Do proper type checking for type handles.

Instead of relying purely on the assumption that type handles can be compared
cheaply by pointer equality, fallback to a more expensive walk of the
type tree that recursively compares types structurally.

This allows different components to call into each other as long as
their types are structurally equivalent.

crates/wasmtime/src/component/types.rs

@@ -3,14 +3,15 @@
 use crate::component::matching::InstanceType;
 use crate::component::values::{self, Val};
 use anyhow::{anyhow, Result};
+use std::collections::{HashMap, HashSet};
 use std::fmt;
 use std::mem;
 use std::ops::Deref;
 use std::sync::Arc;
 use wasmtime_environ::component::{
     CanonicalAbiInfo, ComponentTypes, InterfaceType, ResourceIndex, TypeEnumIndex, TypeFlagsIndex,
-    TypeListIndex, TypeOptionIndex, TypeRecordIndex, TypeResultIndex, TypeTupleIndex,
-    TypeVariantIndex,
+    TypeListIndex, TypeOptionIndex, TypeRecordIndex, TypeResourceTableIndex, TypeResultIndex,
+    TypeTupleIndex, TypeVariantIndex,
 };
 use wasmtime_environ::PrimaryMap;
 
@@ -56,6 +57,29 @@ impl<T> Handle<T> {
             resources: &self.resources,
         }
     }
+
+    fn equivalent<'a>(
+        &'a self,
+        other: &'a Self,
+        type_check: fn(&TypeChecker<'a>, T, T) -> bool,
+    ) -> bool
+    where
+        T: PartialEq + Copy,
+    {
+        (self.index == other.index
+            && Arc::ptr_eq(&self.types, &other.types)
+            && Arc::ptr_eq(&self.resources, &other.resources))
+            || type_check(
+                &TypeChecker {
+                    a_types: &self.types,
+                    b_types: &other.types,
+                    a_resource: &self.resources,
+                    b_resource: &self.resources,
+                },
+                self.index,
+                other.index,
+            )
+    }
 }
 
 impl<T: fmt::Debug> fmt::Debug for Handle<T> {
@@ -66,23 +90,188 @@ impl<T: fmt::Debug> fmt::Debug for Handle<T> {
     }
 }
 
-impl<T: PartialEq> PartialEq for Handle<T> {
-    fn eq(&self, other: &Self) -> bool {
-        // FIXME: This is an overly-restrictive definition of equality in that it doesn't consider types to be
-        // equal unless they refer to the same declaration in the same component.  It's a good shortcut for the
-        // common case, but we should also do a recursive structural equality test if the shortcut test fails.
-        self.index == other.index
-            && Arc::ptr_eq(&self.types, &other.types)
-            && Arc::ptr_eq(&self.resources, &other.resources)
-    }
+/// Type checker for two
+struct TypeChecker<'a> {
+    a_types: &'a ComponentTypes,
+    a_resource: &'a PrimaryMap<ResourceIndex, ResourceType>,
+    b_types: &'a ComponentTypes,
+    b_resource: &'a PrimaryMap<ResourceIndex, ResourceType>,
 }
 
