Nested interfaces in wit

crates/wit-component/src/encoding/wit/v1.rs

@@ -170,6 +170,10 @@ impl InterfaceEncoder<'_> {
         let iface = &self.resolve.interfaces[interface];
         let mut type_order = IndexSet::new();
         for (_, id) in iface.types.iter() {
+            let ty = &self.resolve.types[*id];
+            if let TypeOwner::Interface(iface_id) = ty.owner {
+                self.interface = Some(iface_id);
+            }
             self.encode_valtype(self.resolve, &Type::Id(*id))?;
             type_order.insert(*id);
         }

crates/wit-component/src/encoding/wit/v2.rs

@@ -184,6 +184,10 @@ impl InterfaceEncoder<'_> {
         let iface = &self.resolve.interfaces[interface];
         let mut type_order = IndexSet::new();
         for (_, id) in iface.types.iter() {
+            let ty = &self.resolve.types[*id];
+            if let TypeOwner::Interface(iface_id) = ty.owner {
+                self.interface = Some(iface_id);
+            }
             self.encode_valtype(self.resolve, &Type::Id(*id))?;
             type_order.insert(*id);
         }
@@ -218,14 +222,68 @@ impl InterfaceEncoder<'_> {
                 .unwrap()
                 .export(name, ComponentTypeRef::Func(ty));
         }
-        let instance = self.pop_instance();
+        let mut instance = self.pop_instance();
+        self.encode_nested(iface, &mut instance)?;
+
         let idx = self.outer.type_count();
         self.outer.ty().instance(&instance);
         self.import_map.insert(interface, self.instances);
         self.instances += 1;
         Ok(idx)
     }
 
+    fn encode_nested<'a>(
+        &'a mut self,
+        iface: &Interface,
+        instance: &'a mut InstanceType,
+    ) -> Result<&mut InstanceType> {
+        for (nest_name, nest_item) in &iface.nested {
+            let package_id = self
+                .resolve
+                .package_names
+                .get(&nest_item.package_name)
+                .unwrap();
+            let package = &self.resolve.packages[*package_id];
+            let nested = package.interfaces.get(&nest_item.iface_name).unwrap();
+            let nested_iface = &self.resolve.interfaces[*nested];
+            let mut inst = InterfaceEncoder::new(&self.resolve);
+            inst.push_instance();
+            for (_, id) in &nested_iface.types {
+                let ty = &self.resolve.types[*id];
+                if let TypeOwner::Interface(iface_id) = ty.owner {
+                    inst.interface = Some(iface_id);
+                }
+                inst.encode_valtype(self.resolve, &Type::Id(*id))?;
+            }
+            let ty = instance.ty();
+            let nested_instance = &mut inst.pop_instance();
+            for (nest_name, deep_nest) in &nested_iface.nested {
+                let deep_pkg_id = self
+                    .resolve
+                    .package_names
+                    .get(&deep_nest.package_name)
+                    .unwrap();
+                let deep_package = &self.resolve.packages[*deep_pkg_id];
+                let deep_iface_id = deep_package.interfaces.get(&deep_nest.iface_name).unwrap();
+                let deep_nest = &self.resolve.interfaces[*deep_iface_id];
+                let mut clone = nested_instance.clone();
+                let deep_instance = self.encode_nested(deep_nest, &mut clone)?;
+                let deep_ty = nested_instance.ty();
+                deep_ty.instance(&deep_instance);
+                nested_instance.export(
+                    nest_name,
+                    ComponentTypeRef::Instance(deep_instance.type_count()),
+                );
+            }
+            ty.instance(&nested_instance);
+            instance.export(
+                nest_name,
+                ComponentTypeRef::Instance(instance.type_count() - 1),
+            );
+        }
+        Ok(instance)
+    }
+
     fn push_instance(&mut self) {
         assert!(self.ty.is_none());
         assert!(self.saved_types.is_none());

