Fix iterator crash on single-element trees and compilation errors

.gitignore

@@ -9,3 +9,4 @@ callgrind.*
 cmake-build-debug
 .idea
 *.log
+_codeql_build_dir/

include/art/node.hpp

@@ -9,6 +9,7 @@
 #include <algorithm>
 #include <array>
 #include <cassert>
+#include <cstdint>
 #include <cstring>
 #include <iostream>
 #include <iterator>

include/art/tree_it.hpp

@@ -110,9 +110,11 @@ typename tree_it<T>::step &tree_it<T>::step::operator++() {
   child_node_ = child_it_ != child_it_end_ 
     ? child_it_.get_child_node()
     : nullptr;
-  key_[depth_ - 1] = child_it_ != child_it_end_
-    ? child_it_.get_partial_key()
-    : '\0';
+  if (depth_ > 0) {
+    key_[depth_ - 1] = child_it_ != child_it_end_
+      ? child_it_.get_partial_key()
+      : '\0';
+  }
   return *this;
 }
 
@@ -311,6 +313,9 @@ void tree_it<T>::seek_leaf() {
   /* traverse up until a node on the right is found or stack gets empty */
   for (; get_step().child_it_ == get_step().child_it_end_; ++get_step()) {
     traversal_stack_.pop_back();
+    if (traversal_stack_.empty()) {
+      return;
+    }
     if (get_step().child_node_ == root_) { // root guard
       traversal_stack_.pop_back();
       assert(traversal_stack_.empty());

test/tree_it.cpp

@@ -22,6 +22,45 @@ using std::string;
 using std::to_string;
 
 TEST_SUITE("tree_it") {
+  TEST_CASE("single element iteration") {
+    SUBCASE("iterate over single element") {
+      int value = 42;
+      art::art<int*> m;
+
+      m.set("key1", &value);
+
+      auto it = m.begin();
+      auto it_end = m.end();
+
+      // First element should be accessible
+      REQUIRE(it != it_end);
+      REQUIRE_EQ(&value, *it);
+      REQUIRE_EQ("key1", it.key());
+
+      // Increment past the only element
+      ++it;
+
+      // Should now be at end
+      REQUIRE(it == it_end);
+    }
+
+    SUBCASE("iterate over single element with for loop") {
+      int value = 1;
+      art::art<int*> m;
+
+      m.set("key1", &value);
+
+      int count = 0;
+      for(auto itor = m.begin(); itor != m.end(); ++itor) {
+        REQUIRE_EQ("key1", itor.key());
+        REQUIRE_EQ(&value, *itor);
+        ++count;
+      }
+
+      REQUIRE_EQ(1, count);
+    }
+  }
+
   TEST_CASE("full lexicographic traversal") {
     SUBCASE("controlled test") {
       int int0 = 0;