@belkadan any idea what's going on?

I think we decided that something funny was going on where we thought arclite was going to be in the toolchain but then it wasn't (maybe the arc/ directory exists but it's empty).

Stupid question: why would a SwiftPM build (from the same toolchain) not generate the same error?

Whether or not you need arclite depends on your deployment target. I suspect SwiftPM is always building for the host OS.

Ahh, figured it out today. It's because we're now shipping Clang in the downloadable toolchain too.

#22911

5.1: #22923

Thanks!

I'm still seeing this error, even in recent toolchains. Any idea why?

Hm, no. Fully the same, with your toolchain name in the path and then libarclite_macosx.a at the end?

Exactly the same, yes.

And which toolchain?

For example, here's the error on march 26th toolchain:

ld: file not found: /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2019-03-26-a.xctoolchain/usr/lib/arc/libarclite_macosx.a 

I'll try with a more recent one.

Same with the latest master toolchain:

ld: file not found: /Library/Developer/Toolchains/swift-DEVELOPMENT-SNAPSHOT-2019-04-10-a.xctoolchain/usr/lib/arc/libarclite_macosx.a 

@belkadan I'm not the only one with the issue: #23701 (comment)

Oh, bah. Xcode probably needs the same fix that the Swift driver took. Do you want to file a Radar or should I?

If you can, I'd appreciate it. If not, I'll try to find some time tomorrow.

…it's even worse than I thought. Xcode just calls Clang to link. It doesn't add arclite itself. But the Clang in the toolchain doesn't have a copy of arclite, because that's not an open-source library. (Well, it's not part of the Swift project, anyway.)

I'm not sure what the right fix is here, but "don't use an open-source toolchain" definitely isn't it. A workaround is to change your deployment target to 10.11 or newer.

Filed rdar://problem/49947573 and talking to the Apple Clang folks.