From 3fddc86890026ff0b81b91a03b9a099481a18029 Mon Sep 17 00:00:00 2001
From: Ben Linsay <blinsay@gmail.com>
Date: Mon, 14 Apr 2025 22:35:10 -0400
Subject: [PATCH 1/3] convert string templates to syn/quote

---
 Cargo.lock                    |   6 +-
 crates/twirp-build/Cargo.toml |   4 +
 crates/twirp-build/src/lib.rs | 215 ++++++++++++++++++----------------
 3 files changed, 122 insertions(+), 103 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 2d52e3d..b7589f0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1256,9 +1256,13 @@ dependencies = [
 
 [[package]]
 name = "twirp-build"
-version = "0.8.0"
+version = "0.7.0"
 dependencies = [
+ "prettyplease",
+ "proc-macro2",
  "prost-build",
+ "quote",
+ "syn",
 ]
 
 [[package]]
diff --git a/crates/twirp-build/Cargo.toml b/crates/twirp-build/Cargo.toml
index 9a84091..941d535 100644
--- a/crates/twirp-build/Cargo.toml
+++ b/crates/twirp-build/Cargo.toml
@@ -16,3 +16,7 @@ license-file = "./LICENSE"
 
 [dependencies]
 prost-build = "0.13"
+prettyplease = { version = "0.2" }
+quote = "1.0"
+syn = "2.0"
+proc-macro2 = "1.0"
diff --git a/crates/twirp-build/src/lib.rs b/crates/twirp-build/src/lib.rs
index 62dd6a9..4d366fa 100644
--- a/crates/twirp-build/src/lib.rs
+++ b/crates/twirp-build/src/lib.rs
@@ -1,4 +1,5 @@
-use std::fmt::Write;
+use proc_macro2::TokenStream;
+use quote::{format_ident, quote, ToTokens};
 
 /// Generates twirp services for protobuf rpc service definitions.
 ///
@@ -13,121 +14,131 @@ pub fn service_generator() -> Box<ServiceGenerator> {
 
 pub struct ServiceGenerator;
 
+fn as_path(s: &str) -> TokenStream {
+    syn::parse_str::<syn::Path>(s)
+        .expect("twirp-build generated invalid Rust. this is a bug in twirp-build, please file an issue")
+        .to_token_stream()
+}
+
 impl prost_build::ServiceGenerator for ServiceGenerator {
     fn generate(&mut self, service: prost_build::Service, buf: &mut String) {
-        let service_name = service.name;
+        let service_name = format_ident!("{}", &service.name);
         let service_fqn = format!("{}.{}", service.package, service.proto_name);
-        writeln!(buf).unwrap();
 
