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 ++++++++++++++++++---
 test-suite/output/bug_12908.out |  2 ++
 test-suite/output/bug_12908.v   |  6 ++++++
 3 files changed, 26 insertions(+), 3 deletions(-)
 create mode 100644 test-suite/output/bug_12908.out
 create mode 100644 test-suite/output/bug_12908.v

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
   | [] ->
diff --git a/test-suite/output/bug_12908.out b/test-suite/output/bug_12908.out
new file mode 100644
index 0000000000..fca6dde704
--- /dev/null
+++ b/test-suite/output/bug_12908.out
@@ -0,0 +1,2 @@
+forall m n : nat, m * n = (2 * m * n)%nat
+     : Prop
diff --git a/test-suite/output/bug_12908.v b/test-suite/output/bug_12908.v
new file mode 100644
index 0000000000..558c9f9f6a
--- /dev/null
+++ b/test-suite/output/bug_12908.v
@@ -0,0 +1,6 @@
+Definition mult' m n := 2 * m * n.
+Module A.
+(* Test hiding of a scoped notation by a lonely notation *)
+Infix "*" := mult'.
+Check forall m n, mult' m n = Nat.mul (Nat.mul 2 m) n.
+End A.
-- 
cgit v1.2.3


From a0090dc6930c1f0c60ca6144d1551019ecbcc837 Mon Sep 17 00:00:00 2001
From: Hugo Herbelin
Date: Sun, 30 Aug 2020 07:58:06 +0200
Subject: Adding change log for #12946.

---
 ...946-master+fix12908-part1-collision-lonely-notation-printing.rst | 6 ++++++
 1 file changed, 6 insertions(+)
 create mode 100644 doc/changelog/03-notations/12946-master+fix12908-part1-collision-lonely-notation-printing.rst

diff --git a/doc/changelog/03-notations/12946-master+fix12908-part1-collision-lonely-notation-printing.rst b/doc/changelog/03-notations/12946-master+fix12908-part1-collision-lonely-notation-printing.rst
new file mode 100644
index 0000000000..95a9093272
--- /dev/null
+++ b/doc/changelog/03-notations/12946-master+fix12908-part1-collision-lonely-notation-printing.rst
@@ -0,0 +1,6 @@
+- **Fixed:**
+  Undetected collision between a lonely notation and a notation in
+  scope at printing time
+  (`#12946 <https://github.com/coq/coq/pull/12946>`_,
+  fixes the first part of `#12908 <https://github.com/coq/coq/issues/12908>`_,
+  by Hugo Herbelin).
-- 
cgit v1.2.3