clang should diagnose cases where comparison operators (< or >) are used instead of shift operators (<< or >>) in enumerator initializers. This is a common mistake that often occurs when defining bit flags or option enums.

For example:

enum E { kOptionOne = 1ull << 0, // correct kOptionTwo = 1ull < 1, // oops! kOptionThree = 1ull < 2, // oops! }; 

Although these are valid C/C++ expressions, they are very likely to be errors in this context.