Allow floats to decode from integer terms (#641)

rustler/src/types/primitive.rs

@@ -1,27 +1,43 @@
 use crate::types::atom;
 use crate::{Decoder, Encoder, Env, Error, NifResult, Term};
 
-macro_rules! impl_number_transcoder {
-    ($dec_type:ty, $nif_type:ty, $encode_fun:ident, $decode_fun:ident) => {
+macro_rules! erl_make {
+    ($self:expr, $env:ident, $encode_fun:ident, $type:ty) => {
+        #[allow(clippy::cast_lossless)]
+        unsafe {
+            Term::new(
+                $env,
+                rustler_sys::$encode_fun($env.as_c_arg(), $self as $type),
+            )
+        }
+    };
+}
+
+macro_rules! erl_get {
+    ($decode_fun:ident, $term:ident, $dest:ident) => {
+        unsafe {
+            rustler_sys::$decode_fun($term.get_env().as_c_arg(), $term.as_c_arg(), &mut $dest)
+        }
+    };
+}
+
+macro_rules! impl_number_encoder {
+    ($dec_type:ty, $nif_type:ty, $encode_fun:ident) => {
         impl Encoder for $dec_type {
             fn encode<'a>(&self, env: Env<'a>) -> Term<'a> {
-                #[allow(clippy::cast_lossless)]
-                unsafe {
-                    Term::new(
-                        env,
-                        rustler_sys::$encode_fun(env.as_c_arg(), *self as $nif_type),
-                    )
-                }
+                erl_make!(*self, env, $encode_fun, $nif_type)
             }
         }
+    };
+}
+
+macro_rules! impl_number_decoder {
+    ($dec_type:ty, $nif_type:ty, $decode_fun:ident) => {
         impl<'a> Decoder<'a> for $dec_type {
             fn decode(term: Term) -> NifResult<$dec_type> {
                 #![allow(unused_unsafe)]
                 let mut res: $nif_type = Default::default();
-                if unsafe {
-                    rustler_sys::$decode_fun(term.get_env().as_c_arg(), term.as_c_arg(), &mut res)
-                } == 0
-                {
+                if erl_get!($decode_fun, term, res) == 0 {
                     return Err(Error::BadArg);
                 }
                 Ok(res as $dec_type)
@@ -30,12 +46,19 @@ macro_rules! impl_number_transcoder {
     };
 }
 
+macro_rules! impl_number_transcoder {
+    ($dec_type:ty, $nif_type:ty, $encode_fun:ident, $decode_fun:ident) => {
+        impl_number_encoder!($dec_type, $nif_type, $encode_fun);
+        impl_number_decoder!($dec_type, $nif_type, $decode_fun);
+    };
+}
+
 // Base number types
 impl_number_transcoder!(i32, i32, enif_make_int, enif_get_int);
 impl_number_transcoder!(u32, u32, enif_make_uint, enif_get_uint);
 impl_number_transcoder!(i64, i64, enif_make_int64, enif_get_int64);
 impl_number_transcoder!(u64, u64, enif_make_uint64, enif_get_uint64);
-impl_number_transcoder!(f64, f64, enif_make_double, enif_get_double);
+impl_number_encoder!(f64, f64, enif_make_double);
 
 // Casted number types
 impl_number_transcoder!(i8, i32, enif_make_int, enif_get_int);
@@ -44,25 +67,18 @@ impl_number_transcoder!(i16, i32, enif_make_int, enif_get_int);
 impl_number_transcoder!(u16, u32, enif_make_uint, enif_get_uint);
 impl_number_transcoder!(usize, u64, enif_make_uint64, enif_get_uint64);
 impl_number_transcoder!(isize, i64, enif_make_int64, enif_get_int64);
+impl_number_encoder!(f32, f64, enif_make_double);
 
-impl Encoder for bool {
-    fn encode<'a>(&self, env: Env<'a>) -> Term<'a> {
-        if *self {
-            atom::true_().to_term(env)
-        } else {
-            atom::false_().to_term(env)
+// Manual Decoder impls for floats so they can fall back to decoding from integer terms
+impl<'a> Decoder<'a> for f64 {
+    fn decode(term: Term) -> NifResult<f64> {
+        #![allow(unused_unsafe)]
+        let mut res: f64 = Default::default();
+        if erl_get!(enif_get_double, term, res) == 0 {
+            let res_fallback: i64 = term.decode()?;
+            return Ok(res_fallback as f64);
         }
-    }
-}
-impl<'a> Decoder<'a> for bool {
-    fn decode(term: Term<'a>) -> NifResult<bool> {
-        atom::decode_bool(term)
-    }
-}
-
-impl Encoder for f32 {
-    fn encode<'a>(&self, env: Env<'a>) -> Term<'a> {
-        f64::from(*self).encode(env)
+        Ok(res)
     }
 }
 
@@ -78,3 +94,18 @@ impl<'a> Decoder<'a> for f32 {
         }
     }
 }
+
+impl Encoder for bool {
+    fn encode<'a>(&self, env: Env<'a>) -> Term<'a> {
+        if *self {
+            atom::true_().to_term(env)
+        } else {
+            atom::false_().to_term(env)
+        }
+    }
+}
+impl<'a> Decoder<'a> for bool {
+    fn decode(term: Term<'a>) -> NifResult<bool> {
+        atom::decode_bool(term)
+    }
+}

rustler_tests/lib/rustler_test.ex

@@ -23,6 +23,7 @@ defmodule RustlerTest do
 
   def add_u32(_, _), do: err()
   def add_i32(_, _), do: err()
+  def add_floats(_, _), do: err()
   def echo_u8(_), do: err()
   def echo_u128(_), do: err()
   def echo_i128(_), do: err()

rustler_tests/native/rustler_test/src/test_primitives.rs

@@ -10,6 +10,11 @@ pub fn add_i32(a: i32, b: i32) -> i32 {
     a + b
 }
 
+#[rustler::nif]
+pub fn add_floats(a: f32, b: f64) -> f64 {
+    (a as f64) + b
+}
+
 #[rustler::nif]
 pub fn echo_u8(n: u8) -> u8 {
     n

rustler_tests/test/primitives_test.exs

@@ -6,6 +6,10 @@ defmodule RustlerTest.PrimitivesTest do
     assert 3 == RustlerTest.add_i32(6, -3)
     assert -3 == RustlerTest.add_i32(3, -6)
     assert 3 == RustlerTest.echo_u8(3)
+    assert 2.0 == RustlerTest.add_floats(3.0, -1.0)
+    assert 2.0 == RustlerTest.add_floats(3, -1)
+    assert 2.0 == RustlerTest.add_floats(3.0, -1)
+    assert 2.0 == RustlerTest.add_floats(3, -1.0)
   end
 
   test "number decoding should fail on invalid terms" do