feat(c-api) Implement wasm_extern_copy.

This patch also moves `wasm_extern_delete` into the correct Rust module.

lib/c-api/src/wasm_c_api/externals/mod.rs

@@ -20,6 +20,84 @@ pub struct wasm_extern_t {
 
 wasm_declare_boxed_vec!(extern);
 
+/// Copy a `wasm_extern_t`.
+///
+/// # Example
+///
+/// ```rust
+/// # use inline_c::assert_c;
+/// # fn main() {
+/// #     (assert_c! {
+/// # #include "tests/wasmer_wasm.h"
+/// #
+/// int main() {
+///     // Create the engine and the store.
+///     wasm_engine_t* engine = wasm_engine_new();
+///     wasm_store_t* store = wasm_store_new(engine);
+///
+///     // Create a WebAssembly module from a WAT definition.
+///     wasm_byte_vec_t wat;
+///     wasmer_byte_vec_new_from_string(
+///         &wat,
+///         "(module\n"
+///         "  (func (export \"function\")))"
+///     );
+///     wasm_byte_vec_t wasm;
+///     wat2wasm(&wat, &wasm);
+///
+///     // Create the module.
+///     wasm_module_t* module = wasm_module_new(store, &wasm);
+///
+///     // Instantiate the module.
+///     wasm_extern_vec_t imports = WASM_EMPTY_VEC;
+///     wasm_trap_t* traps = NULL;
+///
+///     wasm_instance_t* instance = wasm_instance_new(store, module, &imports, &traps);
+///     assert(instance);
+///
+///     // Read the exports.
+///     wasm_extern_vec_t exports;
+///     wasm_instance_exports(instance, &exports);
+///
+///     // We have 1 of them.
+///     assert(exports.size == 1);
+///
+///     // It is a function.
+///     wasm_extern_t* function = exports.data[0];
+///     assert(wasm_extern_kind(function) == WASM_EXTERN_FUNC);
+///
+///     // Let's copy the function.
+///     wasm_extern_t* function_copy = wasm_extern_copy(function);
+///     assert(wasm_extern_kind(function_copy) == WASM_EXTERN_FUNC);
+///
+///     // Free everything.
+///     wasm_extern_delete(function_copy);
+///     wasm_instance_delete(instance);
+///     wasm_module_delete(module);
+///     wasm_byte_vec_delete(&wasm);
+///     wasm_byte_vec_delete(&wat);
+///     wasm_store_delete(store);
+///     wasm_engine_delete(engine);
+///
+///     return 0;
+/// }
+/// #     })
+/// #     .success();
+/// # }
+/// ```
+#[no_mangle]
+pub unsafe extern "C" fn wasm_extern_copy(r#extern: &wasm_extern_t) -> Box<wasm_extern_t> {
+    Box::new(r#extern.clone())
+}
+
+/// Delete an extern.
+///
+/// # Example
+///
+/// See `wasm_extern_copy`.
+#[no_mangle]
+pub unsafe extern "C" fn wasm_extern_delete(_extern: Option<Box<wasm_extern_t>>) {}
+
 #[no_mangle]
 pub unsafe extern "C" fn wasm_func_as_extern(
     func: Option<&wasm_func_t>,

lib/c-api/src/wasm_c_api/wasi/mod.rs

@@ -524,12 +524,6 @@ pub unsafe extern "C" fn wasi_get_start_function(
     }))
 }
 
-/// Delete a `wasm_extern_t` allocated by the API.
-///
-/// cbindgen:ignore
-#[no_mangle]
-pub unsafe extern "C" fn wasm_extern_delete(_item: Option<Box<wasm_extern_t>>) {}
-
 #[cfg(test)]
 mod tests {
     use inline_c::assert_c;