feat(rust): qualify named types in future/stream payload vtables

crates/rust/src/interface.rs

@@ -655,12 +655,46 @@ macro_rules! {macro_name} {{
             }
         }
 
+        // `use` statements to bring every named type reachable from the
+        // payload into scope of the generated `vtable{ordinal}` module.
+        //
+        // Without these, a type like `future<result<R, string>>` where
+        // `R` is brought in via `use t.{r}` at world level emits
+        // `-> Result<R, super::super::_rt::String>` inside `vtable1`,
+        // with `R` unresolved: the composite type is anonymous so no
+        // owner-qualified path is inserted, and the world-level alias
+        // `pub type R = ...;` lives two modules up. Importing it here
+        // makes the bare identifier resolve regardless of how deeply
+        // nested the payload type is.
+        let mut type_imports = BTreeSet::new();
+        if let Some(ty) = payload_type {
+            collect_named_type_ids(self.resolve, ty, &mut type_imports);
+        }
+        let type_imports: String = type_imports
+            .into_iter()
+            .map(|id| {
+                let path = self.type_path(id, /*owned=*/ true);
+                // `type_path` emits the full `super::super::...::Name`
+                // when the type is owned by an interface, but falls
+                // back to a bare name when the owner is a world (the
+                // `use interface.{T}` alias case). Bare names need the
+                // `super::super::` prefix to reach the world-level
+                // `pub type T = ...;` alias at macro root.
+                let path = if path.starts_with("super::") {
+                    path
+                } else {
+                    format!("super::super::{path}")
+                };
+                format!("    use {path};\n")
+            })
+            .collect();
+
         let code = format!(
             r#"
 #[doc(hidden)]
-#[allow(unused_unsafe)]
+#[allow(unused_unsafe, unused_imports)]
 pub mod vtable{ordinal} {{
-
+{type_imports}
     #[cfg(not(target_arch = "wasm32"))]
     unsafe extern "C" fn cancel_write(_: u32) -> u32 {{ unreachable!() }}
     #[cfg(not(target_arch = "wasm32"))]
@@ -3157,3 +3191,96 @@ impl<'a, 'b> wit_bindgen_core::AnonymousTypeGenerator<'a> for AnonTypeGenerator<
         self.interface.push_str(&format!("; {size}]"));
     }
 }
+
+/// Walk `ty`'s type tree and insert every named type id into `out`.
+///
+/// A type id is "named" if `resolve.types[id].name` is set, i.e. it is
+/// a user-defined type (record, variant, enum, flags, resource, type
+/// alias) as opposed to an anonymous structural one (`result<_, _>`,
+/// `tuple<_, _>`, `list<_>`, etc.). We still recurse through the
+/// anonymous composites to collect their inner named types — that's
+/// the whole reason this exists: `future<result<R, _>>` hides `R` one
+/// level below an anonymous `result` that the emitter never flags.
+///
+/// Used by stream/future payload emission to pre-compute `use`
+/// statements for every named type the emitted `vtable{ordinal}`
+/// module will reference, so bare identifiers inside the `fn lift` /
+/// `fn lower` / `impl StreamPayload` bodies resolve even when the
+/// type lives at macro-root via a world-level `use` alias.
+fn collect_named_type_ids(resolve: &Resolve, ty: &Type, out: &mut BTreeSet<TypeId>) {
+    let Type::Id(id) = ty else { return };
+    collect_named_type_ids_from_id(resolve, *id, out);
+}
+
+fn collect_named_type_ids_from_id(resolve: &Resolve, id: TypeId, out: &mut BTreeSet<TypeId>) {
+    // Avoid cycles: a named type we've already queued doesn't need a
+    // second walk through its structure.
+    if out.contains(&id) {
+        return;
+    }
+    let ty = &resolve.types[id];
+    let named = ty.name.is_some();
+    if named {
+        out.insert(id);
+        // A named alias (e.g. `use t.{r};` or `type x = r;`) is what
+        // the emitter references verbatim — its target is a separate
+        // type def reachable by its own name. Walking through the
+        // alias would import both the alias and its target under the
+        // same Rust identifier and trip E0252. Stop at the alias.
+        if matches!(ty.kind, TypeDefKind::Type(_)) {
+            return;
+        }
+    }
+    match &ty.kind {
+        TypeDefKind::Record(r) => {
+            for field in &r.fields {
+                collect_named_type_ids(resolve, &field.ty, out);
+            }
+        }
+        TypeDefKind::Variant(v) => {
+            for case in &v.cases {
+                if let Some(ty) = &case.ty {
+                    collect_named_type_ids(resolve, ty, out);
+                }
+            }
+        }
+        TypeDefKind::Tuple(t) => {
+            for ty in &t.types {
+                collect_named_type_ids(resolve, ty, out);
+            }
+        }
+        TypeDefKind::Option(t)
+        | TypeDefKind::List(t)
+        | TypeDefKind::FixedLengthList(t, _)
+        | TypeDefKind::Type(t) => {
+            collect_named_type_ids(resolve, t, out);
+        }
+        TypeDefKind::Result(r) => {
+            if let Some(ty) = &r.ok {
+                collect_named_type_ids(resolve, ty, out);
+            }
+            if let Some(ty) = &r.err {
+                collect_named_type_ids(resolve, ty, out);
+            }
+        }
+        TypeDefKind::Map(k, v) => {
+            collect_named_type_ids(resolve, k, out);
+            collect_named_type_ids(resolve, v, out);
+        }
+        TypeDefKind::Future(inner) | TypeDefKind::Stream(inner) => {
+            if let Some(ty) = inner {
+                collect_named_type_ids(resolve, ty, out);
+            }
+        }
+        TypeDefKind::Handle(h) => {
+            let resource_id = match h {
+                Handle::Own(id) | Handle::Borrow(id) => *id,
+            };
+            collect_named_type_ids_from_id(resolve, resource_id, out);
+        }
+        TypeDefKind::Enum(_)
+        | TypeDefKind::Flags(_)
+        | TypeDefKind::Resource
+        | TypeDefKind::Unknown => {}
+    }
+}

crates/rust/tests/codegen.rs

@@ -235,3 +235,29 @@ mod method_chaining {
         enable_method_chaining: true
     });
 }
+
+// Regression: a named type brought in via `use interface.{T}` at world
+// level, embedded inside `future<result<T, _>>` on an exported function,
+// used to emit unresolved bare `T` references in the generated
+// `wit_future::vtable{N}` module. See issue #1598. The fix walks the
+// payload type tree and emits a `use super::super::...;` per named type
+// at the top of each vtable module.
+#[allow(unused, reason = "testing codegen, not functionality")]
+mod issue_1598_future_result_use {
+    wit_bindgen::generate!({
+        inline: r#"
+        package a:b;
+
+        world w {
+            use t.{r};
+            export f: func() -> future<result<r, string>>;
+        }
+
+        interface t {
+            record r {
+                x: u32,
+            }
+        }
+        "#,
+    });
+}