[framework] Adds peel_enum to bcs (#20984)

## Description 

Minor improvement for `bcs` library, helper to parse enums.

## Test plan 

Features tests.

---

## Release notes

Check each box that your changes affect. If none of the boxes relate to
your changes, release notes aren't required.

For each box you select, include information after the relevant heading
that describes the impact of your changes that a user might notice and
any actions they must take to implement updates.

- [x] Protocol: bumps protocol version to 74
- [ ] Nodes (Validators and Full nodes): 
- [ ] gRPC:
- [ ] JSON-RPC: 
- [ ] GraphQL: 
- [ ] CLI: 
- [ ] Rust SDK:

crates/sui-framework/docs/sui/bcs.md

@@ -60,6 +60,7 @@ let leftovers = prepared.into_remainder_bytes();
 -  [Function `peel_vec_u64`](#sui_bcs_peel_vec_u64)
 -  [Function `peel_vec_u128`](#sui_bcs_peel_vec_u128)
 -  [Function `peel_vec_u256`](#sui_bcs_peel_vec_u256)
+-  [Function `peel_enum_tag`](#sui_bcs_peel_enum_tag)
 -  [Macro function `peel_option`](#sui_bcs_peel_option)
 -  [Function `peel_option_address`](#sui_bcs_peel_option_address)
 -  [Function `peel_option_bool`](#sui_bcs_peel_option_bool)
@@ -766,6 +767,46 @@ Peel a vector of <code>u256</code> from serialized bytes.
 
 
 
+</details>
+
+<a name="sui_bcs_peel_enum_tag"></a>
+
+## Function `peel_enum_tag`
+
+Peel enum from serialized bytes, where <code>$f</code> takes a <code>tag</code> value and returns
+the corresponding enum variant. Move enums are limited to 127 variants,
+however the tag can be any <code>u32</code> value.
+
+Example:
+```rust
+let my_enum = match (bcs.peel_enum_tag()) {
+0 => Enum::Empty,
+1 => Enum::U8(bcs.peel_u8()),
+2 => Enum::U16(bcs.peel_u16()),
+3 => Enum::Struct { a: bcs.peel_address(), b: bcs.peel_u8() },
+_ => abort,
+};
+```
+
+
+<pre><code><b>public</b> <b>fun</b> <a href="../sui/bcs.md#sui_bcs_peel_enum_tag">peel_enum_tag</a>(<a href="../sui/bcs.md#sui_bcs">bcs</a>: &<b>mut</b> <a href="../sui/bcs.md#sui_bcs_BCS">sui::bcs::BCS</a>): u32
+</code></pre>
+
+
+
+<details>
+<summary>Implementation</summary>
+
+
+<pre><code><b>public</b> <b>fun</b> <a href="../sui/bcs.md#sui_bcs_peel_enum_tag">peel_enum_tag</a>(<a href="../sui/bcs.md#sui_bcs">bcs</a>: &<b>mut</b> <a href="../sui/bcs.md#sui_bcs_BCS">BCS</a>): u32 {
+    <b>let</b> tag = <a href="../sui/bcs.md#sui_bcs">bcs</a>.<a href="../sui/bcs.md#sui_bcs_peel_vec_length">peel_vec_length</a>();
+    <b>assert</b>!(tag &lt;= <a href="../std/u32.md#std_u32_max_value">std::u32::max_value</a>!() <b>as</b> u64, <a href="../sui/bcs.md#sui_bcs_EOutOfRange">EOutOfRange</a>);
+    tag <b>as</b> u32
+}
+</code></pre>
+
+
+
 </details>
 
 <a name="sui_bcs_peel_option"></a>

crates/sui-framework/packages/sui-framework/sources/bcs.move

@@ -217,6 +217,28 @@ public fun peel_vec_u256(bcs: &mut BCS): vector<u256> {
     bcs.peel_vec!(|bcs| bcs.peel_u256())
 }
 
