Consolidate all Hello World examples into one dir

examples/hello-world/rust-platform/src/lib.rs

@@ -0,0 +1,71 @@
+#![allow(non_snake_case)]
+
+use core::ffi::c_void;
+use roc_std::RocStr;
+use std::ffi::CStr;
+use std::os::raw::c_char;
+
+extern "C" {
+    #[link_name = "roc__mainForHost_1_exposed"]
+    fn roc_main() -> RocStr;
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn roc_alloc(size: usize, _alignment: u32) -> *mut c_void {
+    return libc::malloc(size);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn roc_realloc(
+    c_ptr: *mut c_void,
+    new_size: usize,
+    _old_size: usize,
+    _alignment: u32,
+) -> *mut c_void {
+    return libc::realloc(c_ptr, new_size);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn roc_dealloc(c_ptr: *mut c_void, _alignment: u32) {
+    return libc::free(c_ptr);
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn roc_panic(c_ptr: *mut c_void, tag_id: u32) {
+    match tag_id {
+        0 => {
+            let slice = CStr::from_ptr(c_ptr as *const c_char);
+            let string = slice.to_str().unwrap();
+            eprintln!("Roc hit a panic: {}", string);
+            std::process::exit(1);
+        }
+        _ => todo!(),
+    }
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn roc_memcpy(dst: *mut c_void, src: *mut c_void, n: usize) -> *mut c_void {
+    libc::memcpy(dst, src, n)
+}
+
+#[no_mangle]
+pub unsafe extern "C" fn roc_memset(dst: *mut c_void, c: i32, n: usize) -> *mut c_void {
+    libc::memset(dst, c, n)
+}
+
+#[no_mangle]
+pub extern "C" fn rust_main() -> i32 {
+    unsafe {
+        let roc_str = roc_main();
+
+        let len = roc_str.len();
+        let str_bytes = roc_str.as_bytes().as_ptr() as *const libc::c_void;
+
+        if libc::write(1, str_bytes, len) < 0 {
+            panic!("Writing to stdout failed!");
+        }
+    }
+
+    // Exit code
+    0
+}