Fix declaration-block-no-duplicate-properties syntax error

.changeset/modern-hornets-sniff.md

@@ -0,0 +1,5 @@
+---
+"stylelint": patch
+---
+
+Fixed: `declaration-block-no-duplicate-properties` syntax error

lib/rules/declaration-block-no-duplicate-properties/__tests__/index.js

@@ -307,6 +307,8 @@ testRule({
 		{ code: 'p { width: min(10px, 11px); width: max(10px, 11px); }' },
 		{ code: 'p { width: calc((10px + 2px)); width: calc((10rem + 2rem)); }' },
 		{ code: 'p { width: calc((10px + 2px) + 10px); width: calc((10rem + 2rem) + 10px); }' },
+		{ code: 'p { width: $a; width: calc(1 + $a); }', description: 'using SCSS variables' },
+		{ code: 'p { width: _$a; width: _$a2; }', description: 'using invalid value' },
 	],
 
 	reject: [

lib/rules/declaration-block-no-duplicate-properties/index.js

@@ -4,6 +4,7 @@ const { parse, List } = require('css-tree');
 const eachDeclarationBlock = require('../../utils/eachDeclarationBlock');
 const isCustomProperty = require('../../utils/isCustomProperty');
 const isStandardSyntaxProperty = require('../../utils/isStandardSyntaxProperty');
+const isStandardSyntaxValue = require('../../utils/isStandardSyntaxValue');
 const optionsMatches = require('../../utils/optionsMatches');
 const report = require('../../utils/report');
 const ruleMessages = require('../../utils/ruleMessages');
@@ -76,8 +77,20 @@ const isEqualValueSyntaxes = (value1, value2) => {
 		return true;
 	}
 
-	const value1Node = parse(value1, { context: 'value' });
-	const value2Node = parse(value2, { context: 'value' });
+	if (!(isStandardSyntaxValue(value1) && isStandardSyntaxValue(value2))) {
+		return false;
+	}
+
+	let value1Node;
+	let value2Node;
+
+	try {
+		value1Node = parse(value1, { context: 'value' });
+		value2Node = parse(value2, { context: 'value' });
+	} catch (error) {
+		return false;
+	}
+
 	const node1Children = hasChildren(value1Node) ? value1Node.children.toArray() : [];
 	const node2Children = hasChildren(value2Node) ? value2Node.children.toArray() : [];