# Session summary — 2026-10-16 (b): two-phase thread complete, `Check` removed

Branch **`resolve-check`**, HEAD `a89a1c0`, tree clean.  Suite
**201/201**; fixpoint **OK (3,555,791 bytes)**.

Tags added this session: `v3-two-phase-m2a`, `m2b`, `m2c`,
`m2-summary`, `v3-two-phase-flip`, `v3-forward-machinery-deleted`,
`v3-two-phase-m2d-summary`, `v3-check-removed`.

## What this session did

1. **Landed milestone 2c** — real deferral + re-parse (behind
   `-twophase` then flipped on by default).  Two bugs found and fixed:
   the re-parse loop clobbered the unit's `astDecl`/`astStmt`, and
   `PopPos` restored `errors`, wiping every diagnostic from repassed
   bodies.  Details in `docs/summary_two-phase-m2-2026-10-16.md`.
2. **Pinned + fixed the spurious `ident expected`** (a `DeferSkip`
   snapshot leak: `PushPos` without `PopPos` on the success path, fixed
   with `scanner.DropPos`) and **flipped deferral on by default**
   (`-notwophase` restores the old inline parse).
3. **Deleted the forward-reference machinery** — the thread's original
   goal: `SymTab.FwdVarRef`/`FwdVarName`/`FwdVarResolve` (+ tables),
   `Check.NoteForward`/`FlushForward`, the `Design` forward branch, the
   dead `Check.SelType`/`LeafName`.  New semantics: a module-level body
   may call a procedure declared later (no `FORWARD`); a nested-local
   forward is a plain `201` instead of a broken image.  (Nested
   deferral was tried and reverted — it regressed nested-proc codegen.)
4. **Removed `Check` entirely** after proving it vestigial: gutting
   `Resolve` left the `.ssa` byte-identical across all 141 suite files
   and emitted no diagnostics.  Deleted `Check.def`/`Check.mod`, its
   driver calls, the `-noresolve` option, and the atg import; dropped
   `build.sh`'s `Check`.  Also removed the unused `procNest` and the
   always-true L7 flag `twoPhase`.

## Architecture now

```
per unit:
  Parse   -> AST + declarations (procedure bodies are skipped and
             re-parsed at unit end, so forward references bind normally)
  Lower   -> walk the AST, emit QBE (unchanged)
  Emit    -> buffered image, EndModule
```

No separate resolve/check pass: binding is late by construction.
`compiler/src` is `M2.atg` (grammar+scanner+parser+driver frames),
`FileIO`, `AST`, `SymTab`, `QbeGen`, `Lower`.

## Verification

- Suite **201/201** (`t_fwdproc -> 7`, `t_bad_nestfwd` `201`);
  `twophase_same` gate compares the default (deferral) against
  `-notwophase` for forward-free files; forward tests run to 42.
- **Fixpoint OK with deferral on** — the self-hosted compiler
  self-compiles byte-identically under the deferral.
- Corpus (612 gm2 testsuite files): **365 OK vs 358** with
  `-notwophase` — **+7 files, 0 regressions, 0 crashes**.
- `.ssa` byte-identical to pre-cleanup on spot-checks and the 141-file
  set.

## Next

1. **Generics: multi-formal instantiation link bug** (top — a real
   in-scope defect): `GENERIC … M(T,U)` + `X = M(INTEGER,CHAR)`
   compiles but fails to link (`undefined First_4`; the `.ssa` has the
   call but no body).  Repro in `docs/summary_generics-2026-10-15.md`.
2. Generics increment 3 (const/proc params, constraints), `GENERIC
   CLASS`, instance dedup.
3. stdlib gaps; robustness (`M2` exit codes, weak recovery); the
   latent size-sensitive V3 miscompile.

## Resume

```sh
cd .../m2compiler-V3
git checkout resolve-check          # HEAD a89a1c0
cd compiler && ./build.sh && ./run_tests.sh   # 201/201
cd .. && ./bootstrap/fixpoint.sh    # FIXPOINT OK
./M2 -notwophase tests/foo.mod       # legacy inline parse (debug)
```