Rename None to Null because of conflict with an xlib.h macro

format.cc

@@ -95,11 +95,11 @@ using fmt::internal::Arg;
 
 // Dummy implementations of strerror_r and strerror_s called if corresponding
 // system functions are not available.
-static inline fmt::internal::None<> strerror_r(int, char *, ...) {
-  return fmt::internal::None<>();
+static inline fmt::internal::Null<> strerror_r(int, char *, ...) {
+  return fmt::internal::Null<>();
 }
-static inline fmt::internal::None<> strerror_s(char *, std::size_t, ...) {
-  return fmt::internal::None<>();
+static inline fmt::internal::Null<> strerror_s(char *, std::size_t, ...) {
+  return fmt::internal::Null<>();
 }
 
 namespace fmt {
@@ -185,7 +185,7 @@ int safe_strerror(
     }
 
     // Handle the case when strerror_r is not available.
-    int handle(fmt::internal::None<>) {
+    int handle(fmt::internal::Null<>) {
       return fallback(strerror_s(buffer_, buffer_size_, error_code_));
     }
 
@@ -197,7 +197,7 @@ int safe_strerror(
     }
 
     // Fallback to strerror if strerror_r and strerror_s are not available.
-    int fallback(fmt::internal::None<>) {
+    int fallback(fmt::internal::Null<>) {
       errno = 0;
       buffer_ = strerror(error_code_);
       return errno;

format.h

@@ -833,20 +833,20 @@ template <typename Char>
 struct NamedArg;
 
 template <typename T = void>
-struct None {};
+struct Null {};
 
 // A helper class template to enable or disable overloads taking wide
 // characters and strings in MakeValue.
 template <typename T, typename Char>
 struct WCharHelper {
-  typedef None<T> Supported;
+  typedef Null<T> Supported;
   typedef T Unsupported;
 };
 
 template <typename T>
 struct WCharHelper<T, wchar_t> {
   typedef T Supported;
-  typedef None<T> Unsupported;
+  typedef Null<T> Unsupported;
 };
 
 template <typename T>

test/format-test.cc

@@ -42,6 +42,9 @@
 
 #include "gmock/gmock.h"
 
+// Test that the library compiles if None is defined to 0 as done by xlib.h.
+#define None 0
+
 #include "format.h"
 #include "util.h"
 #include "mock-allocator.h"