M2compiler-V3/docs/summary_two-phase-session-2026-10-04.md

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

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