feat: add isVar meta data (#83)

* feat: added isVar meta tag

* test: added var usage example

* feat: added proper var check

* test: updated tests

* fix: isVar test

* test: fix tests

* fix: isVar check was too restrictive

* test: added default fallback for variable

* docs: added isVar to func docs

Author: AndyOGo

docs/Func.md

@@ -9,6 +9,11 @@ Type: `Boolean`<br>
 
 If `true`, denotes that the function represents a color-producing function. Valid color-producing functions are: `hsl()`, `hsla()`, `rgb()`, and `rgba()`.
 
+### `isVar`
+Type: `Boolean`<br>
+
+If `true`, denotes that the function represents a CSS variable usage function. Valid var function is: `var( <custom-property-name> , <declaration-value>? )`.
+
 ### `name`
 Type: `String`<br>
 

lib/nodes/Func.js

@@ -13,12 +13,14 @@ const { registerWalker } = require('../walker');
 const Container = require('./Container');
 
 const colorFunctions = ['hsl', 'hsla', 'rgb', 'rgba'];
+const reVar = /^--[^\s]+$/;
 
 class Func extends Container {
   constructor(options = {}) {
     super(options);
     this.type = 'func';
     this.isColor = false;
+    this.isVar = false;
     this.name = options.name || '';
     if (!this.nodes) {
       this.nodes = [];
@@ -101,7 +103,10 @@ class Func extends Container {
     parser.back(rightTokens);
 
     const { lastNode } = parser;
-    lastNode.isColor = colorFunctions.includes(lastNode.name.toLowerCase());
+    const lowerName = lastNode.name.toLowerCase();
+    const { nodes } = node;
+    lastNode.isColor = colorFunctions.includes(lowerName);
+    lastNode.isVar = lowerName === 'var' && nodes.length && reVar.test(nodes[0].value);
   }
 }
 

test/fixtures/func.js

@@ -29,7 +29,12 @@ module.exports = {
     'calc(1px + -2vw - 4px)',
     'calc(((768px - 100vw) / 2) - 15px)',
     'bar(baz(black, 10%), 10%)',
-    '-webkit-linear-gradient(0)'
+    '-webkit-linear-gradient(0)',
+    'var(--foo)',
+    'var( --foo)',
+    'var(--foo )',
+    'var(  --foo   )',
+    'var(--foo, default-value)'
   ],
 
   throws: ['url( /gfx/img/bg.jpg ']