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.

1 files changed, 60 insertions, 53 deletions

diff --git a/kernel/constr.ml b/kernel/constr.ml
index 2cbcdd76e..ba7fecadf 100644
--- a/kernel/constr.ml
+++ b/kernel/constr.ml
@@ -654,6 +654,11 @@ let map_with_binders g f l c0 = match kind c0 with
     let bl' = CArray.Fun1.smartmap f l' bl in
     mkCoFix (ln,(lna,tl',bl'))
 
+type instance_compare_fn = global_reference -> int ->
+  Univ.Instance.t -> Univ.Instance.t -> bool
+
+type constr_compare_fn = int -> constr -> constr -> bool
+
 (* [compare_head_gen_evar k1 k2 u s e eq leq c1 c2] compare [c1] and
    [c2] (using [k1] to expose the structure of [c1] and [k2] to expose
    the structure [c2]) using [eq] to compare the immediate subterms of
@@ -665,38 +670,42 @@ let map_with_binders g f l c0 = match kind c0 with
    optimisation that physically equal arrays are equals (hence the
    calls to {!Array.equal_norefl}). *)
 
-let compare_head_gen_leq_with kind1 kind2 eq_universes leq_sorts eq leq t1 t2 =
+let compare_head_gen_leq_with kind1 kind2 leq_universes leq_sorts eq leq nargs t1 t2 =
   match kind1 t1, kind2 t2 with
   | Rel n1, Rel n2 -> Int.equal n1 n2
   | Meta m1, Meta m2 -> Int.equal m1 m2
   | Var id1, Var id2 -> Id.equal id1 id2
   | Sort s1, Sort s2 -> leq_sorts s1 s2
-  | Cast (c1,_,_), _ -> leq c1 t2
-  | _, Cast (c2,_,_) -> leq t1 c2
-  | Prod (_,t1,c1), Prod (_,t2,c2) -> eq t1 t2 && leq c1 c2
-  | Lambda (_,t1,c1), Lambda (_,t2,c2) -> eq t1 t2 && eq c1 c2
-  | LetIn (_,b1,t1,c1), LetIn (_,b2,t2,c2) -> eq b1 b2 && eq t1 t2 && leq c1 c2
+  | Cast (c1, _, _), _ -> leq nargs c1 t2
+  | _, Cast (c2, _, _) -> leq nargs t1 c2
+  | Prod (_,t1,c1), Prod (_,t2,c2) -> eq 0 t1 t2 && leq 0 c1 c2
+  | Lambda (_,t1,c1), Lambda (_,t2,c2) -> eq 0 t1 t2 && eq 0 c1 c2
+  | LetIn (_,b1,t1,c1), LetIn (_,b2,t2,c2) -> eq 0 b1 b2 && eq 0 t1 t2 && leq nargs c1 c2
   (* Why do we suddenly make a special case for Cast here? *)
-  | App (Cast(c1, _, _),l1), _ -> leq (mkApp (c1,l1)) t2
-  | _, App (Cast (c2, _, _),l2) -> leq t1 (mkApp (c2,l2))
-  | App (c1,l1), App (c2,l2) ->
-      Int.equal (Array.length l1) (Array.length l2) &&
-        eq c1 c2 && Array.equal_norefl eq l1 l2
-  | Proj (p1,c1), Proj (p2,c2) -> Projection.equal p1 p2 && eq c1 c2
-  | Evar (e1,l1), Evar (e2,l2) -> Evar.equal e1 e2 && Array.equal eq l1 l2
-  | Const (c1,u1), Const (c2,u2) -> Constant.equal c1 c2 && eq_universes true u1 u2
-  | Ind (c1,u1), Ind (c2,u2) -> eq_ind c1 c2 && eq_universes false u1 u2
-  | Construct (c1,u1), Construct (c2,u2) -> eq_constructor c1 c2 && eq_universes false u1 u2
+  | App (Cast (c1, _, _), l1), _ -> leq nargs (mkApp (c1, l1)) t2
+  | _, App (Cast (c2, _, _), l2) -> leq nargs t1 (mkApp (c2, l2))
+  | App (c1, l1), App (c2, l2) ->
+    let len = Array.length l1 in
+    Int.equal len (Array.length l2) &&
+    eq (nargs+len) c1 c2 && Array.equal_norefl (eq 0) l1 l2
+  | Proj (p1,c1), Proj (p2,c2) -> Projection.equal p1 p2 && eq 0 c1 c2
+  | Evar (e1,l1), Evar (e2,l2) -> Evar.equal e1 e2 && Array.equal (eq 0) l1 l2
+  | Const (c1,u1), Const (c2,u2) ->
+    (* The args length currently isn't used but may as well pass it. *)
+    Constant.equal c1 c2 && leq_universes (ConstRef c1) nargs u1 u2
+  | Ind (c1,u1), Ind (c2,u2) -> eq_ind c1 c2 && leq_universes (IndRef c1) nargs u1 u2
+  | Construct (c1,u1), Construct (c2,u2) ->
+    eq_constructor c1 c2 && leq_universes (ConstructRef c1) nargs u1 u2
   | Case (_,p1,c1,bl1), Case (_,p2,c2,bl2) ->
-      eq p1 p2 && eq c1 c2 && Array.equal eq bl1 bl2
+    eq 0 p1 p2 && eq 0 c1 c2 && Array.equal (eq 0) bl1 bl2
   | Fix ((ln1, i1),(_,tl1,bl1)), Fix ((ln2, i2),(_,tl2,bl2)) ->
-      Int.equal i1 i2 && Array.equal Int.equal ln1 ln2
-      && Array.equal_norefl eq tl1 tl2 && Array.equal_norefl eq bl1 bl2
+    Int.equal i1 i2 && Array.equal Int.equal ln1 ln2
+    && Array.equal_norefl (eq 0) tl1 tl2 && Array.equal_norefl (eq 0) bl1 bl2
   | CoFix(ln1,(_,tl1,bl1)), CoFix(ln2,(_,tl2,bl2)) ->
-      Int.equal ln1 ln2 && Array.equal_norefl eq tl1 tl2 && Array.equal_norefl eq bl1 bl2
+    Int.equal ln1 ln2 && Array.equal_norefl (eq 0) tl1 tl2 && Array.equal_norefl (eq 0) bl1 bl2
   | (Rel _ | Meta _ | Var _ | Sort _ | Prod _ | Lambda _ | LetIn _ | App _
-     | Proj _ | Evar _ | Const _ | Ind _ | Construct _ | Case _ | Fix _
-     | CoFix _), _ -> false
+    | Proj _ | Evar _ | Const _ | Ind _ | Construct _ | Case _ | Fix _
+    | CoFix _), _ -> false
 
