Don't inject internal names into std (#1120)

include/fmt/format.h

@@ -257,9 +257,12 @@ namespace internal {
 #endif
 
 // A fallback implementation of uintptr_t for systems that lack it.
+namespace uintptr {
 struct uintptr_t {
   unsigned char value[sizeof(void*)];
 };
+}
+using uintptr::uintptr_t;
 typedef std::numeric_limits<uintptr_t> numutil;
 
 template <typename T> inline bool use_grisu() {
@@ -312,7 +315,7 @@ typename Allocator::value_type* allocate(Allocator& alloc, std::size_t n) {
 FMT_END_NAMESPACE
 
 namespace std {
-using namespace fmt::v5::internal;
+using namespace fmt::v5::internal::uintptr;
 // Standard permits specialization of std::numeric_limits. This specialization
 // is used to detect presence of uintptr_t.
 template <>

test/format-test.cc

@@ -2540,6 +2540,11 @@ TEST(FormatTest, EmphasisNonHeaderOnly) {
 }
 
 TEST(FormatTest, CharTraitsIsNotAmbiguous) {
+  // Test that we don't inject internal names into the std namespace.
   using namespace std;
   char_traits<char>::char_type c;
+#if __cplusplus >= 201103L
+  std::string s;
+  begin(s);
+#endif
 }