Support custom derives on Request and Response (#438)

Replace the bespoke "derive_serde" with a more flexible
"derive = [<path>, <path>, ...]" form.

Deprecate the old "derive_serde" form, and emit deprecation warnings.

plugins/tests/service.rs

@@ -1,3 +1,5 @@
+use serde::{Deserialize, Serialize};
+use std::hash::Hash;
 use tarpc::context;
 
 #[test]
@@ -72,7 +74,6 @@ fn service_with_cfg_rpc() {
 
 #[test]
 fn syntax() {
-    #[tarpc::service]
     trait Syntax {
         #[deny(warnings)]
         #[allow(non_snake_case)]
@@ -92,3 +93,53 @@ fn syntax() {
         async fn one_arg_implicit_return_error(one: String);
     }
 }
+
+#[test]
+fn custom_derives() {
+    #[tarpc::service(derive = [Clone, Hash])]
+    trait Foo {
+        async fn foo();
+    }
+
+    fn requires_clone(_: impl Clone) {}
+    fn requires_hash(_: impl Hash) {}
+
+    let x = FooRequest::Foo {};
+    requires_clone(x.clone());
+    requires_hash(x);
+}
+
+#[test]
+fn implicit_serde() {
+    #[tarpc::service]
+    trait Foo {
+        async fn foo();
+    }
+
+    fn requires_serde<T>(_: T)
+    where
+        for<'de> T: Serialize + Deserialize<'de>,
+    {
+    }
+
+    let x = FooRequest::Foo {};
+    requires_serde(x);
+}
+
+#[allow(deprecated)]
+#[test]
+fn explicit_serde() {
+    #[tarpc::service(derive_serde = true)]
+    trait Foo {
+        async fn foo();
+    }
+
+    fn requires_serde<T>(_: T)
+    where
+        for<'de> T: Serialize + Deserialize<'de>,
+    {
+    }
+
+    let x = FooRequest::Foo {};
+    requires_serde(x);
+}

tarpc/tests/compile_fail.rs

@@ -4,4 +4,8 @@ fn ui() {
     t.compile_fail("tests/compile_fail/*.rs");
     #[cfg(all(feature = "serde-transport", feature = "tcp"))]
     t.compile_fail("tests/compile_fail/serde_transport/*.rs");
+    #[cfg(not(feature = "serde1"))]
+    t.compile_fail("tests/compile_fail/no_serde1/*.rs");
+    #[cfg(feature = "serde1")]
+    t.compile_fail("tests/compile_fail/serde1/*.rs");
 }

tarpc/tests/compile_fail/no_serde1/no_explicit_serde_without_feature.rs

@@ -0,0 +1,9 @@
+#[tarpc::service(derive_serde = true)]
+trait Foo {
+    async fn foo();
+}
+
+fn main() {
+    let x = FooRequest::Foo {};
+    x.serialize();
+}

tarpc/tests/compile_fail/no_serde1/no_explicit_serde_without_feature.stderr

@@ -0,0 +1,11 @@
+error: To enable serde, first enable the `serde1` feature of tarpc
+ --> tests/compile_fail/no_serde1/no_explicit_serde_without_feature.rs:1:18
+  |
+1 | #[tarpc::service(derive_serde = true)]
+  |                  ^^^^^^^^^^^^
+
+error[E0433]: failed to resolve: use of undeclared type `FooRequest`
+ --> tests/compile_fail/no_serde1/no_explicit_serde_without_feature.rs:7:13
+  |
+7 |     let x = FooRequest::Foo {};
+  |             ^^^^^^^^^^ use of undeclared type `FooRequest`

tarpc/tests/compile_fail/no_serde1/no_implicit_serde_without_feature.rs

@@ -0,0 +1,9 @@
+#[tarpc::service]
+trait Foo {
+    async fn foo();
+}
+
+fn main() {
+    let x = FooRequest::Foo {};
+    x.serialize();
+}

tarpc/tests/compile_fail/no_serde1/no_implicit_serde_without_feature.stderr

@@ -0,0 +1,12 @@
+error[E0599]: no method named `serialize` found for enum `FooRequest` in the current scope
+ --> tests/compile_fail/no_serde1/no_implicit_serde_without_feature.rs:8:7
+  |
+1 | #[tarpc::service]
+  | ----------------- method `serialize` not found for this enum
+...
+8 |     x.serialize();
+  |       ^^^^^^^^^ method not found in `FooRequest`
+  |
+  = help: items from traits can only be used if the trait is implemented and in scope
+  = note: the following trait defines an item `serialize`, perhaps you need to implement it:
+          candidate #1: `serde::ser::Serialize`

tarpc/tests/compile_fail/serde1/deprecated.rs

@@ -0,0 +1,8 @@
+#![deny(warnings)]
+
+#[tarpc::service(derive_serde = true)]
+trait Foo {
+    async fn foo();
+}
+
+fn main() {}

tarpc/tests/compile_fail/serde1/deprecated.stderr

@@ -0,0 +1,15 @@
+error: use of deprecated constant `_::DEPRECATED_SYNTAX`:
+       The form `tarpc::service(derive_serde = true)` is deprecated.
+       Use `tarpc::service(derive = [Serialize, Deserialize])`.
+ --> tests/compile_fail/serde1/deprecated.rs:3:1
+  |
+3 | #[tarpc::service(derive_serde = true)]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+note: the lint level is defined here
+ --> tests/compile_fail/serde1/deprecated.rs:1:9
+  |
+1 | #![deny(warnings)]
+  |         ^^^^^^^^
+  = note: `#[deny(deprecated)]` implied by `#[deny(warnings)]`
+  = note: this error originates in the attribute macro `tarpc::service` (in Nightly builds, run with -Z macro-backtrace for more info)

tarpc/tests/compile_fail/serde1/incompatible.rs

@@ -0,0 +1,7 @@
+#![allow(deprecated)]
+#[tarpc::service(derive = [Clone], derive_serde = true)]
+trait Foo {
+    async fn foo();
+}
+
+fn main() {}

tarpc/tests/compile_fail/serde1/incompatible.stderr

@@ -0,0 +1,7 @@
+error: tarpc does not support `derive_serde` and `derive` at the same time
+ --> tests/compile_fail/serde1/incompatible.rs:2:1
+  |
+2 | #[tarpc::service(derive = [Clone], derive_serde = true)]
+  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+  |
+  = note: this error originates in the attribute macro `tarpc::service` (in Nightly builds, run with -Z macro-backtrace for more info)

tarpc/tests/compile_fail/serde1/opt_out_serde.rs

@@ -0,0 +1,15 @@
+#![allow(deprecated)]
+
+use std::fmt::Formatter;
+
+#[tarpc::service(derive_serde = false)]
+trait Foo {
+    async fn foo();
+}
+
+fn foo(f: &mut Formatter) {
+    let x = FooRequest::Foo {};
+    tarpc::serde::Serialize::serialize(&x, f);
+}
+
+fn main() {}

tarpc/tests/compile_fail/serde1/opt_out_serde.stderr

@@ -0,0 +1,18 @@
+error[E0277]: the trait bound `FooRequest: Serialize` is not satisfied
+  --> tests/compile_fail/serde1/opt_out_serde.rs:12:40
+   |
+12 |     tarpc::serde::Serialize::serialize(&x, f);
+   |     ---------------------------------- ^^ the trait `Serialize` is not implemented for `FooRequest`
+   |     |
+   |     required by a bound introduced by this call
+   |
+   = help: the following other types implement trait `Serialize`:
+             bool
+             char
+             isize
+             i8
+             i16
+             i32
+             i64
+             i128
+           and $N others