From b74f85accd0347383faeefd62c49d4f47d556084 Mon Sep 17 00:00:00 2001
From: Eric Wieser <wieser.eric@gmail.com>
Date: Tue, 17 Sep 2024 10:57:35 +0100
Subject: [PATCH] fix: do not ban `..` with a `.` on the next line (#4768)

Without this change,
```lean
example : True := by
  refine' trivial ..
  . trivial
```
is a parse error.
---
 src/Lean/Parser/Term.lean |  2 +-
 tests/lean/run/4768.lean  | 10 ++++++++++
 2 files changed, 11 insertions(+), 1 deletion(-)
 create mode 100644 tests/lean/run/4768.lean

diff --git a/src/Lean/Parser/Term.lean b/src/Lean/Parser/Term.lean
index 5a88595b7ec2..e9980bea794f 100644
--- a/src/Lean/Parser/Term.lean
+++ b/src/Lean/Parser/Term.lean
@@ -763,7 +763,7 @@ We use them to implement `macro_rules` and `elab_rules`
 def namedArgument  := leading_parser (withAnonymousAntiquot := false)
   atomic ("(" >> ident >> " := ") >> withoutPosition termParser >> ")"
 def ellipsis       := leading_parser (withAnonymousAntiquot := false)
-  ".." >> notFollowedBy "." "`.` immediately after `..`"
+  ".." >> notFollowedBy (checkNoWsBefore >> ".") "`.` immediately after `..`"
 def argument       :=
   checkWsBefore "expected space" >>
   checkColGt "expected to be indented" >>
diff --git a/tests/lean/run/4768.lean b/tests/lean/run/4768.lean
new file mode 100644
index 000000000000..520f25caed2e
--- /dev/null
+++ b/tests/lean/run/4768.lean
@@ -0,0 +1,10 @@
+/-!
+Test that `..` tokens do not break nearby `.`s.
+
+Note that this tests specifically for issues with `.` that are not present with `·`.
+-/
+
+example : True ∧ True := by
+  constructor
+  refine trivial ..
+  . trivial -- this has to be . not · for this test to be useful