gears.color: Add support for named colors

Oh hey, Pango exports an API that allows to query for named colors based on the
famous rgb.txt! Let's use that!

Signed-off-by: Uli Schlachter <psychon@znc.in>

lib/gears/color.lua

@@ -13,14 +13,16 @@ local tonumber = tonumber
 local ipairs = ipairs
 local pairs = pairs
 local type = type
-local cairo = require("lgi").cairo
+local lgi = require("lgi")
+local cairo = lgi.cairo
+local Pango = lgi.Pango
 local surface = require("gears.surface")
 
 local color = { mt = {} }
 local pattern_cache
 
 --- Parse a HTML-color.
--- This function can parse colors like `#rrggbb` and `#rrggbbaa`.
+-- This function can parse colors like `#rrggbb` and `#rrggbbaa` and also `red`.
 -- Thanks to #lua for this. :)
 --
 -- @param col The color to parse
@@ -28,8 +30,10 @@ local pattern_cache
 -- @usage -- This will return 0, 1, 0, 1
 -- gears.color.parse_color("#00ff00ff")
 function color.parse_color(col)
-    -- Get all hex chars
     local rgb = {}
+    -- Is it a HTML-style color?
+    if string.match(col, "^#%x+$") then
+        -- Get all hex chars
         for char in string.gmatch(col, "[^#]") do
             table.insert(rgb, tonumber(char, 16) / 0xf)
         end
@@ -49,6 +53,17 @@ function color.parse_color(col)
             rgb = merged
             factor = next_factor
         end
+    else
+        -- Let's ask Pango for its opinion (but this doesn't support alpha!)
+        local c = Pango.Color()
+        if c:parse(col) then
+            rgb = {
+                c.red / 0xffff,
+                c.green / 0xffff,
+                c.blue / 0xffff,
+            }
+        end
+    end
     -- Add missing groups (missing alpha)
     while #rgb < 4 do
         table.insert(rgb, 1)

spec/gears/color_spec.lua

@@ -22,6 +22,10 @@ describe("gears.color", function()
             test(0, 0, 0, 0xff, "#000000")
         end)
 
+        it("black", function()
+            test(0, 0, 0, 0xff, "black")
+        end)
+
         it("opaque black", function()
             test(0, 0, 0, 0xff, "#000000ff")
         end)
@@ -34,6 +38,10 @@ describe("gears.color", function()
             test(0xff, 0xff, 0xff, 0x7f, "#ffffff7f")
         end)
 
+        it("chartreuse", function()
+            test(0x7f, 0xff, 0x00, 0xff, "chartreuse")
+        end)
+
         describe("different lengths", function()
             local function gray(e, e_a, input)
                 local o_r, o_g, o_b, o_a, unused = color.parse_color(input)