README.md

@@ -0,0 +1,22 @@
+# rust-on-ios
+
+This is a quick proof-of-concept for a bitcode-enabled library built from Rust intended for consumption in an iOS app built in Unity (2018.4.11f1)
+
+Unity defaults to embedding bitcode meaning all static dependencies must do likewise. Rust, by default, does not embed bitcode for static library targets. We can use `-C lto -Z embed-bitcode` to ask Rust to embed bitcode (afaict `-C lto` is required because the shipped iOS rust-std libs also need to embed bitcode.)
+
+Naturally both Rust and Apple have forked LLVM and they are not always in-sync which is the current major problem [outlined here](https://github.com/rust-lang/rust/issues/35968). For Xcode 11.1 the latest Rust version we can use is `nightly-2019-07-17`.
+
+## Building
+
+- cd librusty
+- cargo install cargo-lipo
+- rustup target add aarch64-apple-ios
+- cargo lipo --targets aarch64-apple-ios --release
+- cp target/universal/release/librusty.a ../unity/Assets/Plugins/iOS/librusty.a
+
+## So, what?
+
+Until Rust officially decides to support bitcode we have to jump through hoops in order to do so:
+- We must use a specific (nightly) compiler version
+- Xcode betas/updates **may** break linkability of our static library
+- Downstream developers **may not** all be on the same (latest) version of Xcode

librusty/.cargo/config

@@ -0,0 +1,2 @@
+[build]
+rustflags = ["-C", "lto", "-Z", "embed-bitcode"]

librusty/rust-toolchain

@@ -1 +1 @@
-nightly-2019-09-13
+nightly-2019-07-17

librusty/src/lib.rs

@@ -2,6 +2,7 @@ use std::ffi::CStr;
 use std::ffi::CString;
 use std::os::raw::c_char;
 
+#[no_mangle]
 #[allow(non_snake_case)]
 pub extern "C" fn DoSomeInterestingWork(count: i32, content: *const c_char) -> *const c_char {
     let content_string = unsafe { CStr::from_ptr(content) }
@@ -22,6 +23,7 @@ pub extern "C" fn DoSomeInterestingWork(count: i32, content: *const c_char) -> *
         .into_raw()
 }
 
+#[no_mangle]
 #[allow(non_snake_case)]
 pub extern "C" fn FreeString(content: *mut c_char) {
     unsafe {