From 13e4331494ea5bd2b37cb5730ac15662a9067772 Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Mon, 10 Aug 2020 20:14:47 +0200
Subject: Quick fix to #12787 (injection anomaly due to inconsistent comp. of
 free vars).

We fix it by reducing K-redexes the same in the both places
(make_tuple and minimal_free_rels) which compute the dependencies of a
dependent equality.
---
 tactics/equality.ml                |  1 +
 test-suite/bugs/closed/bug_12787.v | 26 ++++++++++++++++++++++++++
 2 files changed, 27 insertions(+)
 create mode 100644 test-suite/bugs/closed/bug_12787.v

diff --git a/tactics/equality.ml b/tactics/equality.ml
index f1326a51a9..b4def7bb51 100644
--- a/tactics/equality.ml
+++ b/tactics/equality.ml
@@ -1134,6 +1134,7 @@ let make_tuple env sigma (rterm,rty) lind =
   assert (not (noccurn sigma lind rty));
   let sigdata = find_sigma_data env (get_sort_of env sigma rty) in
   let sigma, a = type_of ~refresh:true env sigma (mkRel lind) in
+  let a = simpl env sigma a in
   let na = Context.Rel.Declaration.get_annot (lookup_rel lind env) in
   (* We move [lind] to [1] and lift other rels > [lind] by 1 *)
   let rty = lift (1-lind) (liftn lind (lind+1) rty) in
diff --git a/test-suite/bugs/closed/bug_12787.v b/test-suite/bugs/closed/bug_12787.v
new file mode 100644
index 0000000000..2566e1f261
--- /dev/null
+++ b/test-suite/bugs/closed/bug_12787.v
@@ -0,0 +1,26 @@
+Inductive sigT3 {A: Type} {P: A -> Type} (Q: forall a: A, P a -> Type) :=
+  existT3: forall a: A, forall b: P a, Q a b -> sigT3 Q
+.
+
+Definition projT3_1 {A: Type} {P: A -> Type} {Q: forall a: A, P a -> Type} (a: sigT3 Q) :=
+  let 'existT3 _ x0 _ _ := a in x0.
+
+Definition projT3_2 {A: Type} {P: A -> Type} {Q: forall a: A, P a -> Type} (a: sigT3 Q) : P (projT3_1 a) :=
+  let 'existT3 _ x0 x1 _ := a in x1.
+
+
+
+Lemma projT3_3_eq' (A B: Type) (Q: B -> Type) (a b: sigT3 (fun (_: A) b => Q b)) (H: a = b) :
+  unit.
+Proof.
+  destruct a as [x0 x1 x2], b as [y0 y1 y2].
+  assert (H' := f_equal projT3_1 H).
+  cbn in H'.
+  subst x0.
+  assert (H' := f_equal (projT3_2 (P := fun _ => B)) H).
+  cbn in H'.
+  subst x1.
+
+  injection H as H'.
+  exact tt.
+Qed.
-- 
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