allow clear_origin in safe xcm builder

polkadot/xcm/procedural/src/builder_pattern.rs

@@ -233,6 +233,32 @@ fn generate_builder_impl(name: &Ident, data_enum: &DataEnum) -> Result<TokenStre
  }
  };
 
+ // Some operations are allowed after the holding register is loaded
+ let allowed_after_load_holding_methods: Vec<TokenStream2> = data_enum
+ .variants
+ .iter()
+ .filter(|variant| variant.ident == "ClearOrigin")
+ .map(|variant| {
+ let variant_name = &variant.ident;
+ let method_name_string = &variant_name.to_string().to_snake_case();
+ let method_name = syn::Ident::new(method_name_string, variant_name.span());
+ let docs = get_doc_comments(variant);
+ let method = match &variant.fields {
+ Fields::Unit => {
+ quote! {
+ #(#docs)*
+ pub fn #method_name(mut self) -> XcmBuilder<Call, LoadedHolding> {
+ self.instructions.push(#name::<Call>::#variant_name);
+ self
+ }
+ }
+ },
+ _ => return Err(Error::new_spanned(variant, "ClearOrigin should have no fields")),
+ };
+ Ok(method)
+ })
+ .collect::<std::result::Result<Vec<_>, _>>()?;
+
  // Then we require fees to be paid
  let buy_execution_method = data_enum
  .variants
@@ -276,6 +302,7 @@ fn generate_builder_impl(name: &Ident, data_enum: &DataEnum) -> Result<TokenStre
 
  let second_impl = quote! {
  impl<Call> XcmBuilder<Call, LoadedHolding> {
+ #(#allowed_after_load_holding_methods)*
  #buy_execution_method
  }
  };

polkadot/xcm/procedural/tests/builder_pattern.rs

@@ -79,3 +79,24 @@ fn default_builder_requires_buy_execution() {
  ])
  );
 }
+
+#[test]
+fn default_builder_allows_clear_origin_before_buy_execution() {
+ let asset: Asset = (Here, 100u128).into();
+ let beneficiary: Location = [0u8; 32].into();
+ let message: Xcm<()> = Xcm::builder()
+ .receive_teleported_asset(asset.clone())
+ .clear_origin()
+ .buy_execution(asset.clone(), Unlimited)
+ .deposit_asset(asset.clone(), beneficiary.clone())
+ .build();
+ assert_eq!(
+ message,
+ Xcm(vec![
+ ReceiveTeleportedAsset(asset.clone().into()),
+ ClearOrigin,
+ BuyExecution { fees: asset.clone(), weight_limit: Unlimited },
+ DepositAsset { assets: asset.into(), beneficiary },
+ ])
+ );
+}

prdoc/pr_4777.prdoc

@@ -0,0 +1,27 @@
+# Schema: Polkadot SDK PRDoc Schema (prdoc) v1.0.0
+# See doc at https://raw.githubusercontent.com/paritytech/polkadot-sdk/master/prdoc/schema_user.json
+
+title: XCM builder pattern allows clear_origin before buy_execution.
+
+doc:
+ - audience: Runtime Dev
+ description: |
+ Added clear_origin as an allowed command after commands that load the holdings register, in the safe xcm builder.
+ Previously, although it's logically allowed, an XCM could not be built like this:
+ ```rust
+ let xcm = Xcm::builder()
+ .withdraw_asset((Parent, 100u128))
+ .clear_origin()
+ .buy_execution((Parent, 1u128))
+ .deposit_asset(All, [0u8; 32])
+ .build();
+ ```
+ You had to use the unsafe_builder.
+ Now, it's allowed using the default builder.
+
+crates: 
+- name: "xcm-procedural"
+ bump: minor
+- name: "staging-xcm"
+ bump: minor
+