From c26349f4d25d4542d99092afb9a4f9f141afb900 Mon Sep 17 00:00:00 2001
From: Victor Zverovich <viz@fb.com>
Date: Tue, 14 Jul 2020 11:13:21 -0700
Subject: [PATCH] Improve error reporting

---
 include/fmt/core.h   |  9 ++++-----
 test/compile-test.cc | 12 ++++++------
 2 files changed, 10 insertions(+), 11 deletions(-)

diff --git a/include/fmt/core.h b/include/fmt/core.h
index 891555d4..3805d44e 100644
--- a/include/fmt/core.h
+++ b/include/fmt/core.h
@@ -1214,6 +1214,8 @@ struct is_contiguous<std::basic_string<Char>> : std::true_type {};
 template <typename Char>
 struct is_contiguous<detail::buffer<Char>> : std::true_type {};
 
+template <typename T> struct formattable : std::false_type {};
+
 namespace detail {
 
 template <typename OutputIt>
@@ -1258,14 +1260,11 @@ FMT_CONSTEXPR basic_format_arg<Context> make_arg(const T& value) {
   return arg;
 }
 
-template <typename T> struct formattable : std::false_type {};
-
 template <typename T> int check(unformattable) {
   static_assert(
       formattable<T>(),
-      "Cannot format argument. To make type T formattable provide a "
-      "formatter<T> specialization: "
-      "https://fmt.dev/latest/api.html#formatting-user-defined-types");
+      "Cannot format an argument. To make type T formattable provide a "
+      "formatter<T> specialization: https://fmt.dev/dev/api.html#udt");
   return 0;
 }
 template <typename T, typename U> inline const U& check(const U& val) {
diff --git a/test/compile-test.cc b/test/compile-test.cc
index c4d7ce74..6dca548d 100644
--- a/test/compile-test.cc
+++ b/test/compile-test.cc
@@ -114,20 +114,20 @@ TEST(CompileTest, MultipleTypes) {
   EXPECT_EQ(fmt::format(f, 42, 42), "42 42");
 }
 
-struct formattable {};
+struct test_formattable {};
 
 FMT_BEGIN_NAMESPACE
-template <> struct formatter<formattable> : formatter<const char*> {
+template <> struct formatter<test_formattable> : formatter<const char*> {
   template <typename FormatContext>
-  auto format(formattable, FormatContext& ctx) -> decltype(ctx.out()) {
+  auto format(test_formattable, FormatContext& ctx) -> decltype(ctx.out()) {
     return formatter<const char*>::format("foo", ctx);
   }
 };
 FMT_END_NAMESPACE
 
 TEST(CompileTest, FormatUserDefinedType) {
-  auto f = fmt::detail::compile<formattable>("{}");
-  EXPECT_EQ(fmt::format(f, formattable()), "foo");
+  auto f = fmt::detail::compile<test_formattable>("{}");
+  EXPECT_EQ(fmt::format(f, test_formattable()), "foo");
 }
 
 TEST(CompileTest, EmptyFormatString) {
@@ -146,7 +146,7 @@ TEST(CompileTest, FormatDefault) {
   EXPECT_EQ("4.2", fmt::format(FMT_COMPILE("{}"), 4.2));
   EXPECT_EQ("foo", fmt::format(FMT_COMPILE("{}"), "foo"));
   EXPECT_EQ("foo", fmt::format(FMT_COMPILE("{}"), std::string("foo")));
-  EXPECT_EQ("foo", fmt::format(FMT_COMPILE("{}"), formattable()));
+  EXPECT_EQ("foo", fmt::format(FMT_COMPILE("{}"), test_formattable()));
 }
 
 TEST(CompileTest, FormatSpecs) {