Add error handling for objsequence and objstr index overflow

tests/snippets/index_overflow.py

@@ -0,0 +1,26 @@
+import sys
+
+
+def expect_cannot_fit_index_error(s, index):
+    try:
+        s[index]
+    except IndexError:
+        pass
+    # TODO: Replace current except block with commented
+    # after solving https://github.com/RustPython/RustPython/issues/322
+    # except IndexError as error:
+    #     assert str(error) == "cannot fit 'int' into an index-sized integer"
+    else:
+        assert False
+
+
+MAX_INDEX = sys.maxsize + 1
+MIN_INDEX = -(MAX_INDEX + 1)
+
+test_str = "test"
+expect_cannot_fit_index_error(test_str, MIN_INDEX)
+expect_cannot_fit_index_error(test_str, MAX_INDEX)
+
+test_list = [0, 1, 2, 3]
+expect_cannot_fit_index_error(test_list, MIN_INDEX)
+expect_cannot_fit_index_error(test_list, MAX_INDEX)

vm/src/obj/objsequence.rs

@@ -76,17 +76,20 @@ pub fn get_item(
     subscript: PyObjectRef,
 ) -> PyResult {
     match &(subscript.borrow()).payload {
-        PyObjectPayload::Integer { value } => {
-            let value = value.to_i32().unwrap();
-            let pos_index = elements.to_vec().get_pos(value);
-            if pos_index < elements.len() {
-                let obj = elements[pos_index].clone();
-                Ok(obj)
-            } else {
-                let index_error = vm.context().exceptions.index_error.clone();
-                Err(vm.new_exception(index_error, "Index out of bounds!".to_string()))
+        PyObjectPayload::Integer { value } => match value.to_i32() {
+            Some(value) => {
+                let pos_index = elements.to_vec().get_pos(value);
+                if pos_index < elements.len() {
+                    let obj = elements[pos_index].clone();
+                    Ok(obj)
+                } else {
+                    Err(vm.new_index_error("Index out of bounds!".to_string()))
+                }
             }
-        }
+            None => {
+                Err(vm.new_index_error("cannot fit 'int' into an index-sized integer".to_string()))
+            }
+        },
         PyObjectPayload::Slice {
             start: _,
             stop: _,

vm/src/obj/objstr.rs

@@ -1015,13 +1015,19 @@ fn to_graphemes<S: AsRef<str>>(value: S) -> Vec<String> {
 
 pub fn subscript(vm: &mut VirtualMachine, value: &str, b: PyObjectRef) -> PyResult {
     if objtype::isinstance(&b, &vm.ctx.int_type()) {
-        let pos = objint::get_value(&b).to_i32().unwrap();
-        let graphemes = to_graphemes(value);
-        let idx = graphemes.get_pos(pos);
-        graphemes
-            .get(idx)
-            .map(|c| vm.new_str(c.to_string()))
-            .ok_or(vm.new_index_error("string index out of range".to_string()))
+        match objint::get_value(&b).to_i32() {
+            Some(pos) => {
+                let graphemes = to_graphemes(value);
+                let idx = graphemes.get_pos(pos);
+                graphemes
+                    .get(idx)
+                    .map(|c| vm.new_str(c.to_string()))
+                    .ok_or(vm.new_index_error("string index out of range".to_string()))
+            }
+            None => {
+                Err(vm.new_index_error("cannot fit 'int' into an index-sized integer".to_string()))
+            }
+        }
     } else {
         match &(*b.borrow()).payload {
             &PyObjectPayload::Slice {