Have the GFlags portability header stick things in namespaces

Summary:
Just like the real thing does.
This was causing some issues when trying to link against glog, which expects the flags to be namespaced like this.

Reviewed By: mzlee

Differential Revision: D3230630

fb-gh-sync-id: a73ab3044560d561a39eb91ceee1588c147a46c5
fbshipit-source-id: a73ab3044560d561a39eb91ceee1588c147a46c5

folly/portability/GFlags.h

@@ -27,25 +27,35 @@
 #define DECLARE_VARIABLE() \
   static_assert(false, "You shouldn't be using GFlags internals.");
 
-#define FOLLY_DECLARE_FLAG(_type, _name) extern _type FLAGS_##_name
-#define DECLARE_bool(_name) FOLLY_DECLARE_FLAG(bool, _name)
-#define DECLARE_double(_name) FOLLY_DECLARE_FLAG(double, _name)
-#define DECLARE_int32(_name) FOLLY_DECLARE_FLAG(int, _name)
-#define DECLARE_int64(_name) FOLLY_DECLARE_FLAG(long long, _name)
-#define DECLARE_uint64(_name) FOLLY_DECLARE_FLAG(unsigned long long, _name)
-#define DECLARE_string(_name) FOLLY_DECLARE_FLAG(std::string, _name)
+#define FOLLY_DECLARE_FLAG(_type, _shortType, _name) \
+  namespace fL##_shortType {                         \
+    extern _type FLAGS_##_name;                      \
+  }                                                  \
+  using fL##_shortType::FLAGS_##_name
+
+#define DECLARE_bool(_name) FOLLY_DECLARE_FLAG(bool, B, _name)
+#define DECLARE_double(_name) FOLLY_DECLARE_FLAG(double, D, _name)
+#define DECLARE_int32(_name) FOLLY_DECLARE_FLAG(int, I, _name)
+#define DECLARE_int64(_name) FOLLY_DECLARE_FLAG(long long, I64, _name)
+#define DECLARE_uint64(_name) FOLLY_DECLARE_FLAG(unsigned long long, U64, _name)
+#define DECLARE_string(_name) FOLLY_DECLARE_FLAG(std::string, S, _name)
+
+#define FOLLY_DEFINE_FLAG(_type, _shortType, _name, _default) \
+  namespace fL##_shortType {                                  \
+    _type FLAGS_##_name = _default;                           \
+  }                                                           \
+  using fL##_shortType::FLAGS_##_name
 
-#define FOLLY_DEFINE_FLAG(_type, _name, _default) _type FLAGS_##_name = _default
 #define DEFINE_bool(_name, _default, _description) \
-  FOLLY_DEFINE_FLAG(bool, _name, _default)
+  FOLLY_DEFINE_FLAG(bool, B, _name, _default)
 #define DEFINE_double(_name, _default, _description) \
-  FOLLY_DEFINE_FLAG(double, _name, _default)
+  FOLLY_DEFINE_FLAG(double, D, _name, _default)
 #define DEFINE_int32(_name, _default, _description) \
-  FOLLY_DEFINE_FLAG(int, _name, _default)
+  FOLLY_DEFINE_FLAG(int, I, _name, _default)
 #define DEFINE_int64(_name, _default, _description) \
-  FOLLY_DEFINE_FLAG(long long, _name, _default)
+  FOLLY_DEFINE_FLAG(long long, I64, _name, _default)
 #define DEFINE_uint64(_name, _default, _description) \
-  FOLLY_DEFINE_FLAG(unsigned long long, _name, _default)
+  FOLLY_DEFINE_FLAG(unsigned long long, U64, _name, _default)
 #define DEFINE_string(_name, _default, _description) \
-  FOLLY_DEFINE_FLAG(std::string, _name, _default)
+  FOLLY_DEFINE_FLAG(std::string, S, _name, _default)
 #endif