[Bug 1873920] Re: default vi on focal emits escape sequences unrecognized by bionic's terminal?

[Allen McIntosh]

Workaround:

ex file

visual
("visual" can be abbreviated as "vi")

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Title:
  default vi on focal emits escape sequences unrecognized by bionic's
  terminal?

Status in vim package in Ubuntu:
  Confirmed

Bug description:
  On ubuntu 18.04, opening the default terminal (gnome-terminal
  3.28.2-1ubuntu1~18.04.1), ssh'ing to an up-to-date ubuntu 20.04
  system, running 'vi', and pressing 'i' shows the unwelcome garbage ESC
  [>4;m.  Pressing ESC emits more garbage: ESC [>4;2m

  Focal's default vi is provided by vim.tiny via alternatives.  Oddly,
  when running vim.tiny by itself, or if you install vim and let it
  provide vi, the garbage does not appear.

  Evidently focal's vim.tiny is confused about what escape sequences
  ubu1804's Terminal accepts.

  TERM is xterm-256color.  The problem also occurs if TERM is xterm.

  There is no .vimrc.

  If I use xterm on ubuntu 18.04, all is well.  Evidently xterm accepts
  ESC[>4;m and gnome-terminal doesn't?

  I captured a session using 'script' and dumped typescript via hexdump -C. 
  In this session, I typed i, Q, and escape. Here's an excerpt
  showing the end of vi's welcome message, followed by five escape sequences
  and then the Q I typed.  The unrecognized ESC > 4;m is visible in the dump,
  followed by ESC[?25l (CURSOR OFF)

  00001070  66 61 75 6c 74 1b 5b 33  34 6d 3c 45 6e 74 65 72  |fault.[34m<Enter|
  00001080  3e 1b 5b 6d 20 66 6f 72  20 69 6e 66 6f 20 6f 6e  |>.[m for info on|
  00001090  20 74 68 69 73 1b 5b 31  3b 31 48 1b 5b 3f 32 35  | this.[1;1H.[?25|
  000010a0  68 1b 5b 3f 32 30 30 34  6c 1b 5b 3e 34 3b 6d 1b  |h.[?2004l.[>4;m.|
  000010b0  5b 3f 32 35 6c 51 1b 5b  38 3b 34 37 48 1b 5b 31  |[?25lQ.[8;47H.[1|

  The mystery sequence ESC [ > 4;m appears to be "Set/reset key modifier options, xterm",
  per https://invisible-island.net/xterm/ctlseqs/ctlseqs.html.  So it's trying
  to modify function keys, or something.

  ssh'ing in from a mac worked fine (TERM there was also xterm-256color),
  as did ssh'ing from an ubuntu 19.04 system with gnome-terminal.
  ssh'ing from another ubuntu 18.04 system exhibited the same problem.

  So it's a little family squabble between focal's vim.tiny and ubuntu
  18.04/bionic's gnome-terminal...?

  Given how long 18.04's going to be supported, this seems worth
  resolving somehow.

  ProblemType: Bug
  DistroRelease: Ubuntu 20.04
  Package: vim-tiny 2:8.1.2269-1ubuntu5 [modified: usr/share/vim/vim81/doc/help.txt usr/share/vim/vim81/doc/tags]
  ProcVersionSignature: Ubuntu 5.4.0-25.29-generic 5.4.30
  Uname: Linux 5.4.0-25-generic x86_64
  ApportVersion: 2.20.11-0ubuntu27
  Architecture: amd64
  CasperMD5CheckResult: skip
  Date: Mon Apr 20 09:27:50 2020
  InstallationDate: Installed on 2020-01-27 (83 days ago)
  InstallationMedia: Ubuntu 20.04 LTS "Focal Fossa" - Alpha amd64 (20200124)
  SourcePackage: vim
  UpgradeStatus: No upgrade log present (probably fresh install)

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