expose wasmtime_linker_define_func for Linker class (#16)

Author: dshiell15

include/wasmtime.hh

@@ -843,6 +843,7 @@ public:
  */
 class FuncType {
   friend class Func;
+  friend class Linker;
 
   struct deleter {
     void operator()(wasm_functype_t *p) const { wasm_functype_delete(p); }
@@ -2067,6 +2068,7 @@ inline Store::Context::Context(Caller *caller) : Context(*caller) {}
 class Func {
   friend class Val;
   friend class Instance;
+  friend class Linker;
 
   wasmtime_func_t func;
 
@@ -2684,6 +2686,24 @@ public:
     return std::nullopt;
   }
 
+  /// Defines a new function in this linker
+  template <typename F>
+  [[nodiscard]] Result<std::monostate> define_func(std::string_view module,
+                                                   std::string_view name,
+                                                   const FuncType &ty, F f) {
+
+    auto *error = wasmtime_linker_define_func(
+        ptr.get(), module.data(), module.length(), name.data(), name.length(),
+        ty.ptr.get(), Func::raw_callback<F>, std::make_unique<F>(f).release(),
+        Func::raw_finalize<F>);
+
+    if (error != nullptr) {
+      return Error(error);
+    }
+
+    return std::monostate();
+  }
+
   /// Loads the "default" function, according to WASI commands and reactors, of
   /// the module named `name` in this linker.
   [[nodiscard]] Result<Func> get_default(Store::Context cx,

tests/simple.cc

@@ -294,14 +294,20 @@ TEST(Linker, Smoke) {
   Global g = unwrap(Global::create(store, GlobalType(ValKind::I32, false), 1));
   unwrap(linker.define("a", "g", g));
   unwrap(linker.define_wasi());
-
+  unwrap(linker.define_func(
+      "a", "f", FuncType({}, {}),
+      [](auto caller, auto params, auto results) -> auto {
+        return std::monostate();
+      }));
   Module mod = unwrap(Module::compile(engine, "(module)"));
   Instance i = unwrap(Instance::create(store, mod, {}));
   unwrap(linker.define_instance(store, "x", i));
   unwrap(linker.instantiate(store, mod));
   unwrap(linker.module(store, "y", mod));
   EXPECT_TRUE(linker.get(store, "a", "g"));
   unwrap(linker.get_default(store, "g"));
+  EXPECT_TRUE(linker.get(store, "a", "f"));
+  EXPECT_TRUE(std::holds_alternative<Func>(*linker.get(store, "a", "f")));
 }
 
 TEST(Caller, Smoke) {