From 510df14124259ef19b27fd90554905ce6dbcd4d5 Mon Sep 17 00:00:00 2001
From: Aaron Gokaslan <skylion.aaron@gmail.com>
Date: Wed, 14 Jul 2021 14:14:07 -0400
Subject: [PATCH 1/2] Enable constexpr in casting for C++17

---
 include/pybind11/cast.h          | 25 ++++++++++++++++++-------
 include/pybind11/detail/common.h |  6 ++++++
 2 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index a748c77c0f..92cedec71a 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -887,13 +887,24 @@ T cast(const handle &handle) { return T(reinterpret_borrow<object>(handle)); }
 template <typename T, detail::enable_if_t<!detail::is_pyobject<T>::value, int> = 0>
 object cast(T &&value, return_value_policy policy = return_value_policy::automatic_reference,
             handle parent = handle()) {
-    using no_ref_T = typename std::remove_reference<T>::type;
-    if (policy == return_value_policy::automatic)
-        policy = std::is_pointer<no_ref_T>::value ? return_value_policy::take_ownership :
-                 std::is_lvalue_reference<T>::value ? return_value_policy::copy : return_value_policy::move;
-    else if (policy == return_value_policy::automatic_reference)
-        policy = std::is_pointer<no_ref_T>::value ? return_value_policy::reference :
-                 std::is_lvalue_reference<T>::value ? return_value_policy::copy : return_value_policy::move;
+    // using no_ref_T = PYBIND11_CPP17_CONSTEXPR std::remove_reference<T>::type;
+    if (policy == return_value_policy::automatic) {
+        if PYBIND11_CPP17_CONSTEXPR (std::is_pointer<std::remove_reference<T>>::value) {
+            policy = return_value_policy::take_ownership;
+        } else if PYBIND11_CPP17_CONSTEXPR (std::is_lvalue_reference<T>::value) {
+            policy = return_value_policy::copy;
+        } else {
+            policy = return_value_policy::move;
+        }
+    } else if (policy == return_value_policy::automatic_reference) {
+        if PYBIND11_CPP17_CONSTEXPR (std::is_pointer<std::remove_reference<T>>::value) {
+            policy = return_value_policy::reference;
+        } else if PYBIND11_CPP17_CONSTEXPR (std::is_lvalue_reference<T>::value) {
+            policy = return_value_policy::copy;
+        } else {
+            policy = return_value_policy::move;
+        }
+    }
     return reinterpret_steal<object>(detail::make_caster<T>::cast(std::forward<T>(value), policy, parent));
 }
 
diff --git a/include/pybind11/detail/common.h b/include/pybind11/detail/common.h
index f804e7c85a..3c16a329e6 100644
--- a/include/pybind11/detail/common.h
+++ b/include/pybind11/detail/common.h
@@ -102,6 +102,12 @@
 #  define PYBIND11_MAYBE_UNUSED __attribute__ ((__unused__))
 #endif
 
+#if defined(PYBIND11_CPP17)
+#    define PYBIND11_CPP17_CONSTEXPR constexpr
+#else
+#    define PYBIND11_CPP17_CONSTEXPR
+#endif
+
 /* Don't let Python.h #define (v)snprintf as macro because they are implemented
    properly in Visual Studio since 2015. */
 #if defined(_MSC_VER) && _MSC_VER >= 1900

From 7948b6b53dd9cd512b9bdbcde5d88b0efb222cb2 Mon Sep 17 00:00:00 2001
From: Aaron Gokaslan <skylion.aaron@gmail.com>
Date: Wed, 14 Jul 2021 14:15:59 -0400
Subject: [PATCH 2/2] Remove comment

---
 include/pybind11/cast.h | 1 -
 1 file changed, 1 deletion(-)

diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index 92cedec71a..b478ed3491 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -887,7 +887,6 @@ T cast(const handle &handle) { return T(reinterpret_borrow<object>(handle)); }
 template <typename T, detail::enable_if_t<!detail::is_pyobject<T>::value, int> = 0>
 object cast(T &&value, return_value_policy policy = return_value_policy::automatic_reference,
             handle parent = handle()) {
-    // using no_ref_T = PYBIND11_CPP17_CONSTEXPR std::remove_reference<T>::type;
     if (policy == return_value_policy::automatic) {
         if PYBIND11_CPP17_CONSTEXPR (std::is_pointer<std::remove_reference<T>>::value) {
             policy = return_value_policy::take_ownership;