From ee64a71f5e071b7fa0495847388c19d83bc5c9bd Mon Sep 17 00:00:00 2001
From: Gaëtan Gilbert
Date: Tue, 31 Mar 2020 15:21:40 +0200
Subject: Close #11935: section variables do not have universe instances.

---
 interp/constrintern.ml             |  2 +-
 pretyping/pretyping.ml             | 10 +++++++++-
 test-suite/bugs/closed/bug_11935.v |  6 ++++++
 3 files changed, 16 insertions(+), 2 deletions(-)
 create mode 100644 test-suite/bugs/closed/bug_11935.v

diff --git a/interp/constrintern.ml b/interp/constrintern.ml
index 905d9f1e5b..45255609e0 100644
--- a/interp/constrintern.ml
+++ b/interp/constrintern.ml
@@ -989,7 +989,7 @@ let string_of_ty = function
   | Variable -> "var"
 
 let gvar (loc, id) us = match us with
-| None -> DAst.make ?loc @@ GVar id
+| None | Some [] -> DAst.make ?loc @@ GVar id
 | Some _ ->
   user_err ?loc  (str "Variable " ++ Id.print id ++
     str " cannot have a universe instance")
diff --git a/pretyping/pretyping.ml b/pretyping/pretyping.ml
index 015c26531a..940150b15a 100644
--- a/pretyping/pretyping.ml
+++ b/pretyping/pretyping.ml
@@ -438,7 +438,15 @@ let pretype_ref ?loc sigma env ref us =
   match ref with
   | GlobRef.VarRef id ->
       (* Section variable *)
-      (try sigma, make_judge (mkVar id) (NamedDecl.get_type (lookup_named id !!env))
+    (try
+       let ty = NamedDecl.get_type (lookup_named id !!env) in
+       (match us with
+        | None | Some [] -> ()
+        | Some (_ :: _) ->
+          CErrors.user_err ?loc
+            Pp.(str "Section variables are not polymorphic:" ++ spc ()
+                ++ str "universe instance should have length 0."));
+       sigma, make_judge (mkVar id) ty
        with Not_found ->
          (* This may happen if env is a goal env and section variables have
             been cleared - section variables should be different from goal
diff --git a/test-suite/bugs/closed/bug_11935.v b/test-suite/bugs/closed/bug_11935.v
new file mode 100644
index 0000000000..ad5ffc68b5
--- /dev/null
+++ b/test-suite/bugs/closed/bug_11935.v
@@ -0,0 +1,6 @@
+Section S.
+  Variable A : Prop.
+
+  Fail Check A@{Type}.
+  Check A@{}.
+End S.
-- 
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