Avoid type checking private_constants (side_eff) again during Qed (#4357).

Side effects are now an opaque data type, called private_constant, you can
only obtain from safe_typing.  When add_constant is called on a
definition_entry that contains private constants, they are either
- inlined in the main proof term but not re-checked
- declared globally without re-checking them
As a safety measure, the opaque data type contains a pointer to the
revstruct (an internal field of safe_env that changes every time a new
constant is added), and such pointer is compared with the current value
store in safe_env when the private_constant is inlined.  Only when the
comparison is successful the private_constant is not re-checked.  Otherwise
else it is.  In short, we accept into the kernel private constant only
when they arrive in the very same order and on top of the very same env
they arrived when we fist checked them.

Note: private_constants produced by workers never pass the safety
measure (the revstruct pointer is an Ephemeron).  Sending back the
entire revstruct is possible but: 1. we lack a way to quickly compare
two revstructs, 2. it can be large.

1 files changed, 5 insertions, 4 deletions

diff --git a/proofs/proof_global.ml b/proofs/proof_global.ml
index a0ead42ef..809ed41c7 100644
--- a/proofs/proof_global.ml
+++ b/proofs/proof_global.ml
@@ -67,7 +67,7 @@ type proof_universes = Evd.evar_universe_context
 
 type proof_object = {
   id : Names.Id.t;
-  entries : Entries.definition_entry list;
+  entries : Safe_typing.private_constants Entries.definition_entry list;
   persistence : Decl_kinds.goal_kind;
   universes: proof_universes;
   (* constraints : Univ.constraints; *)
@@ -315,13 +315,14 @@ let close_proof ~keep_body_ucst_separate ?feedback_id ~now fpl =
         let open Universes in
         let body = c in
 	let typ =
-	  if not (keep_body_ucst_separate || not (Declareops.side_effects_is_empty eff)) then
+	  if not (keep_body_ucst_separate || not (Safe_typing.empty_private_constants = eff)) then
 	    nf t
 	  else t
 	in
         let used_univs_body = Universes.universes_of_constr body in
         let used_univs_typ = Universes.universes_of_constr typ in
-        if keep_body_ucst_separate || not (Declareops.side_effects_is_empty eff) then
+        if keep_body_ucst_separate ||
+           not (Safe_typing.empty_private_constants = eff) then
           let initunivs = Evd.evar_context_universe_context initial_euctx in
           let ctx = Evd.evar_universe_context_set initunivs universes in
           (* For vi2vo compilation proofs are computed now but we need to
@@ -365,7 +366,7 @@ let close_proof ~keep_body_ucst_separate ?feedback_id ~now fpl =
   { id = pid; entries = entries; persistence = strength; universes = universes },
   fun pr_ending -> Ephemeron.get terminator pr_ending
 
-type closed_proof_output = (Term.constr * Declareops.side_effects) list * Evd.evar_universe_context
+type closed_proof_output = (Term.constr * Safe_typing.private_constants) list * Evd.evar_universe_context
 
 let return_proof ?(allow_partial=false) () =
  let { pid; proof; strength = (_,poly,_) } = cur_pstate () in