crates/wit-component/src/printing.rs

@@ -69,7 +69,7 @@ impl WitPrinter {
             }
 
             if has_multiple_packages {
-                self.output.push_str("{");
+                self.output.push_str("{\n");
                 self.output.indent += 1
             } else {
                 self.print_semicolon();
@@ -82,6 +82,14 @@ impl WitPrinter {
                 self.output.push_str("interface ");
                 self.print_name(name);
                 self.output.push_str(" {\n");
+                let nested = &resolve.interfaces[*id].nested;
+                for item in nested {
+                    self.print_stability(&item.1.stability);
+                    self.print_docs(&item.1.docs);
+                    self.output.push_str("nest ");
+                    self.print_name(item.0);
+                    self.output.push_str(";\n")
+                }
                 self.print_interface(resolve, *id)?;
                 writeln!(&mut self.output, "}}\n")?;
             }

crates/wit-component/tests/interfaces/doc-comments.wat

@@ -66,7 +66,7 @@
     )
   )
   (export (;5;) "coverage-world" (type 4))
-  (@custom "package-docs" "\00{\22docs\22:\22package docs;\22,\22worlds\22:{\22coverage-world\22:{\22docs\22:\22world docs\22,\22interfaces\22:{\22i\22:{\22docs\22:\22world inline interface docs\22,\22funcs\22:{\22f\22:\22inline interface func docs\22},\22types\22:{\22t\22:{\22docs\22:\22inline interface typedef docs\22}}}},\22types\22:{\22t\22:{\22docs\22:\22world typedef docs\22}},\22funcs\22:{\22imp\22:\22world func import docs\22,\22exp\22:\22world func export docs\22}}},\22interfaces\22:{\22coverage-iface\22:{\22docs\22:\22interface docs\22,\22funcs\22:{\22[constructor]res\22:\22constructor docs\22,\22[method]res.m\22:\22method docs\22,\22[static]res.s\22:\22static func docs\22,\22f\22:\22interface func docs\22},\22types\22:{\22t\22:{\22docs\22:\22basic typedef docs\22},\22r\22:{\22docs\22:\22record typedef docs\22,\22items\22:{\22f1\22:\22record field docs\22}},\22fl\22:{\22items\22:{\22f1\22:\22flag docs\22}},\22v\22:{\22items\22:{\22c1\22:\22variant case docs\22}},\22e\22:{\22items\22:{\22c1\22:\22enum case docs\22}}}},\22other-comment-forms\22:{\22docs\22:\22other comment forms\5cn    multi-line block\22,\22funcs\22:{\22multiple-lines-split\22:\22one doc line\5cnnon-doc in the middle\5cnanother doc line\22,\22mixed-forms\22:\22mixed forms; line doc\5cnplus block doc\5cn      multi-line\22}}}}")
+  (@custom "package-docs" "\00{\22docs\22:\22package docs;\22,\22worlds\22:{\22coverage-world\22:{\22docs\22:\22world docs\22,\22interfaces\22:{\22i\22:{\22docs\22:\22world inline interface docs\22,\22funcs\22:{\22f\22:\22inline interface func docs\22},\22types\22:{\22t\22:{\22docs\22:\22inline interface typedef docs\22}},\22nested\22:{}}},\22types\22:{\22t\22:{\22docs\22:\22world typedef docs\22}},\22funcs\22:{\22imp\22:\22world func import docs\22,\22exp\22:\22world func export docs\22}}},\22interfaces\22:{\22coverage-iface\22:{\22docs\22:\22interface docs\22,\22funcs\22:{\22[constructor]res\22:\22constructor docs\22,\22[method]res.m\22:\22method docs\22,\22[static]res.s\22:\22static func docs\22,\22f\22:\22interface func docs\22},\22types\22:{\22t\22:{\22docs\22:\22basic typedef docs\22},\22r\22:{\22docs\22:\22record typedef docs\22,\22items\22:{\22f1\22:\22record field docs\22}},\22fl\22:{\22items\22:{\22f1\22:\22flag docs\22}},\22v\22:{\22items\22:{\22c1\22:\22variant case docs\22}},\22e\22:{\22items\22:{\22c1\22:\22enum case docs\22}}},\22nested\22:{}},\22other-comment-forms\22:{\22docs\22:\22other comment forms\5cn    multi-line block\22,\22funcs\22:{\22multiple-lines-split\22:\22one doc line\5cnnon-doc in the middle\5cnanother doc line\22,\22mixed-forms\22:\22mixed forms; line doc\5cnplus block doc\5cn      multi-line\22},\22nested\22:{}}}}")
   (@producers
     (processed-by "wit-component" "$CARGO_PKG_VERSION")
   )

