copy: recommend `--at-rev .` if target was added in parent commit

If the target file was added in the working copy parent, it's much
more likely that the user meant to use `--at-rev .` (to record the
copy/rename in the that commit) than `--force` (to replace the
just-added file by another file).

Differential Revision: https://phab.mercurial-scm.org/D11667

mercurial/cmdutil.py

@@ -1678,6 +1678,24 b' def copy(ui, repo, pats, opts, rename=Fa'
             if not opts[b'force']:
                 if already_commited:
                     msg = _(b'%s: not overwriting - file already committed\n')
+                    # Check if if the target was added in the parent and the
+                    # source already existed in the grandparent.
+                    looks_like_copy_in_pctx = abstarget in pctx and any(
+                        abssrc in gpctx and abstarget not in gpctx
+                        for gpctx in pctx.parents()
+                    )
+                    if looks_like_copy_in_pctx:
+                        if rename:
+                            hint = _(
+                                b"('hg rename --at-rev .' to record the rename "
+                                b"in the parent of the working copy)\n"
+                            )
+                        else:
+                            hint = _(
+                                b"('hg copy --at-rev .' to record the copy in "
+                                b"the parent of the working copy)\n"
+                            )
+                    else:
                     if after:
                         flags = b'--after --force'
                     else:

tests/test-rename-rev.t

@@ -42,6 +42,17 b' Test single file'
     d1/b
   A d1/d
     d1/b
+# Should get helpful message if we try to copy or rename after commit
+  $ hg cp --forget --at-rev . d1/d
+  saved backup bundle to $TESTTMP/.hg/strip-backup/3f7c325d3f9e-46f377bb-uncopy.hg
+  $ hg cp d1/b d1/d
+  d1/d: not overwriting - file already committed
+  ('hg copy --at-rev .' to record the copy in the parent of the working copy)
+  [1]
+  $ hg mv d1/b d1/d
+  d1/d: not overwriting - file already committed
+  ('hg rename --at-rev .' to record the rename in the parent of the working copy)
+  [1]
 
 Test moved file (not copied) using 'hg cp' command