copy: distinguish "file exists" cases and add a hint (BC) Users that want to add a copy record to an existing commit with 'hg commit --amend' should be guided towards this workflow, rather than reaching for some sort of uncommit-recommit flow. As part of this, distinguish in the top-line error message whether the file merely already exists (untracked) on disk or the file already exists in history. The full list of copy and rename cases and how they interact with flags are listed below: target exists --after --force | action n n * | copy n y * | (1) untracked n n | (4) NEWHINT untracked n y | (3) untracked y * | (2) y n n | (4) NEWHINT y n y | (3) y y n | (2) y y y | (3) deleted n n | copy deleted n y | (3) deleted y n | (1) deleted y y | (1) * = don't care (1) <src>: not recording move - <target> does not exist (2) preserve target contents (3) replace target contents (4) <target>: not overwriting - file {exists,already committed} Credit to Kevin for wholly rewriting my table to cover more cases we discovered at the sprint. I think this change gets the hints correct in all cases, but I'd appreciate close inspection of the test cases to make sure I haven't gotten turned around in here.

--- a/mercurial/cmdutil.py	Sun Oct 09 01:03:20 2016 +0900
+++ b/mercurial/cmdutil.py	Mon Sep 19 17:15:39 2016 -0400
@@ -646,8 +646,26 @@
 
         if not after and exists or after and state in 'mn':
             if not opts['force']:
-                ui.warn(_('%s: not overwriting - file exists\n') %
-                        reltarget)
+                if state in 'mn':
+                    msg = _('%s: not overwriting - file already committed\n')
+                    if after:
+                        flags = '--after --force'
+                    else:
+                        flags = '--force'
+                    if rename:
+                        hint = _('(hg rename %s to replace the file by '
+                                 'recording a rename)\n') % flags
+                    else:
+                        hint = _('(hg copy %s to replace the file by '
+                                 'recording a copy)\n') % flags
+                else:
+                    msg = _('%s: not overwriting - file exists\n')
+                    if rename:
+                        hint = _('(hg rename --after to record the rename)\n')
+                    else:
+                        hint = _('(hg copy --after to record the copy)\n')
+                ui.warn(msg % reltarget)
+                ui.warn(hint)
                 return
 
         if after: