Empty .cpp file with just #include "src/mongo/util/ctype.h" results on v4gcc in: [2022/03/17 21:40:19.736] Command execution time: build/cached/mongo/db/exec/sbe/sbe_test.o: 0.254931 seconds [2022/03/17 21:40:19.803] In file included from src/mongo/db/exec/sbe/util/print_options.h:33, [2022/03/17 21:40:19.803] from src/mongo/db/exec/sbe/values/write_value_to_stream_test.cpp:34: [2022/03/17 21:40:19.803] src/mongo/util/ctype.h:75:15: error: found ':' in nested-name-specifier, expected '::' [2022/03/17 21:40:19.803] 75 | enum ClassBit : uint16_t { [2022/03/17 21:40:19.803] | ^ [2022/03/17 21:40:19.803] | :: [2022/03/17 21:40:19.803] src/mongo/util/ctype.h:75:6: error: 'ClassBit' has not been declared [2022/03/17 21:40:19.803] 75 | enum ClassBit : uint16_t { [2022/03/17 21:40:19.803] | ^~~~~~~~ [2022/03/17 21:40:19.803] src/mongo/util/ctype.h:75:26: error: expected unqualified-id before '{' token [2022/03/17 21:40:19.803] 75 | enum ClassBit : uint16_t { [2022/03/17 21:40:19.803] | ^ [2022/03/17 21:40:19.803] src/mongo/util/ctype.h:91:11: error: 'uint16_t' does not name a type [2022/03/17 21:40:19.803] 91 | constexpr uint16_t calculateClassBits(unsigned char c) { [2022/03/17 21:40:19.803] | ^~~~~~~~ [2022/03/17 21:40:19.803] src/mongo/util/ctype.h:70:1: note: 'uint16_t' is defined in header '<cstdint>' ; did you forget to '#include <cstdint>' ? [2022/03/17 21:40:19.803] 69 | #include <array> [2022/03/17 21:40:19.803] +++ |+#include <cstdint> [2022/03/17 21:40:19.803] 70 | See https://jira.mongodb.org/browse/BF-24654  for actual build failure