insertRule() must try parsing declarations for grouping rules

Author: cdoublev

lib/parse/parser.js

@@ -5,9 +5,11 @@ import * as grammar from './grammar.js'
 import * as substitutions from '../values/substitutions.js'
 import {
     CSSFontFeatureValuesMap,
+    CSSGroupingRule,
     CSSImportRule,
     CSSLayerStatementRule,
     CSSNamespaceRule,
+    CSSNestedDeclarations,
     CSSRule,
     CSSStyleSheet,
 } from '../cssom/index.js'
@@ -124,19 +126,31 @@ function isInvalidNamespaceRule(list, rule) {
 
 /**
  * @param {CSSRuleListImpl[]} list
- * @param {CSSRuleImpl} rule
+ * @param {string} input
  * @param {number} index
  * @param {object} context
  * @param {boolean} [allowImport]
  * @returns {number}
  * @see {@link https://drafts.csswg.org/cssom-1/#insert-a-css-rule}
  */
-function insertRule(list, rule, index, context, allowImport) {
+function insertRule(list, input, index, context, allowImport) {
     if (list.length < index) {
         throw error(INVALID_RULE_INDEX_ERROR)
     }
-    rule = parseRule(rule, context)
+    let rule = parseRule(input, context)
     if (isError(rule)) {
+        if (CSSGroupingRule.isImpl(context)) {
+            const declarations = parseDeclarationList(input, context)
+            if (0 < declarations.length) {
+                rule = CSSNestedDeclarations.createImpl(context._globalObject, undefined, {
+                    declarations,
+                    parentRule: context,
+                    parentStyleSheet: context.parentStyleSheet,
+                })
+                list.splice(index, 0, rule)
+                return index
+            }
+        }
         throw error(rule)
     }
     if (!allowImport && CSSImportRule.isImpl(rule)) {