From dffe222e9d84c423a3e3c1e9b36d36a37727dc7b Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Sun, 30 Aug 2020 06:49:22 +0200
Subject: Fixes part 1 of #12908 (collision involving a lonely notation).

Strangely, this was not yet noticed. Hiding of a scoped notation by a
lonely notation should be checked at printing time.
---
 interp/notation.ml | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

(limited to 'interp/notation.ml')

diff --git a/interp/notation.ml b/interp/notation.ml
index 17ae045187..7e90e15b72 100644
--- a/interp/notation.ml
+++ b/interp/notation.ml
@@ -1198,10 +1198,25 @@ let rec find_without_delimiters find (ntn_scope,ntn) = function
           find_without_delimiters find (ntn_scope,ntn) scopes
       end
   | LonelyNotationItem ntn' :: scopes ->
-      begin match ntn_scope, ntn with
-      | LastLonelyNotation, Some ntn when notation_eq ntn ntn' ->
-        Some (None, None)
+      begin match ntn with
+      | Some ntn'' when notation_eq ntn' ntn'' ->
+        begin match ntn_scope with
+        | LastLonelyNotation ->
+          (* If the first notation with same string in the visibility stack
+             is the one we want to print, then it can be used without
+             risking a collision *)
+           Some (None, None)
+        | NotationInScope _ ->
+          (* A lonely notation is liable to hide the scoped notation
+             to print, we check if the lonely notation is active to
+             know if the delimiter of the scoped notationis needed *)
+          if find default_scope then
+            find_with_delimiters ntn_scope
+          else
+            find_without_delimiters find (ntn_scope,ntn) scopes
+        end
       | _ ->
+        (* A lonely notation which does not interfere with the notation to use *)
         find_without_delimiters find (ntn_scope,ntn) scopes
       end
   | [] ->
-- 
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