[Bug 6207] New: output after quitting pager on python3.7

[mercurial-bugs at mercurial-scm.org]

https://bz.mercurial-scm.org/show_bug.cgi?id=6207

            Bug ID: 6207
           Summary: output after quitting pager on python3.7
           Product: Mercurial
           Version: 5.2rc0
          Hardware: PC
                OS: Linux
            Status: UNCONFIRMED
          Severity: feature
          Priority: wish
         Component: pager
          Assignee: bugzilla at mercurial-scm.org
          Reporter: zash at zash.se
                CC: mercurial-devel at mercurial-scm.org
    Python Version: 3.8

To reproduce:

$ hg log # ( or anything that invokes the pager )
observe output and pager prompt
quit pager
observe output

Python2 behavior:
after quitting pager, no additional output is printed, shell prompt replaces
pager prompt

Python3 behavior:
after quitting pager, some amount of additional output is shown, causing output
shown prior to quitting pager to move up.
The extra output does not appear to be the lines that would have directly
followed the previously shown lines, but seems to have jumped a bit.

Example:

(in a clone of mercurial itself, terminal window about 23 lines high)

$ hg log <enter>
Terminal shows:
===============================================================================
changeset:   43316:4565a0afc289
branch:      stable
bookmark:    @
tag:         tip
user:        Gregory Szorc <gregory.szorc at gmail.com>
date:        Mon Oct 21 19:53:30 2019 -0700
summary:     packaging: upgrade packages distributed with Windows installers

changeset:   43315:388ada1c07c6
branch:      stable
user:        Gregory Szorc <gregory.szorc at gmail.com>
date:        Mon Oct 21 19:28:23 2019 -0700
summary:     automation: install Python 2.7.17, 3.7.5, and PyPy 7.2.0

changeset:   43314:8676a8b2d20a
branch:      stable
user:        Gregory Szorc <gregory.szorc at gmail.com>
date:        Mon Oct 21 19:25:06 2019 -0700
summary:     contrib: install Python 2.7.17 and 3.7.5 in Windows environment

changeset:   43313:a882c088dc2e
branch:      stable
user:        Denis Laxalde <denis at laxalde.org>
:
===============================================================================

After pressing 'q':

===============================================================================
user:        Denis Laxalde <denis at laxalde.org>
changeset:   43039:7902001aaf41
user:        Pierre-Yves David <pierre-yves.david at octobus.net>
date:        Fri Sep 27 16:40:07 2019 +0200
summary:     sidedata: make sure we don't use the flag if there are not
sidedata

changeset:   43038:7bb5a2465501
user:        Pierre-Yves David <pierre-yves.david at octobus.net>
date:        Tue Sep 03 23:45:38 2019 +0200
summary:     revlog: add the appropriate flag is sidedata are passed to
`addrevision`

changeset:   43037:142deb539ccf
user:        Pierre-Yves David <pierre-yves.david at octobus.net>
date:        Wed Sep 04 03:20:55 2019 +0200
summary:     sidedata: register the flag processors if the repository allows
for it

changeset:   43036:e8bc4c3d9a0b
user:        Pierre-Yves David <pierre-yves.david at octobus.net>
date:        Wed Sep 04 03:19:58 2019 +0200
summary:     sidedata: add a function for _processflagsraw usage

hg$ 
===============================================================================

$ hg debuginstall
checking encoding (UTF-8)...
checking Python executable (/usr/bin/python3)
checking Python version (3.7.3)
checking Python lib (/usr/lib/python3.7)...
checking Python security support (sni,tls1.0,tls1.1,tls1.2)
checking Mercurial version (5.2rc0)
checking Mercurial custom build (10-4565a0afc289)
checking module policy (c)
checking installed modules (/usr/lib/python3/dist-packages/mercurial)...
checking registered compression engines (bz2, bz2truncated, none, zlib, zstd)
checking available compression engines (bz2, bz2truncated, none, zlib, zstd)
checking available compression engines for wire protocol (zstd, zlib, bz2,
none)
checking "re2" regexp engine (missing)
checking templates (/usr/lib/python3/dist-packages/mercurial/templates)...
checking default template
(/usr/lib/python3/dist-packages/mercurial/templates/map-cmdline.default)
checking commit editor... (sensible-editor)
checking username...
 no username supplied
 (specify a username in your configuration file) (actually ignore, semi-clean
environment to ensure my config didn't interfere)
1 problems detected, please check your install!

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