Support Linux Cross Compiling

README.md

@@ -1,3 +1,27 @@
 # coreaudio-sys [![Build Status](https://travis-ci.org/RustAudio/coreaudio-sys.svg?branch=master)](https://travis-ci.org/RustAudio/coreaudio-sys) [![Crates.io](https://img.shields.io/crates/v/coreaudio-sys.svg)](https://crates.io/crates/coreaudio-sys) [![Crates.io](https://img.shields.io/crates/l/coreaudio-sys.svg)](https://github.com/RustAudio/coreaudio-sys/blob/master/LICENSE)
 
 Raw bindings to Apple's Core Audio API for macos and iOS generated using [rust-bindgen](https://github.com/rust-lang-nursery/rust-bindgen). [coreaudio-rs](https://github.com/RustAudio/coreaudio-rs) is an attempt at offering a higher level API around this crate.
+
+## Cross Compiling
+
+[Rust Cross](https://github.com/japaric/rust-cross) has a good explanation of how cross-compiling Rust works in general. While the author of Rust Cross advises against it, it is perfectly possible to cross-compile Rust for MacOS on Linux. [OSXCross](https://github.com/tpoechtrager/osxcross) can be used to create a compiler toolchain that can compile for MacOS on Linux.
+
+### Environment Variables
+
+When cross-compiling for MacOS on Linux there are two environment variables that are used to configure how `coreaudio-sys` finds the required headers and libraries. The following examples assume that you have OSXCross installed at `/build/osxcross`.
+
+#### `COREAUDIO_CFLAGS`
+
+This allows you to add arbitrary flags to the `clang` call that is made when auto-generating the Rust bindings to coreaudio. This will need to be set to include some headers used by coreaudio:
+
+```bash
+export COREAUDIO_CFLAGS=-I/build/osxcross/target/SDK/MacOSX10.11.sdk/System/Library/Frameworks/Kernel.framework/Headers -I/build/osxcross/target/SDK/MacOSX10.11.sdk/usr/include
+```
+
+#### `COREAUDIO_FRAMEWORKS_PATH`
+
+This tell `coreaudio-sys` where to find the Frameworks path of the MacOS SDK:
+
+```bash
+export COREAUDIO_FRAMEWORKS_PATH=/build/osxcross/target/SDK/MacOSX10.11.sdk/System/Library/Frameworks
+```

build.rs

@@ -30,6 +30,11 @@ fn frameworks_path() -> Result<String, std::io::Error> {
     // for actually linking against them (especially for cross-compilation) once
     // has to refer to the frameworks as found within "Xcode.app/Contents/Developer/…".
 
+    // Use environment variable if set
+    if let Ok(path) = std::env::var("COREAUDIO_FRAMEWORKS_PATH") {
+        return Ok(path)
+    }
+
     if osx_version()
         .and_then(|version| Ok(parse_version(&version).map(|v| v >= 13).unwrap_or(false)))
         .unwrap_or(false)
@@ -40,9 +45,10 @@ fn frameworks_path() -> Result<String, std::io::Error> {
         let prefix_str = std::str::from_utf8(&output).expect("invalid output from `xcode-select`");
         let prefix = prefix_str.trim_right();
 
-        let platform = if cfg!(target_os = "macos") {
+        let target = std::env::var("TARGET").unwrap();
+        let platform = if target.contains("apple-darwin") {
             "MacOSX"
-        } else if cfg!(target_os = "ios") {
+        } else if target.contains("apple-ios") {
             "iPhoneOS"
         } else {
             unreachable!();
@@ -111,11 +117,13 @@ fn build(frameworks_path: &str) {
         headers.push("OpenAL.framework/Headers/alc.h");
     }
 
-    #[cfg(all(feature = "core_midi", target_os = "macos"))]
+    #[cfg(all(feature = "core_midi"))]
     {
-        println!("cargo:rustc-link-lib=framework=CoreMIDI");
-        frameworks.push("CoreMIDI");
-        headers.push("CoreMIDI.framework/Headers/CoreMIDI.h");
+        if std::env::var("TARGET").unwrap().contains("apple-darwin") {
+            println!("cargo:rustc-link-lib=framework=CoreMIDI");
+            frameworks.push("CoreMIDI");
+            headers.push("CoreMIDI.framework/Headers/CoreMIDI.h");
+        }
     }
 
     // Get the cargo out directory.
@@ -139,10 +147,16 @@ fn build(frameworks_path: &str) {
     }
 
     // Generate the bindings.
-    let bindings = builder
+    builder = builder
         .trust_clang_mangling(false)
         .derive_default(true)
-        .rustfmt_bindings(false)
+        .rustfmt_bindings(false);
+
+    if let Ok(cflags) = std::env::var("COREAUDIO_CFLAGS") {
+        builder = builder.clang_args(cflags.split(" "));
+    }
+
+    let bindings = builder
         .generate()
         .expect("unable to generate bindings");
 
@@ -152,16 +166,16 @@ fn build(frameworks_path: &str) {
         .expect("could not write bindings");
 }
 
-#[cfg(any(target_os = "macos", target_os = "ios"))]
 fn main() {
+    let target = std::env::var("TARGET").unwrap();
+    if ! (target.contains("apple-darwin") || target.contains("apple-ios")) {
+        eprintln!("coreaudio-sys requires macos or ios target");
+    }
+
     if let Ok(directory) = frameworks_path() {
         build(&directory);
     } else {
         eprintln!("coreaudio-sys could not find frameworks path");
     }
 }
 
-#[cfg(not(any(target_os = "macos", target_os = "ios")))]
-fn main() {
-    eprintln!("coreaudio-sys requires macos or ios target");
-}