Do not require prefix in configure when lib and mandir have been set (#…

…497)

configure.ml

@@ -111,12 +111,17 @@ let opam_var v =
 
 (* Compute actual values for config options *)
 let () =
-  let prefix_set = !prefix <> "" in
-  update "prefix" prefix (fun () -> opam_var "prefix");
-  update "libdir" libdir (fun () ->
-      if prefix_set then Filename.concat !prefix "lib" else opam_var "lib");
-  update "mandir" mandir (fun () ->
-      if prefix_set then Filename.concat !prefix "man" else opam_var "man");
+  if !prefix <> "" then begin
+    update "libdir" libdir (fun () -> Filename.concat !prefix "lib");
+    update "mandir" mandir (fun () -> Filename.concat !prefix "man");
+    ()
+  end else begin
+    update "libdir" libdir (fun () -> opam_var "lib");
+    update "mandir" mandir (fun () -> opam_var "man");
+    ()
+  end;
+  assert (!libdir <> "");
+  assert (!mandir <> "");
   ()
 
 (* Output config options into lib/util/config.ml *)
@@ -185,7 +190,6 @@ let () =
   let ch = open_out "Makefile.config" in
   let fmt = Format.formatter_of_out_channel ch in
   let () = Format.fprintf fmt "# Generated by configure@." in
-  let () = Format.fprintf fmt "prefix=%s@." !prefix in
   let () = Format.fprintf fmt "libdir=%s@." !libdir in
   let () = Format.fprintf fmt "mandir=%s@." !mandir in
   let () = close_out ch in