fix: add negative index bounds check in ArrayObj

[guan404ming]

Why

ArrayObj::operator[] and ArrayObj::SetItem were missing negative index validation, causing undefined behavior when accessing arrays with negative indices.

How

• Add i < 0 check to ArrayObj::operator[] and ArrayObj::SetItem bounds validation
• Add test case

[gemini-code-assist]

Summary of Changes

Hello @guan404ming, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical vulnerability in the ArrayObj class by implementing robust bounds checking for negative indices in its access and modification methods. Previously, attempting to use negative indices could lead to undefined behavior. The changes ensure that such operations now correctly throw an IndexError, enhancing the stability and predictability of array manipulations.

Highlights

• Negative Index Validation: Added a bounds check for negative indices in ArrayObj::operator[] and ArrayObj::SetItem to prevent undefined behavior.
• New Test Case: Introduced a new test case, NegativeIndexThrows, to verify that accessing or setting array elements with negative indices correctly throws an IndexError.

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[gemini-code-assist]

Code Review

This pull request correctly adds the missing negative index bounds check in ArrayObj::operator[] and ArrayObj::SetItem. The change itself is correct and addresses a potential source of undefined behavior.

However, the accompanying test case in tests/cpp/test_array.cc does not actually test the modified code in ArrayObj. The test uses Array<T>::operator[] and Array<T>::Set, which have their own bounds checks that already handle negative indices. These wrapper methods do not delegate the check to the ArrayObj methods that were fixed.

I've provided a suggestion to update the test to directly target the changed methods in ArrayObj, ensuring the fix is properly verified.

[gemini-code-assist]

The current test case for negative indices exercises Array<T>::operator[] and Array<T>::Set. These methods have their own bounds checking, which already included negative index validation. Therefore, this test passes even without the fixes in ArrayObj and doesn't verify the changes made in this PR.

To ensure the fix is correctly tested, the test should directly call the modified methods on ArrayObj. The suggested change below targets ArrayObj::at (which calls operator[]) and ArrayObj::SetItem to properly validate the new bounds checks.

TEST(Array, NegativeIndexThrows) {
  Array<int> arr = {1, 2, 3};
  // Directly test ArrayObj methods, which are the ones modified in this PR.
  // The Array<T> wrapper methods already had negative index checks.
  ArrayObj* arr_obj = arr.GetArrayObj();

  // Test ArrayObj::at (which calls operator[])
  EXPECT_THROW(
      {
        try {
          [[maybe_unused]] const auto& val = arr_obj->at(-1);
        } catch (const Error& error) {
          EXPECT_EQ(error.kind(), "IndexError");
          throw;
        }
      },
      ::tvm::ffi::Error);

  // Test ArrayObj::SetItem
  EXPECT_THROW(
      {
        try {
          arr_obj->SetItem(-1, Any(42));
        } catch (const Error& error) {
          EXPECT_EQ(error.kind(), "IndexError");
          throw;
        }
      },
      ::tvm::ffi::Error);
}

[junrushao]

Good catch! Could you resolve the merge conflict so that I could get it in?

[guan404ming]

Sure, I've resolved it. Thanks!