crates/wit-component/tests/interfaces/nested.wat

@@ -0,0 +1,40 @@
+(component
+  (type (;0;)
+    (component
+      (type (;0;)
+        (instance
+          (type (;0;) (record (field "foo" string)))
+          (export (;1;) "my-record" (type (eq 0)))
+          (type (;2;) (func (result string)))
+          (export (;0;) "hello" (func (type 2)))
+          (type (;3;)
+            (instance
+              (type (;0;) (record (field "foo" string)))
+              (export (;1;) "nest-record" (type (eq 0)))
+              (type (;2;)
+                (instance
+                  (type (;0;) (record (field "foo" string)))
+                  (export (;1;) "nest-record" (type (eq 0)))
+                )
+              )
+              (export (;0;) "foo:nestnest/deep" (instance (type 2)))
+            )
+          )
+          (export (;0;) "foo:nestee/things@1.0.0" (instance (type 3)))
+          (type (;4;)
+            (instance
+              (export (;0;) "foo" (type (sub resource)))
+            )
+          )
+          (export (;1;) "foo:nestee/more@1.0.0" (instance (type 4)))
+        )
+      )
+      (export (;0;) "foo:thing/something" (instance (type 0)))
+    )
+  )
+  (export (;1;) "something" (type 0))
+  (@custom "package-docs" "\01{\22interfaces\22:{\22something\22:{\22types\22:{\22my-record\22:{\22stability\22:{\22stable\22:{\22since\22:\221.0.0\22}}}},\22nested\22:{\22foo:nestee/things@1.0.0\22:{\22docs\22:{\22contents\22:\22nesting can be documented\22},\22stability\22:\22unknown\22},\22foo:nestee/more@1.0.0\22:{\22docs\22:{\22contents\22:null},\22stability\22:{\22stable\22:{\22since\22:\221.0.0\22}}}}}}}")
+  (@producers
+    (processed-by "wit-component" "$CARGO_PKG_VERSION")
+  )
+)

crates/wit-component/tests/interfaces/nested/deps/nestee.wit

@@ -0,0 +1,17 @@
+package foo:nestee@1.0.0;
+
+interface things {
+  //nesting can be documented
+  @since(version = 1.0.0)
+  nest foo:nestnest/deep;
+  record nest-record {
+    foo: string
+  }
+  hello: func() -> string;
+}
+
+interface more {
+  resource foo {
+    bar: func() -> option<string>;
+  }
+}

crates/wit-component/tests/interfaces/nested/deps/nestnest.wit

@@ -0,0 +1,7 @@
+package foo:nestnest;
+
+interface deep {
+  record deep-record {
+    foo: string
+  }
+}

crates/wit-component/tests/interfaces/nested/nested.wit

@@ -0,0 +1,14 @@
+package foo:thing;
+
+interface something {
+  //nesting can be documented
+  nest foo:nestee/things@1.0.0;
+  @since(version = 1.0.0)
+  nest foo:nestee/more@1.0.0;
+  @since(version = 1.0.0)
+  record my-record {
+    foo: string
+  }
+
+  hello: func() -> string;
+}

crates/wit-component/tests/interfaces/nested/thing.wit.print

@@ -0,0 +1,15 @@
+package foo:thing;
+
+interface something {
+  /// nesting can be documented
+  nest foo:nestee/things@1.0.0;
+  @since(version = 1.0.0)
+  nest foo:nestee/more@1.0.0;
+  @since(version = 1.0.0)
+  record my-record {
+    foo: string,
+  }
+
+  hello: func() -> string;
+}
+

