Loosen restriction on top-level resource alias imports.

Previously, we assumed that all resource aliases had some owning
interface, but that might not be the case. Users can alias resources at
the world level. This lifts two restrictions that erroneously encoded
this incorrect assumption.

Fixes #81

Author: rylev

crates/wac-graph/src/encoding.rs

@@ -577,7 +577,6 @@ impl<'a> TypeEncoder<'a> {
     }
 
     fn own(&self, state: &mut State, res: ResourceId) -> u32 {
-        assert!(!state.scopes.is_empty());
         let res = state.current.resources[self.0[res].name.as_str()];
         let index = state.current.encodable.type_count();
         state.current.encodable.ty().defined_type().own(res);

crates/wac-graph/tests/graphs/import-resource-alias/encoded.wat

@@ -0,0 +1,25 @@
+(component
+  (import "x" (type (;0;) (sub resource)))
+  (import "y" (type (;1;) (eq 0)))
+  (type (;2;) (own 0))
+  (type (;3;) (own 1))
+  (type (;4;) (func (param "x" 2) (result 3)))
+  (import "f" (func (;0;) (type 4)))
+  (type (;5;)
+    (component
+      (import "x" (type (;0;) (sub resource)))
+      (import "y" (type (;1;) (eq 0)))
+      (type (;2;) (own 0))
+      (type (;3;) (own 1))
+      (type (;4;) (func (param "x" 2) (result 3)))
+      (import "f" (func (;0;) (type 4)))
+    )
+  )
+  (import "unlocked-dep=<test:foo>" (component (;0;) (type 5)))
+  (instance (;0;) (instantiate 0
+      (with "x" (type 0))
+      (with "y" (type 1))
+      (with "f" (func 0))
+    )
+  )
+)

crates/wac-graph/tests/graphs/import-resource-alias/graph.json

@@ -0,0 +1,14 @@
+{
+    "packages": [
+        {
+            "name": "test:foo",
+            "path": "world.wit"
+        }
+    ],
+    "nodes": [
+        {
+            "type": "instantiation",
+            "package": 0
+        }
+    ]
+}

crates/wac-graph/tests/graphs/import-resource-alias/world.wit

@@ -0,0 +1,7 @@
+package example:foo;
+
+world w {
+  resource x;
+  type y = x;
+  import f: func(x: x) -> y;
+}

crates/wac-types/src/package.rs

@@ -765,11 +765,8 @@ impl<'a> TypeConverter<'a> {
             let alias_id = self.types.add_resource(Resource {
                 name: name.to_owned(),
                 alias: Some(ResourceAlias {
-                    owner: match self
-                        .find_owner(ComponentAnyTypeId::Resource(id))
-                        .expect("should have owner")
-                    {
-                        (Owner::Interface(id), _) => Some(*id),
+                    owner: match self.find_owner(ComponentAnyTypeId::Resource(id)) {
+                        Some((Owner::Interface(id), _)) => Some(*id),
                         _ => None,
                     },
                     source: *resource_id,