So yeah looks like I'm tethered to the nightly toolchain after all. :/

Before I ended up going down the TryFrom rabbit hole I ran into two issues with bindgen:

1.) Bindgen segfaults with the ancient LLVM on OSX 10.9. Issue #1006. Solution: use LLVM >= 5 binaries from the LLVM site.

2.) Stable (deprecated) rustfmt causes bindgen to segfault. Solution: cargo install -f rustfmt-nightly. It could be as simple as "stable rustfmt requires --force to run because it's been deprecated", but more helpful error messages would be a great thing here.

(TryFrom is being stabilized fairly soon, it got caught up in some silly stuff but is basically good to go)

Custom { kind: Other, error: StringError("Internal rustfmt error") }

I get the same results if I call the bindgen executable or have build.rs call the bindgen API. I've stuck with having build.rs call the bindgen executable because if I use the bindgen API, compilation is SLOW.

    rustup component add rustfmt-preview

  $ cargo uninstall rustfmt && rustup component add rustfmt-preview
      Removing /home/alex/.cargo/bin/cargo-fmt
      Removing /home/alex/.cargo/bin/rustfmt
  info: downloading component 'rustfmt-preview'
  info: installing component 'rustfmt-preview'
  $ bindgen bindings.h -- -I/usr/local/include/libr > /dev/null
  Custom { kind: Other, error: StringError("Cannot find binary path") }
  $ rustc --version
  rustc 1.28.0-nightly (29f48ccf3 2018-06-03)
  $ cat bindings.h 
  #include <r_lib.h>
  #include <r_asm.h>
  #include <r_reg.h>
  #include <r_anal.h>
  #include <r_bin.h>