From 4e529454022b7d2dc0c57d29c813c5801dfd438c Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Sun, 16 Dec 2018 20:33:09 +0100
Subject: Fixes #9229 (Infix not robust wrt choice of variable names).

---
 vernac/metasyntax.ml | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

(limited to 'vernac')

diff --git a/vernac/metasyntax.ml b/vernac/metasyntax.ml
index 4e79b50b79..3da12e7714 100644
--- a/vernac/metasyntax.ml
+++ b/vernac/metasyntax.ml
@@ -1563,14 +1563,17 @@ let add_notation_extra_printing_rule df k v =
 
 (* Infix notations *)
 
-let inject_var x = CAst.make @@ CRef (qualid_of_ident (Id.of_string x),None)
+let inject_var x = CAst.make @@ CRef (qualid_of_ident x,None)
 
 let add_infix local env ({CAst.loc;v=inf},modifiers) pr sc =
   check_infix_modifiers modifiers;
   (* check the precedence *)
-  let metas = [inject_var "x"; inject_var "y"] in
+  let vars = names_of_constr_expr pr in
+  let x = Namegen.next_ident_away (Id.of_string "x") vars in
+  let y = Namegen.next_ident_away (Id.of_string "y") vars in
+  let metas = [inject_var x; inject_var y] in
   let c = mkAppC (pr,metas) in
-  let df = CAst.make ?loc @@ "x "^(quote_notation_token inf)^" y" in
+  let df = CAst.make ?loc @@ Id.to_string x ^" "^(quote_notation_token inf)^" "^Id.to_string y in
   add_notation local env c (df,modifiers) sc
 
 (**********************************************************************)
-- 
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