feat(cycles-minting): Cycles Minting canister refunds automatically.

rs/nns/cmc/BUILD.bazel

@@ -55,6 +55,7 @@ DEV_DEPENDENCIES = [
     "//rs/types/types_test_utils",
     "@crate_index//:candid_parser",
     "@crate_index//:futures",
+    "@crate_index//:maplit",
     "@crate_index//:serde_bytes",
 ]
 

rs/nns/cmc/Cargo.toml

@@ -45,6 +45,7 @@ yansi = "0.5.0"
 
 [dev-dependencies]
 candid_parser = { workspace = true }
+maplit = "1.0.2"
 futures = { workspace = true }
 ic-types-test-utils = { path = "../../types/types_test_utils" }
 serde_bytes = { workspace = true }

rs/nns/cmc/src/lib.rs

@@ -12,6 +12,8 @@ use icp_ledger::{
 use icrc_ledger_types::icrc1::account::Account;
 use serde::{Deserialize, Serialize};
 
+pub const IS_AUTOMATIC_REFUND_ENABLED: bool = false;
+
 pub const DEFAULT_CYCLES_PER_XDR: u128 = 1_000_000_000_000u128; // 1T cycles = 1 XDR
 
 pub const PERMYRIAD_DECIMAL_PLACES: u32 = 4;
@@ -313,10 +315,23 @@ pub struct CyclesLedgerDepositResult {
     pub block_index: Nat,
 }
 
+// When a user sends us ICP, they indicate via memo (or icrc1_memo) what
+// operation they want to perform.
+//
+// We promise that we will NEVER use 0 as one of these values. (This would be
+// very bad, because if no memo is explicitly supplied, the Transaction might
+// implicitly have 0 in the memo field.)
+//
+// Note to developers: If you add new values, update MEANINGFUL_MEMOS.
 pub const MEMO_CREATE_CANISTER: Memo = Memo(0x41455243); // == 'CREA'
 pub const MEMO_TOP_UP_CANISTER: Memo = Memo(0x50555054); // == 'TPUP'
 pub const MEMO_MINT_CYCLES: Memo = Memo(0x544e494d); // == 'MINT'
 
+// New values might be added to this later. Do NOT assume that values won't be
+// added to this array later.
+pub const MEANINGFUL_MEMOS: [Memo; 3] =
+    [MEMO_CREATE_CANISTER, MEMO_TOP_UP_CANISTER, MEMO_MINT_CYCLES];
+
 pub fn create_canister_txn(
     amount: Tokens,
     from_subaccount: Option<Subaccount>,