Update support for the module linking proposal

This commit updates the various tooling used by wasmtime which has new
updates to the module linking proposal. This is done primarily to sync
with WebAssembly/module-linking#26. The main change implemented here is
that wasmtime now supports creating instances from a set of values, nott
just from instantiating a module. Additionally subtyping handling of
modules with respect to imports is now properly handled by desugaring
two-level imports to imports of instances.

A number of small refactorings are included here as well, but most of
them are in accordance with the changes to `wasmparser` and the updated
binary format for module linking.

crates/runtime/src/instance.rs

@@ -14,6 +14,7 @@ use crate::vmcontext::{
     VMSharedSignatureIndex, VMTableDefinition, VMTableImport,
 };
 use crate::{ExportFunction, ExportGlobal, ExportMemory, ExportTable};
+use indexmap::IndexMap;
 use memoffset::offset_of;
 use more_asserts::assert_lt;
 use std::alloc::{self, Layout};
@@ -22,17 +23,22 @@ use std::cell::RefCell;
 use std::collections::HashMap;
 use std::convert::TryFrom;
 use std::ptr::NonNull;
+use std::rc::Rc;
 use std::sync::Arc;
 use std::{mem, ptr, slice};
 use thiserror::Error;
 use wasmtime_environ::entity::{packed_option::ReservedValue, BoxedSlice, EntityRef, PrimaryMap};
 use wasmtime_environ::wasm::{
     DataIndex, DefinedFuncIndex, DefinedGlobalIndex, DefinedMemoryIndex, DefinedTableIndex,
-    ElemIndex, EntityIndex, FuncIndex, GlobalIndex, GlobalInit, InstanceIndex, MemoryIndex,
-    ModuleIndex, SignatureIndex, TableElementType, TableIndex, WasmType,
+    ElemIndex, EntityIndex, FuncIndex, GlobalIndex, GlobalInit, MemoryIndex, SignatureIndex,
+    TableElementType, TableIndex, WasmType,
 };
 use wasmtime_environ::{ir, DataInitializer, Module, ModuleType, TableElements, VMOffsets};
 
+/// Runtime representation of an instance value, which erases all `Instance`
+/// information since instances are just a collection of values.
+pub type RuntimeInstance = Rc<IndexMap<String, Export>>;
+
 /// A WebAssembly instance.
 ///
 /// This is repr(C) to ensure that the vmctx field is last.
@@ -50,15 +56,6 @@ pub(crate) struct Instance {
     /// WebAssembly table data.
     tables: BoxedSlice<DefinedTableIndex, Table>,
 
-    /// Instances our module defined and their handles.
-    instances: PrimaryMap<InstanceIndex, InstanceHandle>,
-
-    /// Modules that are located in our index space.
-    ///
-    /// For now these are `Box<Any>` so the caller can define the type of what a
-    /// module looks like.
-    modules: PrimaryMap<ModuleIndex, Box<dyn Any>>,
-
     /// Passive elements in this instantiation. As `elem.drop`s happen, these
     /// entries get removed. A missing entry is considered equivalent to an
     /// empty slice.
@@ -266,18 +263,8 @@ impl Instance {
         self.vmctx() as *const VMContext as *mut VMContext
     }
 
-    /// Lookup an export with the given name.
-    pub fn lookup(&self, field: &str) -> Option<Export> {
-        let export = if let Some(export) = self.module.exports.get(field) {
-            export.clone()
-        } else {
-            return None;
-        };
-        Some(self.lookup_by_declaration(&export))
-    }
-
     /// Lookup an export with the given export declaration.
-    pub fn lookup_by_declaration(&self, export: &EntityIndex) -> Export<'_> {
+    pub fn lookup_by_declaration(&self, export: &EntityIndex) -> Export {
         match export {
             EntityIndex::Function(index) => {
                 let anyfunc = self.get_caller_checked_anyfunc(*index).unwrap();
@@ -326,8 +313,9 @@ impl Instance {
             }
             .into(),
 
-            EntityIndex::Instance(index) => Export::Instance(&self.instances[*index]),
-            EntityIndex::Module(index) => Export::Module(&*self.modules[*index]),
+            EntityIndex::Instance(_) | EntityIndex::Module(_) => {
+                panic!("can't use this api for modules/instances")
+            }
         }
     }
 
@@ -855,8 +843,6 @@ impl InstanceHandle {
                 passive_elements: Default::default(),
                 passive_data,
                 host_state,
-                instances: imports.instances,
-                modules: imports.modules,
                 vmctx: VMContext {},
             };
             let layout = instance.alloc_layout();
@@ -1015,11 +1001,6 @@ impl InstanceHandle {
         self.instance().module()
     }
 
-    /// Lookup an export with the given name.
-    pub fn lookup(&self, field: &str) -> Option<Export> {
-        self.instance().lookup(field)
-    }
-
     /// Lookup an export with the given export declaration.
     pub fn lookup_by_declaration(&self, export: &EntityIndex) -> Export {
         self.instance().lookup_by_declaration(export)