c.unformat has logic for resetting specific attributes for the
instance of Color 'c'. This is useful when applying several Colors with
different attributes to a string or io stream, as Colors will aim to
only reset escape codes *they* applied, leaving others' intact.
c.format is invoked in 3 places, but c.unformat is invoked only in one
spot, highlighting an asymmetry. If we look at these missing spots, they
are:
 1. c.Set vs. c.unset
 2. c.SetWriter vs. c.UnsetWriter
It makes sense to apply the 'c.unformat' logic to these two cases. We
don't touch the global 'Unset' function as it does not have the context
of a particular Color, and so continues to apply a global reset code.
While here, we also make the private 'c.unset' into an exported
'c.Unset' so that 'c.Set' has a counterpart.
The added tests all fail prior to this commit, but pass after.

[1] lays out a standard for terminals to support hyperlinked text.
Support is quite widespread but not universal. Examples of support
include iTerm2, Ghostty, Alacritty, Hyper, Kitty, and more [2].
This OSC 8 standard is achieved via escape codes, very similar to what
this project does with colors and other attributes - it's a natural fit.
Because it is a little unique in how it functions, this 'hyperlink'
feature doesn't follow the existing 'Attribute' pattern. Instead, it's a
standalone field which gets special handling. That said, updating just
c.format and c.unformat is enough, as with the last commit, these are
now used in all relevant spots that affect formatting.
[1] https://gist.github.com/egmontkob/eb114294efbcd5adb1944c9f3cb5feda
[2] https://github.com/Alhadis/OSC8-Adoption/?tab=readme-ov-file 

@rhansen rhansen left a comment

Prior to this commit, when a hyperlink with no color attributes
(example:)
 color.New().Hyperlink(url)
is nested inside colored text, the outer color is being reset instead
of preserved. The root cause is that format() and unformat() are
unconditionally emitting SGR codes even when c.params are empty. An
empty params array results in '\x1b[m' (equivalent to reset-all), which
kills surrounding colors.
The fix in this commit adds a conditional check: only emit SGR codes
when 'len(c.params) > 0'. This allows plain hyperlinks to emit only OSC
8 hyperlink codes without any color resets, preserving any outer color
context. Hyperlinks with color attributes continue to work as before
since they have non-empty params.
We add a test case to cover this case.

@rhansen rhansen left a comment