Fixed type spec

The AST type is very complicated, and dialyzer was telling us I got it wrong.

Author: scohen

apps/language_server/lib/language_server/experimental/code_mod/ast.ex

@@ -1,6 +1,7 @@
 defmodule ElixirLS.LanguageServer.Experimental.CodeMod.Ast do
   alias ElixirLS.LanguageServer.Experimental.SourceFile
-  @opaque t :: tuple()
+
+  @type t :: any()
 
   def from(%SourceFile{} = source_file) do
     source_file

apps/language_server/lib/language_server/experimental/code_mod/replace_with_underscore.ex

@@ -3,7 +3,7 @@ defmodule ElixirLS.LanguageServer.Experimental.CodeMod.ReplaceWithUnderscore do
   alias ElixirLS.LanguageServer.Experimental.CodeMod.Ast
   alias ElixirLS.LanguageServer.Experimental.CodeMod.Diff
 
-  @spec text_edits(String.t(), Ast.t(), String.t() | atom) :: {:ok, [TextEdit.t()]}
+  @spec text_edits(String.t(), Ast.t(), String.t() | atom) :: {:ok, [TextEdit.t()]} | :error
   def text_edits(original_text, ast, variable_name) do
     variable_name = ensure_atom(variable_name)