Extend looses @supports imported by reference

New logic: directive with body that contains something referenced (for
example by extend) will be shown in output too. @Media works with the same
logic - it shows up in output if it contains something visible.

Related to: #2359

lib/less/tree/directive.js

@@ -73,6 +73,9 @@ Directive.prototype.markReferenced = function () {
         }
     }
 };
+Directive.prototype.getIsReferenced = function () {
+    return !this.currentFileInfo || !this.currentFileInfo.reference || this.isReferenced;
+};
 Directive.prototype.outputRuleset = function (context, output, rules) {
     var ruleCnt = rules.length, i;
     context.tabLevel = (context.tabLevel | 0) + 1;

lib/less/tree/ruleset.js

@@ -414,13 +414,44 @@ Ruleset.prototype.genCSS = function (context, output) {
     }
 };
 Ruleset.prototype.markReferenced = function () {
-    if (!this.selectors) {
-        return;
+    var s;
+    if (this.selectors) {
+        for (s = 0; s < this.selectors.length; s++) {
+            this.selectors[s].markReferenced();
+        }
     }
-    for (var s = 0; s < this.selectors.length; s++) {
-        this.selectors[s].markReferenced();
+
+    if (this.rules) {
+        for (s = 0; s < this.rules.length; s++) {
+            if (this.rules[s].markReferenced)
+                this.rules[s].markReferenced();
+        }
     }
 };
+Ruleset.prototype.getIsReferenced = function() {
+    var i, j, path, selector;
+
+    if (this.paths) {
+        for (i=0; i<this.paths.length; i++) {
+            path = this.paths[i];
+            for (j=0; j<path.length; j++) {
+                if (path[j].getIsReferenced && path[j].getIsReferenced())
+                    return true;
+            }
+        }
+    }
+
+    if (this.selectors) {
+        for (i=0;i<this.selectors.length;i++) {
+            selector = this.selectors[i];
+            if (selector.getIsReferenced && selector.getIsReferenced())
+                return true;
+        }
+    }
+    return false;
+};
+
+
 Ruleset.prototype.joinSelectors = function (paths, context, selectors) {
     for (var s = 0; s < selectors.length; s++) {
         this.joinSelector(paths, context, selectors[s]);

lib/less/visitors/to-css-visitor.js

@@ -46,10 +46,10 @@ ToCSSVisitor.prototype = {
     },
 
     visitDirective: function(directiveNode, visitArgs) {
-        if (directiveNode.currentFileInfo.reference && !directiveNode.isReferenced) {
-            return;
-        }
         if (directiveNode.name === "@charset") {
+            if (!directiveNode.getIsReferenced()) {
+                return;
+            }
             // Only output the debug info together with subsequent @charset definitions
             // a comment (or @media statement) before the actual @charset directive would
             // be considered illegal css as it has to be on the first line
@@ -65,6 +65,37 @@ ToCSSVisitor.prototype = {
         }
         if (directiveNode.rules && directiveNode.rules.rules) {
             this._mergeRules(directiveNode.rules.rules);
+            //process childs
+            directiveNode.accept(this._visitor);
+            visitArgs.visitDeeper = false;
+
+            // the directive was directly referenced and therefore needs to be shown in the output
+            if (directiveNode.getIsReferenced()) {
+                return directiveNode;
+            }
+
+            if (!directiveNode.rules.rules) {
+                return ;
+            }
+
+            //the directive was not directly referenced
+            for (var r = 0; r<directiveNode.rules.rules.length; r++) {
+                var rule = directiveNode.rules.rules[r];
+                if (rule.getIsReferenced && rule.getIsReferenced()) {
+                    //the directive contains something that was referenced (likely by extend)
+                    //therefore it needs to be shown in output too
+
+                    //marking as referenced in case the directive is stored inside another directive
+                    directiveNode.markReferenced();
+                    return directiveNode;
+                }
+            }
+            //The directive was not directly referenced and does not contain anything that
+            //was referenced. Therefore it must not be shown in output.
+            return ;
+        } else {
+            if (!directiveNode.getIsReferenced())
+                return;
         }
         return directiveNode;
     },

test/css/import-reference.css

@@ -34,6 +34,14 @@ div#id.class[a=1][b=2].class:not(1) {
 .visible + .visible .sub {
   color: green;
 }
+@supports (something: else) {
+  .class {
+    something: else;
+  }
+  .nestedToo .class {
+    something: else;
+  }
+}
 .b {
   color: red;
   color: green;

test/less/import-reference.less

@@ -18,4 +18,4 @@
 }
 
 .class:extend(.class all) {
-}
+}

test/less/import/import-reference.less

@@ -48,4 +48,18 @@
   @media (max-size: @max-size) {
     color: red;
   }
-}
+}
+
+@supports (something: else) {
+  .class {
+    something: else;
+  }
+  .nestedToo {
+    .class {
+      something: else;
+    }
+  }
+  .invisible {
+    something: else;
+  }
+}