feat(fonts): Allow for code to be run when a font is first loaded

core/font.lua

@@ -42,6 +42,11 @@ SILE.registerCommand("font", function (options, content)
     SILE.settings.set("font.hyphenchar", SU.utf8charfromcodepoint(options.hyphenchar))
   end
 
+  -- We must *actually* load the font here, because by the time we're inside
+  -- SILE.shaper.shapeToken, it's too late to respond appropriately to things
+  -- that the post-load hook might want to do.
+  SILE.font.cache(SILE.font.loadDefaults({}), SILE.shaper.getFace)
+
   if type(content) == "function" or content[1] then
     SILE.process(content)
     SILE.settings.popState()
@@ -95,10 +100,20 @@ SILE.font = {
     local key = _key(options)
     if not SILE.fontCache[key] then
       SU.debug("fonts", "Looking for "..key)
-      SILE.fontCache[key] = callback(options)
+      local face = callback(options)
+      SILE.font.postLoadHook(face)
+      SILE.fontCache[key] = face
     end
     return SILE.fontCache[key]
   end,
 
+  postLoadHook = function(face)
+    local ot = SILE.require("core/opentype-parser")
+    local font = ot.parseFont(face)
+    if font.cpal then
+      SILE.require("packages/color-fonts")
+    end
+  end,
+
   _key = _key
 }