mercurial/bookmarks.py

--- a/mercurial/bookmarks.py	Thu Mar 24 20:31:44 2022 -0700
+++ b/mercurial/bookmarks.py	Thu Mar 24 22:04:38 2022 -0700
@@ -27,6 +27,7 @@
     util,
 )
 from .utils import (
+    stringutil,
     urlutil,
 )
 
@@ -342,7 +343,7 @@
     # No readline() in osutil.posixfile, reading everything is
     # cheap.
     content = repo.vfs.tryread(b'bookmarks.current')
-    mark = encoding.tolocal((content.splitlines() or [b''])[0])
+    mark = encoding.tolocal(stringutil.firstline(content))
     if mark == b'' or mark not in marks:
         mark = None
     return mark