correctly delete preprocessor output after usage

Author: jboillot

CHANGES.md

@@ -7,6 +7,7 @@ unreleased
     - Add `-unboxed-types` and `-no-unboxed-types` as ocaml ignored flags (#1795, fixes #1794)
   + editor modes
     - vim: fix python-3.12 syntax warnings in merlin.py (#1798)
+    - Fix merlinpp not removing temporary files (#1801, partly fixes #1802)
 
 merlin 5.1
 ==========

src/ocaml/driver/pparse.ml

@@ -180,6 +180,7 @@ let apply_pp ~workdir ~filename ~source ~pp =
     let ic = open_in_bin fn_out in
     let result = Misc.string_of_file ic in
     close_in ic;
+    Misc.remove_file fn_out;
     Ok result
 
 let decode_potential_ast source =