Add root_module and wrap_in_module options

* When root_module=true do not emit code that fails to compile
  as a root module.
* When wrap_in_module=name is given, add a wrapper around output:
        pub mod name { ... }
  This allows the output file to be "included" and compiled.

Author: chih-hung

protobuf-codegen/src/code_writer.rs

@@ -1,6 +1,7 @@
 // TODO: used by grpc-rust, should move it into separate crate.
 #![doc(hidden)]
 
+use crate::customize::Customize;
 use crate::rust_name::RustRelativePath;
 use std::io::Write;
 
@@ -34,12 +35,18 @@ impl<'a> CodeWriter<'a> {
         .unwrap();
     }
 
-    pub fn write_generated(&mut self) {
+    pub fn write_generated(&mut self, customize: &Customize) {
         self.write_line("// This file is generated. Do not edit");
-        self.write_generated_common();
+        self.write_generated_common(customize);
     }
 
-    pub fn write_generated_by(&mut self, pkg: &str, version: &str, parser: &str) {
+    pub fn write_generated_by(
+        &mut self,
+        pkg: &str,
+        version: &str,
+        parser: &str,
+        customize: &Customize,
+    ) {
         self.write_line(format!(
             "// This file is generated by {pkg} {version}. Do not edit",
             pkg = pkg,
@@ -49,10 +56,10 @@ impl<'a> CodeWriter<'a> {
             "// .proto file is parsed by {parser}",
             parser = parser
         ));
-        self.write_generated_common();
+        self.write_generated_common(customize);
     }
 
-    fn write_generated_common(&mut self) {
+    fn write_generated_common(&mut self, customize: &Customize) {
         // https://secure.phabricator.com/T784
         self.write_line("// @generated");
 
@@ -62,7 +69,10 @@ impl<'a> CodeWriter<'a> {
         self.write_line("#![allow(clippy::all)]");
         self.write_line("");
         self.write_line("#![allow(unused_attributes)]");
-        self.write_line("#![rustfmt::skip]");
+        if customize.root_module != Some(true) {
+            // does not compile as a root module
+            self.write_line("#![rustfmt::skip]");
+        }
         self.write_line("");
         self.write_line("#![allow(box_pointers)]");
         self.write_line("#![allow(dead_code)]");

protobuf-codegen/src/customize.rs

@@ -29,6 +29,10 @@ pub struct Customize {
     /// Used internally to generate protos bundled in protobuf crate
     /// like `descriptor.proto`
     pub inside_protobuf: Option<bool>,
+    /// Generate code suitable for compiling as a root module
+    pub root_module: Option<bool>,
+    /// Wrap output file in the named module
+    pub wrap_in_module: Option<String>,
 
     // When adding more options please keep in sync with `parse_from_parameter` below.
     /// Make sure `Customize` is always used with `..Default::default()`
@@ -78,6 +82,12 @@ impl Customize {
         if let Some(v) = that.inside_protobuf {
             self.inside_protobuf = Some(v);
         }
+        if let Some(v) = that.root_module {
+            self.root_module = Some(v);
+        }
+        if let Some(ref v) = that.wrap_in_module {
+            self.wrap_in_module = Some(v.clone());
+        }
     }
 
     /// Update unset fields of self with fields from other customize
@@ -124,6 +134,10 @@ impl Customize {
                 r.lite_runtime = Some(parse_bool(v)?);
             } else if n == "inside_protobuf" {
                 r.inside_protobuf = Some(parse_bool(v)?);
+            } else if n == "root_module" {
+                r.root_module = Some(parse_bool(v)?);
+            } else if n == "wrap_in_module" {
+                r.wrap_in_module = Some(v.to_owned());
             } else {
                 return Err(CustomizeParseParameterError::UnknownOptionName(
                     n.to_owned(),
@@ -145,6 +159,8 @@ pub fn customize_from_rustproto_for_message(source: &MessageOptions) -> Customiz
     let serde_derive_cfg = rustproto::exts::serde_derive_cfg.get(source);
     let lite_runtime = None;
     let inside_protobuf = None;
+    let root_module = None;
+    let wrap_in_module = None;
     Customize {
         expose_oneof,
         expose_fields,
@@ -156,6 +172,8 @@ pub fn customize_from_rustproto_for_message(source: &MessageOptions) -> Customiz
         serde_derive_cfg,
         lite_runtime,
         inside_protobuf,
+        root_module,
+        wrap_in_module,
         _future_options: (),
     }
 }
@@ -172,6 +190,8 @@ pub fn customize_from_rustproto_for_field(source: &FieldOptions) -> Customize {
     let serde_derive_cfg = None;
     let lite_runtime = None;
     let inside_protobuf = None;
+    let root_module = None;
+    let wrap_in_module = None;
     Customize {
         expose_oneof,
         expose_fields,
@@ -183,6 +203,8 @@ pub fn customize_from_rustproto_for_field(source: &FieldOptions) -> Customize {
         serde_derive_cfg,
         lite_runtime,
         inside_protobuf,
+        root_module,
+        wrap_in_module,
         _future_options: (),
     }
 }
@@ -198,6 +220,8 @@ pub fn customize_from_rustproto_for_file(source: &FileOptions) -> Customize {
     let serde_derive_cfg = rustproto::exts::serde_derive_cfg_all.get(source);
     let lite_runtime = rustproto::exts::lite_runtime_all.get(source);
     let inside_protobuf = None;
+    let root_module = None;
+    let wrap_in_module = None;
     Customize {
         expose_oneof,
         expose_fields,
@@ -209,6 +233,8 @@ pub fn customize_from_rustproto_for_file(source: &FileOptions) -> Customize {
         serde_derive_cfg,
         lite_runtime,
         inside_protobuf,
+        root_module,
+        wrap_in_module,
         _future_options: (),
     }
 }

protobuf-codegen/src/lib.rs

@@ -274,8 +274,16 @@ fn gen_file(
 
     {
         let mut w = CodeWriter::new(&mut v);
+        if let Some(ref m) = customize.wrap_in_module {
+            w.write_line(&format!("pub mod {} {{", m));
+        }
 
-        w.write_generated_by("rust-protobuf", env!("CARGO_PKG_VERSION"), parser);
+        w.write_generated_by(
+            "rust-protobuf",
+            env!("CARGO_PKG_VERSION"),
+            parser,
+            &customize,
+        );
 
         w.write_line("");
         w.write_line(&format!(
@@ -353,6 +361,10 @@ fn gen_file(
             w.write_line("");
             write_file_descriptor_data(file_descriptor, &customize, &mut w);
         }
+
+        if let Some(ref m) = customize.wrap_in_module {
+            w.write_line(format!("}} // {}", m));
+        }
     }
 
     Some(compiler_plugin::GenResult {