dylib outputs required for TARGET when cross-compiling with syntax extension

[mcoffin]

When you list a syntax extension as a cargo dependency, even with plugin = true, if your chosen target doesn't have dylib outputs available, cargo will complain even if the target being built is a staticlib/executable.

This isn't working as intended, right?

For an example, try compiling the zinc (root crate) with --target=thumbv7m-none-eabi from mcoffin/zinc@ac834f2 which depends on the syntax extension crate ioreg from the same project. The syntax extension crate is correctly compiled for the host architecture, but cargo gives an error after compilation about dylib outputs not being available for thumbv7m-none-eabi (which is correct, but shouldn't matter).

[alexcrichton]

Hm it could be that Cargo is mixing up a host/target triple somewhere, could you gist the full error logs of a compile?

[mcoffin]

Here's the log, though spectacularly uninteresting: https://gist.github.com/mcoffin/fdc1358787dea6ca570b

I actually didn't think to check if it actually built the archive until just now (it does). I just saw the error and assumed it didn't. The error is given afterwards for some reason.

[alexcrichton]

Hm ok, I think I've found the issue but I'm not quite sure if it'll fix the bug you found, could you try out this branch of cargo and see if it works for you?

[posborne]

Hi @alexcrichton, I have been working on zinc as well and tried your branch and it does appear to fix the issue that @mcoffin reported.

[mcoffin]

@alexcrichton @posborne Works for me as well.

[alexcrichton]

Excellent, thanks for testing @posborne and @mcoffin! I've submitted #1617 now