$ RUST_BACKTRACE=1 cargo build
   Compiling leaf v0.2.1 (file:///home/<user>/work/leaf)
   Compiling num-rational v0.1.35
Build failed, waiting for other jobs to finish...
error: failed to run custom build command for `leaf v0.2.1 (file:///home/<user>/work/leaf)`
Process didn't exit successfully: `/home/<user>/work/leaf/target/debug/build/leaf-87f43ad88e5c8bb2/build-script-build` (exit code: 101)
--- stderr
thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: Error { kind: Failed, description: "Error while trying to execute `capnp compile`: Failed: No such file or directory (os error 2).  Please verify that version 0.5.2 or higher of the capnp executable is installed on your system. See https://capnproto.org/install.html" }', src/libcore/result.rs:788
stack backtrace:
   1:     0x55e338350a6b - std::sys::backtrace::tracing::imp::write::h00e948915d1e4c72
   2:     0x55e338355ebf - std::panicking::default_hook::_{{closure}}::h7b8a142818383fb8
   3:     0x55e33835511d - std::panicking::default_hook::h41cf296f654245d7
   4:     0x55e3383557d5 - std::panicking::rust_panic_with_hook::h4cbd7ca63ce1aee9
   5:     0x55e338355622 - std::panicking::begin_panic::h93672d0313d5e8e9
   6:     0x55e338355591 - std::panicking::begin_panic_fmt::hd0daa02942245d81
   7:     0x55e338355511 - rust_begin_unwind
   8:     0x55e33838c97f - core::panicking::panic_fmt::hbfc935564d134c1b
   9:     0x55e3382950c2 - core::result::unwrap_failed::h14ae321fa6665b8d
                        at /build/rustc-1.12.0+dfsg1/src/libcore/result.rs:29
  10:     0x55e338294251 - _<core..result..Result<T, E>>::unwrap::hbe110bf6bea72ca6
                        at /build/rustc-1.12.0+dfsg1/src/libcore/result.rs:726
  11:     0x55e338297306 - build_script_build::main::he5071e1b00fcfe0e
                        at /home/<user>/work/leaf/build.rs:4
  12:     0x55e33835d896 - __rust_maybe_catch_panic
  13:     0x55e33835480d - std::rt::lang_start::h53bf99b0829cc03c
  14:     0x55e3382974e3 - main
  15:     0x7fa0f6ae52b0 - __libc_start_main
  16:     0x55e3382935e9 - _start
  17:                0x0 - <unknown>