Add support for wrapping message in Option

proto/rustproto.proto

@@ -19,6 +19,8 @@ extend google.protobuf.FileOptions {
     optional bool tokio_bytes_all = 17011;
     // Use `bytes::Bytes` for `string` fields
     optional bool tokio_bytes_for_string_all = 17012;
+    // Use `Option` for `message` fields.
+    optional bool option_for_message_all = 17013;
 
     // When true, will only generate codes that works with lite runtime.
     optional bool lite_runtime_all = 17035;
@@ -33,6 +35,8 @@ extend google.protobuf.MessageOptions {
     optional bool tokio_bytes = 17011;
     // Use `bytes::Bytes` for `string` fields
     optional bool tokio_bytes_for_string = 17012;
+    // Use `Option` for `message` fields.
+    optional bool option_for_message = 17013;
 }
 
 extend google.protobuf.FieldOptions {
@@ -44,4 +48,6 @@ extend google.protobuf.FieldOptions {
     optional bool tokio_bytes_field = 17011;
     // Use `bytes::Bytes` for `string` fields
     optional bool tokio_bytes_for_string_field = 17012;
+    // Use `Option` for `message` fields.
+    optional bool option_for_message_field = 17013;
 }

protobuf-codegen/src/customize/mod.rs

@@ -98,6 +98,8 @@ pub struct Customize {
     pub(crate) tokio_bytes: Option<bool>,
     /// Use `bytes::Bytes` for `string` fields
     pub(crate) tokio_bytes_for_string: Option<bool>,
+    /// Use `Option` for `message` fields.
+    pub(crate) option_for_message: Option<bool>,
     /// Enable lite runtime.
     pub(crate) lite_runtime: Option<bool>,
     /// Generate `mod.rs` in the output directory.
@@ -148,6 +150,11 @@ impl Customize {
         self
     }
 
+    pub fn option_for_message(mut self, option_for_message: bool) -> Self {
+        self.option_for_message = Some(option_for_message);
+        self
+    }
+
     /// Generate code for "lite runtime". Generated code contains no code for reflection.
     /// So the generated code (and more importantly, generated binary size) is smaller,
     /// but reflection, text format, JSON serialization won't work.
@@ -188,6 +195,9 @@ impl Customize {
         if let Some(v) = that.tokio_bytes_for_string {
             self.tokio_bytes_for_string = Some(v);
         }
+        if let Some(v) = that.option_for_message {
+            self.option_for_message = Some(v)
+        }
         if let Some(v) = that.lite_runtime {
             self.lite_runtime = Some(v);
         }
@@ -232,6 +242,8 @@ impl Customize {
                 r.tokio_bytes = Some(parse_bool(v)?);
             } else if n == "tokio_bytes_for_string" {
                 r.tokio_bytes_for_string = Some(parse_bool(v)?);
+            } else if n == "option_for_message" {
+                r.option_for_message = Some(parse_bool(v)?);
             } else if n == "lite_runtime" {
                 r.lite_runtime = Some(parse_bool(v)?);
             } else if n == "gen_mod_rs" {

protobuf-codegen/src/customize/rustproto_proto.rs

@@ -12,6 +12,7 @@ pub(crate) fn customize_from_rustproto_for_message(source: &MessageOptions) -> C
     let generate_getter = rustproto::exts::generate_getter.get(source);
     let tokio_bytes = rustproto::exts::tokio_bytes.get(source);
     let tokio_bytes_for_string = rustproto::exts::tokio_bytes_for_string.get(source);
+    let option_for_message = rustproto::exts::option_for_message.get(source);
     let lite_runtime = None;
     let gen_mod_rs = None;
     let inside_protobuf = None;
@@ -21,6 +22,7 @@ pub(crate) fn customize_from_rustproto_for_message(source: &MessageOptions) -> C
         generate_getter,
         tokio_bytes,
         tokio_bytes_for_string,
+        option_for_message,
         lite_runtime,
         gen_mod_rs,
         inside_protobuf,
@@ -37,6 +39,7 @@ pub(crate) fn customize_from_rustproto_for_field(source: &FieldOptions) -> Custo
     let generate_getter = rustproto::exts::generate_getter_field.get(source);
     let tokio_bytes = rustproto::exts::tokio_bytes_field.get(source);
     let tokio_bytes_for_string = rustproto::exts::tokio_bytes_for_string_field.get(source);
+    let option_for_message = rustproto::exts::option_for_message_field.get(source);
     let lite_runtime = None;
     let gen_mod_rs = None;
     let inside_protobuf = None;
@@ -46,6 +49,7 @@ pub(crate) fn customize_from_rustproto_for_field(source: &FieldOptions) -> Custo
         generate_getter,
         tokio_bytes,
         tokio_bytes_for_string,
+        option_for_message,
         lite_runtime,
         gen_mod_rs,
         inside_protobuf,
@@ -58,6 +62,7 @@ pub(crate) fn customize_from_rustproto_for_file(source: &FileOptions) -> Customi
     let generate_getter = rustproto::exts::generate_getter_all.get(source);
     let tokio_bytes = rustproto::exts::tokio_bytes_all.get(source);
     let tokio_bytes_for_string = rustproto::exts::tokio_bytes_for_string_all.get(source);
+    let option_for_message = rustproto::exts::option_for_message_all.get(source);
     let lite_runtime = rustproto::exts::lite_runtime_all.get(source);
     let gen_mod_rs = None;
     let inside_protobuf = None;
@@ -67,6 +72,7 @@ pub(crate) fn customize_from_rustproto_for_file(source: &FileOptions) -> Customi
         generate_getter,
         tokio_bytes,
         tokio_bytes_for_string,
+        option_for_message,
         lite_runtime,
         inside_protobuf,
         gen_mod_rs,

