From 17a0dccfe91d6f837ce285e62b8d843720f8c1a1 Mon Sep 17 00:00:00 2001
From: Gaëtan Gilbert
Date: Fri, 16 Feb 2018 15:44:44 +0100
Subject: Allow using cumulativity without forcing strict constraints.

Previously [fun x : Ind@{i} => x : Ind@{j}] with Ind some cumulative
inductive would try to generate a constraint [i = j] and use
cumulativity only if this resulted in an inconsistency. This is
confusingly different from the behaviour with [Type] and means
cumulativity can only be used to lift between universes related by
strict inequalities. (This isn't a kernel restriction so there might
be some workaround to send the kernel the right constraints, but
not in a nice way.)

See modified test for more details of what is now possible.

Technical notes:

When universe constraints were inferred by comparing the shape of
terms without reduction, cumulativity was not used and so too-strict
equality constraints were generated. Then in order to use cumulativity
we had to make this comparison fail to fall back to full conversion.

When unifiying 2 instances of a cumulative inductive type, if there
are any Irrelevant universes we try to unify them if they are
flexible.
---
 kernel/term.mli | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

(limited to 'kernel/term.mli')

diff --git a/kernel/term.mli b/kernel/term.mli
index ba521978e7..7cb3b662d4 100644
--- a/kernel/term.mli
+++ b/kernel/term.mli
@@ -477,7 +477,7 @@ val iter_constr_with_binders :
   ('a -> 'a) -> ('a -> constr -> unit) -> 'a -> constr -> unit
 [@@ocaml.deprecated "Alias for [Constr.iter_with_binders]"]
 
-val compare_constr : (constr -> constr -> bool) -> constr -> constr -> bool
+val compare_constr : (int -> constr -> constr -> bool) -> int -> constr -> constr -> bool
 [@@ocaml.deprecated "Alias for [Constr.compare_head]"]
 
 type constr = Constr.constr
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