Do a runtime check for Macro.classify_atom/1 (#294)

Author: zachallaun

lib/elixir_sense/providers/completion/completion_engine.ex

@@ -850,19 +850,18 @@ defmodule ElixirSense.Providers.Completion.CompletionEngine do
 
   ## Helpers
 
-  # Version.match? is slow, we need to avoid it in a hot loop
-  if Version.match?(System.version(), ">= 1.14.0-dev") do
-    defp usable_as_unquoted_module?(name) do
-      # Conversion to atom is not a problem because
-      # it is only called with existing modules names.
-      # credo:disable-for-lines:7
-      Macro.classify_atom(String.to_atom(name)) in [:identifier, :unquoted] and
-        not String.starts_with?(name, "Elixir.")
-    end
-  else
-    defp usable_as_unquoted_module?(name) do
-      Code.Identifier.classify(String.to_atom(name)) != :other and
-        not String.starts_with?(name, "Elixir.")
+  defp usable_as_unquoted_module?(name) do
+    unquoted_atom_or_identifier?(String.to_atom(name)) and
+      not String.starts_with?(name, "Elixir.")
+  end
+
+  defp unquoted_atom_or_identifier?(atom) when is_atom(atom) do
+    # Macro.classify_atom/1 was introduced in 1.14.0. If it's not available,
+    # assume we're on an older version and fall back to a private API.
+    if function_exported?(Macro, :classify_atom, 1) do
+      apply(Macro, :classify_atom, [atom]) in [:identifier, :unquoted]
+    else
+      apply(Code.Identifier, :classify, [atom]) != :other
     end
   end