error instead of panic on wit parse failures

lib/wasmex/components/component.ex

@@ -33,7 +33,7 @@ defmodule Wasmex.Components.Component do
   end
 
   defmacro __using__(opts) do
-    genserver_stuff =
+    genserver_setup =
       quote do
         use GenServer
 
@@ -65,6 +65,6 @@ defmodule Wasmex.Components.Component do
         []
       end
 
-    [genserver_stuff, functions]
+    [genserver_setup, functions]
   end
 end

lib/wasmex/native.ex

@@ -93,7 +93,7 @@ defmodule Wasmex.Native do
 
   def component_call_function(_store, _instance, _function_name, _params), do: error()
 
-  def wit_exported_functions(path, wit), do: error()
+  def wit_exported_functions(_path, _wit), do: error()
 
   # When the NIF is loaded, it will override functions in this module.
   # Calling error is handles the case when the nif could not be loaded.

native/wasmex/src/wit.rs

@@ -4,8 +4,10 @@ use wit_parser::{Resolve, WorldItem};
 #[rustler::nif(name = "wit_exported_functions")]
 pub fn exported_functions(env: rustler::Env, path: String, wit: String) -> NifResult<Term> {
     let mut resolve = Resolve::new();
-    let id = resolve.push_str(path, &wit).unwrap();
-    let world_id = resolve.select_world(id, None).unwrap();
+    let id = resolve.push_str(path, &wit)
+        .map_err(|e| rustler::Error::Term(Box::new(format!("Failed to parse WIT: {}", e))))?;
+    let world_id = resolve.select_world(id, None)
+        .map_err(|e| rustler::Error::Term(Box::new(format!("Failed to select world: {}", e))))?;
     let exports = &resolve.worlds[world_id].exports;
     let exported_functions = exports
         .iter()

test/components/wit_parser_test.exs

@@ -1,10 +1,19 @@
 defmodule Components.WitParserTest do
   use ExUnit.Case
 
-  test "exported_functions" do
-    wit = File.read!("test/component_fixtures/hello_world/hello-world.wit")
+  describe "exports" do
+    test "exported_functions" do
+      wit = File.read!("test/component_fixtures/hello_world/hello-world.wit")
 
-    assert %{"greet" => 1, "greet-many" => 1, "multi-greet" => 2} =
-             Wasmex.Native.wit_exported_functions("hello-world.wit", wit)
+      assert %{"greet" => 1, "greet-many" => 1, "multi-greet" => 2} =
+                Wasmex.Native.wit_exported_functions("hello-world.wit", wit)
+    end
+
+    test "wit parse errors" do
+      wit = "goo goo"
+      assert {:error, error} = Wasmex.Native.wit_exported_functions("hello-world.wit", wit)
+      assert error =~ "Failed to parse WIT"
+    end
   end
+
 end