irmin-lwt: link top-level types to Schema in module type S

Without these equalities, [Irmin_lwt.S with module Schema = Schema] in a
downstream consumer (Tezos' [Tezos_context_helpers.Context.DB]) only
substituted [Schema] but left [hash], [contents], [step], etc. abstract.
Cue type errors like "Store.Tree.hash returns Store.hash but Tezos
expects Hash.t (= Schema.Hash.t)".

Mirror the pattern of [Irmin.Generic_key.S]: declare [Schema] first and
define the types it derives as type aliases:

  type step = Schema.Path.step
  type path = Schema.Path.t
  type metadata = Schema.Metadata.t
  type contents = Schema.Contents.t
  type branch = Schema.Branch.t
  type info = Schema.Info.t
  type hash = Schema.Hash.t

Now [Irmin_lwt.S with module Schema = Schema] propagates the equalities
to every Schema-derived type. The redundant [type X = S.X] constraints
in [Make]'s output type are dropped accordingly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: balat

src/irmin-lwt/irmin_lwt.ml

@@ -16,19 +16,25 @@ let run_with_env env f =
   Lwt_eio.Promise.await_lwt (f ())
 
 module type S = sig
+  (** {1 Schema} *)
+
+  module Schema : Irmin.Schema.S
+
+  (** {1 Types} *)
+
   type repo
   type t
-  type step
-  type path
-  type metadata
-  type contents
+  type step = Schema.Path.step
+  type path = Schema.Path.t
+  type metadata = Schema.Metadata.t
+  type contents = Schema.Contents.t
   type node
   type tree
   type commit
-  type branch
+  type branch = Schema.Branch.t
   type slice
-  type info
-  type hash
+  type info = Schema.Info.t
+  type hash = Schema.Hash.t
   type contents_key
   type node_key
   type commit_key
@@ -40,7 +46,6 @@ module type S = sig
 
   (** {1 Type-level submodules} *)
 
-  module Schema : Irmin.Schema.S
   module Info : Irmin.Info.S with type t = info
   module Hash : Irmin.Hash.S with type t = hash
   module Path : Irmin.Path.S with type t = path and type step = step

src/irmin-lwt/irmin_lwt.mli

@@ -30,19 +30,25 @@ val run_with_env : < clock : _ Eio.Time.clock ; .. > -> (unit -> 'a Lwt.t) -> 'a
     See {!Make} for the functor that produces a module conforming to [S] from an
     arbitrary [Irmin.Generic_key.S]. *)
 module type S = sig
+  (** {1 Schema} *)
+
+  module Schema : Irmin.Schema.S
+
+  (** {1 Types} *)
+
   type repo
   type t
-  type step
-  type path
-  type metadata
-  type contents
+  type step = Schema.Path.step
+  type path = Schema.Path.t
+  type metadata = Schema.Metadata.t
+  type contents = Schema.Contents.t
   type node
   type tree
   type commit
-  type branch
+  type branch = Schema.Branch.t
   type slice
-  type info
-  type hash
+  type info = Schema.Info.t
+  type hash = Schema.Hash.t
   type contents_key
   type node_key
   type commit_key
@@ -54,7 +60,6 @@ module type S = sig
 
   (** {1 Type-level submodules} *)
 
-  module Schema : Irmin.Schema.S
   module Info : Irmin.Info.S with type t = info
   module Hash : Irmin.Hash.S with type t = hash
   module Path : Irmin.Path.S with type t = path and type step = step
@@ -704,27 +709,20 @@ end
 
 module Make (S : Irmin.Generic_key.S) :
   S
-    with type repo = S.repo
+    with module Schema = S.Schema
+     and type repo = S.repo
      and type t = S.t
-     and type step = S.step
-     and type path = S.path
-     and type metadata = S.metadata
-     and type contents = S.contents
      and type node = S.node
      and type tree = S.tree
      and type commit = S.commit
-     and type branch = S.branch
      and type slice = S.slice
-     and type info = S.info
-     and type hash = S.hash
      and type contents_key = S.contents_key
      and type node_key = S.node_key
      and type commit_key = S.commit_key
      and type lca_error = S.lca_error
      and type ff_error = S.ff_error
      and type write_error = S.write_error
      and type watch = S.watch
-     and module Schema = S.Schema
      and module Info = S.Info
      and module Hash = S.Hash
      and module Path = S.Path