refactor: use Task.async_stream in parallel compiler (#63)

lib/fika/compiler/type_checker/parallel_type_checker.ex

@@ -52,11 +52,21 @@ defmodule Fika.Compiler.TypeChecker.ParallelTypeChecker do
   def handle_continue(:start, state) do
     pid = self()
 
-    Enum.each(state.unchecked_functions, fn {signature, function} ->
-      Task.start_link(fn ->
+    state.unchecked_functions
+    |> Task.async_stream(
+      fn {signature, function} ->
         result = TypeChecker.check(function, %{type_checker_pid: pid})
         __MODULE__.post_result(pid, signature, result)
-      end)
+      end,
+      max_concurrency: Enum.count(state.unchecked_functions)
+    )
+    |> Enum.each(fn
+      {:ok, _} ->
+        :ok
+
+      error ->
+        Logger.error("Error while running ParallelTypeChecker: #{inspect(error)}")
+        raise CompileError, description: "failed to run ParallelTypeChecker"
     end)
 
     {:noreply, state}

test/fika/compiler/module_compiler_test.exs

@@ -24,6 +24,33 @@ defmodule Fika.Compiler.ModuleCompilerTest do
     File.rm!(temp_file)
   end
 
+  test "can compile a file with many functions" do
+    tmp_dir = System.tmp_dir!()
+    temp_file = Path.join(tmp_dir, "foo.fi")
+
+    # Show that we're not limited to the number of online schedulers
+    n = System.schedulers_online() * 2
+
+    str =
+      1..n
+      |> Enum.map(fn number ->
+        """
+        fn foo_#{number} : String do
+          "Hello world"
+        end
+        """
+      end)
+      |> Enum.join("\n")
+
+    File.write!(temp_file, str)
+
+    File.cd!(tmp_dir, fn ->
+      assert {:ok, "foo", "foo.fi", _binary} = ModuleCompiler.compile("foo")
+    end)
+
+    File.rm!(temp_file)
+  end
+
   test "returns error when file doesn't exist" do
     module = Path.join(System.tmp_dir!(), "foo") |> String.to_atom()