 (* [compare_head_gen_leq u s eq leq c1 c2] compare [c1] and [c2] using [eq] to compare
    the immediate subterms of [c1] of [c2] for conversion if needed, [leq] for cumulativity,
@@ -704,8 +713,8 @@ let compare_head_gen_leq_with kind1 kind2 eq_universes leq_sorts eq leq t1 t2 =
    application associativity, binders name and Cases annotations are
    not taken into account *)
 
-let compare_head_gen_leq eq_universes leq_sorts eq leq t1 t2 =
-  compare_head_gen_leq_with kind kind  eq_universes leq_sorts eq leq t1 t2
+let compare_head_gen_leq leq_universes leq_sorts eq leq t1 t2 =
+  compare_head_gen_leq_with kind kind leq_universes leq_sorts eq leq t1 t2
 
 (* [compare_head_gen u s f c1 c2] compare [c1] and [c2] using [f] to
    compare the immediate subterms of [c1] of [c2] if needed, [u] to
@@ -722,7 +731,7 @@ let compare_head_gen_with kind1 kind2 eq_universes eq_sorts eq t1 t2 =
 let compare_head_gen eq_universes eq_sorts eq t1 t2 =
   compare_head_gen_leq eq_universes eq_sorts eq eq t1 t2
 
-let compare_head = compare_head_gen (fun _ -> Univ.Instance.equal) Sorts.equal
+let compare_head = compare_head_gen (fun _ _ -> Univ.Instance.equal) Sorts.equal
 
 (*******************************)
 (*  alpha conversion functions *)
@@ -730,41 +739,41 @@ let compare_head = compare_head_gen (fun _ -> Univ.Instance.equal) Sorts.equal
 
 (* alpha conversion : ignore print names and casts *)
 
-let rec eq_constr m n =
-  (m == n) || compare_head_gen (fun _ -> Instance.equal) Sorts.equal eq_constr m n
+let rec eq_constr nargs m n =
+  (m == n) || compare_head_gen (fun _ _ -> Instance.equal) Sorts.equal eq_constr nargs m n
 
