fix: let unary traits work at comptime

compiler/noirc_frontend/src/hir/comptime/interpreter.rs

@@ -613,7 +613,12 @@ impl<'a> Interpreter<'a> {
             UnaryOp::MutableReference => self.evaluate_no_dereference(prefix.rhs)?,
             _ => self.evaluate(prefix.rhs)?,
         };
-        self.evaluate_prefix_with_value(rhs, prefix.operator, id)
+
+        if self.interner.get_selected_impl_for_expression(id).is_some() {
+            self.evaluate_overloaded_prefix(prefix, rhs, id)
+        } else {
+            self.evaluate_prefix_with_value(rhs, prefix.operator, id)
+        }
     }
 
     fn evaluate_prefix_with_value(
@@ -953,6 +958,25 @@ impl<'a> Interpreter<'a> {
         }
     }
 
+    fn evaluate_overloaded_prefix(
+        &mut self,
+        prefix: HirPrefixExpression,
+        rhs: Value,
+        id: ExprId,
+    ) -> IResult<Value> {
+        let method =
+            prefix.trait_method_id.expect("ice: expected prefix operator trait at this point");
+        let operator = prefix.operator;
+
+        let method_id = resolve_trait_method(self.interner, method, id)?;
+        let type_bindings = self.interner.get_instantiation_bindings(id).clone();
+
+        let rhs = (rhs, self.interner.expr_location(&prefix.rhs));
+
+        let location = self.interner.expr_location(&id);
+        self.call_function(method_id, vec![rhs], type_bindings, location)
+    }
+
     /// Given the result of a `cmp` operation, convert it into the boolean result of the given operator.
     /// - `<`:  `ordering == Ordering::Less`
     /// - `<=`: `ordering != Ordering::Greater`

test_programs/compile_success_empty/comptime_traits/src/main.nr

@@ -1,3 +1,5 @@
+use std::ops::Neg;
+
 fn main() {
     comptime
     {
@@ -13,3 +15,22 @@ fn main() {
         assert([1, 2] != array);
     }
 }
+
+struct MyType {
+    value: i32,
+}
+
+comptime impl Neg for MyType {
+    comptime fn neg(self) -> Self {
+        self
+    }
+}
+
+fn neg_at_comptime() {
+    comptime
+    {
+        let value = MyType { value: 1 };
+        let _result = -value;
+    }
+}
+