refactor: refactor child context to be child context return data

crates/evm/src/context.cairo

@@ -116,6 +116,12 @@ impl DefaultBoxCallContext of Default<Box<CallContext>> {
     }
 }
 
+impl DefaultOptionSpanU8 of Default<Option<Span<u8>>> {
+    fn default() -> Option<Span<u8>> {
+        Option::None
+    }
+}
+
 
 // *************************************************************************
 //                              ExecutionContext
@@ -136,7 +142,7 @@ struct ExecutionContext {
     create_addresses: Array<EthAddress>,
     return_data: Array<u8>,
     parent_context: Nullable<ExecutionContext>,
-    child_context: Nullable<ExecutionContext>,
+    child_context_return_data: Option<Span<u8>>,
 }
 
 impl DefaultBoxExecutionContext of Default<Box<ExecutionContext>> {
@@ -159,7 +165,7 @@ impl ExecutionContextImpl of ExecutionContextTrait {
         starknet_address: ContractAddress,
         call_context: CallContext,
         parent_context: Nullable<ExecutionContext>,
-        child_context: Nullable<ExecutionContext>,
+        child_context_return_data: Option<Span<u8>>,
         return_data: Array<u8>,
     ) -> ExecutionContext {
         ExecutionContext {
@@ -184,7 +190,7 @@ impl ExecutionContextImpl of ExecutionContextTrait {
             create_addresses: Default::default(),
             return_data,
             parent_context,
-            child_context,
+            child_context_return_data,
         }
     }
 
@@ -314,4 +320,9 @@ impl ExecutionContextImpl of ExecutionContextTrait {
     fn pc(self: @ExecutionContext) -> u32 {
         *self.program_counter
     }
+
+    #[inline(always)]
+    fn child_context_return_data(self: @ExecutionContext) -> Option<Span<u8>> {
+        *self.child_context_return_data
+    }
 }

crates/evm/src/machine.cairo

@@ -252,4 +252,14 @@ impl MachineCurrentContextImpl of MachineCurrentContextTrait {
         current_execution_ctx.return_data = value;
         self.current_context = BoxTrait::new(current_execution_ctx);
     }
+
+    /// Getter for the return data of a child context, accessed from its parent context
+    /// Enabler for RETURNDATASIZE and RETURNDATACOPY opcodes
+    #[inline(always)]
+    fn child_context_return_data(ref self: Machine) -> Option<Span<u8>> {
+        let mut current_execution_ctx = self.current_context.unbox();
+        let child_context_return_data = current_execution_ctx.child_context_return_data();
+        self.current_context = BoxTrait::new(current_execution_ctx);
+        child_context_return_data
+    }
 }

crates/evm/src/tests/test_execution_context.cairo

@@ -1,6 +1,8 @@
 use core::nullable::{NullableTrait, null};
 use debug::PrintTrait;
-use evm::context::{CallContext, CallContextTrait, ExecutionContext, ExecutionContextTrait};
+use evm::context::{
+    CallContext, CallContextTrait, ExecutionContext, ExecutionContextTrait, DefaultOptionSpanU8
+};
 use evm::memory::{Memory, MemoryTrait};
 use evm::model::Event;
 use evm::stack::{Stack, StackTrait};
@@ -64,7 +66,6 @@ fn test_execution_context_new() {
     let read_only: bool = false;
 
     let parent_context: Nullable<ExecutionContext> = null();
-    let child_context: Nullable<ExecutionContext> = null();
 
     // When
     let mut execution_context = ExecutionContextTrait::new(
@@ -73,7 +74,7 @@ fn test_execution_context_new() {
         starknet_address,
         call_context,
         parent_context,
-        child_context,
+        Default::default(),
         return_data
     );
 
@@ -143,12 +144,27 @@ fn test_execution_context_read_code() {
 #[available_gas(300000)]
 #[ignore]
 fn test_is_root() {
-    // TODO: finish this test once calling_contexts are implemented
     // Given
     let mut execution_context = setup_execution_context();
 
     // When
     let is_root = execution_context.is_root();
-// Then
-// assert(is_root == true, 'should not be a leaf');
+
+    // Then
+    assert(is_root, 'should not be a leaf');
+}
+
+
+#[test]
+#[available_gas(300000)]
+#[ignore]
+fn test_child_context_return_data() {
+    // Given
+    let mut execution_context = setup_execution_context();
+
+    // When
+    let child_return_data = execution_context.child_context_return_data().unwrap();
+
+    // Then
+    assert(child_return_data == array![1, 2, 3].span(), 'should not be a leaf');
 }

crates/evm/src/tests/test_machine.cairo

@@ -161,3 +161,13 @@ fn test_return_data() {
     let return_data = machine.return_data();
     assert(return_data.len() == 0, 'wrong length');
 }
+
+
+#[test]
+#[available_gas(20000000)]
+fn test_child_context_return_data() {
+    let mut machine: Machine = setup_machine();
+
+    let return_data = machine.child_context_return_data().unwrap();
+    assert(return_data == array![1, 2, 3].span(), 'wrong child return data');
+}

crates/evm/src/tests/test_utils.cairo

@@ -1,4 +1,6 @@
-use evm::context::{CallContext, CallContextTrait, ExecutionContext, ExecutionContextTrait,};
+use evm::context::{
+    CallContext, CallContextTrait, ExecutionContext, ExecutionContextTrait, DefaultOptionSpanU8
+};
 
 use evm::machine::Machine;
 use starknet::{contract_address_try_from_felt252, ContractAddress, EthAddress};
@@ -37,14 +39,15 @@ fn setup_execution_context() -> ExecutionContext {
     let starknet_address: ContractAddress = starknet_address();
     let evm_address: EthAddress = evm_address();
     let return_data = Default::default();
+    let child_context_return_data = Option::Some(array![1, 2, 3].span());
 
     ExecutionContextTrait::new(
         context_id,
         evm_address,
         starknet_address,
         call_context,
         Default::default(),
-        Default::default(),
+        child_context_return_data,
         return_data,
     )
 }