Add tests for FMT_ENFORCE_COMPILE_STRING, fix several errors

doc/api.rst

@@ -165,6 +165,11 @@ functions in their ``formatter`` specializations.
 
 .. _udt:
 
+To force the use of compile-time checks, define the preprocessor variable
+``FMT_ENFORCE_COMPILE_STRING``. When set, functions accepting ``FMT_STRING``
+will fail to compile with regular strings. Runtime-checked
+formatting is still possible using ``fmt::vformat``, ``fmt::vprint``, etc.
+
 Formatting User-defined Types
 -----------------------------
 

include/fmt/chrono.h

@@ -768,19 +768,16 @@ inline std::chrono::duration<Rep, std::milli> get_milliseconds(
 template <typename Char, typename Rep, typename OutputIt,
           FMT_ENABLE_IF(std::is_integral<Rep>::value)>
 OutputIt format_duration_value(OutputIt out, Rep val, int) {
-  static FMT_CONSTEXPR_DECL const Char format[] = {'{', '}', 0};
-  return format_to(out, compile_string_to_view(format), val);
+  return write<Char>(out, val);
 }
 
 template <typename Char, typename Rep, typename OutputIt,
           FMT_ENABLE_IF(std::is_floating_point<Rep>::value)>
 OutputIt format_duration_value(OutputIt out, Rep val, int precision) {
-  static FMT_CONSTEXPR_DECL const Char pr_f[] = {'{', ':', '.', '{',
-                                                 '}', 'f', '}', 0};
-  if (precision >= 0)
-    return format_to(out, compile_string_to_view(pr_f), val, precision);
-  static FMT_CONSTEXPR_DECL const Char fp_f[] = {'{', ':', 'g', '}', 0};
-  return format_to(out, compile_string_to_view(fp_f), val);
+  basic_format_specs<Char> specs;
+  specs.precision = precision;
+  specs.type = precision > 0 ? 'f' : 'g';
+  return write<Char>(out, val, specs);
 }
 
 template <typename Char, typename OutputIt>
@@ -800,13 +797,20 @@ template <typename Char, typename Period, typename OutputIt>
 OutputIt format_duration_unit(OutputIt out) {
   if (const char* unit = get_units<Period>())
     return copy_unit(string_view(unit), out, Char());
-  static FMT_CONSTEXPR_DECL const Char num_f[] = {'[', '{', '}', ']', 's', 0};
-  if (const_check(Period::den == 1))
-    return format_to(out, compile_string_to_view(num_f), Period::num);
-  static FMT_CONSTEXPR_DECL const Char num_def_f[] = {'[', '{', '}', '/', '{',
-                                                      '}', ']', 's', 0};
-  return format_to(out, compile_string_to_view(num_def_f), Period::num,
-                   Period::den);
+
+  basic_memory_buffer<Char> buffer;
+  auto bufOut = std::back_inserter(buffer);
+  *bufOut++ = '[';
+  bufOut = write<Char>(bufOut, Period::num);
+
+  if (const_check(Period::den != 1)) {
+    *bufOut++ = '/';
+    bufOut = write<Char>(bufOut, Period::den);
+  }
+
+  *bufOut++ = ']';
+  *bufOut++ = 's';
+  return write<Char>(out, {buffer.data(), buffer.size()});
 }
 
 template <typename FormatContext, typename OutputIt, typename Rep,

include/fmt/format.h

@@ -3828,7 +3828,7 @@ inline std::string to_string(T value) {
   Converts *value* to ``std::wstring`` using the default format for type *T*.
  */
 template <typename T> inline std::wstring to_wstring(const T& value) {
-  return format(L"{}", value);
+  return format(FMT_STRING(L"{}"), value);
 }
 
 template <typename Char, size_t SIZE>

include/fmt/ranges.h

@@ -291,10 +291,10 @@ struct formatter<TupleT, Char, enable_if_t<fmt::is_tuple_like<TupleT>::value>> {
         }
         out = detail::copy(formatting.delimiter, out);
       }
-      out = format_to(out,
-                      detail::format_str_quoted(
-                          (formatting.add_delimiter_spaces && i > 0), v),
-                      v);
+      out = vformat_to(out,
+                       detail::format_str_quoted(
+                           (formatting.add_delimiter_spaces && i > 0), v),
+                       make_format_args<FormatContext>(v));
       ++i;
     }
 
