`test-macro-snapshot.R` does not test R & Rust integration

[JosiahParry]

`test-macro-snapshot.R` does not test R & Rust integration

[yutannihilation]

I've been wondering how I can use insta for snapshot tests on macro expansion, and I finally found it can be done with prettyplease, which converts an AST into a String of the formatted Rust code.

I write a helper function like this.

    fn assert_snapshot_helper(orig: syn::ItemFn) {
        let result: syn::ItemFn = generate_fn(&orig);
        let formatted = prettyplease::unparse(&parse_quote!(#result));
        let lines = formatted.lines().collect::<Vec<&str>>();
        insta::assert_yaml_snapshot!(lines);
    }

    #[test]
    fn test_generate_inner_fn() {
        assert_snapshot_helper(parse_quote!(
            #[my_macro]
            fn foo() -> Bar {
                bar()
            }
        ));

c.f. yutannihilation/savvy#175

extendr-macros' function also takes ItemFn or so and returns TokenStream, so I think the similar thing can be done.

extendr/extendr-macros/src/extendr_function.rs

Lines 7 to 21 in 70720e2

	pub fn extendr_function(mut func: ItemFn, opts: &wrappers::ExtendrOptions) -> TokenStream {
	let mut wrappers: Vec<ItemFn> = Vec::new();
	let res =
	wrappers::make_function_wrappers(opts, &mut wrappers, "", &func.attrs, &mut func.sig, None);
	if let Err(e) = res {
	return e.into_compile_error().into();
	};
	TokenStream::from(quote! {
	#func
	# ( #wrappers )*
	})
	}