Alpha hex support

[Soviut]

#697 proposes single and double character hex color support (eg: #E would convert to #EEEEEE).

In the spirit of this, I'm proposing support for alpha hex support.

#FF000080

The extra two hex digits at the end would represent the alpha/opacity. LESS could convert this to:

rgba(255, 0, 0, 0.5)

Producing a pure red with 50% opacity.

[lukeapage]

will this get in the way of the old IE 8 hex digits? As I remember that begins with alpha.. where as here you would expect it to end in alpha.. Plus I imagine taking an old css sheet and suddenly accepting 8 hex digits and then outputting rgba would also break things.

[Synchro]

Yes, while I agree that #RRGGBBAA makes more sense to me, that would indeed clash with argb (#AARRGGBB) that's already in LESS. Admittedly it's done via a function, not a language construct, but it would seem to make sense to use the same format in both if we're to do that.

[Soviut]

I didn't realize IE had 8 digit hex. LESS could still normalize this but it could potentially break existing IE-specific sheets. Somehow, I doubt many people are using said IE-specific hex values these day though.

That, or support the #AARRGGBB format throughout. But I think that is backwards-looking.

[lukeapage]

.. just recently someone went to the trouble of extending dotless to leave these type of hex values alone

dotless/dotless@52ba9a4

TBH I think I see more gain in allowing #E then stepping into the minefield of 8 digit hex

[Synchro]

Yes, I don't think this is really worth doing.

[Soviut]

Perhaps as a sub-proposal, some way of indicating that the colour is ARGB vs RGBA?

#RRGGBBAA

versus

##AARRGGBB

or

#RRGGBB,AA
#RRGGBB|AA
#RRGGBB_AA

[lukeapage]

closing due to general lack of support for this feature.

[ashsearle]

Can this be reopened bearing in mind 4 and 8-digit hex are defined in CSS Color Module Level 4
and already supported in various browsers?

[matthew-dean]

I assume Less could auto-convert #RRGGBBAA to rgba()?

[seven-phases-max]

Yes, it's just a matter of adding add a few lines to handle #4 and #8 cases everywhere (it's not too many) #3 and #6 things are parsed.

[LordPachelbel]

I don't know when it happened, but at some point rgba() became able to convert #rrggbbaa colors to rgba().

Example:
box-shadow: 0 3px 6px rgba(#00000029); will output as box-shadow: 0 3px 6px rgba(0, 0, 0, 0.16078431);

It isn't documented but it should be, so I did so in this pull request.