Give better warning for incomplete erlang install (#434)

Author: axelson

apps/language_server/lib/language_server/cli.ex

@@ -6,7 +6,8 @@ defmodule ElixirLS.LanguageServer.CLI do
     WireProtocol.intercept_output(&JsonRpc.print/1, &JsonRpc.print_err/1)
     Launch.start_mix()
 
-    {:ok, _} = Application.ensure_all_started(:language_server, :temporary)
+    start_language_server()
+
     IO.puts("Started ElixirLS v#{Launch.language_server_version()}")
     Launch.print_versions()
 
@@ -16,4 +17,26 @@ defmodule ElixirLS.LanguageServer.CLI do
 
     WireProtocol.stream_packets(&JsonRpc.receive_packet/1)
   end
+
+  defp start_language_server do
+    guide =
+      "https://github.com/elixir-lsp/elixir-ls/blob/master/guides/incomplete-installation.md"
+
+    case Application.ensure_all_started(:language_server, :temporary) do
+      {:ok, _} ->
+        :ok
+
+      {:error, {:edoc, {'no such file or directory', 'edoc.app'}}} ->
+        raise "Unable to start ElixirLS due to an incomplete erlang installation. " <>
+                "See #{guide}#edoc-missing for guidance."
+
+      {:error, {:dialyzer, {'no such file or directory', 'dialyzer.app'}}} ->
+        raise "Unable to start ElixirLS due to an incomplete erlang installation. " <>
+                "See #{guide}#dialyzer-missing for guidance."
+
+      {:error, _} ->
+        raise "Unable to start ElixirLS due to an incomplete erlang installation. " <>
+                "See #{guide} for guidance."
+    end
+  end
 end

guides/incomplete-installation.md

@@ -0,0 +1,23 @@
+Incomplete installations is a frequent cause of ElixirLS failures. Generally
+this is resolved by:
+* Installing elixir and erlang with ASDF https://github.com/asdf-vm/asdf
+  (recommended)
+* Installing a full version of Erlang via the package manager
+
+## dialyzer missing
+
+On Ubuntu this is caused by the required `erlang-dialyzer` package not being
+installed. For Ubuntu this can be fixed by running `sudo apt-get install erlang
+erlang-dialyzer` or installing Elixir and Erlang via ASDF
+https://github.com/asdf-vm/asdf
+
+Relevant issue: https://github.com/elixir-lsp/vscode-elixir-ls/issues/134
+
+## edoc missing
+
+On fedora this is caused by the required `erlang-edoc `package not being
+installed. For fedora this can be fixed by running `sudo dnf install erlang
+erlang-edoc` or installing Elixir and Erlang via ASDF
+https://github.com/asdf-vm/asdf
+
+Relevant issue: https://github.com/elixir-lsp/elixir-ls/issues/431