array elements, so an ARRAY OF record has correct element size and
       flat field access works (see tests/t_recarr.mod, exit 42).
     - This nested case is FIXED: ArrBodyItems now expands array-of-record
       elements per element (EmitRec) when the record (recursively) has a
       nested-array field, and ArrData emits the matching per-element
       sub-descriptors (EmitRecStatics).  Plain record arrays (no nested
       array field) stay a compact zero blob, so AST.arena does not
       balloon.  Regression test: tests/t_nestarr.mod (exit 42).

   Compare with docs/wip/local-array-bug.mod (local arrays) and the
   Stage-A array-of-record stride fix (QbeGen.ElemSize). *)

VAR ExitCode : INTEGER;

CONST MaxName = 63; MaxProc = 4;

TYPE PE = RECORD
  name  : ARRAY [0..MaxName] OF CHAR;
  npar  : CARDINAL;
  pname : ARRAY [0..3] OF ARRAY [0..MaxName] OF CHAR;  (* nested *)
END;

VAR procs : ARRAY [0..MaxProc-1] OF PE;
    nProcs : CARDINAL;

PROCEDURE Reset;
BEGIN nProcs := 0 END Reset;

PROCEDURE NoteProc (name : ARRAY OF CHAR);
VAR i : CARDINAL;
BEGIN
  IF nProcs >= MaxProc THEN RETURN END;
  i := 0;
  WHILE (i < MaxName) AND (name[i] # CHR(0)) DO
    procs[nProcs].name[i] := name[i]; INC(i)
  END;
  procs[nProcs].name[i] := CHR(0);
  procs[nProcs].npar := 0; INC(nProcs)
END NoteProc;

PROCEDURE NoteParam (name : ARRAY OF CHAR);
VAR j, i : CARDINAL;
BEGIN
  IF nProcs = 0 THEN RETURN END;
  j := procs[nProcs-1].npar;
  i := 0;
  WHILE (i < MaxName) AND (name[i] # CHR(0)) DO
    procs[nProcs-1].pname[j][i] := name[i]; INC(i)
  END;
  procs[nProcs-1].pname[j][i] := CHR(0);
  procs[nProcs-1].npar := j + 1
END NoteParam;

BEGIN
  Reset; NoteProc("Add"); NoteParam("a");
  IF (nProcs = 1) AND (procs[0].pname[0][0] = "a")
  THEN ExitCode := 42 ELSE ExitCode := 1 END
END NestedArrayFieldBug.