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less with -r option causes strange display behavior for input with ANSI control characters #9176
Description
Environment
Windows build number: [run `[Environment]::OSVersion` for powershell, or `ver` for cmd]: 10.0.19041.0
Windows Terminal version (if applicable): 1.5.10411.0
Any other software?
Ubuntu on WSL 1
Steps to reproduce
Have a long file, in this case produced with git reflog. Examine with less. Notice that output does not include the first ~10 lines.
git reflog > reflog.out
head reflog.out
5240aea1 HEAD@{0}: checkout: moving from zachmu/windows to aaron/indexed-in-subquery-filter
56ac2928 HEAD@{1}: checkout: moving from aaron/indexed-in-subquery-filter to zachmu/windows
5240aea1 HEAD@{2}: checkout: moving from zachmu/windows to aaron/indexed-in-subquery-filter
56ac2928 HEAD@{3}: checkout: moving from aaron/indexed-in-subquery-filter to zachmu/windows
5240aea1 HEAD@{4}: checkout: moving from master to aaron/indexed-in-subquery-filter
1acb0aab HEAD@{5}: pull: Fast-forward
66627818 HEAD@{6}: checkout: moving from zachmu/windows to master
56ac2928 HEAD@{7}: commit: Added some more query tests for window funcs
cb14e839 HEAD@{8}: commit: Working row_number() function
5f08c885 HEAD@{9}: commit: Semi working sort order. Moved more functions and types around to avoid cycles.
less reflog presents me with a screen that starts like this:
rtField up to the sql package and gave it some more methods.
e9c3d6d8 HEAD@{11}: commit: Added window setting to function analysis
98044728 HEAD@{12}: commit: Chalked in outline of adding all rows to a window expression. Now need a way to get Window values into the functions.
d8fcf55e HEAD@{13}: commit: Sketched out an iter
000efaba HEAD@{14}: commit: Chalked out a window node. This involved moving some Sort related types out of the plan package to the expression package
66627818 HEAD@{15}: checkout: moving from master to zachmu/windows
As you can see, the first ~10 lines of the file are not there. If I press the up arrow, less does not respond (chimes the bell). If I press the down arrow key twice, then the up arrow key twice, I see this:
5240aea1 HEAD@{0}: checkout: moving from zachmu/windows to aaron/indexed-in-subquery-filter
56ac2928 HEAD@{1}: checkout: moving from aaron/indexed-in-subquery-filter to zachmu/windows
98044728 HEAD@{12}: commit: Chalked in outline of adding all rows to a window expression. Now need a way to get Window values into the functions.
d8fcf55e HEAD@{13}: commit: Sketched out an iter
Something very strange is happening with the display buffering here. I've noticed this on other invocations of less as well, not just when examining this particular file.
Expected behavior
When less is invoked the terminal should contain the first page of text from the input. Instead, it's starting about 10 lines in.
Actual behavior
As described above
Activity
DHowett commentedon Feb 15, 2021
Do you have anything in your startup scripts that would change the size of the console window (
MODE CON LINES=,$Host.UI.RawUI.WindowSize=,stty,printf "\e[..........t", etc.?)zachmu commentedon Feb 15, 2021
Good question!
Digging through my .zshrc, it appears this line is the culprit:
export LESS=-rUnsetting this var fixes the issue. Presumably triggered by ANSI color codes in the output of various git commands where I've noticed this?
I don't know if this is a windows terminal problem or not. I do know I've had that line in my .zshrc for over a decade and never noticed a problem before using windows terminal.
DHowett commentedon Feb 15, 2021
Really curious, that. When you remove
-r, do you see any control sequences in thelessoutput?zachmu commentedon Feb 15, 2021
Nope, I don't see any printed control sequences in the output.
I notice that the man page for less has this to say about the -r option:
So maybe this is the whole of the story? Still not sure if this is a problem with WSL / windows terminal or not.
For anyone reading, this is the current value of $LESS, which gets rid of the problem for me:
2 remaining items
DHowett commentedon Feb 17, 2021
Alright, one more thing to troubleshoot.
Can you get it in a state where it'll reproduce, and then hit me with a
script? It should be in thebsdutilspackage.If you're not comfortable sharing
typescriptpublicly, you can send it to my GitHub profile's e-mail address.If you're not comfortable sharing
typescriptprivately, you get to pick through it to find what control sequence less is emitting that we're catching and handling.DHowett commentedon Feb 17, 2021
(It'll capture all the unparsed VT coming out of any of its child processes.)
zachmu commentedon Feb 22, 2021
Here you go! (zipped because github only accepts certain file types)
Repro was:
less reflog.outWith
LESS=-rtypescript.zip