+// === Enum ===
+
+/// Peel enum from serialized bytes, where `$f` takes a `tag` value and returns
+/// the corresponding enum variant. Move enums are limited to 127 variants,
+/// however the tag can be any `u32` value.
+///
+/// Example:
+/// ```rust
+/// let my_enum = match (bcs.peel_enum_tag()) {
+///    0 => Enum::Empty,
+///    1 => Enum::U8(bcs.peel_u8()),
+///    2 => Enum::U16(bcs.peel_u16()),
+///    3 => Enum::Struct { a: bcs.peel_address(), b: bcs.peel_u8() },
+///    _ => abort,
+/// };
+/// ```
+public fun peel_enum_tag(bcs: &mut BCS): u32 {
+    let tag = bcs.peel_vec_length();
+    assert!(tag <= std::u32::max_value!() as u64, EOutOfRange);
+    tag as u32
+}
+
 // === Option<T> ===
 
 /// Peel `Option<$T>` from serialized bytes, where `$peel: |&mut BCS| -> $T` gives the

crates/sui-framework/packages/sui-framework/tests/bcs_tests.move

@@ -14,6 +14,12 @@ module sui::bcs_tests {
     const U256_MAX: u256 =
         0xFFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF_FFFF;
 
+    public enum Enum has copy, drop {
+        Empty,
+        U8(u8),
+        U16(u16),
+    }
+
     public struct Info has copy, drop {
         a: bool,
         b: u8,
@@ -182,6 +188,22 @@ module sui::bcs_tests {
         );
     }
 
+    #[test]
+    fun test_enum() {
+        let enum_cases = vector[Enum::Empty, Enum::U8(1), Enum::U16(2)];
+        cases!(enum_cases, |bytes| bytes.peel_test_enum());
+    }
+
+    use fun peel_test_enum as BCS.peel_test_enum;
+    fun peel_test_enum(bytes: &mut BCS): Enum {
+        match (bytes.peel_enum_tag()) {
+            0 => Enum::Empty,
+            1 => Enum::U8(bytes.peel_u8()),
+            2 => Enum::U16(bytes.peel_u16()),
+            _ => abort,
+        }
+    }
+
     #[test]
     fun test_complex() {
         let vec_vec_u8_cases = vector[vector[], vector[b"hello world"], vector[b"hello", b"world"]];

crates/sui-framework/published_api.txt

@@ -1507,6 +1507,9 @@ peel_vec_u128
 peel_vec_u256
 	public fun
 	0x2::bcs
+peel_enum_tag
+	public fun
+	0x2::bcs
 peel_option_address
 	public fun
 	0x2::bcs

crates/sui-open-rpc/spec/openrpc.json

@@ -1294,7 +1294,7 @@
             "name": "Result",
             "value": {
               "minSupportedProtocolVersion": "1",
-              "maxSupportedProtocolVersion": "73",
+              "maxSupportedProtocolVersion": "74",
               "protocolVersion": "6",
               "featureFlags": {
                 "accept_zklogin_in_multisig": false,

crates/sui-protocol-config/src/lib.rs

@@ -18,7 +18,7 @@ use tracing::{info, warn};
 
 /// The minimum and maximum protocol versions supported by this build.
 const MIN_PROTOCOL_VERSION: u64 = 1;
-const MAX_PROTOCOL_VERSION: u64 = 73;
+const MAX_PROTOCOL_VERSION: u64 = 74;
 
 // Record history of protocol version allocations here:
 //
@@ -213,6 +213,8 @@ const MAX_PROTOCOL_VERSION: u64 = 73;
 //             Enable zstd compression for consensus tonic network in testnet.
 //             Enable smart ancestor selection in mainnet.
 //             Enable probing for accepted rounds in round prober in mainnet
+// Version 74:
+//
 
 #[derive(Copy, Clone, Debug, Hash, Serialize, Deserialize, PartialEq, Eq, PartialOrd, Ord)]
 pub struct ProtocolVersion(u64);
@@ -3195,6 +3197,7 @@ impl ProtocolConfig {
                     cfg.feature_flags
                         .consensus_round_prober_probe_accepted_rounds = true;
                 }
+                74 => {}
                 // Use this template when making changes:
                 //
                 //     // modify an existing constant.