Let definitions must not contain side-effects when reaching the kernel.

Let definitions have the same behaviour if they are ended with a Qed or a
Defined command, i.e. they are treated as if they were transparent. Indeed,
it doesn't make sense for them to be opaque as they are going to be expanded
away at the end of the section.

For an unknown reason, handling of side-effects in Let definitions considers
them as if they were opaque, i.e. the effects are inlined in the definition.

This discrepancy has bad consequences in the kernel, where one is forced to
juggle with universe constraints generated by polymorphic Let definitions.
As a first phase of cleaning, we simply enforce by typing that Let definitions
should be purified before reaching the kernel.

This has the intended side-effect to make side-effects persistent in Let
definitions, as if they were indeed truly transparent.

4 files changed, 11 insertions, 16 deletions

diff --git a/kernel/safe_typing.ml b/kernel/safe_typing.ml
index 5150ad411..fa984515a 100644
--- a/kernel/safe_typing.ml
+++ b/kernel/safe_typing.ml
@@ -383,8 +383,7 @@ let safe_push_named d env =
 
 let push_named_def (id,de) senv =
   let open Entries in
-  let trust = Term_typing.SideEffects senv.revstruct in
-  let c,typ,univs = Term_typing.translate_local_def trust senv.env id de in
+  let c,typ,univs = Term_typing.translate_local_def senv.env id de in
   let poly = match de.Entries.const_entry_universes with
   | Monomorphic_const_entry _ -> false
   | Polymorphic_const_entry _ -> true
diff --git a/kernel/safe_typing.mli b/kernel/safe_typing.mli
index a30bb37e6..fbc398a2a 100644
--- a/kernel/safe_typing.mli
+++ b/kernel/safe_typing.mli
@@ -90,7 +90,7 @@ val push_named_assum :
 (** Returns the full universe context necessary to typecheck the definition
   (futures are forced) *)
 val push_named_def :
-  Id.t * private_constants Entries.definition_entry -> Univ.ContextSet.t safe_transformer
+  Id.t * unit Entries.definition_entry -> Univ.ContextSet.t safe_transformer
 
 (** Insertion of global axioms or definitions *)
 
@@ -106,8 +106,8 @@ type exported_private_constant =
   Constant.t * private_constant_role
 
 val export_private_constants : in_section:bool ->
-  private_constants Entries.constant_entry ->
-  (unit Entries.constant_entry * exported_private_constant list) safe_transformer
+  private_constants Entries.definition_entry ->
+  (unit Entries.definition_entry * exported_private_constant list) safe_transformer
 
 (** returns the main constant plus a list of auxiliary constants (empty
     unless one requires the side effects to be exported) *)
diff --git a/kernel/term_typing.ml b/kernel/term_typing.ml
index 70dd6438d..761eab511 100644
--- a/kernel/term_typing.ml
+++ b/kernel/term_typing.ml
@@ -533,14 +533,10 @@ type side_effect_role =
 type exported_side_effect = 
   Constant.t * constant_body * side_effect_role
 
-let export_side_effects mb env ce =
-  match ce with
-  | ParameterEntry e -> [], ParameterEntry e
-  | ProjectionEntry e -> [], ProjectionEntry e
-  | DefinitionEntry c ->
+let export_side_effects mb env c =
       let { const_entry_body = body } = c in
       let _, eff = Future.force body in
-      let ce = DefinitionEntry { c with
+      let ce = { c with
         const_entry_body = Future.chain body
           (fun (b_ctx, _) -> b_ctx, ()) } in
       let not_exists (c,_,_,_) =
@@ -609,9 +605,9 @@ let translate_recipe env kn r =
   let hcons = DirPath.is_empty dir in
   build_constant_declaration kn env (Cooking.cook_constant ~hcons env r)
 
-let translate_local_def mb env id centry =
+let translate_local_def env id centry =
   let open Cooking in
-  let decl = infer_declaration ~trust:mb env None (DefinitionEntry centry) in
+  let decl = infer_declaration ~trust:Pure env None (DefinitionEntry centry) in
   let typ = decl.cook_type in
   if Option.is_empty decl.cook_context && !Flags.record_aux_file then begin
     match decl.cook_body with
diff --git a/kernel/term_typing.mli b/kernel/term_typing.mli
index 55da4197e..c771452a1 100644
--- a/kernel/term_typing.mli
+++ b/kernel/term_typing.mli
@@ -18,7 +18,7 @@ type _ trust =
 | Pure : unit trust
 | SideEffects : structure_body -> side_effects trust
 
-val translate_local_def : 'a trust -> env -> Id.t -> 'a definition_entry ->
+val translate_local_def : env -> Id.t -> unit definition_entry ->
   constant_def * types * Univ.ContextSet.t
 
 val translate_local_assum : env -> types -> types
@@ -62,8 +62,8 @@ type exported_side_effect =
  * be pushed in the safe_env by safe typing.  The main constant entry
  * needs to be translated as usual after this step. *)
 val export_side_effects :
-  structure_body -> env -> side_effects constant_entry ->
-    exported_side_effect list * unit constant_entry
+  structure_body -> env -> side_effects definition_entry ->
+    exported_side_effect list * unit definition_entry
 
 val translate_mind :
   env -> MutInd.t -> mutual_inductive_entry -> mutual_inductive_body