Allow arbitrary function names (#593)

* Allow arbitrary ASCII strings as NIF names
* Just to be sure, reject control chars

Author: filmor

CHANGELOG.md

@@ -16,6 +16,10 @@ versions.
 
 ### Changed
 
+- Adjust C char types to use the proper FFI type (#592)
+- Allow arbitrary (ASCII) NIF function names (#593, idea and initial
+  implementation by @KoviRobi)
+
 ### Removed
 
 ## [0.31.0] - 2024-02-13

rustler_codegen/src/nif.rs

@@ -48,15 +48,18 @@ pub fn transcoder_decorator(nif_attributes: NifAttributes, fun: syn::ItemFn) ->
     let argument_names = create_function_params(inputs.clone());
     let erl_func_name = nif_attributes
         .custom_name
-        .map(|n| syn::Ident::new(n.value().as_str(), Span::call_site()))
-        .unwrap_or_else(|| name.clone());
+        .map_or_else(|| name.to_string(), |n| n.value().to_string());
+
+    if !erl_func_name.is_ascii() || erl_func_name.chars().any(|x| x.is_ascii_control()) {
+        panic!("Only non-Control ASCII strings are supported as function names");
+    }
 
     quote! {
         #[allow(non_camel_case_types)]
         pub struct #name;
 
         impl rustler::Nif for #name {
-            const NAME: *const rustler::codegen_runtime::c_char = concat!(stringify!(#erl_func_name), "\0").as_ptr() as *const rustler::codegen_runtime::c_char;
+            const NAME: *const rustler::codegen_runtime::c_char = concat!(#erl_func_name, "\0").as_ptr() as *const rustler::codegen_runtime::c_char;
             const ARITY: rustler::codegen_runtime::c_uint = #arity;
             const FLAGS: rustler::codegen_runtime::c_uint = #flags as rustler::codegen_runtime::c_uint;
             const RAW_FUNC: unsafe extern "C" fn(

rustler_tests/lib/rustler_test.ex

@@ -121,7 +121,7 @@ defmodule RustlerTest do
   def raise_term_with_atom_error(), do: err()
   def term_with_tuple_error(), do: err()
 
-  def nif_attrs_can_rename(), do: err()
+  def nif_attrs_can_rename!(), do: err()
 
   def add_from_tuple(_tuple), do: err()
   def add_one_to_tuple(_tuple), do: err()

rustler_tests/native/rustler_test/src/test_nif_attrs.rs

@@ -1,4 +1,4 @@
-#[rustler::nif(name = "nif_attrs_can_rename")]
+#[rustler::nif(name = "nif_attrs_can_rename!")]
 pub fn can_rename() -> bool {
     true
 }

rustler_tests/test/nif_attrs_test.exs

@@ -2,6 +2,6 @@ defmodule NifAttrsTest do
   use ExUnit.Case
 
   test "can rename a NIF with an attribute" do
-    assert RustlerTest.nif_attrs_can_rename()
+    assert RustlerTest.nif_attrs_can_rename!()
   end
 end