[protoc-gen-tonic] Honor default_package_filename for package-less protos

[fivetran-auslacroix]

Summary

For a proto file with no package, protoc-gen-prost honors default_package_filename, but protoc-gen-tonic still derives its filename from the empty package name. This produces a hidden .tonic.rs file and inserts include!(".tonic.rs"); into the Prost output.

Tested with protoc-gen-prost and protoc-gen-tonic 0.5.0 built from current main at 3e44d8a, using protoc 36.0.

Reproduction

package_less.proto:

syntax = "proto3";

message PingRequest {}
message PingResponse {}

service PingService {
  rpc Ping(PingRequest) returns (PingResponse);
}

With both plugin binaries on PATH:

mkdir out
protoc -I . package_less.proto \
  --prost_out=out --prost_opt=default_package_filename=_ \
  --tonic_out=out --tonic_opt=default_package_filename=_
find out -maxdepth 1 -type f -print

Actual behavior

The generated files are out/_ and out/.tonic.rs. The Prost output contains:

include!(".tonic.rs");

Expected behavior

The Tonic output should use the filename already selected by ModuleRequestSet: out/_.tonic.rs, with include!("_.tonic.rs"); in out/_.

The current implementation constructs the name from proto_package_name(), even though ModuleRequest already exposes output_filename().

Proposed patch

I compiled this patch and reran the reproduction. It generated out/_ and out/_.tonic.rs, and the include changed to include!("_.tonic.rs");.

Patch against current main

diff --git a/protoc-gen-tonic/src/generator.rs b/protoc-gen-tonic/src/generator.rs
index 6eefc8b..8f55150 100644
--- a/protoc-gen-tonic/src/generator.rs
+++ b/protoc-gen-tonic/src/generator.rs
@@ -130,7 +130,11 @@ impl TonicGenerator {
     fn handle_module_request(&self, module: &Module, request: &ModuleRequest) -> Option<Vec<File>> {
         const PROTO_PATH: &str = "super";
 
-        let output_filename = format!("{}.tonic.rs", request.proto_package_name());
+        let output_stem = request
+            .output_filename()
+            .unwrap_or_else(|| request.proto_package_name());
+        let output_stem = output_stem.strip_suffix(".rs").unwrap_or(output_stem);
+        let output_filename = format!("{output_stem}.tonic.rs");
 
         let services = request
             .files()