From 0c7650373c9699dccf6388572dd710b06ee17411 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <victor.zverovich@gmail.com>
Date: Fri, 4 Oct 2019 17:21:10 -0700
Subject: [PATCH] Fix handling of types convertible to std::string_view

---
 include/fmt/core.h |  8 ++++++++
 test/core-test.cc  | 11 +++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index 0d7d15b5..8cdc9cdc 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -828,6 +828,14 @@ template <typename Context> struct arg_mapper {
   FMT_CONSTEXPR basic_string_view<char_type> map(const T& val) {
     return basic_string_view<char_type>(val);
   }
+  template <typename T,
+            FMT_ENABLE_IF(
+                std::is_constructible<std_string_view<char_type>, T>::value &&
+                !std::is_constructible<basic_string_view<char_type>, T>::value &&
+                !is_string<T>::value)>
+  FMT_CONSTEXPR basic_string_view<char_type> map(const T& val) {
+    return std_string_view<char_type>(val);
+  }
   FMT_CONSTEXPR const char* map(const signed char* val) {
     static_assert(std::is_same<char_type, char>::value, "invalid string type");
     return reinterpret_cast<const char*>(val);
diff --git a/test/core-test.cc b/test/core-test.cc
index 0de26dbe..84d2b9eb 100644
--- a/test/core-test.cc
+++ b/test/core-test.cc
@@ -613,6 +613,17 @@ TEST(FormatterTest, FormatExplicitlyConvertibleToStringView) {
   EXPECT_EQ("foo", fmt::format("{}", explicitly_convertible_to_string_view()));
 }
 
+#ifdef FMT_USE_STRING_VIEW
+struct explicitly_convertible_to_std_string_view {
+  explicit operator std::string_view() const { return "foo"; }
+};
+
+TEST(FormatterTest, FormatExplicitlyConvertibleToStdStringView) {
+  EXPECT_EQ("foo",
+            fmt::format("{}", explicitly_convertible_to_std_string_view()));
+}
+#endif
+
 struct explicitly_convertible_to_wstring_view {
   explicit operator fmt::wstring_view() const { return L"foo"; }
 };