fix dialyzer errors

Author: lukaszsamson

.dialyzer_ignore.exs

@@ -1,3 +1,4 @@
 [
-  {"lib/language_server/providers/execute_command/restart.ex", :no_return}
+  {"lib/language_server/providers/execute_command/restart.ex", :no_return},
+  {"lib/language_server/experimental/protocol/proto.ex", :no_return}
 ]

apps/language_server/lib/language_server/experimental/source_file.ex

@@ -238,12 +238,6 @@ defmodule ElixirLS.LanguageServer.Experimental.SourceFile do
   end
 
   defp increment_version(%__MODULE__{} = source) do
-    version =
-      case source.version do
-        v when is_integer(v) -> v + 1
-        _ -> 1
-      end
-
-    %__MODULE__{source | version: version}
+    %__MODULE__{source | version: source.version + 1}
   end
 end

apps/language_server/lib/language_server/experimental/source_file/store.ex

@@ -9,15 +9,15 @@ defmodule ElixirLS.LanguageServer.Experimental.SourceFile.Store do
       %__MODULE__{}
     end
 
-    @spec fetch(t, Store.uri()) :: SourceFile.t()
+    @spec fetch(t, Store.uri()) :: {:ok, SourceFile.t()} | {:error, :not_open}
     def fetch(%__MODULE__{} = store, uri) do
       case Map.fetch(store.source_files, uri) do
         :error -> {:error, :not_open}
         success -> success
       end
     end
 
-    @spec save(t, Store.uri()) :: t()
+    @spec save(t, Store.uri()) :: {:ok, t()} | {:error, :not_open}
     def save(%__MODULE__{} = store, uri) do
       case Map.fetch(store.source_files, uri) do
         {:ok, source_file} ->