impl Default for &MyMessage

Simply return MyMessage::default_instance()

protobuf-codegen/src/code_writer.rs

@@ -163,7 +163,19 @@ impl<'a> CodeWriter<'a> {
     where
         F: Fn(&mut CodeWriter),
     {
-        self.expr_block(&format!("impl {} for {}", tr.as_ref(), ty.as_ref()), cb);
+        self.impl_args_for_block(&[], tr.as_ref(), ty.as_ref(), cb);
+    }
+
+    pub fn impl_args_for_block<F>(&mut self, args: &[&str], tr: &str, ty: &str, cb: F)
+    where
+        F: Fn(&mut CodeWriter),
+    {
+        let args_str = if args.is_empty() {
+            "".to_owned()
+        } else {
+            format!("<{}>", args.join(", "))
+        };
+        self.expr_block(&format!("impl{} {} for {}", args_str, tr, ty), cb);
     }
 
     pub fn unsafe_impl(&mut self, what: &str, for_what: &str) {

protobuf-codegen/src/message.rs

@@ -414,6 +414,14 @@ impl<'a> MessageGen<'a> {
         });
     }
 
+    fn write_impl_default_for_amp(&self, w: &mut CodeWriter) {
+        w.impl_args_for_block(&["'a"], "::std::default::Default", &format!("&'a {}", self.type_name), |w| {
+            w.def_fn(&format!("default() -> &'a {}", self.type_name), |w| {
+                w.write_line(&format!("<{} as ::protobuf::Message>::default_instance()", self.type_name));
+            });
+        });
+    }
+
     fn write_dummy_impl_partial_eq(&self, w: &mut CodeWriter) {
         w.impl_for_block("::std::cmp::PartialEq", &self.type_name, |w| {
             w.def_fn("eq(&self, _: &Self) -> bool", |w| {
@@ -426,6 +434,9 @@ impl<'a> MessageGen<'a> {
     pub fn write(&self, w: &mut CodeWriter) {
         self.write_struct(w);
 
+        w.write_line("");
+        self.write_impl_default_for_amp(w);
+
         if !self.supports_derive_partial_eq() {
             w.write_line("");
             self.write_dummy_impl_partial_eq(w);

protobuf-test/src/common/v2/test_default.rs

@@ -0,0 +1,7 @@
+use super::test_default_pb::*;
+
+#[test]
+fn test_default_for_amp_message() {
+    let none: Option<&TestDefault> = None;
+    assert_eq!(0, none.unwrap_or_default().get_i());
+}

protobuf-test/src/common/v2/test_default_pb.proto

@@ -0,0 +1,10 @@
+syntax = "proto2";
+
+import "rustproto.proto";
+option (rustproto.generate_accessors_all) = true;
+
+package test_default;
+
+message TestDefault {
+    optional int32 i = 1;
+}