feat!: add CLI flag handling (#185)

Author: andyleclair

apps/expert/lib/expert/application.ex

@@ -12,13 +12,65 @@ defmodule Expert.Application do
 
   @impl true
   def start(_type, _args) do
+    {opts, _argv, _invalid} =
+      OptionParser.parse(Burrito.Util.Args.argv(),
+        strict: [version: :boolean, help: :boolean, stdio: :boolean, port: :integer]
+      )
+
+    help_text = """
+    Expert v#{Expert.vsn()}
+
+    The official language server for Elixir
+
+      Home page: https://expert-lsp.org
+    Source code: https://github.com/elixir-lang/expert
+
+    expert [flags]
+
+    #{IO.ANSI.bright()}FLAGS#{IO.ANSI.reset()}
+
+      --stdio             Use stdio as the transport mechanism
+      --port <port>       Use TCP as the transport mechanism, with the given port
+      --help              Show this help message
+      --version           Show Expert version
+    """
+
+    cond do
+      opts[:help] ->
+        IO.puts(help_text)
+
+        System.halt(0)
+
+      opts[:version] ->
+        IO.puts("#{Expert.vsn()}")
+        System.halt(0)
+
+      true ->
+        :noop
+    end
+
+    buffer_opts =
+      cond do
+        opts[:stdio] ->
+          []
+
+        is_integer(opts[:port]) ->
+          IO.puts("Starting on port #{opts[:port]}")
+          [communication: {GenLSP.Communication.TCP, [port: opts[:port]]}]
+
+        true ->
+          IO.puts(help_text)
+
+          System.halt(1)
+      end
+
     children = [
       document_store_child_spec(),
       {DynamicSupervisor, Expert.Project.DynamicSupervisor.options()},
       {DynamicSupervisor, name: Expert.DynamicSupervisor},
       {GenLSP.Assigns, [name: Expert.Assigns]},
       {Task.Supervisor, name: :expert_task_queue},
-      {GenLSP.Buffer, name: Expert.Buffer},
+      {GenLSP.Buffer, [name: Expert.Buffer] ++ buffer_opts},
       {Expert,
        name: Expert,
        buffer: Expert.Buffer,