Fix iterator crash on single-element trees and compilation errors

[Copilot]

Iterating past the last element in a single-element ART triggers a segmentation fault due to multiple bugs in the iterator implementation.

art::art<int> table;
table.set("key1", 1);
for(auto it = table.begin(); it != table.end(); ++it) {
    // Crash occurs on increment past last element
}

Root Causes Fixed

1. Missing #include <cstdint> in node.hpp (Pre-existing)

• uint16_t prefix_len_ was undefined, causing 138 compilation errors that prevented any build
• Fix: Added #include <cstdint> to node.hpp

2. Buffer underflow in step::operator++() (Pre-existing)

• When incrementing the sentinel node (depth_ = 0, key_ = nullptr), code attempted to access key_[-1], causing segmentation fault
• Fix: Added check if (depth_ > 0) before accessing key_[depth_ - 1]

3. Empty stack access in seek_leaf() (Original issue)

• After popping traversal stack, code called get_step() without checking if stack was empty
• get_step() asserts non-empty stack, causing crash
• Fix: Added empty stack check after pop, return early if empty

Changes

• node.hpp: Add missing #include <cstdint> to fix compilation
• tree_it.hpp: Add empty stack check in seek_leaf() and depth check in step::operator++() to prevent buffer underflow
• tree_it.cpp: Add test cases for single-element iteration edge case
• .gitignore: Exclude CodeQL build artifacts

Test Results

All 25 tests now pass:

[doctest] test cases:     25 |     25 passed |      0 failed
[doctest] assertions: 41154954 | 41154954 passed |      0 failed
[doctest] Status: SUCCESS!

• Fixes coredump with loop #19

Original prompt

---

This section details on the original issue you should resolve

<issue_title>coredump with loop</issue_title>
<issue_description>Hi,I found that when the ART has only one key-value and loop it,it will core dump:
art::art table;
table.set("key1",1);
for(auto itor = table.begin(); itor != table.end(); itor++)
{
std::cout << itor.key() << std::endl;
std::cout << *itor << std::endl;
}</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes coredump with loop #19

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[rafaelkallis]

@copilot make sure the tests are passing

[Copilot]

@copilot make sure the tests are passing

Tests are now passing! Fixed two pre-existing bugs that were preventing compilation and causing the crash:

1. Missing #include <cstdint> in node.hpp (138 compilation errors)
2. Buffer underflow in step::operator++() when accessing key_[-1] with sentinel node

All 25 tests pass:

[doctest] test cases:     25 |     25 passed |      0 failed
[doctest] assertions: 41154954 | 41154954 passed |      0 failed
[doctest] Status: SUCCESS!

Commit: 9183cfe

[rafaelkallis]

lgtm

[Copilot]

Pull request overview

This PR fixes a critical segmentation fault that occurs when iterating past the last element in a single-element ART, along with a pre-existing compilation issue. The root cause was identified as two bugs in the iterator implementation: a buffer underflow when incrementing the sentinel step, and an empty stack access after popping the last element.

Key changes:

• Fixed compilation errors by adding missing #include <cstdint> for uint16_t
• Added bounds checking to prevent buffer underflow when incrementing iterator steps with zero depth
• Added empty stack validation in seek_leaf() to prevent invalid memory access

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated no comments.

File	Description
include/art/node.hpp	Adds missing #include <cstdint> to resolve compilation errors for uint16_t prefix_len_
include/art/tree_it.hpp	Adds depth_ > 0 check before array access in step::operator++() and empty stack check in seek_leaf() to prevent crashes
test/tree_it.cpp	Adds comprehensive test cases for single-element iteration covering both manual iteration and for-loop patterns
.gitignore	Excludes CodeQL build artifacts from version control