[llvm-dev] How to resolve conflicts between sanitizer_common and system headers

[Anna Zaks via llvm-dev]

Hi Sanitizer Runtime Developers,

We recently ran into a problem building clang because some of the definitions in sanitizer_common conflicted with system definitions and later another system header was trying to use the system definition:

.../usr/include/libkern/OSAtomicDeprecated.h:756:17: error: reference to 'memory_order_relaxed' is ambiguous
__theAmount, memory_order_relaxed) + __theAmount);
^
.../usr/bin/../include/c++/v1/atomic:548:5: note: candidate found by name lookup is 'std::__1::memory_order::memory_order_relaxed'
memory_order_relaxed, memory_order_consume, memory_order_acquire,
^
../src/projects/compiler-rt/lib/tsan/../sanitizer_common/sanitizer_atomic.h:22:3: note: candidate found by name lookup is '__sanitizer::memory_order::memory_order_relaxed'
memory_order_relaxed = 1 << 0,
^

The problem is due to the combination of the following: 
 1. The runtime includes the system headers after the project headers (as per LLVM coding guidelines).
 2. lib/sanitizer_common/sanitizer_internal_defs.h pollutes the namespace of everything defined after it, which is all/most of the sanitizer .h and .cc files and the included system headers with:
    using namespace __sanitizer;  // NOLINT
 3. These are the definitions that conflict in this particular case, but this problem could reoccur in the future with other symbols as well:
enum memory_order {
  memory_order_relaxed = 1 << 0,
  memory_order_consume = 1 << 1,
  memory_order_acquire = 1 << 2,
  memory_order_release = 1 << 3,
  memory_order_acq_rel = 1 << 4,
  memory_order_seq_cst = 1 << 5
};

We currently have a workaround (in the system header) that makes this non-blocking, but it would be good to cleanly address this problem. Removing the "using namespace" from the header seems like the cleanest solution. WDYT?

Thanks,
Anna.
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