errors: move similarity_hint() to error module I want to be able to reuse it from `UnknownIdentifier`'s constructor. Moving it results in a new import of `difflib` in the `error` module. There was a comment at the top of `error.py` saying "Do not import anything but pycompat here, please", which was added (except for the "pycompat" bit) in 08cabecfa8a8 (errors: move revlog errors, 2009-01-11). I don't know the reason for the comment. I'm guessing the point was to not make the module depend on other Mercurial modules. If that was it, then importing `difflib` should be fine. Sorry about the churn (I moved this code from the `dispatch` module to the `scmutil` module very recently). Differential Revision: https://phab.mercurial-scm.org/D9345

--- a/mercurial/dispatch.py	Thu Nov 19 09:19:44 2020 -0800
+++ b/mercurial/dispatch.py	Thu Nov 19 12:20:26 2020 -0800
@@ -484,10 +484,10 @@
         except (error.UnknownCommand, error.Abort):
             suggested = False
             if inst.all_commands:
-                sim = scmutil.getsimilar(inst.all_commands, inst.command)
+                sim = error.getsimilar(inst.all_commands, inst.command)
                 if sim:
                     ui.warn(nocmdmsg)
-                    ui.warn(b"(%s)\n" % scmutil.similarity_hint(sim))
+                    ui.warn(b"(%s)\n" % error.similarity_hint(sim))
                     suggested = True
             if not suggested:
                 ui.warn(nocmdmsg)