I heard from a contributor with a mingw build that they were stuck on the configure step. The log shows that the Rust compiler can't find the standard library since it's looking for a different target than the one that's installed.

I think this aligns with a bug I have not formalized but am vaguely aware of. A patch that may fix it is: --- a/build/moz.configure/rust.configure +++ b/build/moz.configure/rust.configure @@ -165,8 +165,8 @@ def rust_triple_alias(host_or_target): # Windows # XXX better detection of CXX needed here, to figure out whether # we need i686-pc-windows-gnu instead, since mingw32 builds work. - ('x86', 'WINNT'): 'i686-pc-windows-msvc', - ('x86_64', 'WINNT'): 'x86_64-pc-windows-msvc', + ('x86', 'WINNT'): 'i686-pc-windows-gnu', + ('x86_64', 'WINNT'): 'x86_64-pc-windows-gnu', }.get((host_or_target.cpu, os_or_kernel), None) if rustc_target is None: But I don't know if this is a complete fix, I had a different rust error after applying it: make[5]: *** No rule to make target '../../toolkit/library/rust/../i686-pc-windows-gnu/release/libgkrust.a', needed by 'xul.dll'. Stop. /home/tom/Documents/moz/mingw-work/just-build/config/recurse.mk:71: recipe for target 'toolkit/library/target' failed I haven't investigated any of this very deeply.

Comment on attachment 8859653 [details] Bug 1353541 Fix rustc in MinGW build https://reviewboard.mozilla.org/r/131668/#review134430 ::: build/moz.configure/rust.configure:168 (Diff revision 1) > ('arm', 'Android'): 'armv7-linux-androideabi', > ('x86', 'Android'): 'i686-linux-android', > # Windows > # XXX better detection of CXX needed here, to figure out whether > # we need i686-pc-windows-gnu instead, since mingw32 builds work. > - ('x86', 'WINNT'): 'i686-pc-windows-msvc', > + ('x86', 'WINNT'): 'i686-pc-windows-gnu', This is temporary, need to fix in next rev.

Besides the target being incorrect, rustc generates .lib files, when MinGW expects .a. See https://github.com/rust-lang/rust/pull/29520 for the rustc discussion.

Comment on attachment 8859653 [details] Bug 1353541 Fix rustc in MinGW build https://reviewboard.mozilla.org/r/131670/#review134520 Everything else seems fine, but the comment below is a blocker, I think. Or are we just ignoring the possibility of things like clang-cl cross compilation in other mingw patches that you're writing? ::: build/moz.configure/rust.configure:133 (Diff revision 2) > + # If we are targetting Windows but the host is Linux, we need to > + # use a different rustc target > + os_or_kernel = 'WINNT-MINGW' if host.kernel == "Linux" and host_or_target.kernel == "WINNT" else os_or_kernel This seems like the wrong check. What about the (admittedly hypothetical at the moment) world where somebody wants to cross-compile to Windows using clang-cl? That's going to want to use the windows-msvc target, rather than the windows-gnu target. I think you want to check `c_compiler` or similar here, if that's at all possible.

Comment on attachment 8859653 [details] Bug 1353541 Fix rustc in MinGW build https://reviewboard.mozilla.org/r/131670/#review134522 ::: build/moz.configure/rust.configure:133 (Diff revision 2) > + # If we are targetting Windows but the host is Linux, we need to > + # use a different rustc target > + os_or_kernel = 'WINNT-MINGW' if host.kernel == "Linux" and host_or_target.kernel == "WINNT" else os_or_kernel We do not support nor intend to support compiling with clang-cl on Linux for Windows, no. I believe this statement is true not just for 'Tor/MinGW stuff' but all of Mozilla Windows builds. I've talked with the clang-cl team at Google and they are treating 'building for Windows on Linux for clang-cl' as a hobby project and it's not really doable right now. Down the road we might try to do that but it would be a whole new project. Again, I believe this is true for all of Mozilla.

Comment on attachment 8859653 [details] Bug 1353541 Fix rustc in MinGW build https://reviewboard.mozilla.org/r/131670/#review134640

Comment on attachment 8859653 [details] Bug 1353541 Fix rustc in MinGW build https://reviewboard.mozilla.org/r/131670/#review135854 This needs a small change, but otherwise looks good. ::: build/moz.configure/rust.configure:133 (Diff revision 4) > # https://github.com/rust-lang/rust/blob/master/src/librustc_back/target/mod.rs > > # Avoid having to write out os+kernel for all the platforms where > # they don't differ. > os_or_kernel = host_or_target.kernel if host_or_target.kernel == 'Linux' and host_or_target.os != 'Android' else host_or_target.os > + # If we are targetting Windows but the host is Linux, we need to I'm going to concur with froydnj here--this isn't the right check. You'd hit this same issue if you were building on Windows using a mingw toolchain. The right thing to check is whether we're targeting Windows but building with GCC. We already have a `building_with_gcc`: https://dxr.mozilla.org/mozilla-central/rev/e17cbb839dd225a2da7e5d5bec43cf94e11749d8/build/moz.configure/toolchain.configure#835 ...so you can put that in `@depends` and instead write this as: ``` os_or_kernel = 'WINNT-MINGW' if building_with_gcc and host_or_target.kernel == "WINNT" else os_or_kernel ```

Comment on attachment 8859653 [details] Bug 1353541 Fix rustc in MinGW build https://reviewboard.mozilla.org/r/131670/#review136860 Thanks, this looks sensible. ::: build/moz.configure/rust.configure:135 (Diff revision 5) > # Avoid having to write out os+kernel for all the platforms where > # they don't differ. > os_or_kernel = host_or_target.kernel if host_or_target.kernel == 'Linux' and host_or_target.os != 'Android' else host_or_target.os > + # If we are targetting Windows but the compiler is gcc, we need to > + # use a different rustc target > + os_or_kernel = 'WINNT-MINGW' if building_with_gcc and host_or_target.kernel == "WINNT" else os_or_kernel nit: we use single quotes for strings in these files.

Pushed by ryanvm@gmail.com: https://hg.mozilla.org/integration/autoland/rev/51edd4c0ae9f Fix rustc in MinGW build r=froydnj,ted