protobuf-codegen/src/gen/field/accessor.rs

@@ -142,14 +142,21 @@ impl FieldGen<'_> {
     fn accessor_fn_singular_with_flag(
         &self,
         elem: &FieldElem,
-        _option_kind: OptionKind,
+        option_kind: OptionKind,
     ) -> AccessorFn {
         match elem {
-            FieldElem::Message(m) => AccessorFn {
-                name: "make_message_field_accessor".to_owned(),
-                type_params: vec![format!("{}", m.rust_name_relative(&self.file_and_mod()))],
-                callback_params: self.make_accessor_fns_lambda(),
-            },
+            FieldElem::Message(m) => {
+                let name = if option_kind == OptionKind::MessageField {
+                    "make_message_field_accessor".to_owned()
+                } else {
+                    "make_option_accessor".to_owned()
+                };
+                AccessorFn {
+                    name,
+                    type_params: vec![format!("{}", m.rust_name_relative(&self.file_and_mod()))],
+                    callback_params: self.make_accessor_fns_lambda(),
+                }
+            }
             FieldElem::Primitive(..) | FieldElem::Enum(..) => AccessorFn {
                 name: "make_option_accessor".to_owned(),
                 type_params: vec!["_".to_owned()],

protobuf-codegen/src/gen/field/mod.rs

@@ -206,7 +206,11 @@ impl<'a> FieldGen<'a> {
                         let required = field.field.proto().label()
                             == field_descriptor_proto::Label::LABEL_REQUIRED;
                         let option_kind = match field.field.proto().type_() {
-                            field_descriptor_proto::Type::TYPE_MESSAGE => OptionKind::MessageField,
+                            field_descriptor_proto::Type::TYPE_MESSAGE
+                                if customize.option_for_message != Some(true) =>
+                            {
+                                OptionKind::MessageField
+                            }
                             _ => OptionKind::Option,
                         };
 
@@ -995,11 +999,23 @@ impl<'a> FieldGen<'a> {
     fn write_merge_from_singular_case_block(&self, s: &SingularField, w: &mut CodeWriter) {
         w.case_block(&format!("{}", self.tag()), |w| match s.elem {
             FieldElem::Message(..) => {
-                w.write_line(&format!(
-                    "{}::rt::read_singular_message_into_field(is, &mut self.{})?;",
-                    protobuf_crate_path(&self.customize),
-                    self.rust_name,
-                ));
+                if let SingularFieldFlag::WithFlag {
+                    option_kind: OptionKind::Option { .. },
+                    ..
+                } = &s.flag
+                {
+                    w.write_line(&format!(
+                        "{}::rt::read_option_message_into_field(is, &mut self.{})?;",
+                        protobuf_crate_path(&self.customize),
+                        self.rust_name,
+                    ));
+                } else {
+                    w.write_line(&format!(
+                        "{}::rt::read_singular_message_into_field(is, &mut self.{})?;",
+                        protobuf_crate_path(&self.customize),
+                        self.rust_name,
+                    ));
+                }
             }
             _ => {
                 let read_proc = s.elem.read_one_liner();

protobuf-parse/src/proto/rustproto.proto

@@ -19,6 +19,8 @@ extend google.protobuf.FileOptions {
     optional bool tokio_bytes_all = 17011;
     // Use `bytes::Bytes` for `string` fields
     optional bool tokio_bytes_for_string_all = 17012;
+    // Use `Option` for `message` fields.
+    optional bool option_for_message_all = 17013;
 
     // When true, will only generate codes that works with lite runtime.
     optional bool lite_runtime_all = 17035;
@@ -33,6 +35,8 @@ extend google.protobuf.MessageOptions {
     optional bool tokio_bytes = 17011;
     // Use `bytes::Bytes` for `string` fields
     optional bool tokio_bytes_for_string = 17012;
+    // Use `Option` for `message` fields.
+    optional bool option_for_message = 17013;
 }
 
 extend google.protobuf.FieldOptions {
@@ -44,4 +48,6 @@ extend google.protobuf.FieldOptions {
     optional bool tokio_bytes_field = 17011;
     // Use `bytes::Bytes` for `string` fields
     optional bool tokio_bytes_for_string_field = 17012;
+    // Use `Option` for `message` fields.
+    optional bool option_for_message_field = 17013;
 }

protobuf/src/rt/message.rs

@@ -4,6 +4,20 @@ use crate::CodedOutputStream;
 use crate::Message;
 use crate::MessageField;
 
+/// Read option `message` field.
+pub fn read_option_message_into_field<M>(
+    is: &mut CodedInputStream,
+    target: &mut Option<M>,
+) -> crate::Result<()>
+where
+    M: Message,
+{
+    let mut m = M::new();
+    is.merge_message(&mut m)?;
+    *target = Some(m);
+    Ok(())
+}
+
 /// Read singular `message` field.
 pub fn read_singular_message_into_field<M>(
     is: &mut CodedInputStream,

protobuf/src/rt/mod.rs

@@ -11,6 +11,7 @@ pub(crate) mod repeated;
 pub(crate) mod singular;
 pub(crate) mod unknown_or_group;
 
+pub use message::read_option_message_into_field;
 pub use message::read_singular_message_into_field;
 pub use message::write_message_field_with_cached_size;
 pub use packed::vec_packed_bool_size;