Explicitly request file watchers from client (#35)

* Add explicit file watcher request

It is recommended that servers register for the capability to watch
files. Notably, in emacs, clients such as lsp-mode will act
conservatively and not send file change notifications without the added
message.

Added a generic capability registration request and specify file
watchers after initialization.

* Mix format

* Add workspace capabilities, conditionally send file watcher message

apps/language_server/lib/language_server/json_rpc.ex

@@ -77,6 +77,18 @@ defmodule ElixirLS.LanguageServer.JsonRpc do
     notify("window/logMessage", %{type: message_type_code(type), message: to_string(message)})
   end
 
+  def register_capability_request(server \\ __MODULE__, method, options) do
+    send_request(server, "client/registerCapability", %{
+      "registrations" => [
+        %{
+          "id" => :crypto.hash(:sha, method) |> Base.encode16(),
+          "method" => method,
+          "registerOptions" => options
+        }
+      ]
+    })
+  end
+
   def show_message_request(server \\ __MODULE__, type, message, actions) do
     send_request(server, "window/showMessageRequest", %{
       "type" => message_type_code(type),

apps/language_server/lib/language_server/server.ex

@@ -153,6 +153,17 @@ defmodule ElixirLS.LanguageServer.Server do
     super(msg, state)
   end
 
+  def handle_info(:send_file_watchers, state) do
+    JsonRpc.register_capability_request("workspace/didChangeWatchedFiles", %{
+      "watchers" => [
+        %{"globPattern" => "**/*.ex"},
+        %{"globPattern" => "**/*.exs"}
+      ]
+    })
+
+    {:noreply, state}
+  end
+
   def handle_info(:default_config, state) do
     state =
       case state do
@@ -322,6 +333,16 @@ defmodule ElixirLS.LanguageServer.Server do
     # If we don't receive workspace/didChangeConfiguration for 5 seconds, use default settings
     Process.send_after(self(), :default_config, 5000)
 
+    # Explicitly request file watchers from the client if supported
+    supports_dynamic = get_in(client_capabilities, [
+          "textDocument",
+          "codeAction",
+          "dynamicRegistration"
+        ])
+    if supports_dynamic do
+      Process.send_after(self(), :send_file_watchers, 100)
+    end
+
     {:ok, %{"capabilities" => server_capabilities()}, state}
   end
 
@@ -445,7 +466,8 @@ defmodule ElixirLS.LanguageServer.Server do
       "documentSymbolProvider" => true,
       "documentOnTypeFormattingProvider" => %{"firstTriggerCharacter" => "\n"},
       "codeLensProvider" => %{"resolveProvider" => false},
-      "executeCommandProvider" => %{"commands" => ["spec"]}
+      "executeCommandProvider" => %{"commands" => ["spec"]},
+      "workspace" => %{ "workspaceFolders" => %{"supported" => true, "changeNotifications" => true}}
     }
   end