# V3 step 4.3 — separate compilation (done 2026-09-22)

Single-image session model (V1/V2 lineage): one compiler run takes
`lib.def lib.mod prog.mod ...` and produces one `<Prog>.ssa` image
with the definitions, implementations and the program linked
together. Suite 87/87 (44 run — incl. 4 trap-aborts + 4 sessions —
+ 43 reject). LL(1)-clean, zero gm2 warnings.

## Session model

- **Driver** (`compiler.frm`): collects all `NextParameter` files,
  calls `SymTab.Init` and `QbeGen.OpenModule` once, then parses each
  file into the shared table. The program module is last; a session
  without one is `Incorrect source` (nothing to link).
- **DEFINITION MODULE** — opens its own scope, records CONST/TYPE/VAR
  and procedure headings (bodies discarded via `AbortFunc`), emits
  nothing.
- **IMPLEMENTATION MODULE** — resumes the definition's scope, lowers
  procedure bodies to `export function`s, and its `BEGIN` body to
  `<mod>_init`, which `main` calls at startup (before the program
  body).
- **Program MODULE** — imports resolved, emits `main`; the image is
  named after its module (`EndModule(m1)`).

## Modules / imports (SymTab)

- Module registry (`modNames/modScopes/modKind/modImpl`): module
  names live in the global scope as `KindModule`; each module gets a
  child scope that *is* its export table.
- `Materialize` clones an export into the current scope; shared by
  `FROM L IMPORT x` and by qualified `L.x`/`L.P` (flatten-on-first-
  use, idempotent). Unknown modules stay silent stubs (legacy);
  a known module's missing export is 201.
- `ResumeProc` lets an implementation heading re-open a definition's
  procedure (fresh body scope, formals re-entered); its uid — hence
  the mangled `$P_uid` symbol — matches what clients call.
- **Opaque completion**: `OpaqueBase` detects a definition's opaque
  alias (target still `InvalidType`); the implementation's
  `TYPE T = ...` completes it via `SetTarget` instead of
  re-declaring. `TYPE T;` stays usable behind `POINTER TO T`.

## Backend (QbeGen)

- Output is now fully buffered (`sessBuf`, 1 MB) and written at
  `EndModule` under the program module's name, so a session whose
  output name is only known once the program parses still lands
  correctly. Nested-function hoisting keeps its per-depth buffers.
- `BeginInit/EndInit` emit module init functions; `BeginBody` calls
  each recorded init right after `main`'s `@start` and real-const
  flush. `LoadDesignator` is the shared value-load path for
  qualified access. Bare zero-arg function calls (`F` without
  parentheses) now work.

## Tests

Sessions (`expect_run_files`, `expect_fail_files`):
`DBasicProg` 49 (FROM imports of const/var/proc, impl `BEGIN`
init), `DQualProg` 46 (qualified `L.x`/`L.P`, bare `DLib.Bump`),
`DTypesProg` 36 (array + record types shared across units),
`DOpaqueProg` 55 (opaque `Node` completed in the implementation,
factory + accessor), `d_badimp_prog` 201 (missing export). The old
`t_defunit`/`t_implunit`/`t_opaqueptr` "not supported yet" rejects
became session-level rejections (definition-only / no program).

## Deferred

Strict signature checking (231) for impl-vs-def headings (arity is
checked; types are not), variant records, per-file object emission
(this is whole-program single-image), import cycles, `HIGH`/`LEN`,
class lowering.