Disable range formatter if value type is not formattable (#1885)

test/ranges-test.cc

@@ -141,13 +141,16 @@ TEST(RangesTest, FormatStringLike) {
 #endif  // FMT_USE_STRING_VIEW
 
 struct zstring_sentinel {};
+
 bool operator==(const char* p, zstring_sentinel) { return *p == '\0'; }
 bool operator!=(const char* p, zstring_sentinel) { return *p != '\0'; }
+
 struct zstring {
   const char* p;
   const char* begin() const { return p; }
   zstring_sentinel end() const { return {}; }
 };
+
 TEST(RangesTest, JoinSentinel) {
   zstring hello{"hello"};
   EXPECT_EQ("{'h', 'e', 'l', 'l', 'o'}", fmt::format("{}", hello));
@@ -189,3 +192,12 @@ TEST(RangesTest, JoinRange) {
   const std::vector<int> z(3u, 0);
   EXPECT_EQ("0,0,0", fmt::format("{}", fmt::join(z, ",")));
 }
+
+#if !FMT_MSC_VER || FMT_MSC_VER >= 1927
+struct unformattable {};
+
+TEST(RangesTest, UnformattableRange) {
+  EXPECT_FALSE((fmt::has_formatter<std::vector<unformattable>,
+                                   fmt::format_context>::value));
+}
+#endif