Fix check_format_string (#925)

include/fmt/format.h

@@ -2243,7 +2243,7 @@ class format_string_checker {
 };
 
 template <typename Char, typename ErrorHandler, typename... Args>
-FMT_CONSTEXPR bool check_format_string(
+FMT_CONSTEXPR bool do_check_format_string(
     basic_string_view<Char> s, ErrorHandler eh = ErrorHandler()) {
   format_string_checker<Char, ErrorHandler, Args...> checker(s, eh);
   parse_format_string<true>(s, checker);
@@ -2254,7 +2254,7 @@ template <typename... Args, typename S>
 typename std::enable_if<is_compile_string<S>::value>::type
     check_format_string(S format_str) {
   typedef typename S::char_type char_t;
-  FMT_CONSTEXPR_DECL bool invalid_format = internal::check_format_string<
+  FMT_CONSTEXPR_DECL bool invalid_format = internal::do_check_format_string<
       char_t, internal::error_handler, Args...>(to_string_view(format_str));
   (void)invalid_format;
 }
@@ -3583,7 +3583,7 @@ class udl_formatter {
   std::basic_string<Char> operator()(const Args &... args) const {
     FMT_CONSTEXPR_DECL Char s[] = {CHARS..., '\0'};
     FMT_CONSTEXPR_DECL bool invalid_format =
-        check_format_string<Char, error_handler, Args...>(
+        do_check_format_string<Char, error_handler, Args...>(
           basic_string_view<Char>(s, sizeof...(CHARS)));
     (void)invalid_format;
     return format(s, args...);

test/format-test.cc

@@ -1426,13 +1426,14 @@ TEST(FormatterTest, FormatFloat) {
 
 TEST(FormatterTest, FormatDouble) {
   check_unknown_types(1.2, "eEfFgGaA", "double");
-  EXPECT_EQ("0", format("{0:}", 0.0));
-  EXPECT_EQ("0.000000", format("{0:f}", 0.0));
-  EXPECT_EQ("392.65", format("{0:}", 392.65));
-  EXPECT_EQ("392.65", format("{0:g}", 392.65));
-  EXPECT_EQ("392.65", format("{0:G}", 392.65));
-  EXPECT_EQ("392.650000", format("{0:f}", 392.65));
-  EXPECT_EQ("392.650000", format("{0:F}", 392.65));
+  EXPECT_EQ("0", format("{:}", 0.0));
+  EXPECT_EQ("0.000000", format("{:f}", 0.0));
+  EXPECT_EQ("0", format("{:g}", 0.0));
+  EXPECT_EQ("392.65", format("{:}", 392.65));
+  EXPECT_EQ("392.65", format("{:g}", 392.65));
+  EXPECT_EQ("392.65", format("{:G}", 392.65));
+  EXPECT_EQ("392.650000", format("{:f}", 392.65));
+  EXPECT_EQ("392.650000", format("{:F}", 392.65));
   char buffer[BUFFER_SIZE];
   safe_sprintf(buffer, "%e", 392.65);
   EXPECT_EQ(buffer, format("{0:e}", 392.65));
@@ -2315,7 +2316,7 @@ FMT_CONSTEXPR bool equal(const char *s1, const char *s2) {
 template <typename... Args>
 FMT_CONSTEXPR bool test_error(const char *fmt, const char *expected_error) {
   const char *actual_error = FMT_NULL;
-  fmt::internal::check_format_string<char, test_error_handler, Args...>(
+  fmt::internal::do_check_format_string<char, test_error_handler, Args...>(
         string_view(fmt, len(fmt)), test_error_handler(actual_error));
   return equal(actual_error, expected_error);
 }

test/printf-test.cc

@@ -509,3 +509,12 @@ TEST(PrintfTest, VPrintf) {
   EXPECT_WRITE(stdout, fmt::vfprintf(stdout, "%d", args), "42");
   EXPECT_WRITE(stdout, fmt::vfprintf(std::cout, "%d", args), "42");
 }
+
+template<typename... Args>
+void check_format_string_regression(fmt::string_view s, const Args&... args) {
+  fmt::sprintf(s, args...);
+}
+
+TEST(PrintfTest, CheckFormatStringRegression) {
+  check_format_string_regression("%c%s", 'x', "");
+}