Add support for custom Docker registries

Allows the entire process to run without needing to push to Docker hub
(which allows the process to run without needing any real secrets)

Author: dra27

src/conf.ml

@@ -1,3 +1,7 @@
+(* Use None for the main Docker Registry.
+   Do NOT set this to Some "docker.io" *)
+let registry = Some "localhost:5000"
+
 (* For staging arch-specific builds before creating the manifest. *)
 let staging_repo = "ocurrent/opam-staging"
 
@@ -21,7 +25,8 @@ let auth =
     close_in ch;
     Some ("ocurrent", password)
   ) else (
-    Fmt.pr "Password file %S not found; images will not be pushed to hub@." password_path;
+    if registry = None then
+      Fmt.pr "Password file %S not found; images will not be pushed to hub@." password_path;
     None
   )
 

src/tag.ml

@@ -1,3 +1,8 @@
+let public_repo, staging_repo =
+  match Conf.registry with
+  | None -> Conf.public_repo, Conf.staging_repo
+  | Some registry -> registry ^ "/" ^ Conf.public_repo, registry ^ "/" ^ Conf.staging_repo
+
 let pp_arch f = function
   | None -> ()
   | Some arch -> Fmt.pf f "-%s" (Ocaml_version.string_of_arch arch)
@@ -10,7 +15,7 @@ let tag_of_compiler switch =
     )
 
 let v ?arch ?switch distro =
-  let repo = if arch = None then Conf.public_repo else Conf.staging_repo in
+  let repo = if arch = None then public_repo else staging_repo in
   let distro = Dockerfile_distro.tag_of_distro distro in
   let switch =
     match switch with
@@ -24,7 +29,7 @@ let v_alias alias =
     if alias = `Debian `Stable then "debian"
     else Dockerfile_distro.tag_of_distro alias
   in
-  Fmt.strf "%s:%s" Conf.public_repo alias
+  Fmt.strf "%s:%s" public_repo alias
 
 let latest =
-  Fmt.strf "%s:latest" Conf.public_repo
+  Fmt.strf "%s:latest" public_repo