wasmtime-runtime: Allow tables to internally hold externrefs (#1882)

This commit enables `wasmtime_runtime::Table` to internally hold elements of
either `funcref` (all that is currently supported) or `externref` (newly
introduced in this commit).

This commit updates `Table`'s API, but does NOT generally propagate those
changes outwards all the way through the Wasmtime embedding API. It only does
enough to get everything compiling and the current test suite passing. It is
expected that as we implement more of the reference types spec, we will bubble
these changes out and expose them to the embedding API.

crates/runtime/src/instance.rs

@@ -5,7 +5,7 @@
 use crate::export::Export;
 use crate::imports::Imports;
 use crate::memory::{DefaultMemoryCreator, RuntimeLinearMemory, RuntimeMemoryCreator};
-use crate::table::Table;
+use crate::table::{Table, TableElement};
 use crate::traphandlers::Trap;
 use crate::vmcontext::{
     VMBuiltinFunctionsArray, VMCallerCheckedAnyfunc, VMContext, VMFunctionBody, VMFunctionImport,
@@ -455,11 +455,7 @@ impl Instance {
     }
 
     // Get table element by index.
-    fn table_get(
-        &self,
-        table_index: DefinedTableIndex,
-        index: u32,
-    ) -> Option<VMCallerCheckedAnyfunc> {
+    fn table_get(&self, table_index: DefinedTableIndex, index: u32) -> Option<TableElement> {
         self.tables
             .get(table_index)
             .unwrap_or_else(|| panic!("no table for index {}", table_index.index()))
@@ -470,7 +466,7 @@ impl Instance {
         &self,
         table_index: DefinedTableIndex,
         index: u32,
-        val: VMCallerCheckedAnyfunc,
+        val: TableElement,
     ) -> Result<(), ()> {
         self.tables
             .get(table_index)
@@ -547,7 +543,7 @@ impl Instance {
         // TODO(#983): investigate replacing this get/set loop with a `memcpy`.
         for (dst, src) in (dst..dst + len).zip(src..src + len) {
             table
-                .set(dst, elem[src as usize].clone())
+                .set(dst, TableElement::FuncRef(elem[src as usize].clone()))
                 .expect("should never panic because we already did the bounds check above");
         }
 
@@ -993,11 +989,7 @@ impl InstanceHandle {
     /// Get table element reference.
     ///
     /// Returns `None` if index is out of bounds.
-    pub fn table_get(
-        &self,
-        table_index: DefinedTableIndex,
-        index: u32,
-    ) -> Option<VMCallerCheckedAnyfunc> {
+    pub fn table_get(&self, table_index: DefinedTableIndex, index: u32) -> Option<TableElement> {
         self.instance().table_get(table_index, index)
     }
 
@@ -1008,7 +1000,7 @@ impl InstanceHandle {
         &self,
         table_index: DefinedTableIndex,
         index: u32,
-        val: VMCallerCheckedAnyfunc,
+        val: TableElement,
     ) -> Result<(), ()> {
         self.instance().table_set(table_index, index, val)
     }
@@ -1174,7 +1166,10 @@ fn initialize_tables(instance: &Instance) -> Result<(), InstantiationError> {
         for (i, func_idx) in init.elements.iter().enumerate() {
             let anyfunc = instance.get_caller_checked_anyfunc(*func_idx);
             table
-                .set(u32::try_from(start + i).unwrap(), anyfunc)
+                .set(
+                    u32::try_from(start + i).unwrap(),
+                    TableElement::FuncRef(anyfunc),
+                )
                 .unwrap();
         }
     }