Get distributed builds to work with warnings-as-errors

[theres-waldo]

I tried an sccache distributed build today, and the build failed with errors like this:

 1:38.92 /home/botond/dev/mozilla/central/js/src/jit/MIR.h:8337:218: error: result of comparison of unsigned enum expression >= 0 is always true [-Werror,-Wtautological-unsigned-enum-zero-compare]
 1:38.92     do { static_assert( mozilla::detail::AssertionConditionType<decltype(arrayType >= 0 && arrayType < Scalar::MaxTypedArrayViewType)>::isValid, "invalid assertion condition"); if ((__builtin_expect(!!(!(!!(arrayType >= 0 && arrayType < Scalar::MaxTypedArrayViewType))), 0))) { MOZ_ReportAssertionFailure("arrayType >= 0 && arrayType < Scalar::MaxTypedArrayViewType", "/home/botond/dev/mozilla/central/js/src/jit/MIR.h", 8337); AnnotateMozCrashReason("MOZ_ASSERT" "(" "arrayType >= 0 && arrayType < Scalar::MaxTypedArrayViewType" ")"); do { *((volatile int*)__null) = 8337; ::abort(); } while (false); } } while (false);
 1:38.92                                                                                                                                                                                                                ~~~~~~~~~ ^  ~

Removing ac_add_options --enable-warnings-as-errors from my .mozconfig, fixed the problem, but I would prefer to keep that, since automation builds do use that, and not using it locally can result in surprise Try / autoland build failures.

[froydnj]

I think this is essentially the same issue as #521 and will therefore be addressed by #545.

[sigiesec]

Yes, it's the same issue. That's exactly the reason I can't really use sccache without #545.

[froydnj]

@theres-waldo Does this now work for you with #545 resolved?

[theres-waldo]

It does not appear to; I still get a bunch of Werrors, such as:

 1:45.38 /home/botond/dev/mozilla/central/mfbt/tests/TestAlgorithm.cpp:34:229: error: code will never be executed [-Werror,-Wunreachable-code]
 1:45.38   do { static_assert( mozilla::detail::AssertionConditionType<decltype(!AllOf(begin(arr3), end(arr3), odd))>::isValid, "invalid assertion condition"); if ((__builtin_expect(!!(!(!!(!AllOf(begin(arr3), end(arr3), odd)))), 0))) { MOZ_ReportAssertionFailure("!AllOf(begin(arr3), end(arr3), odd)", "/home/botond/dev/mozilla/central/mfbt/tests/TestAlgorithm.cpp", 34); do { } while (false); do { *((volatile int*)__null) = 34; ::abort(); } while (false); } } while (false);
 1:45.38                                                                                                                                                                                                                                     ^~~~~~~~~~~~~~~~~~~~~~~~~~

[chmanchester]

I was just able to complete a warnings-as-errors build sucessfully with sccache-dist and #545, but this wont work out of the box until we have rewrite_includes_only turned on by default and deploy a new release.

[mstange]

What's needed to turn on rewrite_includes_only by default? Is it blocked on adding a detection mechanism for #652?