From 5380ff4d8866d2f37d706859c6223bc22d17dc98 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Sat, 13 Nov 2021 08:26:27 -0800
Subject: [PATCH] Detect types convertible to unformattable pointers

---
 include/fmt/core.h | 7 +++++--
 test/core-test.cc  | 6 ++++++
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index 01cf34cf1d4f..bb56da7fffd6 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -1370,8 +1370,11 @@ template <typename Context> struct arg_mapper {
 
   // We use SFINAE instead of a const T* parameter to avoid conflicting with
   // the C array overload.
-  template <typename T, FMT_ENABLE_IF(std::is_pointer<T>::value)>
-  FMT_CONSTEXPR auto map(T) -> unformattable_pointer {
+  template <
+      typename T,
+      FMT_ENABLE_IF(std::is_convertible<const T&, const void*>::value &&
+                    !std::is_convertible<const T&, const char_type*>::value)>
+  FMT_CONSTEXPR auto map(const T&) -> unformattable_pointer {
     return {};
   }
 
diff --git a/test/core-test.cc b/test/core-test.cc
index 5cf9dbd8c869..da3bc0f96cd1 100644
--- a/test/core-test.cc
+++ b/test/core-test.cc
@@ -733,6 +733,10 @@ template <> struct formatter<nonconst_formattable> {
 };
 FMT_END_NAMESPACE
 
+struct convertible_to_pointer {
+  operator const int*() const { return nullptr; }
+};
+
 TEST(core_test, is_formattable) {
   static_assert(fmt::is_formattable<signed char*>::value, "");
   static_assert(fmt::is_formattable<unsigned char*>::value, "");
@@ -760,6 +764,8 @@ TEST(core_test, is_formattable) {
   static_assert(!fmt::is_formattable<const nonconst_formattable&>::value, "");
 #endif
 
+  static_assert(!fmt::is_formattable<convertible_to_pointer>::value, "");
+
   static_assert(!fmt::is_formattable<signed char*, wchar_t>::value, "");
   static_assert(!fmt::is_formattable<unsigned char*, wchar_t>::value, "");
   static_assert(!fmt::is_formattable<const signed char*, wchar_t>::value, "");