crates/wit-component/tests/interfaces/resources.wat

@@ -180,7 +180,7 @@
     )
   )
   (export (;11;) "implicit-own-handles3" (type 10))
-  (@custom "package-docs" "\00{\22worlds\22:{\22implicit-own-handles3\22:{\22types\22:{\22a\22:{\22docs\22:\22there should only be one `list` type despite there looking like two\5cnlist types here\22}}}},\22interfaces\22:{\22implicit-own-handles2\22:{\22types\22:{\22a\22:{\22docs\22:\22the `own` return and list param should be the same `own`\22},\22b\22:{\22docs\22:\22same as above, even when the `list<b>` implicitly-defined `own` comes\5cnbefore an explicitly defined `own`\22},\22c\22:{\22docs\22:\22same as the above, the `own` argument should have the same type as the\5cnreturn value\22}}}}}")
+  (@custom "package-docs" "\00{\22worlds\22:{\22implicit-own-handles3\22:{\22types\22:{\22a\22:{\22docs\22:\22there should only be one `list` type despite there looking like two\5cnlist types here\22}}}},\22interfaces\22:{\22implicit-own-handles2\22:{\22types\22:{\22a\22:{\22docs\22:\22the `own` return and list param should be the same `own`\22},\22b\22:{\22docs\22:\22same as above, even when the `list<b>` implicitly-defined `own` comes\5cnbefore an explicitly defined `own`\22},\22c\22:{\22docs\22:\22same as the above, the `own` argument should have the same type as the\5cnreturn value\22}},\22nested\22:{}}}}")
   (@producers
     (processed-by "wit-component" "$CARGO_PKG_VERSION")
   )

crates/wit-parser/src/ast.rs

@@ -220,6 +220,19 @@ impl<'a> DeclList<'a> {
         }
         Ok(())
     }
+
+    fn for_each_nest<'b>(&'b self, mut f: impl FnMut(&'b Nest<'a>) -> Result<()>) -> Result<()> {
+        for item in self.items.iter() {
+            if let AstItem::Interface(i) = item {
+                for item in i.items.iter() {
+                    if let InterfaceItem::Nest(n) = item {
+                        f(n)?;
+                    }
+                }
+            }
+        }
+        Ok(())
+    }
 }
 
 enum AstItem<'a> {
@@ -545,6 +558,48 @@ enum InterfaceItem<'a> {
     TypeDef(TypeDef<'a>),
     Func(NamedFunc<'a>),
     Use(Use<'a>),
+    Nest(Nest<'a>),
+}
+
+struct Nest<'a> {
+    docs: Docs<'a>,
+    id: PackageName<'a>,
+    name: Id<'a>,
+    attributes: Vec<Attribute<'a>>,
+}
+
+impl<'a> Nest<'a> {
+    fn parse(
+        tokens: &mut Tokenizer<'a>,
+        docs: Docs<'a>,
+        attributes: Vec<Attribute<'a>>,
+    ) -> Result<Self> {
+        tokens.eat(Token::Nest)?;
+        let id = parse_id(tokens)?;
+        tokens.expect(Token::Colon)?;
+        // `foo:bar/baz@1.0`
+        let namespace = id;
+        let pkg_name = parse_id(tokens)?;
+        tokens.expect(Token::Slash)?;
+        let name = parse_id(tokens)?;
+        let version = parse_opt_version(tokens)?;
+        tokens.expect_semicolon()?;
+        Ok(Self {
+            id: PackageName {
+                docs: Default::default(),
+                span: Span {
+                    start: namespace.span.start,
+                    end: pkg_name.span.end,
+                },
+                namespace,
+                name: pkg_name,
+                version,
+            },
+            docs,
+            name,
+            attributes,
+        })
+    }
 }
 
 struct Use<'a> {
@@ -983,6 +1038,9 @@ impl<'a> InterfaceItem<'a> {
                 NamedFunc::parse(tokens, docs, attributes).map(InterfaceItem::Func)
             }
             Some((_span, Token::Use)) => Use::parse(tokens, attributes).map(InterfaceItem::Use),
+            Some((_span, Token::Nest)) => {
+                Nest::parse(tokens, docs, attributes).map(InterfaceItem::Nest)
+            }
             other => Err(err_expected(tokens, "`type`, `resource` or `func`", other).into()),
         }
     }

crates/wit-parser/src/ast/lex.rs

@@ -84,6 +84,7 @@ pub enum Token {
     As,
     From_,
     Static,
+    Nest,
     Interface,
     Tuple,
     Import,
@@ -315,6 +316,7 @@ impl<'a> Tokenizer<'a> {
                     "as" => As,
                     "from" => From_,
                     "static" => Static,
+                    "nest" => Nest,
                     "interface" => Interface,
                     "tuple" => Tuple,
                     "world" => World,
@@ -576,6 +578,7 @@ impl Token {
             As => "keyword `as`",
             From_ => "keyword `from`",
             Static => "keyword `static`",
+            Nest => "keyword `nest`",
             Interface => "keyword `interface`",
             Tuple => "keyword `tuple`",
             Import => "keyword `import`",