Phase 15. Publish-ready crate metadata + dry-run gate

Field	Value
MEP	MEP-53 §Phases
Status	LANDED
Started	2026-05-29 (GMT+7)
Landed	2026-05-29 (GMT+7)
Tracking issue	#22610
Tracking PR	#22499
Commit	458120b2d3

Gate

TestPhase15Publish in transpiler3/rust/build/phase15_test.go runs two steps:

1. Always-on: build a fixture to TargetRustCrate, then parse the emitted Cargo.toml and assert it carries license, description, and repository fields. These are the three fields crates.io requires for cargo publish to succeed.
2. Opt-in (gated by MOCHI_RUN_PUBLISH_DRYRUN=1): inside the emitted crate, run cargo publish --dry-run --no-verify --allow-dirty and assert exit zero. This confirms cargo accepts the metadata as publishable. Off by default because cargo's dry-run still requires registry index access (it talks to crates.io to check for name collisions).

Lowering decisions

The TargetRustCrate target was added in this phase. Until phase 15, TargetRustSource rendered the source files but not a self-contained crate; TargetNativeExecutable built into the cargo cache; neither produced an artefact a user could cargo publish from. TargetRustCrate copies the full workDir (Cargo.toml + src/ + cffi/ + build.rs) to outDir via a tree-walk that skips target/. The result is a directory that cargo publish accepts.

generateCargoToml was extended to emit:

[package]
name = "mochi-emitted"
version = "0.1.0"
edition = "2021"
license = "Apache-2.0"
description = "Mochi program emitted by transpiler3/rust"
repository = "https://github.com/mochilang/mochi"

The license is Apache-2.0 matching the Mochi project license. description and repository are static defaults; future phases could expose them as mochi.toml fields.

Files changed

File	Purpose
transpiler3/rust/build/build.go	Add TargetRustCrate, copyTree, extend generateCargoToml
transpiler3/rust/build/phase15_test.go	Metadata-assertion gate + opt-in dry-run gate
tests/transpiler3/rust/fixtures/phase15-publish/publish_hello.mochi + .out	Single fixture

Test set

• TestPhase15Publish/metadata (always-on)
• TestPhase15Publish/cargo_publish_dryrun (opt-in, gated on MOCHI_RUN_PUBLISH_DRYRUN=1)

Closeout notes

--no-verify is necessary because the dry-run with verify-on would itself run cargo build on the emitted crate inside an isolated workspace, which fails if any cc-rs dep is missing or if the crate name collides with an in-flight upload. The trade-off: we lose the build-verifies-the-package check, but we still verify the metadata-correctness piece (which is what fails most often when authors first publish to crates.io).

--allow-dirty is necessary because the test runs against a freshly written-out crate that isn't a git repo. Cargo otherwise refuses to publish from non-clean git trees.