Make the unwinding dependency conditional on panic = "unwind".

[sunfishcode]

Similar to sunfishcode/origin#149, make the unwinding dependency conditional on panic = "unwind".

[bjorn3]

For eyra the unwinding dependency will need to be unconditional as libstd has a hard dependency on it. C-gull should probably also have it unconditionally as it pulls in libstd.

[sunfishcode]

This appears to be one of those situations where cargo automatically provides us with an unwind library. I've now added a c-gull-unwinding example to test using c-gull and std::panic::catch_unwind to catch a panic.

[bjorn3]

This appears to be one of those situations where cargo automatically provides us with an unwind library.

libstd by default links against libgcc_s or libunwind depending on the target. Did you check that the example doesn't link against any external dylibs?

[sunfishcode]

Yes:

$ nm -u ./example-crates/c-gull-unwinding/target/debug/c-gull-unwinding
$

and

$ nm -C ./example-crates/c-gull-unwinding/target/debug/c-gull-unwinding | grep unwinding
00000000000bc4c0 T <unwinding::unwinder::find_fde::GlobalFinder as unwinding::unwinder::find_fde::FDEFinder>::find_fde
00000000000bb9f0 T <unwinding::unwinder::find_fde::phdr::PhdrFinder as unwinding::unwinder::find_fde::FDEFinder>::find_fde
0000000000098f50 T <unwinding::unwinder::find_fde::registry::Registry as unwinding::unwinder::find_fde::FDEFinder>::find_fde
...

[bjorn3]

Does it also not link against libgcc_s or libunwind when using panic=abort?

[sunfishcode]

It does not; I've now added an example-crate for that.

[sunfishcode]

I mean, it does automatically link in libunwind even with panic = "abort".

[bjorn3]

Yeah, that is what I meant. libstd needs an unwinder even with panic=abort.

[sunfishcode]

As an update here, cfg(panic = "abort")` did not work in Cargo.toml after all, so unless there are better options, we may need to go back to making unwinding optional and just asking users to figure out when to enable it.