feat: tuple return value typescript decoding

yarn-project/foundation/src/abi/abi.ts

@@ -84,7 +84,14 @@ export interface BasicType<T extends string> {
 /**
  * A variable type.
  */
-export type AbiType = BasicType<'field'> | BasicType<'boolean'> | IntegerType | ArrayType | StringType | StructType;
+export type AbiType =
+  | BasicType<'field'>
+  | BasicType<'boolean'>
+  | IntegerType
+  | ArrayType
+  | StringType
+  | StructType
+  | TupleType;
 
 type Sign = 'unsigned' | 'signed';
 
@@ -116,6 +123,16 @@ export interface ArrayType extends BasicType<'array'> {
   type: AbiType;
 }
 
+/**
+ * A tuple type.
+ */
+export interface TupleType extends BasicType<'tuple'> {
+  /**
+   * The types of the tuple elements.
+   */
+  fields: AbiType[];
+}
+
 /**
  * A string type.
  */

yarn-project/foundation/src/abi/decoder.ts

@@ -56,6 +56,13 @@ class ReturnValuesDecoder {
         }
         return array;
       }
+      case 'tuple': {
+        const array = [];
+        for (const tupleAbiType of abiType.fields) {
+          array.push(this.decodeReturn(tupleAbiType));
+        }
+        return array;
+      }
       default:
         throw new Error(`Unsupported type: ${abiType}`);
     }

yarn-project/foundation/src/abi/encoder.ts

@@ -23,6 +23,8 @@ class ArgumentEncoder {
         return abiType.length * ArgumentEncoder.typeSize(abiType.type);
       case 'struct':
         return abiType.fields.reduce((acc, field) => acc + ArgumentEncoder.typeSize(field.type), 0);
+      case 'tuple':
+        return abiType.fields.reduce((acc, field) => acc + ArgumentEncoder.typeSize(field), 0);
       default: {
         const exhaustiveCheck: never = abiType;
         throw new Error(`Unhandled abi type: ${exhaustiveCheck}`);