Summary

These lines in bson-clock.c are pointless and can be removed:

https://github.com/mongodb/mongo-c-driver/blob/9e7bf882d1fb4e16f5701a152f5c664088ffcda3/src/libbson/src/bson/bson-clock.c#L128-L130

The code essentially says if clock_gettime and CLOCK_MONOTONIC are defined, use them, otherwise if we're on macOS, use clock_gettime_nsec_np and CLOCK_UPTIME_RAW.

This makes no sense since clock_gettime and CLOCK_MONOTONIC were introduced in OS X 10.11 and clock_gettime_nsec_np and CLOCK_UPTIME_RAW were introduced in macOS 10.12. So what happens on OS X 10.11 and later is that the first block of code that uses clock_gettime gets used and this compiles fine. And on OS X 10.10 and earlier the second block that uses clock_gettime_nsec_np is used which fails to compile.

Environment

libbson 1.24.1

OS X 10.10 (or earlier) x86_64 (but this is irrelevant)

Apple LLVM version 7.0.2 (clang-700.1.81) (but this is irrelevant)

How to Reproduce

Build libbson 1.24.1 (with the patch to fix CDRIVER-4609) on OS X 10.10 or earlier

Additional Background

The previous version of the don't-have-clock_gettime fallback code for macOS compiled fine because it used mach_timebase_info and mach_absolute_time which exist on every version of macOS. Now that this code was removed, the headers for the mach time functions can be removed too:

https://github.com/mongodb/mongo-c-driver/blob/9e7bf882d1fb4e16f5701a152f5c664088ffcda3/src/libbson/src/bson/bson-clock.c#L18-L23