Fix code generator and add compilation test

Correct module paths and accessor usage in the generator to ensure
generated code builds. Add a test that verifies this by compiling the
generated code in a temporary project.

codegen/src/generator.rs

@@ -51,7 +51,7 @@ fn map_type_to_rust_accessor(field_type: i32, label: i32, is_map: bool) -> (Stri
     match field_type {
         9 => (
             "&'a str".to_string(),
-            "str::from_utf8(bytes).map_err(|_| roto_runtime::RotoError::WireFormatViolation)".to_string(),
+            "std::str::from_utf8(bytes).map_err(|_| roto_runtime::RotoError::WireFormatViolation)".to_string(),
             "\"\"".to_string(),
         ), // TYPE_STRING
         1 => (
@@ -117,7 +117,7 @@ fn write_enum(enum_proto: &EnumDescriptorProto, output: &mut String) {
         let accessor =
             ProtoAccessor::new(val_data).expect("Failed to parse EnumValueDescriptorProto");
         let (name_bytes, _) = accessor.get_value(1).expect("Enum value name missing");
-        let name = str::from_utf8(name_bytes).expect("Enum value name invalid utf8");
+        let name = std::str::from_utf8(name_bytes).expect("Enum value name invalid utf8");
         let (num_bytes, _) = accessor.get_value(2).expect("Enum value number missing");
         let (num, _) =
             roto_runtime::read_varint(num_bytes).expect("Enum value number invalid varint");
@@ -147,7 +147,7 @@ fn write_enum(enum_proto: &EnumDescriptorProto, output: &mut String) {
         let accessor =
             ProtoAccessor::new(val_data).expect("Failed to parse EnumValueDescriptorProto");
         let (name_bytes, _) = accessor.get_value(1).expect("Enum value name missing");
-        let name = str::from_utf8(name_bytes).expect("Enum value name invalid utf8");
+        let name = std::str::from_utf8(name_bytes).expect("Enum value name invalid utf8");
         let (num_bytes, _) = accessor.get_value(2).expect("Enum value number missing");
         let (num, _) =
             roto_runtime::read_varint(num_bytes).expect("Enum value number invalid varint");
@@ -170,6 +170,7 @@ fn write_enum(enum_proto: &EnumDescriptorProto, output: &mut String) {
 
 fn write_message(msg_proto: &DescriptorProto, output: &mut String) {
     let msg_name = to_pascal_case(msg_proto.name().unwrap());
+    let mod_name = to_snake_case(msg_proto.name().unwrap());
 
     let mut fields_info = Vec::new();
     for field_res in msg_proto.field() {
@@ -332,10 +333,12 @@ fn write_message(msg_proto: &DescriptorProto, output: &mut String) {
         let pascal_oneof_name = to_pascal_case(oneof_name);
         let snake_oneof_name = to_snake_case(oneof_name);
 
-        output.push_str(&format!(
-            "    pub fn which_{}(&self) -> roto_runtime::Result<Option<{}::{}<'a>>> {{\n",
-            snake_oneof_name, msg_name, pascal_oneof_name
-        ));
+        let return_type = format!("{}::{}<'a>", mod_name, pascal_oneof_name);
+        let signature = format!(
+            "    pub fn which_{}(&self) -> roto_runtime::Result<Option<{}> > {{\n",
+            snake_oneof_name, return_type
+        );
+        output.push_str(&signature);
         for (field_name, _tag, _f_type, _f_label, f_oneof_index, _is_map) in &fields_info {
             if *f_oneof_index == Some(oneof_index as i32) {
                 let safe_field_name = if field_name == "type" {
@@ -348,8 +351,8 @@ fn write_message(msg_proto: &DescriptorProto, output: &mut String) {
                     field_name
                 ));
                 output.push_str(&format!(
-                    "            return Ok(Some({}::{} (self.{}()?)));\n",
-                    pascal_oneof_name, safe_field_name, safe_field_name
+                    "            return Ok(Some({}::{}::{} (self.{}()?)));\n",
+                    mod_name, pascal_oneof_name, safe_field_name, safe_field_name
                 ));
                 output.push_str("        }\n");
             }
@@ -414,7 +417,7 @@ fn write_message(msg_proto: &DescriptorProto, output: &mut String) {
         "    pub fn with(mut self, msg: &{}<'_>) -> roto_runtime::Result<Self> {{\n",
         msg_name
     ));
-    output.push_str("        for item in msg.raw_fields() {\n");
+    output.push_str("        for item in msg.accessor.raw_fields() {\n");
     output.push_str("            let (field_number, raw_bytes) = item?;\n");
     output.push_str("            let is_written = match field_number {\n");
     for (field_name, _, tag, _, _) in &builder_fields {
@@ -563,7 +566,7 @@ pub fn generate_rust_code(
 
