Build on OCaml 5.0 and test unread copies with runtime interfaces

Mutex.protect only exists from OCaml 5.1, so the count table locks with
Mutex.lock and Fun.protect like Process_child.with_lock. The unread copy
test asked for Belt modules, which the coverage job doesn't build; it now
uses runtime interfaces only.

Signed-off-by: Jono Prest <jjprest@gmail.com>

Author: JonoPrest

changes/defer-dependency-signature-copy.internal.md

@@ -0,0 +1 @@
+- Build: copy a dependency's interface only when it is read, after the first copy of the same interface in a build, instead of every time a module checks whether the dependency is an alias.

changes/defer-dependency-signature-copy.polish.md

@@ -585,11 +585,16 @@ type pers_sig = {
 let copy_counts : (Digest.t, int * int) Hashtbl.t = Hashtbl.create 64
 let copy_counts_lock = Mutex.create ()
 
+(* [Mutex.protect] needs OCaml 5.1. *)
+let with_copy_counts_lock action =
+  Mutex.lock copy_counts_lock;
+  Fun.protect ~finally:(fun () -> Mutex.unlock copy_counts_lock) action
+
 let find_copy_counts key =
-  Mutex.protect copy_counts_lock (fun () -> Hashtbl.find_opt copy_counts key)
+  with_copy_counts_lock (fun () -> Hashtbl.find_opt copy_counts key)
 
 let record_copy_counts key counts =
-  Mutex.protect copy_counts_lock (fun () ->
+  with_copy_counts_lock (fun () ->
       if Hashtbl.length copy_counts >= 65536 then Hashtbl.reset copy_counts;
       Hashtbl.replace copy_counts key counts)
 

compiler/ml/env.ml

@@ -84,7 +84,7 @@ let deferred_copy_tests _ =
 (* A copy that is never read still takes its stamps and ids. *)
 let unread_copy_tests _ =
   let dirs = interface_dirs () in
-  let names = ["Belt_Array"; "Stdlib_Array"; "Belt_Id"; "Stdlib"] in
+  let names = ["Stdlib_Array"; "Stdlib_List"; "Stdlib_Option"; "Stdlib"] in
   let ask_only ~eager =
     Compiler_request_state.with_fresh (fun () ->
         Request_local.with_fresh (fun () ->