From 77e3ca28bbac9d973fbf0c5cd36de58159356710 Mon Sep 17 00:00:00 2001
From: letouzey
Date: Thu, 30 Sep 2010 17:38:31 +0000
Subject: Improve handling of metas as evars in unification (patch by Hugo)

 Pratical situation: simple eapply foo on a goal ?123, while foo is a
 (forall f, exists ...).

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@13479 85f007b7-540e-0410-9357-904b9bb8a0f7
---
 pretyping/unification.ml   |  3 ++-
 test-suite/success/evars.v | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/pretyping/unification.ml b/pretyping/unification.ml
index b45d23098a..38cf59bc0d 100644
--- a/pretyping/unification.ml
+++ b/pretyping/unification.ml
@@ -673,7 +673,8 @@ let w_merge env with_types flags (evd,metas,evars) =
 		  metas evars' eqns
 
           | _ ->
-	      w_merge_rec (solve_simple_evar_eqn env evd ev rhs')
+	    let evd', rhs'' = pose_all_metas_as_evars env evd rhs' in
+	      w_merge_rec (solve_simple_evar_eqn env evd' ev rhs'')
 		metas evars' eqns
 	end
     | [] ->
diff --git a/test-suite/success/evars.v b/test-suite/success/evars.v
index 6423ad14e8..69f7164c7a 100644
--- a/test-suite/success/evars.v
+++ b/test-suite/success/evars.v
@@ -238,3 +238,19 @@ eapply f_equal with (* should fail because ill-typed *)
         end) in H
 || injection H.
 Abort.
+
+(* A legitimate simple eapply that was failing in coq <= 8.3.
+   Cf. in Unification.w_merge the addition of an extra pose_all_metas_as_evars
+   on 30/9/2010
+*)
+
+Lemma simple_eapply_was_failing :
+ (forall f:nat->nat, exists g, f = g) -> True.
+Proof.
+ assert (modusponens : forall P Q, P -> (P->Q) -> Q) by auto.
+ intros.
+ eapply modusponens.
+ simple eapply H.
+ (* error message with V8.3 :
+    Impossible to unify "?18" with "fun g : nat -> nat => ?6 = g". *)
+Abort.
-- 
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