Add mops generate candid

[Kamirus]

Implements specs/mops-candid.md.

Why

The curated [canisters.<name>].candid file is a build-input contract: mops build subtype-checks the auto-generated interface against it and embeds the curated file into the wasm as candid:service metadata. Downstream tools like @icp-sdk/bindgen read the same file. There was no command to refresh it from source — every interface change required hand-editing the .did, with no committable file at all when the field was unset.

What changes for users

mops generate candid [canisters...] (re)generates the curated .did from current Motoko source.

mops generate candid                  # all canisters
mops generate candid backend          # one canister
mops generate candid backend -o <p>   # ad-hoc path; does not touch mops.toml

Destination resolution:

1. --output <path> — single-canister only; never updates mops.toml.
2. [canisters.<name>].candid if set — overwrites in place.
3. Default — <dirname(main)>/<name>.did (e.g. main = "src/Backend.mo" → src/backend.did); also writes the field to mops.toml so subsequent runs reuse it.

Paths inside .mops/ are rejected (it's a private cache; the .did should be committable). On moc failure, neither the destination file nor mops.toml is touched.

Implementation note

moc invocation logic (sources, [moc].args, migration flags, [build].args, per-canister args, CLI extras + managed-flag warnings) extracted from build.ts into cli/helpers/moc-args.ts. mops build now uses the same helper, guaranteeing the .did mops generate candid produces always satisfies the build's compatibility check. The build refactor is behavior-preserving — verified by all existing build snapshots passing unchanged.

Test plan

• npm test -- generate.test.ts (10 cases — default path, configured path, multi-canister, --output, -o collision warning, multi-canister + -o rejected, unknown canister, moc failure leaves files/toml untouched, missing-but-configured destination, .mops/ rejection)
• npm test -- build.test.ts (refactor regression — all snapshots unchanged)
• npm run check (root — TypeScript + svelte-check)
• npm run lint clean

Out of scope (called out in spec)

• Drift detection in mops check (separate follow-up; spec § "Interaction with mops check")
• [candid].dir global directory config
• --merge mode that preserves hand-edits

Made with Cursor

[github-actions]

Cursor AI review

👍 APPROVE — looks safe to merge

Category	Assessment	Details
Summary	✅	Adds mops generate candid [canisters...] to regenerate curated .did files from Motoko source, and extracts shared prepareMocArgs so build and generate share the same moc invocation inputs.
Code Quality	✅	moc-args.ts cleanly deduplicates build/generate logic without speculative extras; destination resolution and failure semantics match the spec.
Consistency	✅	Mirrors mops build (canister selection, installAll, parseExtraArgs, -- passthrough, all-canisters default); changelog, skill, and CLI docs are updated.
Security	✅	Rejects writes under .mops/; no new identity/registry/secrets surface; collision warning for shared -o paths.
Tests	✅	Ten focused cases cover default/configured paths, multi-canister, -o, errors, .mops/ rejection, and moc-failure atomicity; snapshots cover primary stdout/did output.
Maintainability	✅	Shared helper keeps generate/build candid compatibility from drifting; command is isolated in generate.ts for future mops generate subcommands.

Verdict

Decision: APPROVE
Risk: Low
Reason: This is a well-scoped, user-facing CLI addition with matching docs/changelog/skill, meaningful tests, and a behavior-preserving build refactor verified by unchanged build snapshots. No new defects or production-significant changes warranting human escalation were found in the diff versus base.

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Generated for commit d86303d