# Session summary — 2026-10-04 (AST frontend complete; ready for `Lower`)

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

The two-phase frontend's **inert AST is now feature-complete**: the
parser builds a tree for every declaration (incl. `CLASS`, imports,
nested modules), every statement, and every expression, **alongside**
the legacy emit path (which is unchanged, so the fixpoint stays
byte-identical).  The tree is not consumed yet — `Lower` is the next
phase.

## This session's slices

| Tag | Doc | What |
| --- | --- | --- |
| `v3-ast-slice9` | `summary_two-phase-slice9.md` | brace/set literals (`NkBraceLit`/`NkSetLit`) |
| `v3-ast-slice10` | `summary_two-phase-slice10.md` | `ResultComp` suffixes; **unbounded `NkBlock`/`NkDeclSeq`** (`AstAppend`) |
| `v3-ast-slice11` | `summary_two-phase-slice11.md` | imports (`NkImport`) |
| `v3-ast-slice12` | `summary_two-phase-slice12.md` | nested modules (`NkUnit`) |
| `v3-ast-slice13` | `summary_two-phase-slice13.md` | `CLASS`/`CLASS IMPLEMENTATION`; `TypeBlock` collection fix |

(Slices 1–8 — expressions, designators, calls, statements, declarations,
unit root, builtins, `CASE`/`WITH` — landed 2026-10-03; see
`summary_two-phase-session-2026-10-03.md`.)

## Bugs found & fixed while verifying

- **8-child cap**: `NkBlock`/`NkDeclSeq` silently dropped statements past
  the 7th — now chunked/unbounded.
- **`NkImport` leaf mis-classification** made walks mis-read its child 0.
- **`TypeBlock` never collected its items** — only the last `TYPE`/`CLASS`
  declaration survived to `DeclSeq` (latent since slice 6).
- **`SetChild` cannot skip an unset child** — class-implementation
  methods/body were dropped; a body-less class impl also leaked the last
  method's body.

Each slice was gated by `build.sh` + `run_tests.sh` + `fixpoint.sh`, with
the tree shape checked by a **temporary `AST.Dump`** in the root
production (removed before commit).

## AST conventions (for the `Lower` phase)

- Result slots: `astCur` (expr), `astStmt` (stmt), `astDecl` (decl),
  `astUnit` (root); lists built with `AstAppend` (unbounded chunks).
- `NkDesignator(base, selector…)` — `NkSelector` op `SelField`/`SelIndex`/
  `SelDeref`; `NkCall(callee, actual…)`.
- Declaration nodes reference resolved types by the node's **`ty`**
  (`SymTab.TypeIndex`) rather than structural type trees.
- `NkUnit(name, decls, body, imports)`; `NkClassDecl(name, parents,
  fields, methods)`, methods `NkProcDecl` (`op`: normal/virtual/forward).
- **Do not use local arrays** in grammar actions until the local-array
  miscompile is fixed (`docs/wip/local-array-bug.mod`).

## Remaining before/within `Lower`

1. **`Lower` walk + `.ssa` byte-compare** (plan §3 phase 2): re-emit from
   the AST, compare to the legacy `.ssa`, then flip and delete the inline
   emit + forward-patching (`FwdPatchAll`/`FixLoadClass`/`FixStoreClass`,
   the `Design` forward path, the grammar's `FwdVar*`).
2. `MaxChild` cap still applies to `CASE` arms / `WITH` designators / call
   actuals — give them the chunked treatment.
3. Standalone fix for the **local-array miscompile**.

## Resume

```sh
cd ~/Projets/Projets-Modula2/MyWork/m2compiler-V3
git checkout ast-stage-c
cd compiler && ./build.sh && ./run_tests.sh   # 178/178
cd .. && ./bootstrap/fixpoint.sh              # FIXPOINT OK
```