feat: Implement Wat2Wasm.

It depends on wasmerio/wasmer#1635. The
`include/` and `wasmer_wasm.h` files are already from this PR.

wasmer/wasmer_wasm.h

@@ -142,4 +142,8 @@ int wasmer_last_error_length();
  */
 int wasmer_last_error_message(char* buffer, int length);
 
+// Parses in-memory bytes as either the WAT format, or a binary Wasm
+// module. This is wasmer-specific.
+void wat2wasm(wasm_byte_vec_t* wat, wasm_byte_vec_t* wasm);
+
 #endif /* WASMER_WASM_H */

wasmer/wat.go

@@ -0,0 +1,40 @@
+package wasmer
+
+// #include <wasmer_wasm.h>
+//
+// void to_wat2wasm(uint8_t *wat_data, size_t wat_length, wasm_byte_vec_t *wasm) {
+//     wasm_byte_vec_t wat;
+//     wat.size = wat_length;
+//     wat.data = (wasm_byte_t*) wat_data;
+//
+//     wat2wasm(&wat, wasm);
+// }
+import "C"
+import (
+	"runtime"
+	"unsafe"
+)
+
+func Wat2Wasm(wat string) ([]byte, error) {
+	watAsBytes := []byte(wat)
+	var watPtr *C.uint8_t
+	var watLength = len(wat)
+
+	if watLength > 0 {
+		watPtr = (*C.uint8_t)(unsafe.Pointer(&watAsBytes[0]))
+	}
+
+	wasm := C.wasm_byte_vec_t{}
+
+	C.to_wat2wasm(watPtr, C.size_t(watLength), &wasm)
+	runtime.KeepAlive(wat)
+
+	if wasm.data == nil {
+		return nil, newErrorFromWasmer()
+	}
+
+	wasmBytes := C.GoBytes(unsafe.Pointer(wasm.data), C.int(wasm.size))
+	C.wasm_byte_vec_delete(&wasm)
+
+	return wasmBytes, nil
+}

wasmer/wat_test.go

@@ -0,0 +1,26 @@
+package wasmer
+
+import (
+	"github.com/stretchr/testify/assert"
+	"testing"
+)
+
+func TestWat2Wasm(t *testing.T) {
+	wasm, err := Wat2Wasm("(module)")
+
+	assert.NoError(t, err)
+	assert.Equal(t, wasm, []byte("\x00asm\x01\x00\x00\x00"))
+}
+
+func TestWasm2Wasm(t *testing.T) {
+	wasm, err := Wat2Wasm(string([]byte("\x00asm\x01\x00\x00\x00")))
+
+	assert.NoError(t, err)
+	assert.Equal(t, wasm, []byte("\x00asm\x01\x00\x00\x00"))
+}
+
+func TestBadWat2Wasm(t *testing.T) {
+	_, err := Wat2Wasm("(module")
+
+	assert.EqualError(t, err, "expected `)`\n     --> <anon>:1:8\n      |\n    1 | (module\n      |        ^")
+}