harden rgba() replacement re value signature and use warning to see full calling stack

Author: haschek

src/common/scss/_color-functions.scss

@@ -89,11 +89,33 @@
     @return eccgui-color-mix($color 100% * $alpha, transparent);
 }
 
+$debug-rgba-values: "yes";
+
+/**
+ * Split between rgba(red, green, blue, alpha) and rgba(color, alpha).
+ */
+@function rgba($r, $g, $b: "undefined", $a: 1) {
+    // check if old notation is used
+    @if meta.variable-exists("r") && meta.variable-exists("g") && $b == "undefined" {
+        // rgba(color, alpha) was used
+        // forward to our color check splitter
+        // @debug ("rgba input: #{$r} #{$g}"); // looks like the signature r,g,b,a always get transformed to color,alpha
+        @return rgba-extended($r, $g);
+    } @else {
+        // rgba(r, g, b, a) is used
+        // should never trigger because of the magical transformation
+        $color-new-notation: rgb(#{$r} #{$g} #{$b} / #{$a});
+
+        @error "Old color notation found -> use #{$color-new-notation}";
+        @return $color-new-notation;
+    }
+}
+
 /**
  * Overwrite SCSS built-in rgba function to support colors by custom properties and CSS color methods.
  * TODO: we need to check if this is future proof, maybe this bahaviour is not planned by Dart Sass library.
  */
-@function rgba($color, $alpha) {
+@function rgba-extended($color, $alpha) {
     @if meta.type-of($color) == "color" {
         // value is SASS color value, we use SASS color functionality
         $alphacolor: color.change($color, $alpha: $alpha);
@@ -102,7 +124,10 @@
             $alphacolor: transparent;
         }
 
-        @debug "Color value $color is not defined by CSS custom property: rgba(#{$color}, #{$alpha}) -> #{$alphacolor}";
+        @if $debug-rgba-values == "yes" {
+            @warn "Color value $color is not defined by CSS custom property: rgba(#{$color}, #{$alpha}) -> #{$alphacolor}";
+        }
+
         @return $alphacolor;
     } @else {
         // value is not a SASS color value, we use CSS color method