# Two-phase refactor — slice 13 (CLASS)

Branch `ast-stage-c`.  Suite **178/178**; self-hosting fixpoint **OK**
(**3,042,040 bytes**; slice 12 was 3,034,200).

## What landed

| Construct | AST |
| --- | --- |
| `CLASS T; … END T;` | `NkClassDecl(name, parents, fields, methods)`, `op = 0` |
| `CLASS IMPLEMENTATION T; … END T;` | `NkClassDecl(…, initBody, methodsWithBodies)`, `op = 1` |
| class field/const | `NkVarDecl` (`ty`) / `NkConstDecl` |
| method heading | `NkProcDecl`, `op = 0` normal / `3` virtual / `1` forward |
| method implementation | `NkProcDecl` with the body as child 1 |

Module-level accumulators (`astCls`, `astClsP/F/M` + tails, `astMethod`)
carry the class being parsed; classes are not nested inside one another,
so this is safe.  `ClassRest` and `ClassImplRest` attach
`child[1] = parents`, `child[2] = fields`/init body, `child[3] =
methods`, and set `astDecl` so `DeclSeq`/`TypeBlock` record the class.

## Two bugs found while verifying (both fixed here)

1. **`TypeBlock` never collected its items.**  It ran `TypeItem`/`ClassItem`
   in a loop but only the *last* one's `astDecl` survived to `DeclSeq` — a
   latent slice-6 bug (my earlier test had a single type).  `TypeBlock` now
   builds an `NkDeclSeq` like `ConstBlock`/`VarBlock`, so all `TYPE` and
   class declarations are recorded.
2. **`AST.SetChild` cannot skip an unset child.**  The implementation
   class set `child[2]`/`child[3]` while `child[1]` was unset, so the
   methods and init body were silently dropped; `child[1]` is now set to
   `NoNode` first.  Also reset `astStmt` before the optional class-`BEGIN`
   so a body-less implementation does not inherit the last method's body.

## Verified (temporary `AST.Dump`, then removed)

`tests/t_classmethod.mod` produced an `NkClassDecl` (op 0) with
`NkFieldDecl[x, y]` and methods `Set`/`Sum`/`CopyX`, plus the
implementation `NkClassDecl` (op 1) whose methods carry their bodies.

## Next

Step 2 (imports, `CLASS`, nested modules) is now complete.  Remaining:
the `Lower` walk + `.ssa` byte-compare, and the `MaxChild` cap on
`CASE` arms / `WITH` designators / call actuals.