Fixing #4644 (regression of unification on evar-evar problems with a match).

Typically, a problem of the form "?x args = match ?y with ... end" was
a failure even if miller-unification was applicable.

1 files changed, 52 insertions, 0 deletions

diff --git a/test-suite/bugs/closed/4644.v b/test-suite/bugs/closed/4644.v
new file mode 100644
index 0000000000..f09b27c2b1
--- /dev/null
+++ b/test-suite/bugs/closed/4644.v
@@ -0,0 +1,52 @@
+(* Testing a regression of unification in 8.5 in problems of the form
+   "match ?y with ... end = ?x args" *)
+
+Lemma foo : exists b, forall a, match a with tt => tt end = b a.
+Proof.
+eexists. intro.
+refine (_ : _ = match _ with tt => _ end).
+refine eq_refl.
+Qed.
+
+(**********************************************************************)
+
+Axiom proof_admitted : False.
+Tactic Notation "admit" := case proof_admitted.
+Require Export Coq.Classes.Morphisms.
+Require Import Coq.Lists.List.
+
+Global Set Implicit Arguments.
+
+Definition list_caset A (P : list A -> Type) (N : P nil) (C : forall x xs, P (x::xs))
+           ls
+  : P ls
+  := match ls with
+     | nil => N
+     | x::xs => C x xs
+     end.
+
+Axiom list_caset_Proper'
+  : forall {A P},
+    Proper (eq
+              ==> pointwise_relation _ (pointwise_relation _ eq)
+              ==> eq
+              ==> eq)
+           (@list_caset A (fun _ => P)).
+Goal forall (T T' : Set) (a3 : list T), exists y2, forall (a4 : T' -> bool),
+        match a3 with
+        | nil => 0
+        | (_ :: _)%list => 1
+        end = y2 a4.
+  clear; eexists; intros.
+  reflexivity. Undo.
+  Local Ltac t :=
+    lazymatch goal with
+    | [ |- match ?v with nil => ?N | cons x xs => @?C x xs end = _ :> ?P ]
+      => let T := type of v in
+         let A := match (eval hnf in T) with list ?A => A end in
+         refine (@list_caset_Proper' A P _ _ _ _ _ _ _ _ _
+                 : @list_caset A (fun _ => P) N C v = match _ with nil => _ | cons x xs => _ end)
+    end.
+  (etransitivity; [ t | reflexivity ]) || fail 0 "too early".
+  Undo.
+  t.