Fix #7900 previous commit fixes a bug when using side effects in obligations.

Internal lemmas are inlined in obligations bodies, hence their universes
have to be declared with the obligations themselves. ~sideff:true was
not including the side effects universes and constraints in that case.

4 files changed, 68 insertions, 6 deletions

diff --git a/engine/evd.ml b/engine/evd.ml
index d1c7fef738..9f976b57dd 100644
--- a/engine/evd.ml
+++ b/engine/evd.ml
@@ -774,7 +774,7 @@ let universe_subst evd =
   UState.subst evd.universes
 
 let merge_context_set ?loc ?(sideff=false) rigid evd ctx' =
-  {evd with universes = UState.merge ?loc sideff rigid evd.universes ctx'}
+  {evd with universes = UState.merge ?loc ~sideff ~extend:true rigid evd.universes ctx'}
 
 let merge_universe_subst evd subst = 
   {evd with universes = UState.merge_subst evd.universes subst }
diff --git a/engine/uState.ml b/engine/uState.ml
index b1fe91a21b..29cb3c9bcc 100644
--- a/engine/uState.ml
+++ b/engine/uState.ml
@@ -430,10 +430,17 @@ let univ_rigid = UnivRigid
 let univ_flexible = UnivFlexible false
 let univ_flexible_alg = UnivFlexible true
 
-let merge ?loc sideff rigid uctx ctx' =
+(** ~sideff indicates that it is ok to redeclare a universe.
+    ~extend also merges the universe context in the local constraint structures
+    and not only in the graph. This depends if the
+    context we merge comes from a side effect that is already inlined
+    or defined separately. In the later case, there is no extension,
+    see [emit_side_effects] for example. *)
+let merge ?loc ~sideff ~extend rigid uctx ctx' =
   let open Univ in
   let levels = ContextSet.levels ctx' in
   let uctx =
+    if not extend then uctx else
     match rigid with
     | UnivRigid -> uctx
     | UnivFlexible b ->
@@ -447,7 +454,9 @@ let merge ?loc sideff rigid uctx ctx' =
           uctx_univ_algebraic = LSet.union uctx.uctx_univ_algebraic levels }
         else { uctx with uctx_univ_variables = uvars' }
   in
-  let uctx_local = ContextSet.append ctx' uctx.uctx_local in
+  let uctx_local =
+    if not extend then uctx.uctx_local
+    else ContextSet.append ctx' uctx.uctx_local in
   let declare g =
     LSet.fold (fun u g ->
                try UGraph.add_universe u false g
@@ -476,7 +485,7 @@ let merge_subst uctx s =
 
 let emit_side_effects eff u =
   let uctxs = Safe_typing.universes_of_private eff in
-  List.fold_left (merge true univ_rigid) u uctxs
+  List.fold_left (merge ~sideff:true ~extend:false univ_rigid) u uctxs
 
 let new_univ_variable ?loc rigid name
   ({ uctx_local = ctx; uctx_univ_variables = uvars; uctx_univ_algebraic = avars} as uctx) =
@@ -665,7 +674,7 @@ let update_sigma_env uctx env =
     { uctx with uctx_initial_universes = univs;
                          uctx_universes = univs }
   in
-  merge true univ_rigid eunivs eunivs.uctx_local
+  merge ~sideff:true ~extend:false univ_rigid eunivs eunivs.uctx_local
 
 let pr_weak prl {uctx_weak_constraints=weak} =
   let open Pp in
diff --git a/engine/uState.mli b/engine/uState.mli
index a59e61b894..f833508ebf 100644
--- a/engine/uState.mli
+++ b/engine/uState.mli
@@ -103,7 +103,7 @@ val univ_rigid : rigid
 val univ_flexible : rigid
 val univ_flexible_alg : rigid
 
-val merge : ?loc:Loc.t -> bool -> rigid -> t -> Univ.ContextSet.t -> t
+val merge : ?loc:Loc.t -> sideff:bool -> extend:bool -> rigid -> t -> Univ.ContextSet.t -> t
 val merge_subst : t -> UnivSubst.universe_opt_subst -> t
 val emit_side_effects : Safe_typing.private_constants -> t -> t
 
diff --git a/test-suite/bugs/closed/7900.v b/test-suite/bugs/closed/7900.v
new file mode 100644
index 0000000000..583ef0ef3b
--- /dev/null
+++ b/test-suite/bugs/closed/7900.v
@@ -0,0 +1,53 @@
+Require Import Coq.Program.Program.
+(* Set Universe Polymorphism. *)
+Set Printing Universes.
+
+Axiom ALL : forall {T:Prop}, T.
+
+Inductive Expr : Set := E (a : Expr).
+
+Parameter Value : Set.
+
+Fixpoint eval (e: Expr): Value :=
+  match e with
+  | E a => eval a
+  end.
+
+Class Quote (n: Value) : Set :=
+  { quote: Expr
+    ; eval_quote: eval quote = n }.
+
+Program Definition quote_mult n
+        `{!Quote n} : Quote n :=
+  {| quote := E (quote (n:=n)) |}.
+
+Set Printing Universes.
+Next Obligation.
+Proof.
+  Show Universes.
+  destruct Quote0 as [q eq].
+  Show Universes.
+  rewrite <- eq.
+  clear n eq.
+  Show Universes.
+  apply ALL.
+  Show Universes.
+Qed.
+Print quote_mult_obligation_1.
+(* quote_mult_obligation_1@{} =
+let Top_internal_eq_rew_dep :=
+  fun (A : Type@{Coq.Init.Logic.8}) (x : A) (P : forall a : A, x = a -> Type@{Top.5} (* <- XXX *))
+    (f : P x eq_refl) (y : A) (e : x = y) =>
+  match e as e0 in (_ = y0) return (P y0 e0) with
+  | eq_refl => f
+  end in
+fun (n : Value) (Quote0 : Quote n) =>
+match Quote0 as q return (eval quote = n) with
+| {| quote := q; eval_quote := eq0 |} =>
+    Top_internal_eq_rew_dep Value (eval q) (fun (n0 : Value) (eq1 : eval q = n0) => eval quote = n0)
+      ALL n eq0
+end
+     : forall (n : Value) (Quote0 : Quote n), eval (E quote) = n
+
+quote_mult_obligation_1 is universe polymorphic
+*)