fix(issue:3737) allow blank variable declarations

* Fixes issue with blank CSS variable declarations.

Author: puckowski

packages/less/src/less/parser/parser.js

@@ -1598,7 +1598,11 @@ const Parser = function Parser(context, imports, fileInfo, currentIndex) {
 
                         // Custom property values get permissive parsing
                         if (name[0].value && name[0].value.slice(0, 2) === '--') {
-                            value = this.permissiveValue(/[;}]/);
+                            if (parserInput.$char(';')) {
+                                value = new Anonymous('');
+                            } else {
+                                value = this.permissiveValue(/[;}]/);
+                            }
                         }
                         // Try to store values as anonymous
                         // If we need the value later we'll re-parse it in ruleset.parseValue

packages/test-data/css/_main/variables.css

@@ -69,3 +69,11 @@
   mul-px-2: 140px;
   mul-px-3: 140px;
 }
+*,
+::before,
+::after {
+  --tw-pan-x: ;
+  --tw-pan-y: ;
+  --tw-pinch-zoom: ;
+  --tw-scroll-snap-strictness: proximity;
+}

packages/test-data/less/_main/variables.less

@@ -125,3 +125,10 @@
     mul-px-3: ((@px * 1) * @cm);
   }
 }
+
+*, ::before, ::after {
+	--tw-pan-x:  ;
+	--tw-pan-y:  ;
+	--tw-pinch-zoom:  ;
+	--tw-scroll-snap-strictness: proximity;
+}