Fix bug exposed by previous commit

CHANGES.md

@@ -43,6 +43,9 @@ next
 - Add an `ignored_subdirs` stanza to replace `jbuild-ignore` files
   (#767, @diml)
 
+- Fix a bug where Dune ignored previous occurences of duplicated
+  fields (#779, @diml)
+
 1.0+beta20 (10/04/2018)
 -----------------------
 

src/stdune/sexp.ml

@@ -273,6 +273,8 @@ module Of_sexp = struct
           | List (_, name_sexp :: values) -> begin
               match name_sexp with
               | Atom (_, A name) ->
+                if Name_map.mem acc name then
+                  of_sexp_errorf sexp "Field %S is present too many times" name;
                 Name_map.add acc name { values; entry = sexp }
               | List _ | Quoted_string _ ->
                 of_sexp_error name_sexp "Atom expected"

test/unit-tests/sexp.mlt

@@ -27,5 +27,7 @@ let of_sexp = record (field "foo" int)
 let x = of_sexp sexp
 [%%expect{|
 val of_sexp : int Stdune.Sexp.Of_sexp.t = <fun>
-val x : int = 2
+Exception:
+Stdune__Sexp.Of_sexp.Of_sexp (<abstr>,
+ "Field \"foo\" is present too many times", None).
 |}]