Simpler approach to get helpers included in binary

Author: lionel-

crates/ark/src/debug.rs

@@ -8,6 +8,28 @@ use harp::utils::r_str_to_owned_utf8_unchecked;
 use crate::interface::RMain;
 use crate::interface::CAPTURE_CONSOLE_OUTPUT;
 
+// Ensure the compiler includes the C entry points in `debug.c` in the binary.
+// We store function pointers in global variables that are declared "used". The
+// compiler is able to follow the chain of dependency from these variables to
+// the C functions and ultimately their Rust implementations defined below.
+
+extern "C" {
+    fn ark_print(x: libr::SEXP) -> *const ffi::c_char;
+    fn ark_inspect(x: libr::SEXP) -> *const ffi::c_char;
+    fn ark_trace_back() -> *const ffi::c_char;
+    fn ark_display_value(x: libr::SEXP) -> *const ffi::c_char;
+}
+
+#[used]
+static _ARK_PRINT: unsafe extern "C" fn(x: libr::SEXP) -> *const ffi::c_char = ark_print;
+#[used]
+static _ARK_INSPECT: unsafe extern "C" fn(x: libr::SEXP) -> *const ffi::c_char = ark_inspect;
+#[used]
+static _ARK_TRACE_BACK: unsafe extern "C" fn() -> *const ffi::c_char = ark_trace_back;
+#[used]
+static _ARK_DISPLAY_VALUE: unsafe extern "C" fn(x: libr::SEXP) -> *const ffi::c_char =
+    ark_display_value;
+
 // Implementations for entry points in `debug.c`.
 
 #[no_mangle]

crates/harp/harp-macros/src/lib.rs

@@ -10,7 +10,6 @@ use quote::format_ident;
 use quote::quote;
 use quote::ToTokens;
 use syn::parse_macro_input;
-use syn::ItemFn;
 use syn::ItemStruct;
 
 extern crate proc_macro;
@@ -214,32 +213,3 @@ pub fn register(_attr: TokenStream, item: TokenStream) -> TokenStream {
     let all = quote! { #function #registration };
     all.into()
 }
-
-#[proc_macro_attribute]
-pub fn ensure_used(_attr: TokenStream, item: TokenStream) -> TokenStream {
-    let input = parse_macro_input!(item as ItemFn);
-
-    let fn_name = &input.sig.ident;
-    let static_name = format_ident!("_{fn_name}");
-
-    let inputs = &input.sig.inputs;
-    let output = &input.sig.output;
-    let abi = &input.sig.abi;
-    let fn_type = quote! {
-        #abi fn(#inputs) #output
-    };
-
-    let out = quote! {
-        #[no_mangle]
-        #input
-
-        // Generate a static variable that hold the function pointer to force the
-        // function to be compiled in
-        #[used]
-        #[no_mangle]
-        #[doc(hidden)]
-        static #static_name: #fn_type = #fn_name;
-    };
-
-    TokenStream::from(out)
-}

crates/harp/src/utils.rs

@@ -5,11 +5,9 @@
 //
 //
 
-use std::ffi;
 use std::ffi::CStr;
 use std::ffi::CString;
 
-use harp_macros::ensure_used;
 use itertools::Itertools;
 use libr::*;
 use once_cell::sync::Lazy;
@@ -763,25 +761,6 @@ pub fn r_subset_vec(x: SEXP, indices: Vec<i64>) -> Result<SEXP> {
     Ok(out.sexp)
 }
 
-// Ensure the compiler includes the C entry points in `debug.c` in the binary.
-// This must be in a module that is used by other parts of the program, i.e. not
-// in debug.rs. Otherwise the compiler will still omit the whole thing.
-
-extern "C" {
-    fn ark_print(x: libr::SEXP) -> *const ffi::c_char;
-    fn ark_inspect(x: libr::SEXP) -> *const ffi::c_char;
-    fn ark_trace_back() -> *const ffi::c_char;
-    fn ark_display_value(x: libr::SEXP) -> *const ffi::c_char;
-}
-
-#[ensure_used]
-pub extern "C" fn _placeholder() {
-    unsafe { ark_print(libr::R_NilValue) };
-    unsafe { ark_inspect(libr::R_NilValue) };
-    unsafe { ark_trace_back() };
-    unsafe { ark_display_value(libr::R_NilValue) };
-}
-
 #[cfg(test)]
 mod tests {
     use libr::STRING_ELT;