From b977afefc8038f556e04930bcbceb4422b7d1062 Mon Sep 17 00:00:00 2001
From: Matthieu Sozeau
Date: Tue, 19 Jun 2018 12:09:58 +0100
Subject: Fix #5197, handling of algebraic universes

They were allowed to stay in terms in some cases. We now ensure that if
an evar is defined as e.g. fun x => Type@{foo}, foo is properly
refreshed to be non-algebraic as it could otherwise appear in the term
and break the invariant.

Also cleanup the implementation of refresh_universes to avoid using a
mutable reference and simply rely on the Constr.map smartmap idiom
instead.

This might have compatibility issues, e.g. in HoTT where maybe more
non-algebraic proxy universes could be generated, we'll see.

For the bug report proper, there is a lack of bidirectional
type-checking that makes the initial definition fail (there's a
non-canonical choice of dependency if we don't consider the typing
constraint). With the Program bidir hint it passes.
---
 test-suite/bugs/closed/5197.v | 44 +++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)
 create mode 100644 test-suite/bugs/closed/5197.v

(limited to 'test-suite')

diff --git a/test-suite/bugs/closed/5197.v b/test-suite/bugs/closed/5197.v
new file mode 100644
index 0000000000..b67e93d677
--- /dev/null
+++ b/test-suite/bugs/closed/5197.v
@@ -0,0 +1,44 @@
+Set Universe Polymorphism.
+Set Primitive Projections.
+Unset Printing Primitive Projection Compatibility.
+Axiom Ω : Type.
+
+Record Pack (A : Ω -> Type) (Aᴿ : Ω -> (forall ω : Ω, A ω) -> Type) := mkPack {
+  elt : forall ω, A ω;
+  prp : forall ω, Aᴿ ω elt;
+}.
+
+Record TYPE := mkTYPE {
+  wit : Ω -> Type;
+  rel : Ω -> (forall ω : Ω, wit ω) -> Type;
+}.
+
+Definition El (A : TYPE) : Type := Pack A.(wit) A.(rel).
+
+Definition Typeᶠ : TYPE := {|
+  wit := fun _ => Type;
+  rel := fun _ A => (forall ω : Ω, A ω) -> Type;
+                          |}.
+Set Printing Universes.
+Fail Definition Typeᵇ : El Typeᶠ :=
+  mkPack _ _ (fun w => Type) (fun w A => (forall ω, A ω) -> Type).
+
+Definition Typeᵇ : El Typeᶠ :=
+  mkPack _ (fun _ (A : Ω -> Type) => (forall ω : Ω, A ω) -> _) (fun w => Type) (fun w A => (forall ω, A ω) -> Type).
+
+(** Bidirectional typechecking helps here *)
+Require Import Program.Tactics.
+Program Definition progTypeᵇ : El Typeᶠ :=
+  mkPack _ _ (fun w => Type) (fun w A => (forall ω, A ω) -> Type).
+
+(**
+The command has indeed failed with message:
+Error: Conversion test raised an anomaly
+**)
+
+Definition Typeᵇ' : El Typeᶠ.
+Proof.
+unshelve refine (mkPack _ _ _ _).
++ refine (fun _ => Type).
++ simpl. refine (fun _ A => (forall ω, A ω) -> Type).
+Defined.
-- 
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