-let equal m n = eq_constr m n (* to avoid tracing a recursive fun *)
+let equal n m = eq_constr 0 m n (* to avoid tracing a recursive fun *)
 
 let eq_constr_univs univs m n =
   if m == n then true
   else 
-    let eq_universes _ = UGraph.check_eq_instances univs in
+    let eq_universes _ _ = UGraph.check_eq_instances univs in
     let eq_sorts s1 s2 = s1 == s2 || UGraph.check_eq univs (Sorts.univ_of_sort s1) (Sorts.univ_of_sort s2) in
-    let rec eq_constr' m n = 
-      m == n ||	compare_head_gen eq_universes eq_sorts eq_constr' m n
-    in compare_head_gen eq_universes eq_sorts eq_constr' m n
+    let rec eq_constr' nargs m n =
+      m == n ||	compare_head_gen eq_universes eq_sorts eq_constr' nargs m n
+    in compare_head_gen eq_universes eq_sorts eq_constr' 0 m n
 
 let leq_constr_univs univs m n =
   if m == n then true
   else 
-    let eq_universes _ = UGraph.check_eq_instances univs in
+    let eq_universes _ _ = UGraph.check_eq_instances univs in
     let eq_sorts s1 s2 = s1 == s2 || 
       UGraph.check_eq univs (Sorts.univ_of_sort s1) (Sorts.univ_of_sort s2) in
     let leq_sorts s1 s2 = s1 == s2 || 
       UGraph.check_leq univs (Sorts.univ_of_sort s1) (Sorts.univ_of_sort s2) in
-    let rec eq_constr' m n = 
-      m == n ||	compare_head_gen eq_universes eq_sorts eq_constr' m n
+    let rec eq_constr' nargs m n =
+      m == n || compare_head_gen eq_universes eq_sorts eq_constr' nargs m n
     in
-    let rec compare_leq m n =
-      compare_head_gen_leq eq_universes leq_sorts eq_constr' leq_constr' m n
-    and leq_constr' m n = m == n || compare_leq m n in
-    compare_leq m n
+    let rec compare_leq nargs m n =
+      compare_head_gen_leq eq_universes leq_sorts eq_constr' leq_constr' nargs m n
+    and leq_constr' nargs m n = m == n || compare_leq nargs m n in
+    compare_leq 0 m n
 
 let eq_constr_univs_infer univs m n =
   if m == n then true, Constraint.empty
   else 
     let cstrs = ref Constraint.empty in
-    let eq_universes strict = UGraph.check_eq_instances univs in
+    let eq_universes _ _ = UGraph.check_eq_instances univs in
     let eq_sorts s1 s2 = 
       if Sorts.equal s1 s2 then true
       else
@@ -774,17 +783,17 @@ let eq_constr_univs_infer univs m n =
 	  (cstrs := Univ.enforce_eq u1 u2 !cstrs;
 	   true)
     in
-    let rec eq_constr' m n = 
-      m == n ||	compare_head_gen eq_universes eq_sorts eq_constr' m n
+    let rec eq_constr' nargs m n =
+      m == n || compare_head_gen eq_universes eq_sorts eq_constr' nargs m n
     in
-    let res = compare_head_gen eq_universes eq_sorts eq_constr' m n in
+    let res = compare_head_gen eq_universes eq_sorts eq_constr' 0 m n in
     res, !cstrs
 
 let leq_constr_univs_infer univs m n =
   if m == n then true, Constraint.empty
   else 
     let cstrs = ref Constraint.empty in
-    let eq_universes strict l l' = UGraph.check_eq_instances univs l l' in
+    let eq_universes _ _ l l' = UGraph.check_eq_instances univs l l' in
     let eq_sorts s1 s2 = 
       if Sorts.equal s1 s2 then true
       else
@@ -802,19 +811,17 @@ let leq_constr_univs_infer univs m n =
 	  (cstrs := Univ.enforce_leq u1 u2 !cstrs; 
 	   true)
     in
-    let rec eq_constr' m n = 
-      m == n ||	compare_head_gen eq_universes eq_sorts eq_constr' m n
+    let rec eq_constr' nargs m n =
+      m == n || compare_head_gen eq_universes eq_sorts eq_constr' nargs m n
     in
-    let rec compare_leq m n =
-      compare_head_gen_leq eq_universes leq_sorts eq_constr' leq_constr' m n
-    and leq_constr' m n = m == n || compare_leq m n in
-    let res = compare_leq m n in
+    let rec compare_leq nargs m n =
+      compare_head_gen_leq eq_universes leq_sorts eq_constr' leq_constr' nargs m n
+    and leq_constr' nargs m n = m == n || compare_leq nargs m n in
+    let res = compare_leq 0 m n in
     res, !cstrs
 
-let always_true _ _ = true
-
 let rec eq_constr_nounivs m n =
-  (m == n) || compare_head_gen (fun _ -> always_true) always_true eq_constr_nounivs m n
+  (m == n) || compare_head_gen (fun _ _ _ _ -> true) (fun _ _ -> true) (fun _ -> eq_constr_nounivs) 0 m n
 
 let constr_ord_int f t1 t2 =
   let (=?) f g i1 i2 j1 j2=