Use gpatch on openBSD

src/client/opamInitDefaults.ml

@@ -32,11 +32,14 @@ let eval_variables = [
   "OCaml version present on your system independently of opam, if any";
 ]
 
-let os_filter os =
-  FOp (FIdent ([], OpamVariable.of_string "os", None), `Eq, FString os)
+let os_filter ?(not=false) os =
+  let op = if not then `Neq else `Eq in
+  FOp (FIdent ([], OpamVariable.of_string "os", None), op, FString os)
 
 let linux_filter = os_filter "linux"
 let macos_filter = os_filter "macos"
+let openbsd_filter = os_filter "openbsd"
+let not_openbsd_filter = os_filter ~not:true "openbsd"
 let sandbox_filter = FOr (linux_filter, macos_filter)
 
 let wrappers ~sandboxing () =
@@ -95,7 +98,8 @@ let required_tools ~sandboxing () =
     Some "A download tool is required, check env variables OPAMCURL or OPAMFETCH",
     None;
     ["diff"], None, None;
-    ["patch"], None, None;
+    ["patch"], None, Some not_openbsd_filter;
+    ["gpatch"], None, Some openbsd_filter;
     ["tar"], None, None;
     ["unzip"], None, None;
   ] @

src/core/opamSystem.ml

@@ -1137,7 +1137,12 @@ let patch ?(preprocess=true) ~dir p =
     else
       p
   in
-  make_command ~name:"patch" ~dir "patch" ["-p1"; "-i"; p'] @@> fun r ->
+  let patch_cmd =
+    match OpamStd.Sys.os () with
+    | OpamStd.Sys.OpenBSD -> "gpatch"
+    | _ -> "patch"
+  in
+  make_command ~name:"patch" ~dir patch_cmd ["-p1"; "-i"; p'] @@> fun r ->
     if not (OpamConsole.debug ()) then Sys.remove p';
     if OpamProcess.is_success r then Done None
     else Done (Some (Process_error r))