         for dep_res in file_proto.dependency() {
             let (dep_data, _) = dep_res.expect("Failed to iterate dependency");
-            let dep_name = str::from_utf8(dep_data).expect("Dependency name invalid utf8");
+            let dep_name = std::str::from_utf8(dep_data).expect("Dependency name invalid utf8");
             let dep_mod_path = dep_name.replace(".proto", "").replace('/', "::");
             output.push_str(&format!("use crate::{};\n", dep_mod_path));
         }
@@ -725,9 +728,7 @@ fn write_service(svc_proto: &ServiceDescriptorProto, output: &mut String) {
     output.push_str("            let mut buf = pool.get();\n");
     output.push_str("            let mut stream = body;\n");
     output.push_str("            while let Some(frame_result) = stream.frame().await {\n");
-    output.push_str("                let frame = frame_result.map_err(|e| {\n");
-    output.push_str("                    panic!(\"Body frame error: {}\", e);\n");
-    output.push_str("                })?;\n");
+    output.push_str("                let frame = frame_result.expect(\"Body frame error\");\n");
     output.push_str("                if let Some(data) = frame.data_ref() {\n");
     output.push_str("                    buf.put(data.clone());\n");
     output.push_str("                }\n");

codegen/tests/test_helloworld_build.rs

@@ -0,0 +1,76 @@
+use roto_codegen::google::protobuf::descriptor::FileDescriptorSet;
+use std::fs;
+use std::process::Command;
+
+#[test]
+fn test_helloworld_generated_code_builds() {
+    // 1. Load FileDescriptorSet from helloworld.desc
+    let desc_path = "helloworld.desc";
+    // Note: This assumes helloworld.desc is in the working directory of the test.
+    // We might need to provide the full path or copy it to the test data directory.
+    let data = fs::read(desc_path).expect("Failed to read helloworld.desc");
+    let set = FileDescriptorSet::new(&data)
+        .expect("Failed to create FileDescriptorSet from helloworld.desc");
+
+    let generated_files = roto_codegen::generator::generate_rust_code(&set, None, false);
+    assert!(
+        !generated_files.is_empty(),
+        "Generated code should not be empty"
+    );
+
+    for (path, content) in &generated_files {
+        println!("--- File: {} ---\n{}", path, content);
+    }
+
+    // 2. Setup a temporary Cargo project to verify the code builds
+    let codegen_root = std::path::PathBuf::from(env!("CARGO_MANIFEST_DIR"));
+    let project_root = codegen_root.parent().expect("Failed to get project root");
+    let temp_project_dir = std::path::PathBuf::from("/tmp/roto_helloworld_gen_project");
+
+    // Clean up previous runs
+    if temp_project_dir.exists() {
+        fs::remove_dir_all(&temp_project_dir).expect("Failed to clean up temp project directory");
+    }
+
+    // Create new library project
+    let status = Command::new("cargo")
+        .args(["new", "--lib", temp_project_dir.to_str().expect("Invalid path")])
+        .status()
+        .expect("Failed to run cargo new");
+    assert!(status.success(), "cargo new failed");
+
+    // 3. Configure the project to depend on the current roto crate
+    let cargo_toml_path = temp_project_dir.join("Cargo.toml");
+    let cargo_toml_content =
+        fs::read_to_string(&cargo_toml_path).expect("Failed to read Cargo.toml");
+    let updated_cargo_toml = format!(
+        "{}\n\nroto-codegen = {{ path = \"{}\" }}\nroto-runtime = {{ path = \"{}\" }}\nroto-tonic = {{ path = \"{}\" }}\nbytes = \"1.7\"\ntonic = \"0.12\"\ntokio-stream = \"0.1\"\ntower = \"0.4\"\nfutures-util = \"0.3\"\nhttp-body-util = \"0.1\"\nhttp-body = \"1.0\"\n\n[workspace]\n",
+        cargo_toml_content,
+        codegen_root.to_string_lossy(),
+        project_root.join("runtime").to_string_lossy(),
+        project_root.join("roto-tonic").to_string_lossy()
+    );
+    fs::write(cargo_toml_path, updated_cargo_toml).expect("Failed to write Cargo.toml");
+
+    // 4. Write the generated code to src/lib.rs
+    let mut all_code = String::new();
+    for (_, content) in generated_files {
+        all_code.push_str(&content);
+        all_code.push_str("\n");
+    }
+    let final_code = all_code.replace("use crate::", "use roto::");
+    let lib_path = temp_project_dir.join("src/lib.rs");
+    fs::write(lib_path, final_code).expect("Failed to write generated code to src/lib.rs");
+
+    // 5. Attempt to build the project
+    let build_status = Command::new("cargo")
+        .args(["build"])
+        .current_dir(&temp_project_dir)
+        .status()
+        .expect("Failed to run cargo build");
+
+    assert!(
+        build_status.success(),
+        "The generated Rust code for helloworld.proto failed to build in a standalone project!"
+    );
+}