# HG changeset patch
# User Martin von Zweigbergk <martinvonz@google.com>
# Date 2017-12-01 22:13:55
# Node ID 5cc14407a739ff54739e55907760306c9a9418fe
# Parent  900ed9853017c5f56665f6c900f16e8514e77c92

amend: make a copy of "extra" to avoid mutating an input

I don't know of any problems this has caused, it just seems less
surprising.

Differential Revision: https://phab.mercurial-scm.org/D1575

diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -3137,6 +3137,8 @@ def amend(ui, repo, old, extra, pats, op
         # base     o - first parent of the changeset to amend
         wctx = repo[None]
 
+        # Copy to avoid mutating input
+        extra = extra.copy()
         # Update extra dict from amended commit (e.g. to preserve graft
         # source)
         extra.update(old.extra())