guix: ocaml: Also replace dune when relevant in package-with-explicit-ocaml.

* guix/build-system/ocaml.scm (package-with-explicit-ocaml): Take a dune
argument and add it to transformed packages when relevant.

guix/build-system/ocaml.scm

@@ -92,7 +92,11 @@
   (let ((module (resolve-interface '(gnu packages ocaml))))
     (module-ref module 'ocaml4.07-findlib)))
 
-(define* (package-with-explicit-ocaml ocaml findlib old-prefix new-prefix
+(define (default-ocaml4.07-dune)
+  (let ((module (resolve-interface '(gnu packages ocaml))))
+    (module-ref module 'ocaml4.07-dune)))
+
+(define* (package-with-explicit-ocaml ocaml findlib dune old-prefix new-prefix
                                        #:key variant-property)
   "Return a procedure of one argument, P.  The procedure creates a package
 with the same fields as P, which is assumed to use OCAML-BUILD-SYSTEM, such
@@ -100,6 +104,10 @@ that it is compiled with OCAML and FINDLIB instead.  The inputs are changed
 recursively accordingly.  If the name of P starts with OLD-PREFIX, this is
 replaced by NEW-PREFIX; otherwise, NEW-PREFIX is prepended to the name.
 
+When the package uses the DUNE-BUILD-SYSTEM, the procedure creates a package
+with the same fields as P, such that it is compiled with OCAML, FINDLIB and DUNE
+instead.
+
 When VARIANT-PROPERTY is present, it is used as a key to search for
 pre-defined variants of this transformation recorded in the 'properties' field
 of packages.  The property value must be the promise of a package.  This is a
@@ -132,10 +140,15 @@ pre-defined variants."
                                    name))))
         (arguments
          (let ((ocaml   (if (promise? ocaml) (force ocaml) ocaml))
-               (findlib (if (promise? findlib) (force findlib) findlib)))
+               (findlib (if (promise? findlib) (force findlib) findlib))
+               (dune (if (promise? dune) (force dune) dune)))
            (ensure-keyword-arguments (package-arguments p)
                                      `(#:ocaml   ,ocaml
-                                       #:findlib ,findlib))))))
+                                       #:findlib ,findlib
+                                       ,@(if (eq? (package-build-system p)
+                                                  (default-dune-build-system))
+                                             `(#:dune ,dune)
+                                             '())))))))
      (else p)))
 
   (define (cut? p)
@@ -148,6 +161,7 @@ pre-defined variants."
 (define package-with-ocaml4.07
   (package-with-explicit-ocaml (delay (default-ocaml4.07))
                                (delay (default-ocaml4.07-findlib))
+                               (delay (default-ocaml4.07-dune))
                                "ocaml-" "ocaml4.07-"
                                #:variant-property 'ocaml4.07-variant))