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, 19 insertions, 6 deletions

diff --git a/kernel/entries.mli b/kernel/entries.mli
index 303d27d35..e058519e9 100644
--- a/kernel/entries.mli
+++ b/kernel/entries.mli
@@ -54,11 +54,11 @@ type mutual_inductive_entry = {
   mind_entry_private : bool option }
 
 (** {6 Constants (Definition/Axiom) } *)
-type proof_output = constr Univ.in_universe_context_set * Declareops.side_effects
-type const_entry_body = proof_output Future.computation
+type 'a proof_output = constr Univ.in_universe_context_set * 'a
+type 'a const_entry_body = 'a proof_output Future.computation
 
-type definition_entry = {
-  const_entry_body   : const_entry_body;
+type 'a definition_entry = {
+  const_entry_body   : 'a const_entry_body;
   (* List of section variables *)
   const_entry_secctx : Context.section_context option;
   (* State id on which the completion of type checking is reported *)
@@ -78,8 +78,8 @@ type projection_entry = {
   proj_entry_ind : mutual_inductive;
   proj_entry_arg : int }
 
-type constant_entry =
-  | DefinitionEntry of definition_entry
+type 'a constant_entry =
+  | DefinitionEntry of 'a definition_entry
   | ParameterEntry of parameter_entry
   | ProjectionEntry of projection_entry
 
@@ -96,3 +96,16 @@ type module_entry =
   | MType of module_params_entry * module_struct_entry
   | MExpr of
       module_params_entry * module_struct_entry * module_struct_entry option
+
+type seff_env = [ `Nothing | `Opaque of Constr.t * Univ.universe_context_set ]
+
+type side_eff =
+  | SEsubproof of constant * Declarations.constant_body * seff_env
+  | SEscheme of (inductive * constant * Declarations.constant_body * seff_env) list * string
+
+type side_effect = {
+  from_env : Declarations.structure_body Ephemeron.key;
+  eff      : side_eff;
+}
+
+type side_effects = side_effect list