After bug 1526857 I get the following:
ERROR: Could not find libclang to generate rust bindings for C/C++. Please install the necessary packages, run mach bootstrap, or use --with-libclang-path to give the path containing it.

Running ./mach bootstrap does not help

ac_add_options --with-libclang-path=/home/smaug/.mozbuild/clang/lib
in .mozconfig seems to help, but that really shouldn't be needed.
(since I don't even know if that is the right clang lib)

:mceier in irc also hit this today.

glandium, can you help?

Can you attach $objdir/config.log?

what is the output for /usr/lib64/ccache/clang++ -print-search-dirs?

(Unrelated: Note that your clang is picked from /usr/lib64/ccache, which means it's ccache-wrapped, and that you're building with --with-ccache=sccache, which is going to wrap everything with sccache, so in practice, that means two levels of caching... you probably don't want that)

/usr/lib64/ccache/clang++ -print-search-dirs

programs: =/usr/bin:/usr/bin/../lib/gcc/x86_64-redhat-linux/8/../../../../x86_64-redhat-linux/bin
libraries: =/usr/lib64/clang/7.0.1:/usr/bin/../lib/gcc/x86_64-redhat-linux/8:/usr/bin/../lib/gcc/x86_64-redhat-linux/8/../../../../lib64:/usr/bin/../lib64:/lib/../lib64:/usr/lib/../lib64:/usr/bin/../lib/gcc/x86_64-redhat-linux/8/../../..:/usr/bin/../lib:/lib:/usr/lib

Can you attach config.log from a configure run with bug 1526857 backed out, and MOZ_CONFIGURE_TRACE set to 1 in the environment? I'm actually surprised your setup worked before.

(and without --with-libclang-path)

That is too large file to attach (30MB). I'll send it to you

ah, looks like it compresses well.

Oh, so this is why it worked before:

• clang is picked from the system
• llvm-config is not installed on the system, so it's picked from ~/.mozbuild
• so libclang was found in ~/.mozbuild

llvm-config being found from a different clang was the main problem, and bug 1526857 fixed that by not relying on llvm-config at all. So now, it tries to find the libclang corresponding to your configured clang, which it can't find.

This means there are actually two issues hidden here:

• we should be picking clang from ~/.mozbuild on local builds. There is a bug on file for that but I can't find it right now. ISTR dmajor was involved in that, David, do you have the bug number handy?
• we can't find libclang for a system-installed clang on Fedora. That's actually something I saw while working on bug 1526857, and that was already true before, whether a system llvm-config was installed or not. But that was scope bloat.

• we should be picking clang from ~/.mozbuild on local builds. There is a
  bug on file for that but I can't find it right now. ISTR dmajor was involved
  in that, David, do you have the bug number handy?

Bug 1519954.

Olli, can you check whether bug 1519954 fixes the issue for you? I'll leave this bug open for the remaining issue per comment 11.

Yes, it does seem to fix the issue. Thanks.

Turns out the remaining issue is bug 1413234