Remove no longer necessary MacOS RUSTFLAGS hack

[lrascao]

The two PRs mentioned in the comments have since been merged, this can now be dropped.

[filmor]

The "hack" is still necessary, AFAICT, nothing changed in regard to this. The only thing that changed is that people are working on improving the syntax. The comments are probably outdated, though.

[lrascao]

I noticed this when i bumped rust to 1.49, linking started failing on our tests at rebar3_cargo. Not too sure on the exact root cause for the failure but this is the way i found of going around it.

[belltoy]

Hi, guys. Since rust-lang/rust#36574 had been merged, the hack was also outdated. We still need to specify RUSTFLAGS for different targets, but it can be done via .cargo/config.toml instead of hard-coded hack like that. e.g:

# .cargo/config.toml
[target.'cfg(target_os = "macos")']
rustflags = [
    "-C", "link-arg=-undefined",
    "-C", "link-arg=dynamic_lookup",
]

So, this PR can be merged IMO.

[belltoy]

According to rusterlium/rustler#192 and the Apple reference, the two-level namespace is preferred, and:

When building executables with a two-level namespace, you can allow the remaining undefined symbols to be looked up by the dynamic linker if the program is targeted for OS X v10.3 and later (the MACOSX_DEPLOYMENT_TARGET environment variable is set to 10.3 or higher). To take advantage of this feature, use the -undefined dynamic_lookup option.

So with two-level namespace args in my example lib:

$ otool -hV priv/crates/my_nif/0.1.0/debug/libmy_nif.so
priv/crates/my_nif/0.1.0/debug/libmy_nif.so:
Mach header
      magic  cputype cpusubtype  caps    filetype ncmds sizeofcmds      flags
MH_MAGIC_64   X86_64        ALL  0x00       DYLIB    16       2064   NOUNDEFS DYLDLINK TWOLEVEL NO_REEXPORTED_DYLIBS MH_HAS_TLV_DESCRIPTORS

Meanwhile, the preferred for rust/cargo is to put RUSTFLAGS in the cargo config file.

@filmor cc @lrascao

[lrascao]

i'll take care of the merge conflict

[belltoy]

Great! And should bump a new version to fix rusterlium/rebar3_cargo#6 which may should be update to using the new fix with a cargo config file?

[belltoy]

@filmor Could you bump a new release? And have a review at rusterlium/rebar3_cargo#8 if you have time. 🙂