Do not overwrite values from template

If a value is set in the template, we do not overwrite it in the dune
file.

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

src/opam_create.ml

@@ -13,6 +13,7 @@ let correct_specific
       ; opam = _
       } =
   let open Opam_file.Mutator in
+  let open Opam_file.Mutator.No_overwrite in
   (opt synopsis) (set_string "synopsis") >>>
   (opt description) (set_string "description") >>>
   list depends
@@ -24,6 +25,7 @@ let correct_specific
 
 let correct project (package : Package.t) =
   let open Opam_file.Mutator in
+  let open Opam_file.Mutator.No_overwrite in
   correct_specific package >>>
   opt (Dune_project.maintainer project) (set_string "maintainer") >>>
   opt (Dune_project.bug_reports project) (set_string "bug-reports") >>>
@@ -89,6 +91,7 @@ let add_rule sctx ~project ~pkg =
   let aliases =
     [ Alias.install ~dir
     ; Alias.runtest ~dir
+    ; Alias.check ~dir (* check doesn't pick up the promote target? *)
     ]
   in
   let deps = Path.Set.singleton opam_path in

src/opam_file.ml

@@ -108,9 +108,9 @@ module Mutator = struct
   let remap x f =
     List.filter_map ~f:(function
       | Variable (_, v, y) when v = x -> begin
-        match f (Some y) with
-        | Some y' -> Some (Variable (nopos, v, y'))
-        | None -> None
+          match f (Some y) with
+          | Some y' -> Some (Variable (nopos, v, y'))
+          | None -> None
         end
       | z -> Some z)
 
@@ -136,9 +136,22 @@ module Mutator = struct
   let mkstring x = String (nopos, x)
   let mklist f xs = List (nopos, List.map ~f xs)
 
-  let set_string x y = set_var x (mkstring y)
+  module Make_set(Set_var : sig
+      val set_var : string -> value -> t
+    end) = struct
+    open Set_var
+    let set_string x y = set_var x (mkstring y)
+    let set_list x conv l = set_var x (mklist conv l)
+  end
+  include Make_set(struct let set_var = set_var end)
+
+  module No_overwrite = Make_set(struct
+      let set_var x y zs =
+        if binding_present x zs
+        then zs
+        else add_var x y zs
+    end)
 
-  let set_list x conv l = set_var x (mklist conv l)
   let id x = x
 
   let opt opt f : t = match opt with | None -> id | Some x -> f x

src/opam_file.mli

@@ -57,6 +57,12 @@ module Mutator : sig
       file it is inserted at the top of the file. *)
   val set_list : string -> ('a -> value) -> 'a list -> t
 
+  module No_overwrite : sig
+    (** Same functions but will not modify existing keys *)
+    val set_string : string -> string -> t
+    val set_list : string -> ('a -> value) -> 'a list -> t
+  end
+
   (** [opt v f] returns an identity transformer if [v] is None and if it is
       [Some x] applies [f] to [x] to return a transformer. Useful for
       constructing a mutator that is only applied if an optional value has been