fix(interface): harden generated public API

crates/wip-interface/src/lib.rs

@@ -48,6 +48,21 @@
 //! an application return enum/union and is returned as `Ok(value)`.
 //! [`HostError`] is reserved for host/runtime failure, so the required
 //! [`OperationResult`] convention keeps those two failure classes distinct.
+//!
+//! # Supported interface syntax
+//!
+//! An interface is a public, non-generic trait whose operations use exactly
+//! `&self`, simple named owned parameters, and an explicit
+//! `OperationResult<T>`. `WipType` derives support named-field structs,
+//! all-unit enums, and all-single-payload enums.
+//!
+//! The macros reject trait inheritance and associated items; const, async,
+//! unsafe, extern, variadic, generic, default-bodied, or non-`&self` methods;
+//! borrowed values and custom lifetimes; tuple, unit, or generic structs;
+//! mixed or named-field enum variants; explicit discriminants; Rust unions;
+//! and `Option` anywhere except a direct DTO field or operation parameter.
+//! Unsupported inputs produce source-located compile errors rather than
+//! generating a partial interface.
 
 #![deny(missing_docs)]
 
@@ -619,7 +634,6 @@ pub mod __private {
     /// Decoder for a protocol record or operation's named argument collection.
     pub struct RecordDecoder {
         fields: Vec<NamedValue>,
-        seen: HashSet<String>,
     }
 
     impl RecordDecoder {
@@ -633,7 +647,7 @@ pub mod __private {
                         .at(field.name.clone()));
                 }
             }
-            Ok(Self { fields, seen })
+            Ok(Self { fields })
         }
 
         /// Decodes a required field.
@@ -666,11 +680,5 @@ pub mod __private {
             let index = self.fields.iter().position(|field| field.name == name)?;
             Some(self.fields.remove(index).value)
         }
-
-        /// Returns the set of names supplied to this decoder.
-        #[allow(dead_code)]
-        pub fn supplied_names(&self) -> &HashSet<String> {
-            &self.seen
-        }
     }
 }

crates/wip-interface/tests/ui/async_operation.rs

@@ -0,0 +1,8 @@
+use wip_interface::interface;
+
+#[interface]
+pub trait AsyncOperation {
+    async fn status(&self) -> wip_interface::OperationResult<String>;
+}
+
+fn main() {}

crates/wip-interface/tests/ui/async_operation.stderr

@@ -0,0 +1,5 @@
+error: async operations are not supported
+ --> tests/ui/async_operation.rs:5:5
+  |
+5 |     async fn status(&self) -> wip_interface::OperationResult<String>;
+  |     ^^^^^

crates/wip-interface/tests/ui/default_method.rs

@@ -0,0 +1,10 @@
+use wip_interface::interface;
+
+#[interface]
+pub trait DefaultMethod {
+    fn status(&self) -> wip_interface::OperationResult<String> {
+        Ok(String::new())
+    }
+}
+
+fn main() {}

crates/wip-interface/tests/ui/default_method.stderr

@@ -0,0 +1,8 @@
+error: WIP operation methods must not have a body
+ --> tests/ui/default_method.rs:5:64
+  |
+5 |       fn status(&self) -> wip_interface::OperationResult<String> {
+  |  ________________________________________________________________^
+6 | |         Ok(String::new())
+7 | |     }
+  | |_____^

crates/wip-interface/tests/ui/generic_dto.rs

@@ -0,0 +1,8 @@
+use wip_interface::WipType;
+
+#[derive(WipType)]
+struct GenericDto<T> {
+    value: T,
+}
+
+fn main() {}

crates/wip-interface/tests/ui/generic_dto.stderr

@@ -0,0 +1,5 @@
+error: generic DTOs are not supported by `WipType`
+ --> tests/ui/generic_dto.rs:4:18
+  |
+4 | struct GenericDto<T> {
+  |                  ^^^

crates/wip-interface/tests/ui/nested_option.rs

@@ -0,0 +1,8 @@
+use wip_interface::WipType;
+
+#[derive(WipType)]
+struct NestedOption {
+    values: Vec<Option<String>>,
+}
+
+fn main() {}

crates/wip-interface/tests/ui/nested_option.stderr

@@ -0,0 +1,5 @@
+error: `Option<T>` must appear directly as the DTO field type
+ --> tests/ui/nested_option.rs:5:13
+  |
+5 |     values: Vec<Option<String>>,
+  |             ^^^^^^^^^^^^^^^^^^^