refactor: move Backtrackable_ref into its own sub-library

src/backtrack/Msat_backtrack.ml

@@ -0,0 +1,2 @@
+
+module Ref = Backtrackable_ref

src/backtrack/dune

@@ -0,0 +1,11 @@
+
+(library
+  (name msat_backtrack)
+  (public_name msat.backtrack)
+  (libraries msat)
+  (synopsis "backtrackable data structures for msat")
+  (flags :standard -warn-error -3 -w +a-4-42-44-48-50-58-32-60@8
+         -color always -safe-string -open Msat)
+  (ocamlopt_flags :standard -O3 -bin-annot
+                  -unbox-closures -unbox-closures-factor 20)
+  )

src/core/Msat.ml

@@ -68,8 +68,6 @@ module Make_mcsat = Solver.Make_mcsat
 module Make_cdcl_t = Solver.Make_cdcl_t
 module Make_pure_sat = Solver.Make_pure_sat
 
-module Backtrackable_ref = Backtrackable_ref
-
 (**/**)
 module Vec = Vec
 module Log = Log

src/sudoku/dune

@@ -2,7 +2,7 @@
 (executable
   (name sudoku_solve)
   (modes native)
-  (libraries msat sequence containers)
+  (libraries msat msat.backtrack sequence containers)
   (flags :standard -warn-error -a -w +a-4-42-44-48-50-58-32-60@8 -color always -safe-string)
   (ocamlopt_flags :standard -O3 -bin-annot
                   -unbox-closures -unbox-closures-factor 20)

src/sudoku/sudoku_solve.ml

@@ -125,7 +125,7 @@ end = struct
     a
 end
 
-module B_ref = Msat.Backtrackable_ref
+module B_ref = Msat_backtrack.Ref
 
 module Solver : sig
   type t