# Nested modules + full compiler source set compiles; self image links

Tag `v3-selfcompile-image`. Main suite 111/111.

## Landed

- **Nested modules (Wirth-style local `MODULE … EXPORT …`)** — the
  driver's `ListHandler` now lowers: declarations use the enclosing
  QBE module prefix, a `BEGIN` body becomes an init function that
  `main` calls, and the `EXPORT` list is hoisted into the enclosing
  scope via `SymTab.ExportUp` (called before `PopScope`). Test
  `t_nested` (exit 42) exercises export + init + exported var/proc use.
- **`HALT` builtin** (`QbeGen.HaltQ`, `HaltStat`): `call $exit(w 1)` +
  `hlt`.
- **`Strings.Delete` / `Strings.Append`** added (the driver needs
  them for file names). `Delete` is correct; `Append` works only while
  the descriptor count has not been shrunk (see string-model note).
- **1-char string literal to a `VAR ARRAY OF CHAR`** formal
  (`Strings.Append(".", …)`): synthesizes a 1-char descriptor and
  passes its address.

## Bugs found and fixed on the way

1. **Nested anonymous arrays clobbered the shared bound buffer.**
   `ARRAY [0..3] OF ARRAY [0..7] OF CHAR` emitted the *inner* count
   for the outer level (8 instead of 4): the inner `ArrayType` reset
   the shared `blo/bhi/nBounds` before the outer `NestArray` ran. Fixed
   by snapshotting the bounds (new `BoundCount/BoundLo/BoundHi`) after
   `]`, before parsing the element type, then nesting from the
   snapshot. This also fixed QbeGen's own `nestBufs` (was 65536
   entries).
2. **`sessBuf` too small / `FileIO.WriteString` misbehaves >~2 MB.**
   The compiler's own image text exceeds 1 MB. Enlarged `sessBuf` to
   4 MiB and flush exactly `sessUsed` bytes with a manual byte loop
   (host `FileIO.WriteString` segfaults on multi-MB buffers).
3. **`strNams`/`strTexts` capacity** — the compiler image has >256
   string literals; raised to 4096 (dropped literals previously left
   undefined `$str256` references).

## Milestone

The **entire compiler source set now compiles under V3** (generated
without `-m`, so `M2P` has real `FORWARD`s):

```
SymTab QbeGen M2S M2P M2 (driver)  →  gen_ssa/M2.ssa   (1.31 MB, complete image)
qbe  gen_ssa/M2.ssa                →  ok
cc   …shim.c -lm                   →  /tmp/M2self      (7.9 MB)
```

`M2.ssa` is self-contained (461 exported functions: all modules
inlined, as V3's model does for a program module).

## Next: self-compiled compiler crashes at startup

`/tmp/M2self tests/t_constfold.mod` → SIGSEGV in `SymTab.Init`:

```
Assign_189  <-  RawEnter  <-  Enter  <-  Predef  <-  Init  <-  SymTab_init
```

i.e. an early `ALLOCATE`/field-copy in symbol entry. Likely a V3
codegen/layout issue exposed by the compiler's own code (or the string
model). This plus the `Strings.Append` model are the next tasks, then
cross-stage `FileIO` + `bootstrap/fixpoint.sh`.

## Files

`compiler/src/{M2.atg,SymTab.def,SymTab.mod,QbeGen.def,QbeGen.mod}`,
`compiler/tests/t_nested.mod`, `compiler/run_tests.sh`,
`stdlib/strings.def`, `stdlib/strings.mod`.