-        writeln!(buf, "pub use twirp;").unwrap();
-        writeln!(buf).unwrap();
-        writeln!(buf, "pub const SERVICE_FQN: &str = \"/{service_fqn}\";").unwrap();
-
-        //
         // generate the twirp server
-        //
-        writeln!(buf, "#[twirp::async_trait::async_trait]").unwrap();
-        writeln!(buf, "pub trait {} {{", service_name).unwrap();
-        writeln!(buf, "    type Error;").unwrap();
-        for m in &service.methods {
-            writeln!(
-                buf,
-                "    async fn {}(&self, ctx: twirp::Context, req: {}) -> Result<{}, Self::Error>;",
-                m.name, m.input_type, m.output_type,
-            )
-            .unwrap();
-        }
-        writeln!(buf, "}}").unwrap();
-
-        writeln!(buf, "#[twirp::async_trait::async_trait]").unwrap();
-        writeln!(buf, "impl<T> {service_name} for std::sync::Arc<T>").unwrap();
-        writeln!(buf, "where").unwrap();
-        writeln!(buf, "    T: {service_name} + Sync + Send").unwrap();
-        writeln!(buf, "{{").unwrap();
-        writeln!(buf, "    type Error = T::Error;\n").unwrap();
+        let mut trait_methods = Vec::with_capacity(service.methods.len());
+        let mut proxy_methods = Vec::with_capacity(service.methods.len());
         for m in &service.methods {
-            writeln!(
-                buf,
-                "    async fn {}(&self, ctx: twirp::Context, req: {}) -> Result<{}, Self::Error> {{",
-                m.name, m.input_type, m.output_type,
-            )
-                .unwrap();
-            writeln!(buf, "        T::{}(&*self, ctx, req).await", m.name).unwrap();
-            writeln!(buf, "    }}").unwrap();
+            let name = format_ident!("{}", &m.name);
+            let input_type = as_path(&m.input_type);
+            let output_type = as_path(&m.output_type);
+
+            trait_methods.push(quote! {
+                async fn #name(&self, ctx: twirp::Context, req: #input_type) -> Result<#output_type, Self::Error>;
+            });
+
+            proxy_methods.push(quote! {
+                async fn #name(&self, ctx: twirp::Context, req: #input_type) -> Result<#output_type, Self::Error> {
+                    T::#name(&*self, ctx, req).await
+                }
+            });
         }
-        writeln!(buf, "}}").unwrap();
-
-        // add_service
-        writeln!(
-            buf,
-            r#"pub fn router<T>(api: T) -> twirp::Router
-where
-    T: {service_name} + Clone + Send + Sync + 'static,
-    <T as {service_name}>::Error: twirp::IntoTwirpResponse,
-{{
-    twirp::details::TwirpRouterBuilder::new(api)"#,
-        )
-        .unwrap();
+
+        let server_trait = quote! {
+            #[twirp::async_trait::async_trait]
+            pub trait #service_name {
+                type Error;
+
+                #(#trait_methods)*
+            }
+
+            #[twirp::async_trait::async_trait]
+            impl<T> #service_name for std::sync::Arc<T>
+            where
+                T: #service_name + Sync + Send
+            {
+                type Error = T::Error;
+
+                #(#proxy_methods)*
+            }
+        };
+
+        // generate the router
+        let mut route_calls = Vec::with_capacity(service.methods.len());
         for m in &service.methods {
-            let uri = &m.proto_name;
-            let req_type = &m.input_type;
-            let rust_method_name = &m.name;
-            writeln!(
-                buf,
-                r#"        .route("/{uri}", |api: T, ctx: twirp::Context, req: {req_type}| async move {{
-            api.{rust_method_name}(ctx, req).await
-        }})"#,
-            )
-            .unwrap();
+            let name = format_ident!("{}", &m.name);
+            let uri = format!("/{}", &m.proto_name);
+            let req_type = as_path(&m.input_type);
+            route_calls.push(quote! {
+                .route(#uri, |api: T, ctx: twirp::Context, req: #req_type| async move {
+                    api.#name(ctx, req).await
+                })
+            });
         }
-        writeln!(
-            buf,
-            r#"
-        .build()
-}}"#
-        )
-        .unwrap();
+        let router = quote! {
+            pub fn router<T>(api: T) -> twirp::Router
+                where
+                    T: #service_name + Clone + Send + Sync + 'static,
+                    <T as #service_name>::Error: twirp::IntoTwirpResponse
+                {
+                    twirp::details::TwirpRouterBuilder::new(api)
+                        #(#route_calls)*
+                        .build()
+                }
+        };
 
