Firefox build issues with Rust and the new VS2017 15.5 update

Ryan VanderMeulen rvandermeulen at
Thu Dec 7 15:00:49 UTC 2017

Bug 1423307 has been merged to m-c now. After you've updated m-c, you can
re-run |./mach bootstrap| to pick up the newer clang binaries that will fix
the _Ty problem.


On Tue, Dec 5, 2017 at 2:14 PM, Ryan VanderMeulen <rvandermeulen at
> wrote:

> As a follow-up, it looks like updating to a newer LLVM version fixes the
> problem. That update is being tracked in
> show_bug.cgi?id=1423307.
> For anybody already hitting this bustage locally, you can try updating
> your clang toolchain under ~/.mozbuild/clang to the one below until the
> in-tree changes are landed:
> OAEV5vuGtEA/runs/0/artifacts/public/build/clang.tar.bz2
> -Ryan
> On Tue, Dec 5, 2017 at 11:16 AM, Ryan VanderMeulen <
> rvandermeulen at> wrote:
>> FYI, the VC++ 2017 v14.12 toolset included in the recently-released
>> VS2017 15.5 update appears to have broken building Firefox due to issues
>> with the Rust compiler (in particular, the version of libclang we ship with
>> it) and one of the system headers:
>> C:\PROGRA~2\MIB055~1\2017\COMMUN~1\VC\Tools\MSVC\1412~1.258\include\type_traits:898:47:
>> error: '_Ty' does not refer to a value
>> Which in turns leads to a Rust panic and build failure.
>> The Visual Studio installer allows you to install the prior v14.11
>> toolset as well, but I haven't verified yet that our build system will
>> properly use it if it's there. In the mean time, I'd strongly advise
>> avoiding this update until it's sorted out.
>> -Ryan
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