From 997f19d6ce7817fa3afe5903a8bb90ad6974c8f2 Mon Sep 17 00:00:00 2001
From: Francesco Biscani <bluescarni@gmail.com>
Date: Fri, 20 Sep 2024 22:02:39 +0200
Subject: [PATCH] Fix potentially invalid use of C++20 input iterators as C++17
 iterators.

---
 include/heyoka/detail/rng_to_vec.hpp | 51 ++++++++++++++++++++++++++++
 include/heyoka/expression.hpp        | 10 +++---
 include/heyoka/llvm_state.hpp        |  3 +-
 src/taylor_02.cpp                    |  5 +--
 4 files changed, 61 insertions(+), 8 deletions(-)
 create mode 100644 include/heyoka/detail/rng_to_vec.hpp

diff --git a/include/heyoka/detail/rng_to_vec.hpp b/include/heyoka/detail/rng_to_vec.hpp
new file mode 100644
index 000000000..21b5e9c2a
--- /dev/null
+++ b/include/heyoka/detail/rng_to_vec.hpp
@@ -0,0 +1,51 @@
+// Copyright 2020, 2021, 2022, 2023, 2024 Francesco Biscani (bluescarni@gmail.com), Dario Izzo (dario.izzo@gmail.com)
+//
+// This file is part of the heyoka library.
+//
+// This Source Code Form is subject to the terms of the Mozilla
+// Public License v. 2.0. If a copy of the MPL was not distributed
+// with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+#ifndef HEYOKA_DETAIL_RNG_TO_VEC_HPP
+#define HEYOKA_DETAIL_RNG_TO_VEC_HPP
+
+#include <ranges>
+#include <type_traits>
+#include <utility>
+#include <vector>
+
+#include <heyoka/config.hpp>
+
+HEYOKA_BEGIN_NAMESPACE
+
+namespace detail
+{
+
+// Helper to convert an input range R into a vector.
+// The value type is deduced from the reference type of R.
+template <typename R>
+auto rng_to_vec(R &&r)
+{
+    // Deduce the value type.
+    using value_type = std::remove_cvref_t<std::ranges::range_reference_t<R>>;
+
+    // Prepare the return value, reserving the appropriate
+    // size if R is a sized range.
+    std::vector<value_type> retval;
+    if constexpr (std::ranges::sized_range<R>) {
+        retval.reserve(static_cast<decltype(retval.size())>(std::ranges::size(r)));
+    }
+
+    // Add r's values into retval.
+    for (auto &&val : r) {
+        retval.push_back(std::forward<decltype(val)>(val));
+    }
+
+    return retval;
+}
+
+} // namespace detail
+
+HEYOKA_END_NAMESPACE
+
+#endif
diff --git a/include/heyoka/expression.hpp b/include/heyoka/expression.hpp
index 72b01683b..5bac58cd6 100644
--- a/include/heyoka/expression.hpp
+++ b/include/heyoka/expression.hpp
@@ -54,6 +54,7 @@
 #include <heyoka/detail/fwd_decl.hpp>
 #include <heyoka/detail/igor.hpp>
 #include <heyoka/detail/llvm_fwd.hpp>
+#include <heyoka/detail/rng_to_vec.hpp>
 #include <heyoka/detail/type_traits.hpp>
 #include <heyoka/detail/visibility.hpp>
 #include <heyoka/func.hpp>
@@ -461,8 +462,8 @@ class HEYOKA_DLL_PUBLIC dtens
     [[nodiscard]] size_type index_of(const iterator &) const;
 
     [[nodiscard]] auto get_derivatives(std::uint32_t) const -> decltype(std::ranges::subrange(begin(), end()));
-    [[nodiscard]] auto get_derivatives(std::uint32_t,
-                                       std::uint32_t) const -> decltype(std::ranges::subrange(begin(), end()));
+    [[nodiscard]] auto get_derivatives(std::uint32_t, std::uint32_t) const
+        -> decltype(std::ranges::subrange(begin(), end()));
     [[nodiscard]] std::vector<expression> get_gradient() const;
     [[nodiscard]] std::vector<expression> get_jacobian() const;
     [[nodiscard]] std::vector<expression> get_hessian(std::uint32_t) const;
@@ -846,9 +847,8 @@ class HEYOKA_DLL_PUBLIC_INLINE_CLASS cfunc
     template <typename R>
     static auto rng_to_vecex(R &&r)
     {
-        auto tv = r | std::views::transform([]<typename U>(U &&x) { return expression{std::forward<U>(x)}; });
-
-        return std::vector(std::ranges::begin(tv), std::ranges::end(tv));
+        return detail::rng_to_vec(
+            r | std::views::transform([]<typename U>(U &&x) { return expression{std::forward<U>(x)}; }));
     }
 
 public:
diff --git a/include/heyoka/llvm_state.hpp b/include/heyoka/llvm_state.hpp
index a6fb77d52..07f26c9cf 100644
--- a/include/heyoka/llvm_state.hpp
+++ b/include/heyoka/llvm_state.hpp
@@ -41,6 +41,7 @@
 
 #include <heyoka/detail/fwd_decl.hpp>
 #include <heyoka/detail/llvm_fwd.hpp>
+#include <heyoka/detail/rng_to_vec.hpp>
 #include <heyoka/detail/type_traits.hpp>
 #include <heyoka/detail/visibility.hpp>
 #include <heyoka/kw.hpp>
@@ -390,7 +391,7 @@ class HEYOKA_DLL_PUBLIC llvm_multi_state
         requires std::ranges::input_range<R>
                  && std::same_as<llvm_state, std::remove_cvref_t<std::ranges::range_reference_t<R>>>
     explicit llvm_multi_state(R &&rng, bool parjit = detail::default_parjit)
-        : llvm_multi_state(std::vector(std::ranges::begin(rng), std::ranges::end(rng)), parjit)
+        : llvm_multi_state(detail::rng_to_vec(std::forward<R>(rng)), parjit)
     {
     }
     llvm_multi_state(const llvm_multi_state &);
diff --git a/src/taylor_02.cpp b/src/taylor_02.cpp
index b5d4354d0..274634471 100644
--- a/src/taylor_02.cpp
+++ b/src/taylor_02.cpp
@@ -65,6 +65,7 @@
 #include <heyoka/detail/llvm_helpers.hpp>
 #include <heyoka/detail/llvm_vector_type.hpp>
 #include <heyoka/detail/logging_impl.hpp>
+#include <heyoka/detail/rng_to_vec.hpp>
 #include <heyoka/detail/string_conv.hpp>
 #include <heyoka/detail/type_traits.hpp>
 #include <heyoka/detail/visibility.hpp>
@@ -1200,8 +1201,8 @@ std::vector<llvm_state> taylor_compute_jet_multi(llvm_state &main_state, llvm::T
     // the custom transform:
     //
     // https://en.cppreference.com/w/cpp/ranges/as_rvalue_view
-    auto sview = states | std::views::transform([](auto &s) -> auto && { return std::move(s); });
-    return std::vector(std::ranges::begin(sview), std::ranges::end(sview));
+    auto sview = states | std::views::transform([](llvm_state &s) -> llvm_state && { return std::move(s); });
+    return rng_to_vec(sview);
 }
 
 // Helper for the computation of a jet of derivatives in compact mode,