refactor(motoko/icrc2-swap): import the ICRC .did directly (moc 1.13.0 idl:)

[marc0olo]

What

Types icrc2-swap's token-ledger calls against the ICRC-1/ICRC-2 Candid interface imported directly via Motoko's idl: import (moc 1.13.0+), replacing the hand-written backend/ICRC.mo type module. No bindings are generated or committed, and no extra tooling (didc) is needed.

import ICRC "idl:../candid/icrc.did";

Update: this PR originally committed a didc-generated bindings/ICRC.mo. moc 1.13.0 (release, docs) now imports a .did directly, so the generated bindings and the didc step are gone — only the committed candid/icrc.did remains.

Why this pattern for ICRC

icrc2-swap holds two ledgers at once (token_a, token_b) and picks the target per call (actor(args.token.toText()) : ICRC.Self). That's the "one interface, many ledgers, runtime-chosen principal" case, which --actor-env-alias/--actor-id-alias (which bind one import to one principal) can't express. The idl: import gives types only (ICRC.Self + named types like ICRC.Account, ICRC.TransferArgs); the backend supplies its own actor(principal) per token. This generalizes to any DeFi-shaped backend that talks to many ICRC ledgers (ICP, ckBTC/ckETH, SNS tokens, …).

This completes the inter-canister taxonomy across the Motoko examples:

Situation	Mechanism	Example
id fixed & universal	--actor-id-alias	icp_transfer (#1455)
id varies per environment, injected	--actor-env-alias	parallel_calls, pub-sub, ic-pos, evm_block_explorer, llm_chatbot
id chosen at runtime / many targets	idl: import + actor(id)	icrc2-swap (this PR)

Changes

• candid/icrc.did — the ICRC-1/ICRC-2 interface (focused plain service; types from the ic-icrc1-ledger reference wasm). Committed source of truth, imported directly.
• backend/app.mo — import ICRC "idl:../candid/icrc.did"; types are ICRC.Self/ICRC.Account/ICRC.TransferArgs/…; hand-written ICRC.mo removed.
• mops.toml — moc 1.9.0 → 1.13.0 (required for the idl: import); mo:core 2.5.0 → 2.6.0.
• Unrelated tidy-up in the same example: Map swap (return always discarded) → add.
• README updated: the interface is imported directly; nothing to regenerate, no didc.

On tooling (cc @Kamirus)

Earlier revisions of this PR leaned on didc bind + a committed bindings/ICRC.mo, and flagged dfinity/candid#729 (PascalCase Motoko output) plus the idea of mops generating bindings as a pre-build step. moc 1.13.0's native .did import largely supersedes that for this use case: the compiler reads the .did directly, applies the PascalCase convention itself, and there's nothing to generate, commit, or install. Only the committed .did remains — which is exactly the "commit the interface, not the generated code" end state we were aiming for.

Testing

bash deploy.sh && bash test.sh — all 7 tests pass (deposit via icrc2_transfer_from, atomic swap, withdraw via icrc1_transfer with correct fee-adjusted balance deltas), confirming the idl:-imported types are wire-compatible with the real ledger.

🤖 Generated with Claude Code

[Copilot]

Pull request overview

This PR refactors the motoko/icrc2-swap example to use a committed, didc-generated Motoko binding for the standard ICRC-1/ICRC-2 ledger interface, allowing the backend to type ledgers selected by principal at runtime (actor(<principal>) : ICRC.Self) without maintaining a hand-written interface module.

Changes:

• Adds a focused candid/icrc.did for the ICRC-1/ICRC-2 method subset used by the example and commits the generated Motoko binding in bindings/ICRC.mo.
• Updates the backend to import and use ICRC.Self from the generated bindings, while preserving the runtime-selected-ledger pattern.
• Bumps mo:core from 2.5.0 to 2.6.0 and applies minor map-update tidy-ups (swap → add).

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
motoko/icrc2-swap/README.md	Updates architecture docs and adds binding-regeneration instructions using didc.
motoko/icrc2-swap/mops.toml	Bumps mo:core dependency version.
motoko/icrc2-swap/candid/icrc.did	Introduces the committed Candid interface used as the binding source-of-truth.
motoko/icrc2-swap/bindings/ICRC.mo	Adds committed, generated Motoko service/types binding (ICRC.Self, records, variants).
motoko/icrc2-swap/backend/app.mo	Switches backend to the generated binding import and updates types/usages accordingly.

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[Kamirus]

Yes, I think once dfinity/candid#729 lands it would make sense for mops to adopt this tool.
Mops would handle fetching it via mops toolchain and we could wrap it with mops generate ... command

[Copilot]

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated no new comments.

Suppressed comments (1)

motoko/icrc2-swap/candid/icrc.did:10

• The header comment still instructs generating Motoko bindings with didc bind and refers to “generated bindings”, which contradicts this PR’s idl: import approach (no bindings/tooling). Updating the comment will avoid confusion for readers following the README guidance.

// The type definitions match the ICRC-1 ledger reference implementation
// (dfinity/ic, ledger-suite-icrc). Generate the Motoko bindings with:
//   didc bind -t mo candid/icrc.did > bindings/ICRC.mo