Fix handling of types that are explicitly convertible to std::string_…

…view
fmtlib · Dec 5, 2019 · bbcb02c · bbcb02c
1 parent d22e4ad
commit bbcb02c
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Showing 2 changed files with 29 additions and 1 deletion.
diff --git a/include/fmt/core.h b/include/fmt/core.h
@@ -878,7 +878,9 @@ template <typename Context> struct arg_mapper {
       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)>
+          !is_string<T>::value &&
+          !has_formatter<T, Context>::value &&
+          !has_fallback_formatter<T, Context>::value)>
   FMT_CONSTEXPR basic_string_view<char_type> map(const T& val) {
     return std_string_view<char_type>(val);
   }

diff --git a/test/custom-formatter-test.cc b/test/custom-formatter-test.cc
@@ -54,3 +54,29 @@ TEST(CustomFormatterTest, Format) {
   EXPECT_EQ("0.00", custom_format("{:.2f}", -.00001));
 }
 #endif
+
+#ifdef FMT_USE_STRING_VIEW
+struct explicitly_convertible_to_std_string_view {
+  explicit operator std::string_view() const { return "foo"; }
+};
+
+namespace fmt {
+
+template <>
+class formatter<explicitly_convertible_to_std_string_view>
+    : public formatter<std::string_view> {
+ public:
+  template <typename format_context>
+  auto format(const explicitly_convertible_to_std_string_view& v,
+              format_context& ctx) {
+    return format_to(ctx.out(), "'{}'", static_cast<std::string_view>(v));
+  }
+};
+
+}  // namespace fmt
+
+TEST(CustomFormatterTest, FormatExplicitlyConvertibleToStdStringView) {
+  EXPECT_EQ("'foo'",
+            fmt::format("{}", explicitly_convertible_to_std_string_view()));
+}
+#endif