Re: [ANNOUNCEMENT] Updated: mintty 2.7.4

[Thomas Wolff <towo@towo.net>]

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Am 07.02.2017 um 08:30 schrieb Brian Inglis:
> On 2017-02-06 12:46, Thomas Wolff wrote:
>> Am 05.02.2017 um 21:36 schrieb Brian Inglis:
>>> On 2017-02-05 11:35, Thomas Wolff wrote:
>>>> Am 04.02.2017 um 17:13 schrieb Achim Gratz:
>>>>> Thomas Wolff writes:
>>>>>> I have uploaded mintty 2.7.4 with the following changes:
>>>>> Since about November/December last year I'm having problems with
>>>>> screen and tmux sessions in mintty not correctly refreshing and
>>>>> leaving garbage characters displayed in the terminal. It seems that
>>>>> the terminal size is not always correctly reported, especially if
>>>>> you make the window occupy the left or right half of the screen via
>>>>> Windows shortcut.
>>>> Is this within tmux or after leaving tmux (see comment below)? It
>>>> would be help to cross-test this; if it's mintty, which version
>>>> would show the behaviour first? What happens in xterm?
>>>>> Additionally, there seems to be an off-by-one bug when the last
>>>>> line of the terminal needs to be scrolled up in order to show
>>>>> content that is longer than the remaining width. This happens when
>>>>> you for instance recall a long command from history. It's hard to
>>>>> see what exactoly happens, but it looks like the one character too
>>>>> many gets printed (and wraps onto the next line) before the whole
>>>>> terminal window gest scrolled up and the rest of the command gets
>>>>> printed in the line below the single wrapped character. That
>>>>> remainder is in various states of disarray, showing both remnants
>>>>> from the original prompt on the last line (now three lines up),
>>>>> empty /spaces where there should have been characters from the
>>>>> command and then of course parts of the command.
>>>> This might be related to some issue with terminal geometry as
>>>> perceived by the shell (see
>>>> https://github.com/mintty/mintty/issues/377#issuecomment-137728631).
>>>> Have you checked that? Recently changed your prompt? Try with basic
>>>> prompt (PS1="\w> ") please.
>>> Thanks for supporting and enhancing mintty to be even better in
>>> Cygwin, and able to be used as a console for other environments.
>>> The test below may be relevant to the above problem, or may be
>>> unrelated.
>>> Running vttest 2.7 (20140305)
>>> http://invisible-island.net/vttest/vttest.html
>>> updated by and used by xterm maintainer for testing.
>>> Test 1. Test of cursor movements screens 3 80 col mode and 4 132 col
>>> mode gives results looking like below ...
>> I was aware this test fails, but save any related bug reports so far
>> I had assumed it would not be relevant for applications...
>> Actually, urxvt (rxvt-unicode as invoked on cygwin) fails the same
>> test in the same way, so @Achim: can you please retest with urxvt,
>> for some additional diagnostic information?
> vttest site documents xterm implements VT100 am/xenl compatibly
> and rxvt and some other consoles do not: ignoring non-print characters
> and sequences until a printable character advances to the next row:
> see:
>
> http://invisible-island.net/vttest/vttest-wrap.html
It's even weirder than that (see also your details provided below); in 
no-Wraparound mode, if you output something to the last column, and the 
cursor is staying in that column, a Backspace will go into the previous 
column (e.g. 79), see the attached test file for some surprising 
results. See below for further comments.


>> Actually, also xterm would fail this test if vttest would not disable
>> Reverse Wraparound mode initially.
>> It also enables Wraparound mode which again affects the test case.
>> Mintty does not support Reverse Wraparound mode disabling, it's
>> always implicitly enabled. I could try to change that, however, I'm
>> not sure yet that's really the cause.
>> Also, the "proper" way to handle wraparound situations (in the 4
>> combinations of the 2 modes) is not completely clear, and Reverse
>> Wraparound is an xterm specific mode which did not exist on the DEC
>> terminals. See some links for reference:
>> bash - An obscure one: Documented VT100 'soft-wrap' escape sequence?
>> - Stack Overflow
> http://stackoverflow.com/questions/31360385/an-obscure-one-documented-vt100-soft-wrap-escape-sequence#31360700
>> XTerm – Frequently Asked Questions (FAQ)
>> http://invisible-island.net/xterm/xterm.faq.html#vt100_wrapping
> My last remaining VT ref seems to be (c) 1987 June DEC EK-VT320-UG-001
> VT320 UG which says on pp.23-24:
>
> "Table 4-4  Display Set-Up Features
> Feature		Settings*	Function
> ...
> Auto Wrap			Selects whether on not text automati-
> 				cally wraps to the next line when you
> 				reach the right margin.
>
> 		*No Auto Wrap*	When the cursor reaches the margin,
> 				the VT320 displays each new charac-
> 				ter/
> /
> Auto Wrap	*No Auto Wrap*	in the last column of the line. Each
> (cont)		(cont)		new character overwrites the previous
> 				character.
>
> 		Auto Wrap	When the cursor reaches the margin,
> 				the VT320 displays new characters on
> 				the next line.
> ...
> *     Default settings are in *bold* type."
>
> [The visual effect of characters "piling up" on the right margin when
> sending 132 character lines at low speed to earlier VT terminals set
> to 80 column width seemed amusing to us at the time, and ensured that
> never happened in our code: Auto Wrap was not the default and never
> assumed or set in anything we used.]
See comments above and attachment for the consequences of this 
behaviour; they are logically consistent but still very weird.
I could change mintty to mimic this behaviour, but I'd need some 
evidence that this would solve some real-world issues before I take the 
risk of possibly breaking other applications.
Further comments welcome, and it's Achim's turn to provide further 
diagnostics input as requested in another mail. It could also be that 
screen or tmux simply make invalid assumptions about the setting of 
Wraparound modes.
------
Thomas

>
>> VT100 Termcap Entry (CENG 455)
>> http://www.pitt.edu/%7Ejcaretto/text/cleanup/vt100-termcap.html

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