Add linear-gradient syntax invalid warnings

Author: yuezk

index.js

@@ -176,6 +176,9 @@ function getDirection(gradient) {
 
 function gradientToFilter(gradient) {
     var obj = parseGradient(gradient);
+
+    if (!obj) return null;
+
     var startColor = obj.colorStops[0].color;
     var endColor = obj.colorStops.slice(-1)[0].color;
     var result = getDirection(obj);
@@ -214,7 +217,6 @@ function getGradientFromRule(rule) {
         var len = gradients.length;
         // Only select the first gradienat if there more than one gradients
         if (len) {
-            // skip `linear-gradient`
             gradient.value = gradients[0].trim();
             gradient.decl = decl;
 
@@ -251,6 +253,12 @@ module.exports = postcss.plugin('postcss-filter-gradient', function (opts) {
                 if (gradient.value) {
                     filter = gradientToFilter(gradient.value);
 
+                    // warn users when the gradient value is not valid.
+                    if (!filter) {
+                        gradient.decl.warn(result, '`' + gradient.value + '` is not a valid linear gradient value.');
+                        return;
+                    }
+
                     if (opts.skipMultiColor && filter.isMultiColor) {
                         return;
                     }

test/fixtures/invalid-syntax.css

@@ -0,0 +1,7 @@
+a {
+    background: linear-gradient();
+}
+
+b {
+    background: linear-gradient(#000);
+}

test/fixtures/invalid-syntax.expect.css

@@ -0,0 +1,7 @@
+a {
+    background: linear-gradient();
+}
+
+b {
+    background: linear-gradient(#000);
+}

test/test.js

@@ -13,8 +13,9 @@ var test = function (inputFile, opts, done, warnings) {
     postcss([plugin(opts)]).process(input).then(function (result) {
         expect(result.css).to.eql(output);
         if (warnings) {
-            result.warnings().forEach(function (warn) {
-                expect(warn.text).to.eql(warnings);
+            result.warnings().forEach(function (warn, i) {
+                var expectedWarning = Array.isArray(warnings) ? warnings[i] : warnings;
+                expect(warn.text).to.eql(expectedWarning);
             });
         } else {
             expect(result.warnings()).to.be.empty;
@@ -42,6 +43,15 @@ describe('postcss-filter-gradient', function () {
         test('filter', {}, done, warnings);
     });
 
+    it('should do nothing when handle invalid linear gradient syntax', function (done) {
+        var warnings = [
+            '`linear-gradient()` is not a valid linear gradient value.',
+            '`linear-gradient(#000)` is not a valid linear gradient value.'
+        ];
+
+        test('invalid-syntax', {}, done, warnings);
+    });
+
     it('should support the standard syntax', function (done) {
         test('standard', {}, done);
     });