From a5b631f7260e7d29defd8bd5c67db543742c9ecd Mon Sep 17 00:00:00 2001
From: Matthieu Sozeau
Date: Mon, 9 May 2016 17:40:04 +0200
Subject: congruence/univs: properly refresh (fix #4609)

In congruence, refresh universes including the Set/Prop ones so that
congruence works with cumulativity, not restricting itself to the
inferred types of terms that are manipulated but allowing them to be
used at more general types. This fixes bug #4609.
---
 pretyping/evarsolve.ml  | 7 ++++++-
 pretyping/evarsolve.mli | 8 ++++++--
 2 files changed, 12 insertions(+), 3 deletions(-)

(limited to 'pretyping')

diff --git a/pretyping/evarsolve.ml b/pretyping/evarsolve.ml
index 29af199a1e..c2d47790d5 100644
--- a/pretyping/evarsolve.ml
+++ b/pretyping/evarsolve.ml
@@ -47,7 +47,8 @@ let refresh_level evd s =
   | None -> true
   | Some l -> not (Evd.is_flexible_level evd l)
 
-let refresh_universes ?(status=univ_rigid) ?(onlyalg=false) pbty env evd t =
+let refresh_universes ?(status=univ_rigid) ?(onlyalg=false) ?(propset=false)
+		      pbty env evd t =
   let evdref = ref evd in
   let modified = ref false in
   let rec refresh status dir t = 
@@ -62,6 +63,10 @@ let refresh_universes ?(status=univ_rigid) ?(onlyalg=false) pbty env evd t =
       else set_leq_sort env !evdref s s'
     in
       modified := true; evdref := evd; mkSort s'
+    | Sort (Prop _ as s) when propset && not dir ->
+       let s' = evd_comb0 (new_sort_variable status) evdref in
+       let evd = set_leq_sort env !evdref s s' in
+       modified := true; evdref := evd; mkSort s'
     | Prod (na,u,v) -> 
       mkProd (na,u,refresh status dir v)
     | _ -> t
diff --git a/pretyping/evarsolve.mli b/pretyping/evarsolve.mli
index 918ba12f0f..9ee815ebc0 100644
--- a/pretyping/evarsolve.mli
+++ b/pretyping/evarsolve.mli
@@ -34,8 +34,12 @@ type conv_fun_bool =
 val evar_define : conv_fun -> ?choose:bool -> env -> evar_map -> 
   bool option -> existential -> constr -> evar_map
 
-val refresh_universes : ?status:Evd.rigid ->
-			?onlyalg:bool (* Only algebraic universes *) ->
+val refresh_universes :
+  ?status:Evd.rigid ->
+  ?onlyalg:bool (* Only algebraic universes *) ->
+  ?propset:bool ->
+  (* Also refresh Prop and Set universes, so that the returned type can be any supertype
+     of the original type *)
   bool option (* direction: true for levels lower than the existing levels *) ->
   env -> evar_map -> types -> evar_map * types
 
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