Feature: add a method to retrieve the output builtin from the VM

Problem: the output builtin often needs to be manipulated directly in
the Starknet bootloader and OS hints.

Solution: add a `get_output_builtin() method on the `VirtualMachine` struct to
retrieve a reference to the output builtin easily.

Author: odesenfans

Cargo.lock

@@ -81,6 +81,8 @@ pub enum VirtualMachineError {
     InconsistentAutoDeduction(Box<(&'static str, MaybeRelocatable, Option<MaybeRelocatable>)>),
     #[error("Invalid hint encoding at pc: {0}")]
     InvalidHintEncoding(Box<MaybeRelocatable>),
+    #[error("Expected output builtin to be present")]
+    NoOutputBuiltin,
     #[error("Expected range_check builtin to be present")]
     NoRangeCheckBuiltin,
     #[error("Expected ecdsa builtin to be present")]

vm/src/vm/errors/vm_errors.rs

@@ -32,7 +32,7 @@ use core::num::NonZeroUsize;
 use num_traits::{ToPrimitive, Zero};
 
 use super::errors::runner_errors::RunnerError;
-use super::runners::builtin_runner::OUTPUT_BUILTIN_NAME;
+use super::runners::builtin_runner::{OutputBuiltinRunner, OUTPUT_BUILTIN_NAME};
 
 const MAX_TRACEBACK_ENTRIES: u32 = 20;
 
@@ -942,6 +942,17 @@ impl VirtualMachine {
 
         Err(VirtualMachineError::NoSignatureBuiltin)
     }
+
+    pub fn get_output_builtin(&mut self) -> Result<&mut OutputBuiltinRunner, VirtualMachineError> {
+        for builtin in self.get_builtin_runners_as_mut() {
+            if let BuiltinRunner::Output(output_builtin) = builtin {
+                return Ok(output_builtin);
+            };
+        }
+
+        Err(VirtualMachineError::NoOutputBuiltin)
+    }
+
     pub fn disable_trace(&mut self) {
         self.trace = None
     }
@@ -3842,6 +3853,30 @@ mod tests {
         assert_eq!(builtins[1].name(), BITWISE_BUILTIN_NAME);
     }
 
+    #[test]
+    #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
+    fn test_get_output_builtin() {
+        let mut vm = vm!();
+
+        assert_matches!(
+            vm.get_output_builtin(),
+            Err(VirtualMachineError::NoOutputBuiltin)
+        );
+
+        let output_builtin = OutputBuiltinRunner::new(true);
+        vm.builtin_runners.push(output_builtin.clone().into());
+
+        let vm_output_builtin = vm
+            .get_output_builtin()
+            .expect("Output builtin should be returned");
+
+        assert_eq!(vm_output_builtin.base(), output_builtin.base());
+        assert_eq!(vm_output_builtin.pages, output_builtin.pages);
+        assert_eq!(vm_output_builtin.attributes, output_builtin.attributes);
+        assert_eq!(vm_output_builtin.stop_ptr, output_builtin.stop_ptr);
+        assert_eq!(vm_output_builtin.included, output_builtin.included);
+    }
+
     #[test]
     #[cfg_attr(target_arch = "wasm32", wasm_bindgen_test)]
     fn disable_trace() {