M2compiler-V3/docs/summary_two-phase-slice1.md

Two-phase refactor — slice 1 (twoPhase flag + AST scaffolding)

Branch ast-stage-c off 1c93f19 (v3-two-phase-plan). Suite 178/178; self-hosting fixpoint OK (2,957,466 bytes; +56,684 vs 2,900,782 — the AST module is now linked into the compiler).

What landed

docs/plan-two-phase.md §4 slice 1: the parser now builds AST nodes alongside the legacy emit path, and the AST module is part of the compiler build. The nodes are inert — nothing reads them, so the generated .ssa is unchanged (stage2 == stage3 byte-for-byte).

File	Change
compiler/src/M2.atg	IMPORT … , AST; VAR twoPhase : BOOLEAN; the M2 root production runs AST.Init; twoPhase := TRUE;; the integer expression leaf also builds NkIntLit via AST.MakeLeaf; Fact gets a throwaway astScratch : AST.Node
compiler/build.sh	compile and link AST (after FileIO)
compiler/src/M2.lst	regenerated CR listing

M2P.mod now imports AST and calls AST.Init once per parsed unit (the root production runs per source file), so every unit starts with a fresh arena. The new AST.def/.mod are picked up transitively by M2make during stages 2/3 of the fixpoint.

Notes

• twoPhase is a grammar-level BOOLEAN, set TRUE in the root production. Later slices gate the new lowering walk on it; for now it only guards the inert NkIntLit build.
• Compilation ended with LL(1) errors. from CR is pre-existing (benign) and unchanged.
• No new test: every existing test already exercises the path (each integer literal builds a node), and there is no observable behaviour to assert yet.

Next

Slice 2 (docs/plan-two-phase.md §4): Expr / SimExpr / Term / Fact build NkBinExpr / NkUnary / NkIdent / literals in addition to emitting; add Lower for expressions, exercised by a test-only .ssa byte-compare.