Put alias files in a dedicated directory

src/alias.ml

@@ -2,8 +2,14 @@ open! Import
 
 type t = Path.t
 
+let aliases_path = Path.(relative root) "_build/.aliases"
+
 let make name ~dir =
-  Path.relative dir (".jbuild-alias-" ^ name)
+  if not (Path.is_local dir) then
+    die "Aliases are only supported for local paths!\n\
+         Tried to reference alias %S in %s"
+      name (Path.to_string dir);
+  Path.append aliases_path (Path.relative dir name)
 
 let dep = Build.path
 

src/gen_rules.ml

@@ -1288,8 +1288,7 @@ module Gen(P : Params) = struct
       |> Digest.string
       |> Digest.to_hex in
     let alias = Alias.make alias_conf.name ~dir in
-    let digest_path =
-      Path.relative dir (Path.basename (Alias.file alias) ^ "-" ^ digest) in
+    let digest_path = Path.extend_basename (Alias.file alias) ~suffix:("-" ^ digest) in
     let dummy = Build.touch digest_path in
     Alias.add_deps alias [digest_path];
     let deps =

src/path.ml

@@ -268,3 +268,5 @@ let readdir t = Sys.readdir (to_string t) |> Array.to_list
 let is_directory t = Sys.is_directory (to_string t)
 let rmdir t = Unix.rmdir (to_string t)
 let unlink t = Sys.remove (to_string t)
+
+let extend_basename t ~suffix = t ^ suffix

src/path.mli

@@ -54,6 +54,8 @@ val append : t -> t -> t
 val basename : t -> string
 val parent : t -> t
 
+val extend_basename : t -> suffix:string -> t
+
 val extract_build_context : t -> (string * t) option
 val extract_build_context_dir : t -> (t * t) option
 val is_in_build_dir : t -> bool