@@ -366,12 +366,12 @@ struct formatter<
         if (formatting.add_prepostfix_space) *out++ = ' ';
         out = detail::copy(formatting.delimiter, out);
       }
-      out = format_to(out,
-                      detail::format_str_quoted(
-                          (formatting.add_delimiter_spaces && i > 0), *it),
-                      *it);
+      out = vformat_to(out,
+                       detail::format_str_quoted(
+                           (formatting.add_delimiter_spaces && i > 0), *it),
+                       make_format_args<FormatContext>(*it));
       if (++i > formatting.range_length_limit) {
-        out = format_to(out, " ... <other elements>");
+        out = format_to(out, FMT_STRING("{}"), " ... <other elements>");
         break;
       }
     }

test/CMakeLists.txt

@@ -106,6 +106,14 @@ add_fmt_test(printf-test)
 add_fmt_test(ranges-test)
 add_fmt_test(scan-test)
 
+if (NOT MSVC)
+  # FMT_ENFORCE_COMPILE_STRING not supported under MSVC
+  # See https://developercommunity.visualstudio.com/content/problem/1277597/internal-compiler-c0001-error-on-complex-nested-la.html
+  add_fmt_test(enforce-compile-string-test)
+  target_compile_definitions(enforce-compile-string-test PRIVATE
+    "-DFMT_ENFORCE_COMPILE_STRING")
+endif()
+
 if (NOT DEFINED MSVC_STATIC_RUNTIME AND MSVC)
   foreach (flag_var
 			 CMAKE_CXX_FLAGS CMAKE_CXX_FLAGS_DEBUG CMAKE_CXX_FLAGS_RELEASE

test/enforce-compile-string-test.cc

@@ -0,0 +1,75 @@
+// Formatting library for C++ - formatting library tests
+//
+// Copyright (c) 2012 - present, Victor Zverovich
+// All rights reserved.
+//
+// For the license information refer to format.h.
+
+#include <array>
+#include <chrono>
+#include <iterator>
+#include <list>
+#include <string>
+
+#include "fmt/chrono.h"
+#include "fmt/color.h"
+#include "fmt/format.h"
+#include "fmt/locale.h"
+#include "fmt/ostream.h"
+#include "fmt/ranges.h"
+
+// Exercise the API to verify that everything we expect to can compile.
+void test_format_api() {
+  fmt::format(FMT_STRING("{}"), 42);
+  fmt::format(FMT_STRING(L"{}"), 42);
+  fmt::format(FMT_STRING("noop"));
+
+  fmt::to_string(42);
+  fmt::to_wstring(42);
+
+  std::list<char> out;
+  fmt::format_to(std::back_inserter(out), FMT_STRING("{}"), 42);
+
+  char buffer[4];
+  fmt::format_to_n(buffer, 3, FMT_STRING("{}"), 12345);
+
+  wchar_t wbuffer[4];
+  fmt::format_to_n(wbuffer, 3, FMT_STRING(L"{}"), 12345);
+}
+
+void test_literals_api() {
+#if FMT_USE_UDL_TEMPLATE
+  using namespace fmt::literals;
+  "{}c{}"_format("ab", 1);
+  L"{}c{}"_format(L"ab", 1);
+#endif
+}
+
+void test_chrono() {
+  fmt::format(FMT_STRING("{}"), std::chrono::seconds(42));
+  fmt::format(FMT_STRING(L"{}"), std::chrono::seconds(42));
+}
+
+void test_text_style() {
+  fmt::print(fg(fmt::rgb(255, 20, 30)), FMT_STRING("{}"), "rgb(255,20,30)");
+  fmt::format(fg(fmt::rgb(255, 20, 30)), FMT_STRING("{}"),
+                    "rgb(255,20,30)");
+
+  fmt::text_style ts = fg(fmt::rgb(255, 20, 30));
+  std::string out;
+  fmt::format_to(std::back_inserter(out), ts,
+                 FMT_STRING("rgb(255,20,30){}{}{}"), 1, 2, 3);
+}
+
+void test_range() {
+  std::array<char, 5> hello = {'h','e','l','l','o'};
+  fmt::format(FMT_STRING("{}"), hello);
+}
+
+int main() {
+  test_format_api();
+  test_literals_api();
+  test_chrono();
+  test_text_style();
+  test_range();
+}