Remove helpers.deepFreeze and call Object.freeze only on things that need it for ~11% time reduction measured via profile-fixture.mjs on Apple Silicon M1.

lib/markdownlint.js

@@ -191,13 +191,38 @@ function removeFrontMatter(content, frontMatter) {
 }
 
 /**
- * Annotate tokens with line/lineNumber.
+ * Freeze all freeze-able members of a token and its children.
+ *
+ * @param {MarkdownItToken} token A markdown-it token.
+ * @returns {void}
+ */
+function freezeToken(token) {
+  if (token.attrs) {
+    for (const attr of token.attrs) {
+      Object.freeze(attr);
+    }
+    Object.freeze(token.attrs);
+  }
+  if (token.children) {
+    for (const child of token.children) {
+      freezeToken(child);
+    }
+    Object.freeze(token.children);
+  }
+  if (token.map) {
+    Object.freeze(token.map);
+  }
+  Object.freeze(token);
+}
+
+/**
+ * Annotate tokens with line/lineNumber and freeze them.
  *
  * @param {MarkdownItToken[]} tokens Array of markdown-it tokens.
  * @param {string[]} lines Lines of Markdown content.
  * @returns {void}
  */
-function annotateTokens(tokens, lines) {
+function annotateAndFreezeTokens(tokens, lines) {
   let trMap = null;
   for (const token of tokens) {
     // Provide missing maps for table content
@@ -222,7 +247,9 @@ function annotateTokens(tokens, lines) {
       while (token.map[1] && !((lines[token.map[1] - 1] || "").trim())) {
         token.map[1]--;
       }
-      // Annotate children with lineNumber
+    }
+    // Annotate children with lineNumber
+    if (token.children) {
       let lineNumber = token.lineNumber;
       const codeSpanExtraLines = [];
       helpers.forEachInlineCodeSpan(
@@ -231,7 +258,7 @@ function annotateTokens(tokens, lines) {
           codeSpanExtraLines.push(code.split(helpers.newLineRe).length - 1);
         }
       );
-      for (const child of (token.children || [])) {
+      for (const child of token.children) {
         child.lineNumber = lineNumber;
         child.line = lines[lineNumber - 1];
         if ((child.type === "softbreak") || (child.type === "hardbreak")) {
@@ -241,7 +268,9 @@ function annotateTokens(tokens, lines) {
         }
       }
     }
+    freezeToken(token);
   }
+  Object.freeze(tokens);
 }
 
 /**
@@ -532,14 +561,14 @@ function lintContent(
   // Parse content into tokens and lines
   const tokens = md.parse(content, {});
   const lines = content.split(helpers.newLineRe);
-  annotateTokens(tokens, lines);
-  // Create parameters for rules
-  const paramsBase = helpers.deepFreeze({
+  annotateAndFreezeTokens(tokens, lines);
+  // Create (frozen) parameters for rules
+  const paramsBase = {
     name,
     tokens,
-    lines,
-    frontMatterLines
-  });
+    "lines": Object.freeze(lines),
+    "frontMatterLines": Object.freeze(frontMatterLines)
+  };
   const lineMetadata =
     helpers.getLineMetadata(paramsBase);
   const codeBlockAndSpanRanges =