-impl<T: Eq> Eq for Handle<T> {}
+impl TypeChecker<'_> {
+    fn interface_types_equal(&self, a: InterfaceType, b: InterfaceType) -> bool {
+        match (a, b) {
+            (InterfaceType::Own(o1), InterfaceType::Own(o2)) => self.resources_equal(o1, o2),
+            (InterfaceType::Own(_), _) => false,
+            (InterfaceType::Borrow(b1), InterfaceType::Borrow(b2)) => self.resources_equal(b1, b2),
+            (InterfaceType::Borrow(_), _) => false,
+            (InterfaceType::List(l1), InterfaceType::List(l2)) => self.lists_equal(l1, l2),
+            (InterfaceType::List(_), _) => false,
+            (InterfaceType::Record(r1), InterfaceType::Record(r2)) => self.records_equal(r1, r2),
+            (InterfaceType::Record(_), _) => false,
+            (InterfaceType::Variant(v1), InterfaceType::Variant(v2)) => self.variants_equal(v1, v2),
+            (InterfaceType::Variant(_), _) => false,
+            (InterfaceType::Result(r1), InterfaceType::Result(r2)) => self.results_equal(r1, r2),
+            (InterfaceType::Result(_), _) => false,
+            (InterfaceType::Option(o1), InterfaceType::Option(o2)) => self.options_equal(o1, o2),
+            (InterfaceType::Option(_), _) => false,
+            (InterfaceType::Enum(e1), InterfaceType::Enum(e2)) => self.enums_equal(e1, e2),
+            (InterfaceType::Enum(_), _) => false,
+            (InterfaceType::Tuple(t1), InterfaceType::Tuple(t2)) => self.tuples_equal(t1, t2),
+            (InterfaceType::Tuple(_), _) => false,
+            (InterfaceType::Flags(f1), InterfaceType::Flags(f2)) => self.flags_equal(f1, f2),
+            (InterfaceType::Flags(_), _) => false,
+            (InterfaceType::Bool, InterfaceType::Bool) => true,
+            (InterfaceType::Bool, _) => false,
+            (InterfaceType::U8, InterfaceType::U8) => true,
+            (InterfaceType::U8, _) => false,
+            (InterfaceType::U16, InterfaceType::U16) => true,
+            (InterfaceType::U16, _) => false,
+            (InterfaceType::U32, InterfaceType::U32) => true,
+            (InterfaceType::U32, _) => false,
+            (InterfaceType::U64, InterfaceType::U64) => true,
+            (InterfaceType::U64, _) => false,
+            (InterfaceType::S8, InterfaceType::S8) => true,
+            (InterfaceType::S8, _) => false,
+            (InterfaceType::S16, InterfaceType::S16) => true,
+            (InterfaceType::S16, _) => false,
+            (InterfaceType::S32, InterfaceType::S32) => true,
+            (InterfaceType::S32, _) => false,
+            (InterfaceType::S64, InterfaceType::S64) => true,
+            (InterfaceType::S64, _) => false,
+            (InterfaceType::Float32, InterfaceType::Float32) => true,
+            (InterfaceType::Float32, _) => false,
+            (InterfaceType::Float64, InterfaceType::Float64) => true,
+            (InterfaceType::Float64, _) => false,
+            (InterfaceType::String, InterfaceType::String) => true,
+            (InterfaceType::String, _) => false,
+            (InterfaceType::Char, InterfaceType::Char) => true,
+            (InterfaceType::Char, _) => false,
+        }
+    }
+
+    fn lists_equal(&self, l1: TypeListIndex, l2: TypeListIndex) -> bool {
+        let a = &self.a_types[l1];
+        let b = &self.b_types[l2];
+        self.interface_types_equal(a.element, b.element)
+    }
+
+    fn resources_equal(&self, o1: TypeResourceTableIndex, o2: TypeResourceTableIndex) -> bool {
+        let a = &self.a_types[o1];
+        let b = &self.b_types[o2];
+        self.a_resource[a.ty] == self.b_resource[b.ty]
+    }
+
+    fn records_equal(&self, r1: TypeRecordIndex, r2: TypeRecordIndex) -> bool {
+        let a = &self.a_types[r1];
+        let b = &self.b_types[r2];
+        if a.fields.len() != b.fields.len() {
+            return false;
+        }
+        let b_fields = b
+            .fields
+            .iter()
+            .map(|f| (&f.name, &f.ty))
+            .collect::<HashMap<&String, &InterfaceType>>();
+        a.fields.iter().all(|a_field| {
+            let Some(&&b_field_ty) = b_fields.get(&a_field.name) else {
+                return false;
+            };
+            self.interface_types_equal(a_field.ty, b_field_ty)
+        })
+    }
+
+    fn variants_equal(&self, v1: TypeVariantIndex, v2: TypeVariantIndex) -> bool {
+        let a = &self.a_types[v1];
+        let b = &self.b_types[v2];
+        if a.cases.len() != b.cases.len() {
+            return false;
+        }
+        let b_cases = b
+            .cases
+            .iter()
+            .map(|f| (&f.name, &f.ty))
+            .collect::<HashMap<&String, &Option<InterfaceType>>>();
+        a.cases.iter().all(|a_case| {
+            let Some(&&b_case_ty) = b_cases.get(&a_case.name) else {
+                return false;
+            };
+            match (a_case.ty, b_case_ty) {
+                (Some(a_case_ty), Some(b_case_ty)) => {
+                    self.interface_types_equal(a_case_ty, b_case_ty)
+                }
+                (None, None) => true,
+                _ => false,
+            }
+        })
+    }
+
+    fn results_equal(&self, r1: TypeResultIndex, r2: TypeResultIndex) -> bool {
+        let a = &self.a_types[r1];
+        let b = &self.b_types[r2];
+        let oks = match (a.ok, b.ok) {
+            (Some(ok1), Some(ok2)) => self.interface_types_equal(ok1, ok2),
+            (None, None) => true,
+            _ => false,
+        };
+        if !oks {
+            return false;
+        }
+        match (a.err, b.err) {
+            (Some(err1), Some(err2)) => self.interface_types_equal(err1, err2),
+            (None, None) => true,
+            _ => false,
+        }
+    }
+
+    fn options_equal(&self, o1: TypeOptionIndex, o2: TypeOptionIndex) -> bool {
+        let a = &self.a_types[o1];
+        let b = &self.b_types[o2];
+        self.interface_types_equal(a.ty, b.ty)
+    }
+
+    fn enums_equal(&self, e1: TypeEnumIndex, e2: TypeEnumIndex) -> bool {
+        let a = &self.a_types[e1];
+        let b = &self.b_types[e2];
+        if a.names.len() != b.names.len() {
+            return false;
+        }
+
+        let b_names = b.names.iter().collect::<HashSet<&String>>();
+        a.names.iter().all(|a_name| b_names.contains(a_name))
+    }
+
+    fn tuples_equal(&self, t1: TypeTupleIndex, t2: TypeTupleIndex) -> bool {
+        let a = &self.a_types[t1];
+        let b = &self.b_types[t2];
+        if a.types.len() != b.types.len() {
+            return false;
+        }
+        a.types
+            .iter()
+            .zip(b.types.iter())
+            .all(|(&a, &b)| self.interface_types_equal(a, b))
+    }
+
+    fn flags_equal(&self, f1: TypeFlagsIndex, f2: TypeFlagsIndex) -> bool {
+        let a = &self.a_types[f1];
+        let b = &self.b_types[f2];
+        a.names == b.names
+    }
+}
 