         //
         // generate the twirp client
         //
-        writeln!(buf).unwrap();
-        writeln!(buf, "#[twirp::async_trait::async_trait]").unwrap();
-        writeln!(buf, "pub trait {service_name}Client: Send + Sync {{",).unwrap();
-        for m in &service.methods {
-            // Define: <METHOD>
-            writeln!(
-                buf,
-                "    async fn {}(&self, req: {}) -> Result<{}, twirp::ClientError>;",
-                m.name, m.input_type, m.output_type,
-            )
-            .unwrap();
-        }
-        writeln!(buf, "}}").unwrap();
-
-        // Implement the rpc traits for: `twirp::client::Client`
-        writeln!(buf, "#[twirp::async_trait::async_trait]").unwrap();
-        writeln!(
-            buf,
-            "impl {service_name}Client for twirp::client::Client {{",
-        )
-        .unwrap();
+        let client_name = format_ident!("{}Client", service_name);
+
+        let mut client_trait_methods = Vec::with_capacity(service.methods.len());
+        let mut client_methods = Vec::with_capacity(service.methods.len());
         for m in &service.methods {
-            // Define the rpc `<METHOD>`
-            writeln!(
-                buf,
-                "    async fn {}(&self, req: {}) -> Result<{}, twirp::ClientError> {{",
-                m.name, m.input_type, m.output_type,
-            )
-            .unwrap();
-            writeln!(
-                buf,
-                r#"    self.request("{}/{}", req).await"#,
-                service_fqn, m.proto_name
-            )
-            .unwrap();
-            writeln!(buf, "    }}").unwrap();
+            let name = format_ident!("{}", &m.name);
+            let input_type = as_path(&m.input_type);
+            let output_type = as_path(&m.output_type);
+
+            client_trait_methods.push(quote! {
+                async fn #name(&self, req: #input_type) -> Result<#output_type, twirp::ClientError>;
+            });
+
+            let url = format!("{}/{}", service_fqn, m.proto_name);
+            client_methods.push(quote! {
+                async fn #name(&self, req: #input_type) -> Result<#output_type, twirp::ClientError> {
+                    self.request(#url, req).await
+                }
+            })
         }
-        writeln!(buf, "}}").unwrap();
+        let client_trait = quote! {
+            #[twirp::async_trait::async_trait]
+            pub trait #client_name: Send + Sync {
+                #(#client_trait_methods)*
+            }
+
+            #[twirp::async_trait::async_trait]
+            impl #client_name for twirp::client::Client {
+                #(#client_methods)*
+            }
+        };
+
+        // generate the service and client as a single file. run it through
+        // prettyplease before outputting it.
+        let service_fqn_path = format!("/{}", service_fqn);
+        let generated = quote! {
+            pub use twirp;
+
+            pub const SERVICE_FQN: &str = #service_fqn_path;
+
+            #server_trait
+
+            #router
+
+            #client_trait
+        };
+
+        let ast: syn::File = syn::parse2(generated).expect("generated an invalid token stream");
+        let code = prettyplease::unparse(&ast);
+        buf.push_str(&code);
     }
 }

From 8b3c6e12c4a75e8dd89359abe3092c9cc69fc3bf Mon Sep 17 00:00:00 2001
From: Ben Linsay <blinsay@gmail.com>
Date: Tue, 22 Apr 2025 12:15:25 -0400
Subject: [PATCH 2/3] add a second rpc to Haberdasher for codegen tests

---
 example/proto/haberdash/v1/haberdash_api.proto |  7 +++++++
 example/src/bin/advanced-server.rs             | 14 +++++++++++++-
 example/src/bin/client.rs                      | 11 ++++++++++-
 example/src/bin/simple-server.rs               | 14 +++++++++++++-
 4 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/example/proto/haberdash/v1/haberdash_api.proto b/example/proto/haberdash/v1/haberdash_api.proto
index 6515ba9..e385d4a 100644
--- a/example/proto/haberdash/v1/haberdash_api.proto
+++ b/example/proto/haberdash/v1/haberdash_api.proto
@@ -9,6 +9,7 @@ option go_package = "haberdash.v1";
 service HaberdasherAPI {
   // MakeHat produces a hat of mysterious, randomly-selected color!
   rpc MakeHat(MakeHatRequest) returns (MakeHatResponse);
+  rpc GetStatus(GetStatusRequest) returns (GetStatusResponse);
 }
 
