pkg: dedup package names in dependencies (#10544)

Fixes a bug where depending on a package with a constraint involving a
conjunction would lead to the package appearing in the "depends"
lockfile field multiple times.

Signed-off-by: Stephen Sherratt <stephen@sherra.tt>

src/dune_pkg/resolve_opam_formula.ml

@@ -79,6 +79,19 @@ end
 type unsatisfied_formula =
   [ `Formula_could_not_be_satisfied of Unsatisfied_formula_hint.t list ]
 
+let dedup_package_names package_names =
+  let ret_reversed, _ =
+    List.fold_left
+      package_names
+      ~init:([], Package_name.Set.empty)
+      ~f:(fun (ret_reversed, seen) x ->
+        if Package_name.Set.mem seen x
+        then ret_reversed, seen
+        else x :: ret_reversed, Package_name.Set.add seen x)
+  in
+  List.rev ret_reversed
+;;
+
 let formula_to_package_names version_by_package_name opam_formula =
   let check_conjunction conjunction =
     Result.List.map conjunction ~f:(fun (opam_package_name, version_constraint_opt) ->
@@ -129,9 +142,16 @@ let formula_to_package_names version_by_package_name opam_formula =
   match satisfied_or_error_hint_per_conjunction with
   | Error hints -> Error (`Formula_could_not_be_satisfied hints)
   | Ok satisfied_conjunction ->
-    Ok
-      (List.map satisfied_conjunction ~f:(fun (opam_package_name, _) ->
-         Package_name.of_opam_package_name opam_package_name))
+    let package_names_from_conjunctions =
+      List.map satisfied_conjunction ~f:(fun (opam_package_name, _) ->
+        Package_name.of_opam_package_name opam_package_name)
+    in
+    let package_names =
+      (* If a package name appeared in multiple conjunctions then it
+         will be duplicated in [package_names_from_conjunctions]. *)
+      dedup_package_names package_names_from_conjunctions
+    in
+    Ok package_names
 ;;
 
 let filtered_formula_to_package_names env ~with_test version_by_package_name formula =

test/blackbox-tests/test-cases/pkg/constraint-conjunction.t

@@ -17,9 +17,7 @@ constraints.
   - a.0.0.1
   - foo.0.0.1
 
-Note that this is currently incorrect as the package "a" is duplicated
-in the "depends" field.
   $ cat dune.lock/foo.pkg
   (version 0.0.1)
   
-  (depends a a)
+  (depends a)