Revert with proper panic if array index out of bounds (#606)

crates/test-files/fixtures/features/arrays.fe

@@ -0,0 +1,9 @@
+contract Foo:
+    my_array: Array<u256, 10>
+
+    pub fn get_from_storage(self, index: u256) -> u256:
+        return self.my_array[index]
+
+    pub fn get_from_memory(index: u256) -> u256:
+        let my_array: Array<u256, 10> = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
+        return my_array[index]

crates/test-utils/src/lib.rs

@@ -230,6 +230,10 @@ pub fn encoded_over_or_underflow() -> Vec<u8> {
     encode_revert("Panic(uint256)", &[uint_token(0x11)])
 }
 
+pub fn encoded_panic_out_of_bounds() -> Vec<u8> {
+    encode_revert("Panic(uint256)", &[uint_token(0x32)])
+}
+
 pub fn encoded_div_or_mod_by_zero() -> Vec<u8> {
     encode_revert("Panic(uint256)", &[uint_token(0x12)])
 }

crates/tests/src/features.rs

@@ -221,6 +221,37 @@ fn test_assert() {
     })
 }
 
+#[test]
+fn test_arrays() {
+    with_executor(&|mut executor| {
+        let harness = deploy_contract(&mut executor, "arrays.fe", "Foo", &[]);
+
+        harness.test_function(
+            &mut executor,
+            "get_from_memory",
+            &[uint_token(9)],
+            Some(&uint_token(10)),
+        );
+
+        validate_revert(
+            harness.capture_call(&mut executor, "get_from_memory", &[uint_token(10)]),
+            &encoded_panic_out_of_bounds(),
+        );
+
+        harness.test_function(
+            &mut executor,
+            "get_from_storage",
+            &[uint_token(9)],
+            Some(&uint_token(0)),
+        );
+
+        validate_revert(
+            harness.capture_call(&mut executor, "get_from_storage", &[uint_token(10)]),
+            &encoded_panic_out_of_bounds(),
+        );
+    })
+}
+
 #[rstest(fixture_file, input, expected,
     case("for_loop_with_static_array.fe", &[], uint_token(30)),
     case("for_loop_with_static_array_from_sto.fe", &[], uint_token(6)),

crates/yulgen/src/constants.rs

@@ -64,6 +64,7 @@ pub fn numeric_min_max() -> HashMap<Integer, (yul::Expression, yul::Expression)>
 pub const PANIC_FAILED_ASSERTION: usize = 0x01;
 pub const PANIC_OVER_OR_UNDERFLOW: usize = 0x11;
 pub const PANIC_DIV_OR_MOD_BY_ZERO: usize = 0x12;
+pub const PANIC_OUT_OF_BOUNDS: usize = 0x32;
 
 pub const ERROR_INSUFFICIENT_FUNDS_TO_SEND_VALUE: usize = 0x100;
 pub const ERROR_FAILED_SEND_VALUE: usize = 0x101;

crates/yulgen/src/operations/data.rs

@@ -139,5 +139,6 @@ pub fn indexed_array(
     index: yul::Expression,
 ) -> yul::Expression {
     let inner_size = literal_expression! { (typ.inner.size()) };
-    expression! { add([array], (mul([index], [inner_size]))) }
+    let array_length = literal_expression! { (typ.size) };
+    expression! { get_array_item([array], [array_length], [index], [inner_size] ) }
 }

crates/yulgen/src/runtime/functions/data.rs

@@ -1,3 +1,6 @@
+use crate::constants::PANIC_OUT_OF_BOUNDS;
+use crate::operations::revert as revert_operations;
+
 use yultsur::*;
 
 /// Return all data runtime functions
@@ -15,6 +18,7 @@ pub fn all() -> Vec<yul::Statement> {
         ceil32(),
         cloadn(),
         free(),
+        get_array_item(),
         load_data_string(),
         map_value_ptr(),
         mcopym(),
@@ -366,3 +370,16 @@ pub fn load_data_string() -> yul::Statement {
         }
     }
 }
+
+/// Returns a pointer to the array item at the requested index.
+/// Reverts with a panic if the index is out of bounds.
+pub fn get_array_item() -> yul::Statement {
+    function_definition! {
+        function get_array_item(array_ptr, array_length, index, inner_size) -> ptr {
+            (if (iszero((lt(index, array_length)))) {
+                [revert_operations::panic_revert(PANIC_OUT_OF_BOUNDS)]
+            } )
+            (ptr := add(array_ptr, (mul(index, inner_size))))
+        }
+    }
+}

newsfragments/606.feature.md

@@ -0,0 +1,3 @@
+Added an out of bounds check for accessing array items.
+If an array index is retrieved at an index that is not within
+the bounds of the array it now reverts with `Panic(0x32)`.