From 4c3064c6e679cfbe4ce13a76b50a17bcfffe4d71 Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Sun, 30 Aug 2020 21:44:36 +0200
Subject: Fixes a freshness issue with induction (see comment in #12944).

The names computed in consume_pattern were lost when calling
intros_pattern_core. Moreover, the computation of names to avoid was
done several time. We compute it once for all.
---
 tactics/tactics.ml          |  5 +----
 test-suite/success/induct.v | 10 ++++++++++
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/tactics/tactics.ml b/tactics/tactics.ml
index eb7b7e363f..00bd56d8ba 100644
--- a/tactics/tactics.ml
+++ b/tactics/tactics.ml
@@ -3248,13 +3248,10 @@ let rec consume_pattern avoid na isdep gl = let open CAst in function
   | {loc;v=IntroForthcoming true}::names when not isdep ->
       consume_pattern avoid na isdep gl names
   | {loc;v=IntroForthcoming _}::names as fullpat ->
-      let avoid = Id.Set.union avoid (explicit_intro_names names) in
       (CAst.make ?loc @@ intropattern_of_name gl avoid na, fullpat)
   | {loc;v=IntroNaming IntroAnonymous}::names ->
-      let avoid = Id.Set.union avoid (explicit_intro_names names) in
       (CAst.make ?loc @@ intropattern_of_name gl avoid na, names)
   | {loc;v=IntroNaming (IntroFresh id')}::names ->
-      let avoid = Id.Set.union avoid (explicit_intro_names names) in
       (CAst.make ?loc @@ IntroNaming (IntroIdentifier (new_fresh_id avoid id' gl)), names)
   | pat::names -> (pat,names)
 
@@ -3312,7 +3309,7 @@ let get_recarg_dest (recargdests,tophyp) =
 *)
 
 let induct_discharge with_evars dests avoid' tac (avoid,ra) names =
-  let avoid = Id.Set.union avoid avoid' in
+  let avoid = Id.Set.union avoid' (Id.Set.union avoid (explicit_intro_names names)) in
   let rec peel_tac ra dests names thin =
     match ra with
     | (RecArg,_,deprec,recvarname) ::
diff --git a/test-suite/success/induct.v b/test-suite/success/induct.v
index 73fe53c757..a39b17e1f1 100644
--- a/test-suite/success/induct.v
+++ b/test-suite/success/induct.v
@@ -196,3 +196,13 @@ Goal forall m n:nat, n=m.
 double induction m n.
 Abort.
 
+(* Mentioned as part of bug #12944 *)
+
+Inductive test : Set := cons : forall (IHv : nat) (v : test), test.
+
+Goal test -> test.
+induction 1 as [? IHv].
+Undo.
+destruct 1 as [? IHv].
+exact IHv. (* Check that the name is granted *)
+Qed.
-- 
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