UCM ANSI colors invisible in popular color schemes

[runarorama]

Here's iTerm2 with Solarized Dark, the most popular color scheme for iTerm2:

Here's iTerm2 with Gruvbox Light, another popular scheme:

Maybe we can make sure the screen is legible in like the top 6 most popular color schemes (in both dark and light variants):

1. Solarized
2. Monokai
3. Gruvbox
4. Nord
5. Dracula
6. Tomorrow Night

[pchiusano]

Which ANSI colors are causing problems here? We could either not use those colors (seems like kind of a bummer) or submit PRs upstream, since this issue would affect any program using those color schemes with ANSI codes.

[fwip]

It seems that it is unlikely that Solarized Dark will fix this upstream, unfortunately. Here's an open issue from 2012 tracking the problem. altercation/solarized#220

[pchiusano]

Good grief, I just made the mistake of reading that thread and it made me sad. But yeah, let's not counting on upstream ever changing. :)

To fix this (PR welcome!!), check in ColorText.hs. It looks like we should avoid the HiBlack ANSI code (and Black too but I don't think we use that anywhere) since some color schemes have that very similar to the background color.

Also maybe just grep for Black and HiBlack.

defaultColors :: ST.Element r -> Maybe Color
defaultColors = \case
  ST.NumericLiteral -> Nothing
  ST.TextLiteral -> Nothing
  ST.BytesLiteral -> Just HiBlack
  ST.CharLiteral -> Nothing
  ST.BooleanLiteral -> Nothing
  ST.Blank -> Nothing
  ST.Var -> Nothing
  ST.TypeReference _ -> Nothing
  ST.TermReference _ -> Nothing
  ST.Op _ -> Nothing
  ST.Unit -> Nothing
  ST.AbilityBraces -> Just HiBlack
  ST.ControlKeyword -> Just Bold
  ST.LinkKeyword -> Just HiBlack
  ST.TypeOperator -> Just HiBlack
  ST.BindingEquals -> Nothing
  ST.TypeAscriptionColon -> Just Blue
  ST.DataTypeKeyword -> Nothing
  ST.DataTypeParams -> Nothing
  ST.DataTypeModifier -> Nothing
  ST.UseKeyword -> Just HiBlack
  ST.UsePrefix -> Just HiBlack
  ST.UseSuffix -> Just HiBlack
  ST.HashQualifier _ -> Just HiBlack
  ST.DelayForceChar -> Just Yellow
  ST.DelimiterChar -> Nothing
  ST.Parenthesis -> Nothing
  ST.DocDelimiter -> Just Green
  ST.DocKeyword -> Just Bold