# Session summary — 2026-10-03 (two-phase frontend, slices 1–8)

Branch **`ast-stage-c`** (off `1c93f19`; not merged to `master`).
Suite **178/178**; self-hosting fixpoint **OK** (**3,021,285 bytes**).

The day turned the two-phase plan (`docs/plan-two-phase.md`) from a
document into a working, inert AST frontend: the parser now builds an
AST **alongside** the legacy emit path, for essentially every
declaration, statement and expression.  Nothing consumes the tree yet,
so the emitted `.ssa` is unchanged and the fixpoint stays byte-identical.

## Slices

| Tag | Doc | What |
| --- | --- | --- |
| `v3-ast-slice1` | `summary_two-phase-slice1.md` | link `AST` into the build; `twoPhase` flag; `AST.Init` per unit |
| `v3-ast-slice2` | `summary_two-phase-slice2.md` | expression spine + literals + parens + unary minus |
| `v3-ast-slice3` | `summary_two-phase-slice3.md` | `Design`: identifiers, `[i]`, `.f`, `^`, qualified names |
| `v3-ast-slice4` | `summary_two-phase-slice4.md` | calls/`NkCall` + actuals, `NOT`, builtins as named `NkCall`s |
| `v3-ast-slice5` | `summary_two-phase-slice5.md` | statements: block, assign, `IF`/`WHILE`/`REPEAT`/`LOOP`/`EXIT`/`FOR`/`RETURN`/`HALT`, calls |
| `v3-ast-slice6` | `summary_two-phase-slice6.md` | declarations: `NkDeclSeq`, `NkConstDecl`, `NkTypeDecl`, `NkVarDecl`, `NkProcDecl` |
| `v3-ast-slice7` | `summary_two-phase-slice7.md` | unit root `NkUnit(name, decls, body)`; builtin statements as `NkCall`s |
| `v3-ast-slice8` | `summary_two-phase-slice8.md` | `CASE` (`NkCase`/`NkCaseArm`/`NkSubrange`, ELSE arm) and `WITH` |

Also tagged `v3-ast-session-2026-10-03` (state after slices 1–5).

## Conventions established

- **Result slots** (module-level, saved into locals before the next
  operand): `astCur` (expressions), `astStmt` (statements), `astDecl`
  (declarations), `astUnit` (unit root).
- **`Fact` disambiguation**: a per-invocation `astIsLit` local prevents a
  nested `Fact` from making an outer non-literal `Fact` look literal.
- **Calls**: `ActParam` collects actuals into `astArgs`; the shared
  `AstCallNode` helper folds them into `NkCall`.
- **Declarations reference types by `ty` index** (`SymTab.TypeIndex`)
  rather than building structural type-constructor trees.
- **Incremental node building** for `IF`/`ELSIF`, `CASE`, `WITH`: the
  enclosing node is passed to child productions, so no local arrays
  (which are miscompiled) are needed and nested forms stay correct.
- Every slice was gated by `build.sh` + `run_tests.sh` + `fixpoint.sh`,
  with the tree shape checked by a temporary `AST.Dump` (removed before
  commit).

## Finding (pre-existing, not fixed)

**Local arrays inside a `PROCEDURE` are miscompiled** — module-level
arrays are fine.  Repro + detail: `docs/wip/local-array-bug.mod`
(observed 1, want 60).  It surfaced during self-hosting when `IfStat`
used a local `ARRAY`; the grammar now avoids local arrays.  Worth a
dedicated fix, same family as the Stage-A array-of-record stride bug.

## Remaining

- Expressions: **brace/set literals** (`NkBraceLit`/`NkSetLit`) and
  **`ResultComp`** call-result suffixes.
- Declarations: imports (`NkImport`), `CLASS`, nested modules in the
  unit AST.
- **`Lower` + `.ssa` byte-compare**, then delete the inline emit and the
  forward-patching machinery this whole refactor exists to remove.
- Standalone fix for the local-array bug.

## 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
```