Get rid of Blang_decode

Signed-off-by: Rudi Grinberg <rudi.grinberg@gmail.com>

src/blang.ml

@@ -71,5 +71,39 @@ include (
           ; via_sexp String_with_vars.to_sexp s1
           ; via_sexp String_with_vars.to_sexp s2
           ]
-  end)
-)
+  end))
+
+let ops =
+  [ "=", Op.Eq
+  ; ">=", Gte
+  ; "<=", Lt
+  ; ">", Gt
+  ; "<", Lt
+  ; "<>", Neq
+  ]
+
+let decode =
+  let open Stanza.Decoder in
+  let ops =
+    List.map ops ~f:(fun (name, op) ->
+      ( name
+      , (let+ x = String_with_vars.decode
+         and+ y = String_with_vars.decode
+         in
+         Compare (op, x, y))))
+  in
+  let decode =
+    fix begin fun t ->
+      if_list
+        ~then_:(
+          [ "or", repeat t >>| (fun x -> Or x)
+          ; "and", repeat t >>| (fun x -> And x)
+          ] @ ops
+          |> sum)
+        ~else_:(String_with_vars.decode >>| fun v -> Expr v)
+    end
+  in
+  let+ () = Syntax.since Stanza.syntax (1, 1)
+  and+ decode = decode
+  in
+  decode

src/blang.mli

@@ -22,7 +22,9 @@ val true_ : t
 val eval
   :  t
   -> dir:Path.t
-  -> f:Value.t list option  String_with_vars.expander
+  -> f:Value.t list option String_with_vars.expander
   -> bool
 
 include Dyn.S with type t := t
+
+val decode : t Stanza.Decoder.t

src/dune_file.ml

@@ -322,7 +322,7 @@ end
 
 let enabled_if =
   field "enabled_if" ~default:Blang.true_
-    (Syntax.since Stanza.syntax (1, 4) >>> Blang_decode.decode)
+    (Syntax.since Stanza.syntax (1, 4) >>> Blang.decode)
 
 module Per_module = struct
   include Per_item.Make(Module.Name)
@@ -1895,7 +1895,7 @@ module Alias_conf = struct
        and+ action = field_o "action" (located Action_dune_lang.decode)
        and+ locks = field "locks" (list String_with_vars.decode) ~default:[]
        and+ deps = field "deps" (Bindings.decode Dep_conf.decode) ~default:Bindings.empty
-       and+ enabled_if = field "enabled_if" Blang_decode.decode ~default:Blang.true_
+       and+ enabled_if = field "enabled_if" Blang.decode ~default:Blang.true_
        in
        { name
        ; deps

src/dune_project.ml

@@ -182,7 +182,7 @@ end
 
 module Opam = struct
 
-  let decode_constraint = Blang_decode.decode
+  let decode_constraint = Blang.decode
 
   module Package = struct
     module Name = Package.Name