copy: add experimetal support for unmarking committed copies The simplest way I'm aware of to unmark a file as copied after committing is this: hg uncommit --keep <dest> hg forget <dest> hg add <dest> hg amend This patch teaches `hg copy --forget` a `-r` argument to simplify that into: hg copy --forget --at-rev . <dest> In addition to being simpler, it doesn't touch the working copy, so it can easily be used even if the destination file has been modified in the working copy. I'll teach `hg copy` without `--forget` to work with `--at-rev` next. Differential Revision: https://phab.mercurial-scm.org/D8030

--- a/tests/test-rename-after-merge.t	Fri Dec 20 15:50:13 2019 -0800
+++ b/tests/test-rename-after-merge.t	Tue Jan 28 14:07:57 2020 -0800
@@ -120,4 +120,10 @@
   $ hg log -r tip -C -v | grep copies
   copies:      b2 (b1)
 
+Test unmarking copies in merge commit
+
+  $ hg copy --forget --at-rev . b2
+  abort: cannot unmark copy in merge commit
+  [255]
+
   $ cd ..