# Inline record array fields (self-hosting layout fix)

Tag `v3-inline-array-fields`. Main suite 111/111; full compiler source
set still compiles under V3 and links.

## Why

V3 stored a record's array fields as **8-byte pointers to static
descriptors**, initialised only for static records. Heap records
(`ALLOCATE`/`NEW`) never initialised them, so `SymTab.RawEnter`'s
`Assign(node^.name, …)` dereferenced garbage → the self-compiled
compiler crashed at startup.

Standard Modula-2 (and gm2) store record array fields **inline**, so
V3 now does too.

## Changes

- **SymTab layout**: a fixed-array field occupies its full inline
  object (`ArrObjSize = 8 + count*elemBytes`), not 8. `TypeSizeD`'s
  record branch and `ComputeOffsets` use `FieldSize`; new
  `ArrObjSize`/`FieldSize`; `ElemBytes` moved earlier.
- **QbeGen data**: `ArrBodyItems` (inline descriptor contents:
  `l <n>, z <bytes>` or `l <n>, l $sub_i, …`) + `ArrData` (wraps it and
  emits nested `$name_i`). `RecItems` emits array fields inline;
  `RecStatics` only emits sub-descriptors for *nested* array fields.
- **Field access**: `Design`'s `.field` now passes the field *address*
  for array fields (was `ElemLoad` of the pointer).
- **CopyRecord**: array fields copied via `CopyArray(fieldAddr, …)`.
- **InitHeap**: a record's inline array field is initialised in place
  (header = count), no separate allocation.
- **SymTab**: `ALLOCATE(x, TSIZE(T))` → `NEW(x)` (typed allocation runs
  `InitHeap`). `FROM Storage IMPORT ALLOCATE` kept for gm2's `NEW`.

## Remaining blocker (the string model)

Running the self-compiled compiler still aborts, but now in a
reproducible, understood place: the compiler's string helpers scan an
argument for a trailing `NUL` (`SymTab.Assign`, `Equal`, `StrLen`, …),
while V3 strings are **count + bytes with no terminator** and trap when
indexed past the count. Minimal repro:

```modula2
PROCEDURE Copy (VAR d: ARRAY OF CHAR; s: ARRAY OF CHAR);
BEGIN ... WHILE (i < HIGH(d)) AND (s[i] # CHR(0)) DO ... END ... END Copy;
Copy(p^.n, "hi");   (* s[2] out of bounds -> abort *)
```

gm2 strings are NUL-terminated so the sources work there. Options:
1. **NUL-terminate V3 CHAR arrays** (reserve a terminator slot, allow
   reading index = count, emit `z (n+1)`, literals `… , b 0`). Keeps the
   sources unchanged; broad but mechanical.
2. Rewrite every NUL-scanning helper in the compiler sources to be
   length-based (must stay gm2-compatible) — larger.

Then: the rest of the bootstrap (cross-stage `FileIO`, `fixpoint.sh`).

## Files

`compiler/src/{M2.atg,SymTab.mod,QbeGen.mod,M2.lst}`.