TPE: Guard against stack overflow

cedar-policy-core/src/evaluator.rs

@@ -1159,7 +1159,7 @@ impl Value {
 }
 
 #[inline(always)]
-fn stack_size_check() -> Result<()> {
+pub(crate) fn stack_size_check() -> Result<()> {
     // We assume there's enough space if we cannot determine it with `remaining_stack`
     if stacker::remaining_stack().unwrap_or(REQUIRED_STACK_SPACE) < REQUIRED_STACK_SPACE {
         return Err(EvaluationError::recursion_limit(None));

cedar-policy-core/src/tpe/evaluator.rs

@@ -22,6 +22,7 @@ use crate::tpe::err::ExprToResidualError;
 use crate::validator::types::Type;
 use crate::{
     ast::{self, BinaryOp, EntityUID, Expr, PartialValue, Set, Value, ValueKind, Var},
+    evaluator::stack_size_check,
     extensions::Extensions,
 };
 
@@ -60,6 +61,13 @@ impl Evaluator<'_> {
             }
             Residual::Partial { kind, ty: _ty } => kind,
         };
+
+        // Guard against stack overflows (just like the concrete evaluator), given the recursive nature of interpret
+        match stack_size_check() {
+            Ok(_) => (),
+            Err(_) => return Residual::Error(ty),
+        }
+
         match kind {
             ResidualKind::Var(Var::Action) => Residual::Concrete {
                 value: self.request.action.clone().into(),