Phase 0. Skeleton
| Field | Value |
|---|---|
| MEP | MEP-74 §Phases |
| Status | LANDED |
| Started | 2026-05-29 20:55 (GMT+7) |
| Landed | 2026-05-29 21:07 (GMT+7) |
| Tracking issue | (pending) |
| Tracking PR | (pending) |
| Commit | (pending) |
Gate
TestPhase0Skeleton in package3/go/build/phase00_test.go: subtests end_to_end, package_layout, default_workspace_invariants. The first allocates a Driver, prepares a workspace, adds modules and a replace directive, writes the workspace root go.work to a scratch directory, re-reads it, and asserts the expected substrings appear. The second verifies the on-disk layout of package3/go/ (the documented Go packages exist). The third checks that DefaultWorkspace() round-trips through Validate() without error and renders a manifest containing the auto-generated header, the go 1.21 directive, and reports c-archive as the default cgo build mode.
In addition, the package-level test suite covers:
package3/go/errors/: 20 SkipReason variants string-encode round-trip (one constant per refusal case from research note 05 plus four bridge-internal ones for deprecated items, replace-driven publishes, var/const items, and unsupported double pointers), SkipReport renders with and without an override line, BridgeError formats with and without a module, errors.Is unwraps BridgeError.Cause, the unknown-value fallback returns "SkipUnknown".package3/go/build/: DefaultWorkspace defaults (go-version floor 1.21, CgoArchive build mode, trimpath enabled, ldflags-s -w), AddModule sort-and-deduplicate, AddReplace replace semantics with nil-map autovivification, RenderGoWork content + determinism over 10 iterations, replace-directive alphabetisation, empty-workspace short-circuit, Validate rejects malformed go-version / duplicate paths / empty module fields / absolute paths / parent-traversal paths, Driver cache-dir defaults including XDG_CACHE_HOME and HOME fallbacks plus the TMPDIR fallback path, PrepareWorkspace idempotence, Cleanup idempotence and the user-vs-allocated work-dir distinction.
Lowering decisions
Phase 0 ships no go/packages ingest yet, only the scaffolding the later phases depend on. The Driver exports NewDriver(Options) -> *Driver, PrepareWorkspace() -> (*Workspace, error), WriteWorkspaceRoot(*Workspace) -> (string, error), and Cleanup() -> error. Workspace exports DefaultWorkspace(), AddModule, AddReplace, RenderGoWork, and Validate.
The go.work renderer is a small hand-rolled writer. It uses no external library because (1) the schema is fixed and small, (2) the output must be byte-stable for the workspace-cache key (planned for phase 9), and (3) avoiding golang.org/x/mod/modfile keeps the package self-contained at phase 0. Phase 9 may switch to modfile once it joins the bridge's dependency set.
The renderer emits, in order: a comment header identifying the bridge, the go <version> directive, the use (...) block with paths sorted alphabetically, and one replace <module> => <target> line per declared directive (also alphabetised). The trailing block separator between use and replace is suppressed when one or the other is empty.
The default workspace pins go 1.21 as the toolchain floor (matching MEP-54's own floor) and selects CgoArchive as the build mode, -trimpath as the reproducibility flag, and -s -w as the default ldflags. The TinyGo embedded path (phase 16) and the wasm path (phase 17) will switch to CgoNone and select alternative compile paths.
The SkipReason enum lands all 11 refusal classifications from research note 05's table plus 9 internal ones (the closed-form table includes complex64, pointer-to-pointer, func-returning-func, complex variadics, const items, var items, deprecated markers, replace-driven publishes, and a generic SkipUnknown zero value). Each constant's String() produces a stable token used in the SKIPPED.txt golden fixtures. An exhaustive sub-test sweeps every declared constant and asserts a non-SkipUnknown result, so a future addition to the enum that forgets to update the switch is caught immediately.
The BridgeError type carries (Phase, Module, Cause) and formats as phase[module]: cause (with the bracketed segment omitted when module is empty). It implements Unwrap so errors.Is and errors.As traverse through it. The Wrap(phase, module, cause) helper returns nil for a nil cause so callers can use it unconditionally from a happy path.
Files changed
| File | Purpose |
|---|---|
package3/go/build/driver.go | Driver, Options, NewDriver, PrepareWorkspace, WriteWorkspaceRoot, Cleanup, defaultCacheDir |
package3/go/build/workspace.go | Workspace, WorkspaceModule, WorkspaceModuleKind, CgoBuildMode, DefaultWorkspace, AddModule, AddReplace, RenderGoWork, Validate |
package3/go/build/driver_test.go | Driver unit tests (cache-dir resolution, PrepareWorkspace idempotence, Cleanup semantics) |
package3/go/build/workspace_test.go | Workspace unit tests (rendering, determinism, validation, CgoBuildMode mapping) |
package3/go/build/phase00_test.go | TestPhase0Skeleton sentinel with 3 subtests |
package3/go/errors/errors.go | SkipReason (20 variants), SkipReport, BridgeError, Wrap |
package3/go/errors/errors_test.go | Errors unit tests (SkipReason exhaustiveness, SkipReport format, BridgeError unwrap) |
Test set
TestPhase0Skeleton/end_to_endTestPhase0Skeleton/package_layoutTestPhase0Skeleton/default_workspace_invariants- All
package3/go/build/...andpackage3/go/errors/...unit tests.
Local run on darwin-arm64:
$ go test ./package3/go/...
ok mochi/package3/go/build 0.802s
ok mochi/package3/go/errors 0.483s
Closeout notes
Phase 0 is the smallest viable skeleton: enough to render the workspace root go.work that later phases will populate with synthesised wrapper modules plus the user's emitted top-level module. The driver's WorkDir is allocated with a mochi-go- prefix so Cleanup can safely refuse to remove a user-provided directory.
The cache-dir resolution honours $XDG_CACHE_HOME first, then falls back to ~/.cache/mochi/go-deps/, then to $TMPDIR/mochi-cache/go-deps. This matches the behaviour of package3/rust/'s phase 0 (the parallel MEP-73 phase 0 chose ~/.cache/mochi/rust-deps/).
No external runtime dependencies are introduced. The phase adds two Go packages to the repo (package3/go/build/ and package3/go/errors/), both pure-Go with stdlib-only imports. The golang.org/x/mod/modfile dependency is deferred to phase 9 when the wrapper build actually needs to parse / amend go.mod files.
The Go-side workspace model is simpler than MEP-73's cargo workspace: go.work is a flat list of use directives plus replace overrides, whereas cargo workspace carries shared dependencies, profile sections, and resolver version. The simplicity propagates downstream: the bridge does not need to manage workspace-level dependency inheritance because Go modules already carry their own go.mod requires.