 /// A `list` interface type
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, Debug)]
 pub struct List(Handle<TypeListIndex>);
 
+impl PartialEq for List {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.equivalent(&other.0, TypeChecker::lists_equal)
+    }
+}
+
+impl Eq for List {}
+
 impl List {
     /// Instantiate this type with the specified `values`.
     pub fn new_val(&self, values: Box<[Val]>) -> Result<Val> {
@@ -108,7 +297,7 @@ pub struct Field<'a> {
 }
 
 /// A `record` interface type
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, Debug)]
 pub struct Record(Handle<TypeRecordIndex>);
 
 impl Record {
@@ -130,8 +319,16 @@ impl Record {
     }
 }
 
+impl PartialEq for Record {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.equivalent(&other.0, TypeChecker::records_equal)
+    }
+}
+
+impl Eq for Record {}
+
 /// A `tuple` interface type
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, Debug)]
 pub struct Tuple(Handle<TypeTupleIndex>);
 
 impl Tuple {
@@ -153,6 +350,14 @@ impl Tuple {
     }
 }
 
+impl PartialEq for Tuple {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.equivalent(&other.0, TypeChecker::tuples_equal)
+    }
+}
+
+impl Eq for Tuple {}
+
 /// A case declaration belonging to a `variant`
 pub struct Case<'a> {
     /// The name of the case
@@ -162,7 +367,7 @@ pub struct Case<'a> {
 }
 
 /// A `variant` interface type
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, Debug)]
 pub struct Variant(Handle<TypeVariantIndex>);
 
 impl Variant {
@@ -187,8 +392,16 @@ impl Variant {
     }
 }
 
+impl PartialEq for Variant {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.equivalent(&other.0, TypeChecker::variants_equal)
+    }
+}
+
+impl Eq for Variant {}
+
 /// An `enum` interface type
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, Debug)]
 pub struct Enum(Handle<TypeEnumIndex>);
 
 impl Enum {
@@ -210,8 +423,16 @@ impl Enum {
     }
 }
 
+impl PartialEq for Enum {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.equivalent(&other.0, TypeChecker::enums_equal)
+    }
+}
+
+impl Eq for Enum {}
+
 /// An `option` interface type
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, Debug)]
 pub struct OptionType(Handle<TypeOptionIndex>);
 
 impl OptionType {
@@ -230,8 +451,16 @@ impl OptionType {
     }
 }
 
+impl PartialEq for OptionType {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.equivalent(&other.0, TypeChecker::options_equal)
+    }
+}
+
+impl Eq for OptionType {}
+
 /// An `expected` interface type
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, Debug)]
 pub struct ResultType(Handle<TypeResultIndex>);
 
 impl ResultType {
@@ -261,8 +490,16 @@ impl ResultType {
     }
 }
 
+impl PartialEq for ResultType {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.equivalent(&other.0, TypeChecker::results_equal)
+    }
+}
+
+impl Eq for ResultType {}
+
 /// A `flags` interface type
-#[derive(Clone, PartialEq, Eq, Debug)]
+#[derive(Clone, Debug)]
 pub struct Flags(Handle<TypeFlagsIndex>);
 
 impl Flags {
@@ -288,6 +525,14 @@ impl Flags {
     }
 }
 
+impl PartialEq for Flags {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.equivalent(&other.0, TypeChecker::flags_equal)
+    }
+}
+
+impl Eq for Flags {}
+
 /// Represents a component model interface type
 #[derive(Clone, PartialEq, Eq, Debug)]
 #[allow(missing_docs)]