Fixing alpha-conversion bug #2723 introduced in r12485-12486.

The optimisation done of Namegen.visibly_occur_id did not preserve
the previous behavior when pr_constr/constr_extern/detype were
called on a term with free rel variables. We backtrack on it to
go back to the 8.2 behavior.

Seized this opportunity to clarify the meaning of the at_top flag
in constrextern.ml and printer.ml and to rename it into
goal_concl_style. The badly-named at_top flag was introduced in
Coq 6.3 in 1999 to mean that when printing variables bound in the
goal, names had to avoid the names of the variables of the goal
context, so as to keep naming stable when using "intro"; in
r4458, printing improved by not avoiding names that were short
names of global definitions, e.g. "S", or "O" (except when the
at_top flag was on for compatibility reasons).

Other printing strategies could be possible in the
non-goal-concl-style mode. For instance, all bound variables
could be made distinct in a given expression, even if no clash
occur, therefore following so-called Barendregt's
convention. This could be done by setting "avoid"
to "ids_of_rel_context (rel_context env)" in extern_constr and
extern_type (and then, Namegen.visibly_occur_id could be
re-simplified again!).

git-svn-id: svn+ssh://scm.gforge.inria.fr/svn/coq/trunk@15067 85f007b7-540e-0410-9357-904b9bb8a0f7

1 files changed, 6 insertions, 7 deletions

diff --git a/library/impargs.ml b/library/impargs.ml
index b7dbd05fd7..6b01c5fb18 100644
--- a/library/impargs.ml
+++ b/library/impargs.ml
@@ -208,11 +208,10 @@ let rec is_rigid_head t = match kind_of_term t with
 
 (* calcule la liste des arguments implicites *)
 
-let find_displayed_name_in all avoid na b =
-  if all then
-    compute_and_force_displayed_name_in (RenamingElsewhereFor b) avoid na b
-  else
-    compute_displayed_name_in (RenamingElsewhereFor b) avoid na b
+let find_displayed_name_in all avoid na (_,b as envnames_b) =
+  let flag = RenamingElsewhereFor envnames_b in
+  if all then compute_and_force_displayed_name_in flag avoid na b
+  else compute_displayed_name_in flag avoid na b
 
 let compute_implicits_gen strict strongly_strict revpat contextual all env t =
   let rigid = ref true in
@@ -220,7 +219,7 @@ let compute_implicits_gen strict strongly_strict revpat contextual all env t =
     let t = whd_betadeltaiota env t in
     match kind_of_term t with
       | Prod (na,a,b) ->
-	  let na',avoid' = find_displayed_name_in all avoid na b in
+	  let na',avoid' = find_displayed_name_in all avoid na (names,b) in
 	  add_free_rels_until strict strongly_strict revpat n env a (Hyp (n+1))
             (aux (push_rel (na',None,a) env) avoid' (n+1) (na'::names) b)
       | _ ->
@@ -233,7 +232,7 @@ let compute_implicits_gen strict strongly_strict revpat contextual all env t =
   in
   match kind_of_term (whd_betadeltaiota env t) with
     | Prod (na,a,b) ->
-	let na',avoid = find_displayed_name_in all [] na b in
+	let na',avoid = find_displayed_name_in all [] na ([],b) in
 	let v = aux (push_rel (na',None,a) env) avoid 1 [na'] b in
 	!rigid, Array.to_list v
     | _ -> true, []