Prompt is printed with SGR 40, resulting in black bands on supporting terminals

[DHowett]

Purpose of the issue

• Bug report (encountered problems/errors)
• Feature request (request for new functionality)
• Question

Version Information

This was migrated from microsoft/terminal#9693, and it appears to be valid with the latest code on master.
The user is using cmder's shell configuration outside of ConEmu, so I understand if this is not a valid report.

Description of the issue

When updating the prompt here ...

cmder/vendor/clink.lua

Line 50 in c34eb73

local cmder_prompt = "\x1b[1;32;40m{cwd} {git}{hg}{svn} \n\x1b[1;39;40m{lamb} \x1b[0m"

... clink specifically requests graphical rendition 40, "ANSI Color 0 Background". This works fairly well for the traditional Windows console and ConEmu, but it is not entirely correct. There is no guarantee that the user's background color is ANSI color 0! In certain terminals (Windows Terminal, gnome-terminal, ...) the user can specify a background color that cannot be represented via SGR, such as that of an image or a transparency effect.

The result is that when the user has transparency enabled, their terminal looks somewhat like this:

The ideal solution would be to print using SGR 49, "revert to default background". This has been supported on all versions of Windows where ENABLE_VIRTUAL_TERMINAL_PROCESSING supports colors, so there is no compatibility risk.

We had to fix a similar issue here in PowerShell: PowerShell/PSReadLine#1626

In short, the Windows console is getting better at determining when the user wanted a specific background color and when they wanted the default. I need to do an actual write-up about what's changed rather than writing a bunch of different GitHub comments, so that I can point users and developers at it.

[chrisant996]

What about the green text? Using "revert default background" would cause the green text to be invisible when the background is green. I'm pretty sure that's why an explicit background color is used by default.

Instead of changing the default, maybe it would be better to make it more easily configurable.

[DHowett]

That's a fair point, of course. 😄

[DHowett]

Thinking on it a bit more, I'm not certain that we should be so defensive of users who set unexpected settings. Consider the default bash prompt in most Debian-derived distributions:

PS1='${debian_chroot:+($debian_chroot)}\[\033[01;32m\]\u@\h\[\033[00m\]:\[\033[01;34m\]\w\[\033[00m\]\$ '

Or the default root prompt for SLES-12:

Each of those bears a risk, yes, but they've been doing it for ages and all they do is set the foreground! 😄

[chrisant996]

I use green background in some console Windows.

Why would it be "unexpected" for users to make choices about how they will use colors? Programs are not the only things allowed to choose colors.

I think it's a mistake to label it as officially "unexpected" and therefore "unsupported".

If a program makes it easily configurable, then ok, maybe the program can make assumptions since it lets the user override the configuration. That's why I suggested an effective solution could be to make it configurable. It is not currently configurable in Cmder (without editing Cmder scripts, which will be overwritten by the next update).

[chrisant996]

I don’t really have a stake in what Cmder does. Personally, I prefer to use ConEmu directly and have my own script for setting up my command windows.†

But in the relatively short time I’ve been working on Clink, I’ve seen several requests for Cmder to allow easy configuration of the lambda, and colors, etc. If Cmder makes the color and lambda character configurable, then it would seem very reasonable to use SGR 49, since the configurability would enable a user to change the green text color if they want to use a green background for the whole console.

† (Actually I prefer to just use the default console window support in the OS -- I might use Windows Terminal, except that it doesn't seem to let me set the font, and I want to use Consolas NF or Fira Code NF.)

[Lunchb0ne]

I think for now we can add a little note to the wiki page where we detail how to setup the prompt for windows terminal and detail how to fix this and probably add a reference to this issue.

[Hejle]

Note that the SGR 40 is also used for Git status (Line 305) and for mercurial status (Line 350). I think that if the promt color is changed to another value than 40 (or made editable), git status and mercurial status should be edited in the same way.

[Lunchb0ne]

Is there a way to check the terminal at startup and set it according to that?

[chrisant996]

Is there a way to check the terminal at startup and set it according to that?

Check for what, and set what?

