Raise error on invalid @value definitions

Author: cmrn

index.js

@@ -38,7 +38,12 @@ const replaceValueSymbols = (valueString, replacements) => {
 };
 
 const getDefinition = (atRule, existingDefinitions, requiredDefinitions) => {
-  const [/* match */, name, middle, value, end] = matchValueDefinition.exec(atRule.params);
+  const matches = matchValueDefinition.exec(atRule.params);
+  if (!matches) {
+    throw atRule.error('Invalid @value definition');
+  }
+
+  const [/* match */, name, middle, value, end] = matches;
   const valueWithReplacements = replaceValueSymbols(value, existingDefinitions);
 
   if (!requiredDefinitions) {

index.test.js

@@ -67,12 +67,18 @@ test('gives an error when path to imported file is wrong', async (t) => {
   await t.expect(processor.process(input, parserOpts)).rejects.toThrow("Can't resolve './non-existent-file.css'");
 });
 
-test('gives an error when @value statement is invalid', async (t) => {
+test('gives an error when @value import statement is invalid', async (t) => {
   const input = '@value , from "./colors.css"';
   const processor = postcss([plugin]);
   await t.expect(processor.process(input, parserOpts)).rejects.toThrow('@value statement "" is invalid!');
 });
 
+test('gives an error when @value declaration is invalid', async (t) => {
+  const input = '@value oops;';
+  const processor = postcss([plugin]);
+  await t.expect(processor.process(input, parserOpts)).rejects.toThrow('Invalid @value definition');
+});
+
 test('shouldn\'t break on draft spec syntax', async (t) => {
   await run(
     t,