Better names for env_and_file

It didn't return a file. Most of the time it returned a filename, but
even then it would be used in ways where what it returned was a piece of
OCaml code (`--prelude-str`) so calling it `env_and_file` was pretty
inaccurate.

Author: Leonidas-from-XIV

bin/cli.ml

@@ -68,9 +68,11 @@ let verbose_findlib =
 
 let prelude =
   let parse s =
-    let env, file = Mdx.Prelude.env_and_file s in
-    let parse, _print = Arg.non_dir_file in
-    match parse file with `Ok _ -> `Ok (env, file) | `Error e -> `Error e
+    let env, filename = Mdx.Prelude.env_and_payload s in
+    let parse, _pp = Arg.non_dir_file in
+    match parse filename with
+    | `Ok _ -> `Ok (env, filename)
+    | `Error _ as e -> e
   in
   let prelude = (parse, Mdx.Prelude.pp) in
   let doc =
@@ -91,7 +93,7 @@ let prelude_str =
      not contain any spaces. Multiple prelude strings can be provided: they \
      will be evaluated in the order they are provided on the command-line."
   in
-  let parse s = `Ok (Mdx.Prelude.env_and_file s) in
+  let parse s = `Ok (Mdx.Prelude.env_and_payload s) in
   let prelude = (parse, Mdx.Prelude.pp) in
   named
     (fun x -> `Prelude_str x)

lib/prelude.ml

@@ -21,7 +21,7 @@ let pp ppf = function
   | `One ocaml_env, filename ->
       Fmt.pf ppf "(`One %a, %S)" Ocaml_env.pp ocaml_env filename
 
-let env_and_file f =
+let env_and_payload f =
   match Astring.String.cut ~sep:":" f with
   | None -> (`All, f)
   | Some (e, f) ->

lib/prelude.mli

@@ -18,9 +18,9 @@ type t = [ `All | `One of Ocaml_env.t ] * string
 
 val pp : t Fmt.t
 
-val env_and_file : string -> t
-(** [env_and_file s] returns the environment and file/prelude string described
+val env_and_payload : string -> t
+(** [env_and_payload s] returns the environment and file/prelude string described
     by [s].
-    I.e. [env_and_file "a:f"] associates [f] to the environment named [a],
-    [env_and_file " :f"] associates [f] to the default environment, and
-    [env_and_file "f"] associates [f] to all environments. *)
+    I.e. [env_and_payload "a:f"] associates [f] to the environment named [a],
+    [env_and_payload " :f"] associates [f] to the default environment, and
+    [env_and_payload "f"] associates [f] to all environments. *)