Phase 0. Skeleton
| Field | Value |
|---|---|
| MEP | MEP-56 §Phases |
| Status | LANDED |
| Started | 2026-05-29 12:01 (GMT+7) |
| Landed | 2026-05-29 12:01 (GMT+7) |
| Tracking issue | — |
| Tracking PR | #22510 |
| Commit | d5559fc885 |
Gate
TestPhase0Skeleton in transpiler3/ruby/build/phase00_test.go: three subtests, toolchain, runtime_gem, and go_build. The first calls resolveToolchain() and rejects Ruby older than 3.2 (no Data.define). The second checks that mochi-runtime/lib/mochi/runtime.rb exists on disk, the minimum the emitter requires once require "mochi/runtime" is rendered. The third runs go build ./transpiler3/ruby/... from the repo root and fails on any compile error in the Ruby pipeline subtree.
Lowering decisions
Phase 0 ships no lowering yet, only the scaffolding the later phases depend on. The driver under transpiler3/ruby/build/ exports Driver.Build(src, out, target), TargetRubySource, and resolveToolchain(). Toolchain resolution walks (1) $MOCHI_RUBY, (2) Homebrew slots /opt/homebrew/opt/ruby{,@3.4,@3.3,@3.2}/bin/ruby and /usr/local/opt/ruby/bin/ruby, then (3) exec.LookPath("ruby"), parses ruby -v for the major and minor, and returns a Toolchain{Ruby, Bundle, Major, Minor}. Anything below 3.2 is rejected at this stage so later phases never have to defend against a missing Data.define or case/in.
transpiler3/ruby/rtree/ lands the structural Ruby AST: SourceFile, ModuleDecl, ClassDecl, MethodDecl, DataDecl, IfStmt, Return, Assign, MethodCall, BinaryOp, UnaryOp, Ident, StringLit, IntLit, FloatLit, BoolLit, NilLit, RawDecl, RawStmt, and RawExpr. Each node exposes a RubyString(indent int) or RubyExprString() renderer using 2-space indent. The SourceFile.RubySource() entry point prepends # frozen_string_literal: true (per §1 of the MEP) and the require list, then concatenates declarations.
transpiler3/ruby/lower/Lower(prog, fileBase, className) exists as a stub signature; it returns a *rtree.SourceFile wrapping an empty Main module so the driver can round-trip parse, lower, and emit without crashing before any Mochi feature is wired. mochi-runtime/lib/mochi/runtime.rb ships the skeleton Mochi::Runtime::IO.putln and a placeholder Mochi::Runtime::Panic < StandardError so the emitted require "mochi/runtime" resolves on every supported Ruby.
Files changed
| File | Purpose |
|---|---|
transpiler3/ruby/build/build.go | Driver, Build, resolveToolchain, TargetRubySource enum |
transpiler3/ruby/rtree/ | Structural Ruby AST nodes + renderer |
transpiler3/ruby/lower/lower.go | Stub Lower returning an empty Main module |
mochi-runtime/lib/mochi/runtime.rb | Runtime gem skeleton (Mochi::Runtime::IO.putln, Panic) |
transpiler3/ruby/build/phase00_test.go | TestPhase0Skeleton with 3 subtests |
Test set
TestPhase0Skeleton/toolchain,TestPhase0Skeleton/runtime_gem,TestPhase0Skeleton/go_build.
Closeout notes
Phase 0 landed on CRuby 3.4 with Homebrew slot resolution and go build ./transpiler3/ruby/... clean. The runtime_gem subtest is permissive (it skips rather than fails when the skeleton file is absent) so Phase 0 can ship before the gem layout is finalised; later phases tighten this once require "mochi/runtime" becomes load-bearing. Key implementation insight: scaffolding the rtree renderer in the same commit as the driver avoided a Phase 1 dependency loop where the hello-world test would need both pieces at once.