fix zkDSL compiler edge case

Author: TomWambsgans

crates/lean_compiler/src/a_simplify_lang.rs

@@ -1588,6 +1588,31 @@ fn handle_array_assignment(
 ) {
     let simplified_index = simplify_expr(index, res, counters, array_manager, const_malloc, const_arrays);
 
+    if let (ArrayAccessType::VarIsAssigned(var), SimpleExpr::Var(array_var)) = (&access_type, &array)
+        && let Some(const_array) = const_arrays.get(array_var)
+    {
+        let index = simplified_index
+            .as_constant()
+            .expect("Const array access index should be constant")
+            .naive_eval()
+            .unwrap()
+            .to_usize();
+        assert!(
+            index < const_array.len(),
+            "Const array '{}' index {} out of bounds (length {})",
+            array_var,
+            index,
+            const_array.len()
+        );
+        res.push(SimpleLine::Assignment {
+            var: var.clone().into(),
+            operation: HighLevelOperation::Add,
+            arg0: SimpleExpr::Constant(ConstExpression::from(const_array[index])),
+            arg1: SimpleExpr::zero(),
+        });
+        return;
+    }
+
     if let SimpleExpr::Constant(offset) = simplified_index.clone()
         && let SimpleExpr::Var(array_var) = &array
         && let Some(label) = const_malloc.map.get(array_var)

crates/lean_compiler/tests/test_compiler.rs

@@ -1057,6 +1057,24 @@ fn intertwined_unrolled_loops_and_const_function_arguments() {
     );
 }
 
+#[test]
+fn test_direct_const_arr_access() {
+    let program = r#"
+        const ARR = [10, 100];
+        fn main() {
+            a = ARR[0];
+            assert a == 10;
+            return;
+        }
+    "#;
+    compile_and_run(
+        &ProgramSource::Raw(program.to_string()),
+        (&[], &[]),
+        DEFAULT_NO_VEC_RUNTIME_MEMORY,
+        false,
+    );
+}
+
 #[test]
 fn test_const_fibonacci() {
     let program = r#"