don't allow unescaped combining marks

lib/rules/no-misleading-character-class.js

@@ -115,9 +115,14 @@ const findCharacterSequences = {
  }
  },
 
- *combiningClass(chars) {
+ *combiningClass(chars, unfilteredChars) {
+
+ /*
+ * When `allowEscape` is `true`, a combined character should only be allowed if the combining mark appears as an escape sequence.
+ * This means that the base character should be considered even if it's escaped.
+ */
  for (const [index, char] of chars.entries()) {
- const previous = chars[index - 1];
+ const previous = unfilteredChars[index - 1];
 
  if (
  previous && char &&
@@ -359,14 +364,18 @@ module.exports = {
 
  visitRegExpAST(patternNode, {
  onCharacterClassEnter(ccNode) {
- for (let chars of iterateCharacterSequence(ccNode.elements)) {
+ for (const unfilteredChars of iterateCharacterSequence(ccNode.elements)) {
+ let chars;
+
  if (allowEscape) {
 
  // Replace escape sequences with null to avoid having them flagged.
- chars = chars.map(char => (isAcceptableEscapeSequence(char) ? null : char));
+ chars = unfilteredChars.map(char => (isAcceptableEscapeSequence(char) ? null : char));
+ } else {
+ chars = unfilteredChars;
  }
  for (const kind of kinds) {
- const matches = findCharacterSequences[kind](chars);
+ const matches = findCharacterSequences[kind](chars, unfilteredChars);
 
  if (foundKindMatches.has(kind)) {
  foundKindMatches.get(kind).push(...matches);

tests/lib/rules/no-misleading-character-class.js

@@ -126,7 +126,7 @@ ruleTester.run("no-misleading-character-class", rule, {
  options: [{ allowEscape: true }]
  },
  {
- code: String.raw`/[\n̅]/`,
+ code: String.raw`/[\n\u0305]/`,
  options: [{ allowEscape: true }]
  },
  {
@@ -1680,6 +1680,11 @@ ruleTester.run("no-misleading-character-class", rule, {
  options: [{ allowEscape: true }],
  errors: [{ messageId: "combiningClass" }]
  },
+ {
+ code: String.raw`/[\n̅]/`,
+ options: [{ allowEscape: true }],
+ errors: [{ messageId: "combiningClass" }]
+ },
  {
  code: String.raw`/[\👍]/`,
  options: [{ allowEscape: true }],