Allow aliases to core wasm types outside of depth 1 (#1539)

This accompanies WebAssembly/component-model#350 and relaxes the
previous constraint implemented in #640 to reflect the spec-at-the-time,
which has since been relaxed.

crates/wasmparser/src/validator/component.rs

@@ -1503,13 +1503,6 @@ impl ComponentState {
                     state.add_export(name, ty, features, offset, true, types)?;
                 }
                 crate::ModuleTypeDeclaration::OuterAlias { kind, count, index } => {
-                    if count > 1 {
-                        return Err(BinaryReaderError::new(
-                            "outer type aliases in module type declarations are limited to a \
-                             maximum count of 1",
-                            offset,
-                        ));
-                    }
                     match kind {
                         crate::OuterAliasKind::Type => {
                             let ty = if count == 0 {

crates/wast/src/component/resolve.rs

@@ -157,7 +157,7 @@ impl<'a> Resolver<'a> {
             ComponentField::CoreType(t) => self.core_ty(t),
             ComponentField::Component(c) => self.component(c),
             ComponentField::Instance(i) => self.instance(i),
-            ComponentField::Alias(a) => self.alias(a, false),
+            ComponentField::Alias(a) => self.alias(a),
             ComponentField::Type(t) => self.ty(t),
             ComponentField::CanonicalFunc(f) => self.canonical_func(f),
             ComponentField::CoreFunc(_) => unreachable!("should be expanded already"),
@@ -288,7 +288,6 @@ impl<'a> Resolver<'a> {
         index: &mut Index<'a>,
         kind: T,
         span: Span,
-        enclosing_only: bool,
     ) -> Result<(), Error> {
         // Short-circuit when both indices are already resolved as this
         // helps to write tests for invalid modules where wasmparser should
@@ -328,13 +327,6 @@ impl<'a> Resolver<'a> {
             ));
         }
 
-        if enclosing_only && depth > 1 {
-            return Err(Error::new(
-                span,
-                "only the local or enclosing scope can be aliased".to_string(),
-            ));
-        }
-
         *outer = Index::Num(depth, span);
 
         // Resolve `index` within the computed scope depth.
@@ -344,7 +336,7 @@ impl<'a> Resolver<'a> {
         Ok(())
     }
 
-    fn alias(&mut self, alias: &mut Alias<'a>, enclosing_only: bool) -> Result<(), Error> {
+    fn alias(&mut self, alias: &mut Alias<'a>) -> Result<(), Error> {
         match &mut alias.target {
             AliasTarget::Export {
                 instance,
@@ -357,7 +349,7 @@ impl<'a> Resolver<'a> {
                 kind: _,
             } => self.resolve_ns(instance, Ns::CoreInstance),
             AliasTarget::Outer { outer, index, kind } => {
-                self.outer_alias(outer, index, *kind, alias.span, enclosing_only)
+                self.outer_alias(outer, index, *kind, alias.span)
             }
         }
     }
@@ -550,7 +542,7 @@ impl<'a> Resolver<'a> {
         self.resolve_prepending_aliases(
             &mut c.decls,
             |resolver, decl| match decl {
-                ComponentTypeDecl::Alias(alias) => resolver.alias(alias, false),
+                ComponentTypeDecl::Alias(alias) => resolver.alias(alias),
                 ComponentTypeDecl::CoreType(ty) => resolver.core_ty(ty),
                 ComponentTypeDecl::Type(ty) => resolver.ty(ty),
                 ComponentTypeDecl::Import(import) => resolver.item_sig(&mut import.item),
@@ -583,7 +575,7 @@ impl<'a> Resolver<'a> {
         self.resolve_prepending_aliases(
             &mut c.decls,
             |resolver, decl| match decl {
-                InstanceTypeDecl::Alias(alias) => resolver.alias(alias, false),
+                InstanceTypeDecl::Alias(alias) => resolver.alias(alias),
                 InstanceTypeDecl::CoreType(ty) => resolver.core_ty(ty),
                 InstanceTypeDecl::Type(ty) => resolver.ty(ty),
                 InstanceTypeDecl::Export(export) => resolver.item_sig(&mut export.item),
@@ -740,7 +732,7 @@ impl<'a> Resolver<'a> {
         return self.resolve_prepending_aliases(
             &mut ty.decls,
             |resolver, decl| match decl {
-                ModuleTypeDecl::Alias(alias) => resolver.alias(alias, true),
+                ModuleTypeDecl::Alias(alias) => resolver.alias(alias),
                 ModuleTypeDecl::Type(_) => Ok(()),
                 ModuleTypeDecl::Import(import) => resolve_item_sig(resolver, &mut import.item),
                 ModuleTypeDecl::Export(_, item) => resolve_item_sig(resolver, item),

tests/local/component-model/types.wast

@@ -134,14 +134,12 @@
   )
   "type index out of bounds")
 
-(assert_invalid
-  (component $c
-    (type $f (func))
-    (core type $t (module
-      (alias outer 100 0 (type))
-    ))
-  )
-  "outer type aliases in module type declarations are limited to a maximum count of 1")
+(component $c
+  (core type $f (func))
+  (core type $t (module
+    (alias outer $c $f (type))
+  ))
+)
 
 (assert_invalid
   (component $c
@@ -262,17 +260,14 @@
   )
 )
 
-(assert_invalid
-  (component $C
-    (core type $t (func))
-    (component $C2
-      (core type (module
-        (alias outer $C $t (type $a))
-        (import "" "" (func (type $a)))
-      ))
-    )
+(component $C
+  (core type $t (func))
+  (component $C2
+    (core type (module
+      (alias outer $C $t (type $a))
+      (import "" "" (func (type $a)))
+    ))
   )
-  "only the local or enclosing scope can be aliased"
 )
 
 (component
@@ -319,3 +314,12 @@
     (type (tuple))
   )
   "tuple type must have at least one type")
+
+(component $c
+  (core type $f (func))
+  (component $c2
+    (core type $t (module
+      (alias outer $c $f (type))
+    ))
+  )
+)

tests/snapshots/local/component-model/types.wast/17.print

@@ -0,0 +1,8 @@
+(component $c
+  (core type $f (;0;) (func))
+  (core type $t (;1;)
+    (module
+      (alias outer $c $f (type (;0;)))
+    )
+  )
+)

tests/snapshots/local/component-model/types.wast/32.print

@@ -0,0 +1,11 @@
+(component $C
+  (core type $t (;0;) (func))
+  (component $C2 (;0;)
+    (core type (;0;)
+      (module
+        (alias outer $C $t (type (;0;)))
+        (import "" "" (func (type 0)))
+      )
+    )
+  )
+)

tests/snapshots/local/component-model/types.wast/40.print

@@ -0,0 +1,10 @@
+(component $c
+  (core type $f (;0;) (func))
+  (component $c2 (;0;)
+    (core type $t (;0;)
+      (module
+        (alias outer $c $f (type (;0;)))
+      )
+    )
+  )
+)