# Session summary — 2026-09-30 (b): constructors, corpus gaps, String/variant/nested

Suite **169/169**; self-hosting fixpoint **OK** (image **2,754,353
bytes**). `master`, tree clean except the user's uncommitted
`compiler/toto.mod`.

This session closed the aggregate-constructor work and then knocked out
nine corpus-driven gaps.

## Steps, tags and headline commits

| Step | Tag | Commit | What |
| --- | --- | --- | --- |
| Constructor gaps | `v3-ctor-gaps` | `5a74f41` | set fields, string fold, index-type arrays, MIN/MAX |
| Gaps 1–5 | `v3-gaps-1-5` | `619bff9` | libc, enum/char sets, sized types, set builtins, forward types |
| This step | `v3-string-variant-nested` | `6882d63` | String, variant assignment, nested modules, ADDRESS↔pointer |
| Summary | `v3-string-variant-nested-summary` | (this commit) | session save |

(Showcase20, `v3-showcase20` / `b0494da`, opened the session.)

## 1. Constructor gaps (`v3-ctor-gaps`)

- **Set fields in record constructors** (`R{7, S{1,3,5}}`); the global
  `braceCls` dispatch flag is saved/restored around a nested set
  constructor.
- **Constant string concatenation in constructor elements** —
  `arraytype {Hello + " " + World}`: `CONST` string values,
  `QbeGen.StrFold` folds `+` on constants, and a string element expands
  into consecutive `CHAR` elements.
- **Index-type arrays** `ARRAY <ordinalType> OF T`; enum values usable
  as array indices.
- **`MIN`/`MAX`** over ordinal types, arrays and sets.

## 2. Gaps 1–5 (`v3-gaps-1-5`)

1. **`FROM libc` intrinsic** — `printf`/`exit`/… import as permissive
   external C procedures (varargs, no result); string/`CHAR`-array
   actuals pass as `descriptor+8` (`SymTab.DeclareCProc`/`Varargs`,
   `QbeGen.CArg`).
2. **`SET OF enum` and `SET OF <char-range>`** (+ enum/`BOOLEAN`
   subranges); set span limit 256 → 65536.
3. **`MIN`/`MAX` for REAL/LONGREAL/LONGINT** and gm2 sized names
   (`LONGCARD`, `SHORTREAL`, `INTEGER8/16/32/64`, `CARDINAL8/…`).
4. **`INCL`/`EXCL`** statements and **`SHIFT`/`ROTATE`** expressions
   (`QbeGen.SetClearBit`/`SetShift`, bit-by-bit over a runtime amount).
5. **Module-level forward type references** — a global may name a type
   declared further down; emission is deferred (`FlushPend`).

## 3. String / variant / nested / ADDRESS (`v3-string-variant-nested`)

- **Opaque/forward/undeclared aliases are pointer-like** — `ClassOf`
  returns `ClPtr` for an unresolved alias, so `Design`/`DeclVar`/
  `ResClass`/`AssOrCall` treat them as pointers.  This is what gm2's
  opaque **`String`** needs: `String` is *not* built-in, it is an
  opaque type imported from a definition module (`DynamicStrings`, or a
  local `opaque`); an undeclared type name is an error, as in gm2.
- **Variant-record assignment** — `CopyRecord` is a flat byte blit of
  `TypeSize(t)` (records are flat blobs; the only correct choice for
  overlapping variant fields); variant records are emitted as one
  zeroed blob.  Previously `q := r` compiled but corrupted data.
- **Nested local `MODULE`** — verified `EXPORT` lists, procedures,
  nested-nested modules and init bodies (already largely working).
- **`ADDRESS` ↔ pointer assignment** — the ADDRESS checks now precede
  the pointer-subclass test in `SymTab.Assignable` (`p := ADR(x)`).

## Corpus (with `$V3_LIBS`)

| milestone | testsuite | stdlib |
| --- | --- | --- |
| start of session | 283 | 115 |
| `v3-ctor-gaps` | 301 | 115 |
| `v3-gaps-1-5` | 376 | 124 |
| `v3-string-variant-nested` | **395** | **131** |
| after conformant `String` cleanup | **392** | **127** |

CRASH 0 throughout.  Remaining testsuite taxonomy: `undeclared
identifier` 65, `not supported yet` 34, `invalid call` 27,
`incompatible assignment` 12.

## Tests (169, was 159)

New: `t_ctor7` (set field + string fold), `t_minmax`, `t_minmax2`,
`t_libc`, `t_setops`, `t_fwdtype`, `t_variant2`, `t_string`,
`t_addrptr`, `t_nestedmod`.

## Resume

```sh
cd .../m2compiler-V3
./bootstrap/fixpoint.sh                       # FIXPOINT OK
cd compiler && ./build.sh && ./run_tests.sh   # 169/169
```

## Remaining (see `docs/analysis_gaps.md`)

`GOTO`/labels, result suffixes, generics, coroutines, multiple
inheritance (deliberate), full forward *variables*, and the gm2-only
library modules.