Don't use windows.h if FMT_USE_WINDOWS_H is set to 0

format.cc

@@ -35,10 +35,11 @@
 #include <cmath>
 #include <cstdarg>
 
-#ifdef _WIN32
-# ifdef __MINGW32__
+#if defined(_WIN32) && defined(__MINGW32__)
 # include <cstring>
 #endif
+
+#if FMT_USE_WINDOWS_H
 # if defined(NOMINMAX) || defined(FMT_WIN_MINMAX)
 #  include <windows.h>
 # else
@@ -488,7 +489,7 @@ FMT_FUNC void fmt::internal::report_unknown_type(char code, const char *type) {
         static_cast<unsigned>(code), type)));
 }
 
-#ifdef _WIN32
+#if FMT_USE_WINDOWS_H
 
 FMT_FUNC fmt::internal::UTF8ToUTF16::UTF8ToUTF16(fmt::StringRef s) {
   int length = MultiByteToWideChar(
@@ -531,30 +532,6 @@ FMT_FUNC void fmt::WindowsError::init(
   base = std::runtime_error(w.str());
 }
 
-#endif
-
-FMT_FUNC void fmt::internal::format_system_error(
-    fmt::Writer &out, int error_code,
-    fmt::StringRef message) FMT_NOEXCEPT {
-  FMT_TRY {
-    MemoryBuffer<char, INLINE_BUFFER_SIZE> buffer;
-    buffer.resize(INLINE_BUFFER_SIZE);
-    for (;;) {
-      char *system_message = &buffer[0];
-      int result = safe_strerror(error_code, system_message, buffer.size());
-      if (result == 0) {
-        out << message << ": " << system_message;
-        return;
-      }
-      if (result != ERANGE)
-        break;  // Can't get error message, report error code instead.
-      buffer.resize(buffer.size() * 2);
-    }
-  } FMT_CATCH(...) {}
-  format_error_code(out, error_code, message);
-}
-
-#ifdef _WIN32
 FMT_FUNC void fmt::internal::format_windows_error(
     fmt::Writer &out, int error_code,
     fmt::StringRef message) FMT_NOEXCEPT {
@@ -583,7 +560,29 @@ FMT_FUNC void fmt::internal::format_windows_error(
   } FMT_CATCH(...) {}
   format_error_code(out, error_code, message);
 }
-#endif
+
+#endif  // FMT_USE_WINDOWS_H
+
+FMT_FUNC void fmt::internal::format_system_error(
+    fmt::Writer &out, int error_code,
+    fmt::StringRef message) FMT_NOEXCEPT {
+  FMT_TRY {
+    MemoryBuffer<char, INLINE_BUFFER_SIZE> buffer;
+    buffer.resize(INLINE_BUFFER_SIZE);
+    for (;;) {
+      char *system_message = &buffer[0];
+      int result = safe_strerror(error_code, system_message, buffer.size());
+      if (result == 0) {
+        out << message << ": " << system_message;
+        return;
+      }
+      if (result != ERANGE)
+        break;  // Can't get error message, report error code instead.
+      buffer.resize(buffer.size() * 2);
+    }
+  } FMT_CATCH(...) {}
+  format_error_code(out, error_code, message);
+}
 
 template <typename Char>
 void fmt::internal::ArgMap<Char>::init(const ArgList &args) {
@@ -1251,7 +1250,7 @@ FMT_FUNC void fmt::report_system_error(
   report_error(internal::format_system_error, error_code, message);
 }
 
-#ifdef _WIN32
+#if FMT_USE_WINDOWS_H
 FMT_FUNC void fmt::report_windows_error(
     int error_code, fmt::StringRef message) FMT_NOEXCEPT {
   report_error(internal::format_windows_error, error_code, message);

format.h

@@ -682,7 +682,15 @@ inline void format_decimal(Char *buffer, UInt value, unsigned num_digits) {
   buffer[0] = Data::DIGITS[index];
 }
 
-#ifdef _WIN32
+#ifndef _WIN32
+# define FMT_USE_WINDOWS_H 0
+#elif !defined(FMT_USE_WINDOWS_H)
+# define FMT_USE_WINDOWS_H 1
+#endif
+
+// Define FMT_USE_WINDOWS_H to 0 to disable use of windows.h.
+// All the functionality that relies on it will be disabled too.
+#if FMT_USE_WINDOWS_H
 // A converter from UTF-8 to UTF-16.
 // It is only provided for Windows since other systems support UTF-8 natively.
 class UTF8ToUTF16 {
@@ -716,16 +724,14 @@ class UTF16ToUTF8 {
   // in case of memory allocation error.
   int convert(WStringRef s);
 };
+
+void format_windows_error(fmt::Writer &out, int error_code,
+                          fmt::StringRef message) FMT_NOEXCEPT;
 #endif
 
 void format_system_error(fmt::Writer &out, int error_code,
                          fmt::StringRef message) FMT_NOEXCEPT;
 
-#ifdef _WIN32
-void format_windows_error(fmt::Writer &out, int error_code,
-                          fmt::StringRef message) FMT_NOEXCEPT;
-#endif
-
 // A formatting argument value.
 struct Value {
   template <typename Char>
@@ -2486,7 +2492,7 @@ void format(BasicFormatter<Char> &f, const Char *&format_str, const T &value) {
 // Can be used to report errors from destructors.
 void report_system_error(int error_code, StringRef message) FMT_NOEXCEPT;
 
-#ifdef _WIN32
+#if FMT_USE_WINDOWS_H
 
 /** A Windows error. */
 class WindowsError : public SystemError {

test/CMakeLists.txt

@@ -89,4 +89,9 @@ if (FMT_PEDANTIC)
     "${CMAKE_CURRENT_BINARY_DIR}/compile-test"
     --build-generator ${CMAKE_GENERATOR}
     --build-makeprogram ${CMAKE_MAKE_PROGRAM})
+
+  # Test that the library compiles without windows.h.
+  add_library(no-windows-h-test ../format.cc)
+  set_target_properties(no-windows-h-test
+    PROPERTIES COMPILE_DEFINITIONS "FMT_USE_WINDOWS_H=0")
 endif ()