 // Size is passed when requesting a new hat to be made. It's always
@@ -32,3 +33,9 @@ message MakeHatResponse {
   // Demonstrate importing an external message.
   google.protobuf.Timestamp timestamp = 4;
 }
+
+message GetStatusRequest {}
+
+message GetStatusResponse {
+    string status = 1;
+}
diff --git a/example/src/bin/advanced-server.rs b/example/src/bin/advanced-server.rs
index 486c22b..cd24fa3 100644
--- a/example/src/bin/advanced-server.rs
+++ b/example/src/bin/advanced-server.rs
@@ -17,7 +17,9 @@ pub mod service {
         }
     }
 }
-use service::haberdash::v1::{self as haberdash, MakeHatRequest, MakeHatResponse};
+use service::haberdash::v1::{
+    self as haberdash, GetStatusRequest, GetStatusResponse, MakeHatRequest, MakeHatResponse,
+};
 
 async fn ping() -> &'static str {
     "Pong\n"
@@ -95,6 +97,16 @@ impl haberdash::HaberdasherApi for HaberdasherApiServer {
             }),
         })
     }
+
+    async fn get_status(
+        &self,
+        _ctx: Context,
+        _req: GetStatusRequest,
+    ) -> Result<GetStatusResponse, HatError> {
+        Ok(GetStatusResponse {
+            status: "making hats".to_string(),
+        })
+    }
 }
 
 // Demonstrate sending back custom extensions from the handlers.
diff --git a/example/src/bin/client.rs b/example/src/bin/client.rs
index 9f388ed..89c6e71 100644
--- a/example/src/bin/client.rs
+++ b/example/src/bin/client.rs
@@ -12,7 +12,9 @@ pub mod service {
     }
 }
 
-use service::haberdash::v1::{HaberdasherApiClient, MakeHatRequest, MakeHatResponse};
+use service::haberdash::v1::{
+    GetStatusRequest, GetStatusResponse, HaberdasherApiClient, MakeHatRequest, MakeHatResponse,
+};
 
 #[tokio::main]
 pub async fn main() -> Result<(), GenericError> {
@@ -79,4 +81,11 @@ impl HaberdasherApiClient for MockHaberdasherApiClient {
     ) -> Result<MakeHatResponse, twirp::client::ClientError> {
         todo!()
     }
+
+    async fn get_status(
+        &self,
+        _req: GetStatusRequest,
+    ) -> Result<GetStatusResponse, twirp::client::ClientError> {
+        todo!()
+    }
 }
diff --git a/example/src/bin/simple-server.rs b/example/src/bin/simple-server.rs
index 852a543..12eb18b 100644
--- a/example/src/bin/simple-server.rs
+++ b/example/src/bin/simple-server.rs
@@ -12,7 +12,9 @@ pub mod service {
         }
     }
 }
-use service::haberdash::v1::{self as haberdash, MakeHatRequest, MakeHatResponse};
+use service::haberdash::v1::{
+    self as haberdash, GetStatusRequest, GetStatusResponse, MakeHatRequest, MakeHatResponse,
+};
 
 async fn ping() -> &'static str {
     "Pong\n"
@@ -69,6 +71,16 @@ impl haberdash::HaberdasherApi for HaberdasherApiServer {
             }),
         })
     }
+
+    async fn get_status(
+        &self,
+        _ctx: Context,
+        _req: GetStatusRequest,
+    ) -> Result<GetStatusResponse, TwirpErrorResponse> {
+        Ok(GetStatusResponse {
+            status: "making hats".to_string(),
+        })
+    }
 }
 
 // Demonstrate sending back custom extensions from the handlers.

From baa5278eb97c5bddc2d0fd5af8f9aabd1dafc25e Mon Sep 17 00:00:00 2001
From: Ben Linsay <blinsay@gmail.com>
Date: Tue, 22 Apr 2025 17:35:11 -0400
Subject: [PATCH 3/3] hacky debug info

---
 crates/twirp-build/src/lib.rs | 56 +++++++++++++++++++++++++++--------
 1 file changed, 44 insertions(+), 12 deletions(-)

diff --git a/crates/twirp-build/src/lib.rs b/crates/twirp-build/src/lib.rs
index 4d366fa..14ea9e4 100644
--- a/crates/twirp-build/src/lib.rs
+++ b/crates/twirp-build/src/lib.rs
@@ -12,14 +12,41 @@ pub fn service_generator() -> Box<ServiceGenerator> {
     Box::new(ServiceGenerator {})
 }
 
