From 0936c55f626c21a3788545a7fbd6be4424ae3350 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C5=91rinc?= <pap.lorinc@gmail.com>
Date: Tue, 11 Aug 2026 11:50:11 -0700
Subject: [PATCH 1/2] test: characterize kernel range iterators

---
 src/test/kernel/test_kernel.cpp | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/test/kernel/test_kernel.cpp b/src/test/kernel/test_kernel.cpp
index d3886ad58ac..10635937fe2 100644
--- a/src/test/kernel/test_kernel.cpp
+++ b/src/test/kernel/test_kernel.cpp
@@ -745,6 +745,12 @@ BOOST_AUTO_TEST_CASE(btck_block)
     CheckHandle(block, block_100);
     Block block_tx{hex_string_to_byte_vec(REGTEST_BLOCK_DATA[205])};
     CheckRange(block_tx.Transactions(), block_tx.CountTransactions());
+    auto transactions{block_tx.Transactions()};
+    auto transactions_copy{transactions};
+    BOOST_CHECK(transactions.begin() != transactions_copy.begin()); // TODO: Iterators over the same underlying block should compare equal.
+    BOOST_CHECK(transactions.begin() != block_tx.Transactions().begin()); // TODO: Iterators over the same underlying block should compare equal.
+    auto transaction_it{transactions.begin()};
+    BOOST_CHECK((*transaction_it).Txid() == block_tx.GetTransaction(0).Txid());
     auto invalid_data = hex_string_to_byte_vec("012300");
     BOOST_CHECK_THROW(Block{invalid_data}, std::runtime_error);
     auto empty_data = hex_string_to_byte_vec("");

From fc0dcf950f97ef30930960c39a04ac28dcdadee1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C5=91rinc?= <pap.lorinc@gmail.com>
Date: Tue, 11 Aug 2026 11:51:13 -0700
Subject: [PATCH 2/2] kernel: keep range iterators tied to their owner

`Range` iterators point to the view, so iterators saved from temporary views dangle.
Point them to the underlying container, use the range's getter for element access, and remove `operator->`, which returned elements by value and could not support arrow expressions.

Co-authored-by: Daniel Pfeifer <daniel@pfeifer-mail.de>
---
 src/kernel/bitcoinkernel_wrapper.h | 13 ++++++-------
 src/test/kernel/test_kernel.cpp    |  4 ++--
 2 files changed, 8 insertions(+), 9 deletions(-)

diff --git a/src/kernel/bitcoinkernel_wrapper.h b/src/kernel/bitcoinkernel_wrapper.h
index ed686a9fa47..b929bcc1a13 100644
--- a/src/kernel/bitcoinkernel_wrapper.h
+++ b/src/kernel/bitcoinkernel_wrapper.h
@@ -190,7 +190,7 @@ T check(T ptr)
     return ptr;
 }
 
-template <typename Collection, typename ValueType>
+template <typename Collection, typename ValueType, auto GetFunc>
 class Iterator
 {
 public:
@@ -209,8 +209,7 @@ public:
     Iterator(const Collection* ptr, size_t idx) : m_collection{ptr}, m_idx{idx} {}
 
     // This is just a view, so return a copy.
-    auto operator*() const { return (*m_collection)[m_idx]; }
-    auto operator->() const { return (*m_collection)[m_idx]; }
+    auto operator*() const { return std::invoke(GetFunc, *m_collection, m_idx); }
 
     auto& operator++() { m_idx++; return *this; }
     auto operator++(int) { Iterator tmp = *this; ++(*this); return tmp; }
@@ -226,7 +225,7 @@ public:
 
     auto operator-(const Iterator& other) const { return static_cast<difference_type>(m_idx) - static_cast<difference_type>(other.m_idx); }
 
-    ValueType operator[](difference_type n) const { return (*m_collection)[m_idx + n]; }
+    ValueType operator[](difference_type n) const { return *(*this + n); }
 
     auto operator<=>(const Iterator& other) const { return m_idx <=> other.m_idx; }
 
@@ -249,7 +248,7 @@ class Range
 public:
     using value_type = std::invoke_result_t<decltype(GetFunc), const Container&, size_t>;
     using difference_type = std::ptrdiff_t;
-    using iterator = Iterator<Range, value_type>;
+    using iterator = Iterator<Container, value_type, GetFunc>;
     using const_iterator = iterator;
 
 private:
@@ -261,8 +260,8 @@ public:
         static_assert(std::ranges::random_access_range<Range>);
     }
 
-    iterator begin() const { return iterator(this, 0); }
-    iterator end() const { return iterator(this, size()); }
+    iterator begin() const { return iterator(m_container, 0); }
+    iterator end() const { return iterator(m_container, size()); }
 
     const_iterator cbegin() const { return begin(); }
     const_iterator cend() const { return end(); }
diff --git a/src/test/kernel/test_kernel.cpp b/src/test/kernel/test_kernel.cpp
index 10635937fe2..8b919c918fb 100644
--- a/src/test/kernel/test_kernel.cpp
+++ b/src/test/kernel/test_kernel.cpp
@@ -747,8 +747,8 @@ BOOST_AUTO_TEST_CASE(btck_block)
     CheckRange(block_tx.Transactions(), block_tx.CountTransactions());
     auto transactions{block_tx.Transactions()};
     auto transactions_copy{transactions};
-    BOOST_CHECK(transactions.begin() != transactions_copy.begin()); // TODO: Iterators over the same underlying block should compare equal.
-    BOOST_CHECK(transactions.begin() != block_tx.Transactions().begin()); // TODO: Iterators over the same underlying block should compare equal.
+    BOOST_CHECK(transactions.begin() == transactions_copy.begin());
+    BOOST_CHECK(transactions.begin() == block_tx.Transactions().begin());
     auto transaction_it{transactions.begin()};
     BOOST_CHECK((*transaction_it).Txid() == block_tx.GetTransaction(0).Txid());
     auto invalid_data = hex_string_to_byte_vec("012300");