Firefox build issues with Rust and the new VS2017 15.5 update

Ryan VanderMeulen rvandermeulen at
Tue Dec 5 19:14:49 UTC 2017

As a follow-up, it looks like updating to a newer LLVM version fixes the
problem. That update is being tracked in

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:


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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