Introduce options.markdownItFactory (and remove options.markdownItPlugins) so the markdown-it parser can be removed as a direct dependency because it is no longer used by default.

lib/markdownlint.mjs

@@ -447,7 +447,7 @@ function getEnabledRulesPerLineNumber(
  * names.
  * @param {string} name Identifier for the content.
  * @param {string} content Markdown content.
- * @param {Plugin[]} markdownItPlugins Additional plugins.
+ * @param {MarkdownItFactory} markdownItFactory Function to create a markdown-it parser.
  * @param {Configuration} config Configuration object.
  * @param {ConfigurationParser[] | null} configParsers Configuration parsers.
  * @param {RegExp | null} frontMatter Regular expression for front matter.
@@ -462,7 +462,7 @@ function lintContent(
   aliasToRuleNames,
   name,
   content,
-  markdownItPlugins,
+  markdownItFactory,
   config,
   configParsers,
   frontMatter,
@@ -502,7 +502,7 @@ function lintContent(
   // Parse content into lines and get markdown-it tokens
   const lines = content.split(helpers.newLineRe);
   const markdownitTokens = needMarkdownItTokens ?
-    requireMarkdownItCjs().getMarkdownItTokens(markdownItPlugins, preClearedContent, lines) :
+    requireMarkdownItCjs().getMarkdownItTokens(markdownItFactory, preClearedContent, lines) :
     [];
   // Create (frozen) parameters for rules
   /** @type {MarkdownParsers} */
@@ -754,10 +754,9 @@ function lintContent(
  * Lints a file containing Markdown content.
  *
  * @param {Rule[]} ruleList List of rules.
- * @param {Object.<string, string[]>} aliasToRuleNames Map of alias to rule
- * names.
+ * @param {Object.<string, string[]>} aliasToRuleNames Map of alias to rule names.
  * @param {string} file Path of file to lint.
- * @param {Plugin[]} markdownItPlugins Additional plugins.
+ * @param {MarkdownItFactory} markdownItFactory Function to create a markdown-it parser.
  * @param {Configuration} config Configuration object.
  * @param {ConfigurationParser[] | null} configParsers Configuration parsers.
  * @param {RegExp | null} frontMatter Regular expression for front matter.
@@ -773,7 +772,7 @@ function lintFile(
   ruleList,
   aliasToRuleNames,
   file,
-  markdownItPlugins,
+  markdownItFactory,
   config,
   configParsers,
   frontMatter,
@@ -793,7 +792,7 @@ function lintFile(
       aliasToRuleNames,
       file,
       content,
-      markdownItPlugins,
+      markdownItFactory,
       config,
       configParsers,
       frontMatter,
@@ -860,7 +859,9 @@ function lintInput(options, synchronous, callback) {
   const resultVersion = (options.resultVersion === undefined) ?
     3 :
     options.resultVersion;
-  const markdownItPlugins = options.markdownItPlugins || [];
+  const markdownItFactory =
+    options.markdownItFactory ||
+    (() => { throw new Error("The option 'markdownItFactory' was required (due to the option 'customRules' including a rule requiring the 'markdown-it' parser), but 'markdownItFactory' was not set."); });
   const fs = options.fs || nodeFs;
   const aliasToRuleNames = mapAliasToRuleNames(ruleList);
   const results = newResults(ruleList);
@@ -892,7 +893,7 @@ function lintInput(options, synchronous, callback) {
         ruleList,
         aliasToRuleNames,
         currentItem,
-        markdownItPlugins,
+        markdownItFactory,
         config,
         configParsers,
         frontMatter,
@@ -911,7 +912,7 @@ function lintInput(options, synchronous, callback) {
         aliasToRuleNames,
         currentItem,
         strings[currentItem] || "",
-        markdownItPlugins,
+        markdownItFactory,
         config,
         configParsers,
         frontMatter,
@@ -1473,6 +1474,29 @@ export function getVersion() {
  * @property {RuleFunction} function Rule implementation.
  */
 
+/**
+ * Method used by the markdown-it parser to parse input.
+ *
+ * @callback MarkdownItParse
+ * @param {string} src Source string.
+ * @param {Object} env Environment sandbox.
+ * @returns {import("markdown-it").Token[]} Tokens.
+ */
+
+/**
+ * Instance of the markdown-it parser.
+ *
+ * @typedef MarkdownIt
+ * @property {MarkdownItParse} parse Method to parse input.
+ */
+
+/**
+ * Gets an instance of the markdown-it parser. Any plugins should already have been loaded.
+ *
+ * @callback MarkdownItFactory
+ * @returns {MarkdownIt} Instance of the markdown-it parser.
+ */
+
 /**
  * Configuration options.
  *
@@ -1484,7 +1508,7 @@ export function getVersion() {
  * @property {RegExp | null} [frontMatter] Front matter pattern.
  * @property {Object} [fs] File system implementation.
  * @property {boolean} [handleRuleFailures] True to catch exceptions.
- * @property {Plugin[]} [markdownItPlugins] Additional plugins.
+ * @property {MarkdownItFactory} [markdownItFactory] Function to create a markdown-it parser.
  * @property {boolean} [noInlineConfig] True to ignore HTML directives.
  * @property {number} [resultVersion] Results object version.
  * @property {Object.<string, string>} [strings] Strings to lint.
@@ -1501,7 +1525,7 @@ export function getVersion() {
  *
  * @callback ToStringCallback
  * @param {boolean} [ruleAliases] True to use rule aliases.
- * @returns {string}
+ * @returns {string} Pretty-printed results.
  */
 
 /**