Actually merge maps instead of just concatenating

Author: s7eph4n

src/Compiler.php

@@ -4985,7 +4985,17 @@ protected function libMapMerge($args)
         $map1 = $this->assertMap($args[0]);
         $map2 = $this->assertMap($args[1]);
 
-        return [Type::T_MAP, array_merge($map1[1], $map2[1]), array_merge($map1[2], $map2[2])];
+        foreach ($map2[1] as $i2 => $key2) {
+            foreach ($map1[1] as $i1 => $key1) {
+                if ($this->compileStringContent($this->coerceString($key1)) === $this->compileStringContent($this->coerceString($key2))) {
+                    $map1[2][$i1] = $map2[2][$i2];
+                    continue 2;
+                }
+            }
+            $map1[1][] = $map2[1][$i2];
+            $map1[2][] = $map2[2][$i2];
+        }
+        return $map1;
     }
 
     protected static $libKeywords = ['args'];

tests/inputs/map.scss

@@ -25,9 +25,10 @@ div {
     bar: nth(nth($map, 1), 1);
 }
 
-$color: ("black" : #000000);
+$color: ("black" : #000000, "grey" : #777777);
+$color2: ("grey" : #888888, "white" : #ffffff);
 
-@each $color_name, $color_value in $color {
+@each $color_name, $color_value in map_merge( $color, $color2 ) {
     .#{$color_name} {
         background-color: $color_value !important;
     }

tests/outputs/map.css

@@ -12,6 +12,10 @@ div {
   bar: color; }
   .black {
     background-color: #000 !important; }
+  .grey {
+    background-color: #888 !important; }
+  .white {
+    background-color: #fff !important; }
 
 div {
   a: 1;

tests/outputs_numbered/map.css

@@ -11,10 +11,16 @@ div {
 div {
   foo: color black;
   bar: color; }
-/* line 31, inputs/map.scss */
+/* line 32, inputs/map.scss */
 .black {
   background-color: #000 !important; }
-/* line 52, inputs/map.scss */
+/* line 32, inputs/map.scss */
+.grey {
+  background-color: #888 !important; }
+/* line 32, inputs/map.scss */
+.white {
+  background-color: #fff !important; }
+/* line 53, inputs/map.scss */
 div {
   a: 1;
   b: 2;