Tagged most functions in absl/time/time.h as ABSL_ATTRIBUTE_CONST_FUNCTION or ABSL_ATTRIBUTE_PURE_FUNCTION

However, both absl_attributes are now unimplemented to avoid breaking existing users.

PiperOrigin-RevId: 496769399
Change-Id: I9c00cb60b885526300d744f9ea7c0f2178f092bb

Author: Abseil Team

absl/base/attributes.h

@@ -716,26 +716,9 @@
 #define ABSL_CONST_INIT
 #endif
 
-// ABSL_ATTRIBUTE_PURE_FUNCTION
-//
-// ABSL_ATTRIBUTE_PURE_FUNCTION is used to annotate declarations of "pure"
-// functions. A function is pure if its return value is only a function of its
-// arguments. The pure attribute prohibits a function from modifying the state
-// of the program that is observable by means other than inspecting the
-// function's return value. Declaring such functions with the pure attribute
-// allows the compiler to avoid emitting some calls in repeated invocations of
-// the function with the same argument values.
-//
-// Example:
-//
-//  ABSL_ATTRIBUTE_PURE_FUNCTION int64_t ToInt64Milliseconds(Duration d);
-#if ABSL_HAVE_CPP_ATTRIBUTE(gnu::pure)
-#define ABSL_ATTRIBUTE_PURE_FUNCTION [[gnu::pure]]
-#elif ABSL_HAVE_ATTRIBUTE(pure)
-#define ABSL_ATTRIBUTE_PURE_FUNCTION __attribute__((pure))
-#else
+// These annotations are not available yet due to fear of breaking code.
 #define ABSL_ATTRIBUTE_PURE_FUNCTION
-#endif
+#define ABSL_ATTRIBUTE_CONST_FUNCTION
 
 // ABSL_ATTRIBUTE_LIFETIME_BOUND indicates that a resource owned by a function
 // parameter or implicit object parameter is retained by the return value of the