-pub struct ServiceGenerator;
+struct MethodTypes {
+    input_type: TokenStream,
+    output_type: TokenStream,
+}
+
+impl MethodTypes {
+    fn from_prost(m: &prost_build::Method) -> Self {
+        let as_type = |s| -> TokenStream {
+            let Ok(typ) = syn::parse_str::<syn::Type>(s) else {
+                panic!(
+                    "twirp-build generated invalid Rust. this is a bug in twirp-build, please file an issue:\n
+                      method={name}
+                      input_type={input_type}
+                      output_type={output_type}
+                    ",
+                    name = m.name,
+                    input_type = m.input_type,
+                    output_type = m.output_type,
+                );
+            };
+            typ.to_token_stream()
+        };
+
+        let input_type = as_type(&m.input_type);
+        let output_type = as_type(&m.output_type);
 
-fn as_path(s: &str) -> TokenStream {
-    syn::parse_str::<syn::Path>(s)
-        .expect("twirp-build generated invalid Rust. this is a bug in twirp-build, please file an issue")
-        .to_token_stream()
+        Self {
+            input_type,
+            output_type,
+        }
+    }
 }
 
+pub struct ServiceGenerator;
+
 impl prost_build::ServiceGenerator for ServiceGenerator {
     fn generate(&mut self, service: prost_build::Service, buf: &mut String) {
         let service_name = format_ident!("{}", &service.name);
@@ -30,8 +57,10 @@ impl prost_build::ServiceGenerator for ServiceGenerator {
         let mut proxy_methods = Vec::with_capacity(service.methods.len());
         for m in &service.methods {
             let name = format_ident!("{}", &m.name);
-            let input_type = as_path(&m.input_type);
-            let output_type = as_path(&m.output_type);
+            let MethodTypes {
+                input_type,
+                output_type,
+            } = MethodTypes::from_prost(m);
 
             trait_methods.push(quote! {
                 async fn #name(&self, ctx: twirp::Context, req: #input_type) -> Result<#output_type, Self::Error>;
@@ -68,9 +97,9 @@ impl prost_build::ServiceGenerator for ServiceGenerator {
         for m in &service.methods {
             let name = format_ident!("{}", &m.name);
             let uri = format!("/{}", &m.proto_name);
-            let req_type = as_path(&m.input_type);
+            let MethodTypes { input_type, .. } = MethodTypes::from_prost(&m);
             route_calls.push(quote! {
-                .route(#uri, |api: T, ctx: twirp::Context, req: #req_type| async move {
+                .route(#uri, |api: T, ctx: twirp::Context, req: #input_type| async move {
                     api.#name(ctx, req).await
                 })
             });
@@ -96,8 +125,10 @@ impl prost_build::ServiceGenerator for ServiceGenerator {
         let mut client_methods = Vec::with_capacity(service.methods.len());
         for m in &service.methods {
             let name = format_ident!("{}", &m.name);
-            let input_type = as_path(&m.input_type);
-            let output_type = as_path(&m.output_type);
+            let MethodTypes {
+                input_type,
+                output_type,
+            } = MethodTypes::from_prost(&m);
 
             client_trait_methods.push(quote! {
                 async fn #name(&self, req: #input_type) -> Result<#output_type, twirp::ClientError>;
@@ -137,7 +168,8 @@ impl prost_build::ServiceGenerator for ServiceGenerator {
             #client_trait
         };
 
-        let ast: syn::File = syn::parse2(generated).expect("generated an invalid token stream");
+        let ast: syn::File = syn::parse2(generated)
+            .expect("twirp-build generated invalid Rust. this is a bug in twirp-build, please file an issue");
         let code = prettyplease::unparse(&ast);
         buf.push_str(&code);
     }

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