Suggestion: Make Stack.PrettyPrint's styles background agnostic

[mpilgrem]

Should the styles set in module Stack.PrettyPrint force the background to be black ('dull' black)? For example (line 181) styleFile = bold . white . ondullblack. Beauty is in the eye of the beholder, but it seems to me that, for people using terminal themes with coloured backgrounds, the result is not pretty. For example, on a Mac Terminal with theme 'Novel':

I suggest it would be better to be agnostic as to background and have (for example): styleFile = bold . white.

This is on stack --version Version 1.8.0, Git revision 94d302c40d3d08dcaa0213f3f1ffdc1384842714 (6077 commits) x86_64 hpack-0.29.0 (given #4139).

[mihaimaruseac]

The problem is that text becomes harder to read on terminals with white background. So, unless we can find a solution which detects the background before determining what color to use, we will have to also set background color.

[mgsloan]

I agree that it's not pretty. Indeed it was a solution to text not being visible on light backgrounds - #4047 . An alternative may be to remove the background color and pick foreground colors that terminals are likely to display well.

[mpilgrem]

This comment is also in response to the comments of @mihaimaruseac on the pull request #4184.

I acknowledge that if you do not force the background colour, there will always be some choice of terminal background colour that makes certain coloured foreground text 'invisible' - but perhaps stack does not need to accommodate all possible terminal background colours, only the most likely ones (including the extremes of dull black and vivid white)?

On a white (vivid white) terminal do you think it is only the 'bold vivid white' text on white (used by styleFile and styleUrl) that is problematic? If it is, perhaps a different foreground colour there would solve the problem.

For example 'vivid black' (black) or 'dull white' (which are both actually rendered as shades of grey on most terminals - see here) should have contrast on most terminal backgrounds.

This is 'vivid black' for styleFile on macOS Terminal's 'Basic' (white) theme:

This is 'vivid black' on Terminal's 'Novel' theme:

Alternatively (skipping shades of green and red as having special meaning or colours where the unused dull version is not particularly distinct from the vivid one), 'dull magenta' is currently not used by any style.

If that is an acceptable fix, I'll propose another pull request, accordingly.

[mihaimaruseac]

I tend to agree with this.

[mgsloan]

Yep, I agree with removing the background colors that I added, and instead choosing different foreground colors. Glad you're adjusting these details!

[mpilgrem]

I have done some further reading around and experimenting.

To avoid the reported 'vivid yellow' on 'vivid white' contrast problem (#4047), I suggest that 'dull yellow' substitute for 'vivid yellow'.

I do not use it myself, but I understand that 'solarized dark' is a very popular theme on a number of platforms and is, for example, accommodated by the (recent) Windows console colortool. 'vivid black' text does not work at all on solarized dark and, so, I now propose 'dull cyan' where I previously proposed 'vivid back'.

Here are some results:

The (new) Windows default console theme (known as 'campbell') (this is actually a screen shot of macOS Terminal.app; I have reproduced the Windows default there to ease experimentation):

The 'Basic' Terminal.app theme (vivid white):

The 'Solarized Dark' theme (note that stack's choice of 'vivid green' is not distinctive in this theme - however 'dull green' would be; I am going to propose a separate 'issue' to more fully address that sort of issue and the 'bigger picture' of colour choice for stack users):

Finally (for consistency with my earlier comments), the 'Novel' Terminal.app theme:

If this is acceptable, I will propose the corresponding pull request.

[mihaimaruseac]

This looks good to me