check export options for changeset before running

# HG changeset patch
# User [e-mail]
# Node ID 0cc64f4312540b2081c76dc589cc825d734676d8
# Parent  f7bfe827ea381afc89f486b2d93d7f4fe86de04d
check export options for changeset before running

diff -r f7bfe827ea38 -r 0cc64f431254 mercurial/commands.py

mercurial/commands.py

@@ -526,6 +526,9 b' def doexport(ui, repo, changeset, seqno,'
 
 def export(ui, repo, *changesets, **opts):
     """dump the header and diffs for one or more changesets"""
+    if not changesets:
+        ui.warn("error: export requires at least one changeset\n")
+        sys.exit(1)
     seqno = 0
     revs = list(revrange(ui, repo, changesets))
     total = len(revs)