[richyk1]

I'm not really sure how I could contribute and fix this issue on the main branch because I didn't manage to build the project in Visual Studio. However, if anyone is trying to fix this issue then you can create a file called my_prompt.lua in your root directory -> config folder, and the paste the following:

function my_prompt_filter()
    cwd = clink.get_cwd()
    prompt = "\x1b[1;32;49m{cwd} {git}{hg}{svn} \n\x1b[2;37;49m{lamb} \x1b[0m"
    new_value = string.gsub(prompt, "{cwd}", cwd)
    clink.prompt.value = string.gsub(new_value, "{lamb}", "★")
end

clink.prompt.register_filter(my_prompt_filter, 1)

[Lunchb0ne]

Is there a way to check the terminal at startup and set it according to that?

Check for what, and set what?

The values, so 40 if it's a legacy terminal and 49 if it's a terminal that supports extended/ custom backgrounds.

[chrisant996]

Is there a way to check the terminal at startup and set it according to that?

Check for what, and set what?

The values, so 40 if it's a legacy terminal and 49 if it's a terminal that supports extended/ custom backgrounds.

How does one check what terminal system might be hosting it behind the scenes, and what settings are in effect in that terminal system that could be relevant?

Also, I think the issue is about contrast between "current background color" vs "current foreground color". That's why 40 is used instead of 49.

Since there's not a reliable way to check what terminal is being used or what settings are in effect for it, typically it's left as something for the user to configure. Since if the background is solid green, or a photo, both those are things the user had to configure. And they were given an easy way to configure them. So, it seems reasonable to continue with the existing model, and make Cmder have an easy way to configure the prompt colors instead of hard-coding them to 40 or 49.

[Lunchb0ne]

Is there a way to check the terminal at startup and set it according to that?

Check for what, and set what?

The values, so 40 if it's a legacy terminal and 49 if it's a terminal that supports extended/ custom backgrounds.

How does one check what terminal system might be hosting it behind the scenes, and what settings are in effect in that terminal system that could be relevant?

Also, I think the issue is about contrast between "current background color" vs "current foreground color". That's why 40 is used instead of 49.

Since there's not a reliable way to check what terminal is being used or what settings are in effect for it, typically it's left as something for the user to configure. Since if the background is solid green, or a photo, both those are things the user had to configure. And they were given an easy way to configure them. So, it seems reasonable to continue with the existing model, and make Cmder have an easy way to configure the prompt colors instead of hard-coding them to 40 or 49.

Using something like this:
https://github.com/lptstr/winfetch/blob/2c9590df0900c5392657dc452a25e67d9a6646f6/winfetch.ps1#L533-L573

While it can be useful, it would really slow down the startup so, I think the best way would just be declaring another prompt by the user in a lua, which would give really good customization and control. It can also go another way and allow the config to be written/read from a file.

[chrisant996]

How does one check what terminal system might be hosting it behind the scenes, and what settings are in effect in that terminal system that could be relevant?

Using something like this:
https://github.com/lptstr/winfetch/blob/2c9590df0900c5392657dc452a25e67d9a6646f6/winfetch.ps1#L533-L573

While it can be useful, it would really slow down the startup

In fact, Clink does something similar internally; see clink.getansihost() in Clink's Lua API. It's super fast in native code. But the result isn't fully reliable.

The cited script detects some terminals. It doesn't detect their capabilities or configuration. The script can make some guesses, but it can't achieve a reliable answer.

Here are some of the unreliable points:

• In terminals that support image or blur backgrounds, the setting is off by default. And other terminals don't support that at all. Some allow different settings per window.
• Console2/Z does not do any ANSI escape code processing; it lets the OS handle them. So depending on the OS version ANSI escape codes may not be supported, or may be partially supported, or may have the latest and greatest level of support. But even then, Console2/Z are unable to render the colors from xterm-256 and xterm-24bit escape codes, and end up using the closest match out of the basic 16 colors.
• xterm-256 and xterm-24bit escape codes are supported in the Window ConsoleV2 mode. But there isn't a way to query a specific terminal window whether it is currently using ConsoleV2 mode.
• I wonder whether the "parent process" approach depends on OS version. E.g. in older Windows versions Process Explorer shows conhost.exe as the parent of cmd.exe. In recent Windows versions it's reversed; Process Explorer shows cmd.exe as the parent of conhost.exe.

I think the best way would just be declaring another prompt by the user in a lua, which would give really good customization and control. It can also go another way and allow the config to be written/read from a file.

I agree. At the same time, it seems to be a common point of user feedback. That makes me wonder if it might save user frustration and might save time offering support help, if Cmder had a simple configurable setting to change the lambda and/or the prompt color.