Add ndk_glue macro.

Author: dvc94ch

README.md

@@ -10,26 +10,14 @@
 
 ```toml
 [lib]
-crate-type = ["cdylib"]
+crate-type = ["lib", "cdylib"]
 ```
 
 ```rust
 #[cfg(target_os = "android")]
-#[no_mangle]
-pub unsafe extern "C" fn ANativeActivity_onCreate(
-    activity: *mut std::os::raw::c_void,
-    saved_state: *mut std::os::raw::c_void,
-    saved_state_size: usize,
-) {
-    ndk_glue::init(
-        activity as _,
-        saved_state as _,
-        saved_state_size as _,
-        app_main,
-    );
-}
+ndk_glue::ndk_glue!(main);
 
-pub fn app_main() {
+fn main() {
     println!("hello world");
 }
 ```

ndk-examples/examples/hello_world.rs

@@ -1,19 +1,6 @@
 #[cfg(target_os = "android")]
-#[no_mangle]
-pub unsafe extern "C" fn ANativeActivity_onCreate(
-    activity: *mut std::os::raw::c_void,
-    saved_state: *mut std::os::raw::c_void,
-    saved_state_size: usize,
-) {
-    std::env::set_var("RUST_BACKTRACE", "1");
-    ndk_glue::init(
-        activity as _,
-        saved_state as _,
-        saved_state_size as _,
-        app_main,
-    );
-}
+ndk_glue::ndk_glue!(main);
 
-pub fn app_main() {
+fn main() {
     println!("hello world");
 }

ndk-glue/src/lib.rs

@@ -14,6 +14,26 @@ use std::ptr::NonNull;
 use std::sync::{RwLock, RwLockReadGuard};
 use std::thread;
 
+#[macro_export]
+macro_rules! ndk_glue {
+    ($main:ident) => {
+        #[no_mangle]
+        unsafe extern "C" fn ANativeActivity_onCreate(
+            activity: *mut std::os::raw::c_void,
+            saved_state: *mut std::os::raw::c_void,
+            saved_state_size: usize,
+        ) {
+            std::env::set_var("RUST_BACKTRACE", "1");
+            $crate::init(
+                activity as _,
+                saved_state as _,
+                saved_state_size as _,
+                $main,
+            );
+        }
+    }
+}
+
 pub fn android_log(level: Level, tag: &CStr, msg: &CStr) {
     use android_log_sys::LogPriority;
     let prio = match level {