Add options.markdownItPlugins to support using markdown-it plugins when parsing.

.eslintrc.json

@@ -69,8 +69,8 @@
         "max-lines": "off",
         "max-lines-per-function": "off",
         "max-nested-callbacks": "error",
-        "max-params": ["error", 8],
+        "max-params": ["error", 9],
-        "max-statements": ["error", 20],
+        "max-statements": ["error", 22],
         "max-statements-per-line": "error",
         "multiline-comment-style": ["error", "separate-lines"],
         "multiline-ternary": "off",

README.md

@@ -386,6 +386,20 @@ Passing a `resultVersion` of `2` corresponds to a detailed format where each err
 includes information about the line number, rule names, description, as well as any
 additional detail or context that is available. This is the default.
 
+##### options.markdownItPlugins
+
+Type: `Array` of `Array` of `Function` and plugin parameters
+
+Specifies additional [markdown-it plugins](https://www.npmjs.com/search?q=keywords:markdown-it-plugin)
+to use when parsing input. Plugins can be used to support additional syntax and
+features for advanced scenarios.
+
+Each item in the top-level `Array` should be of the form:
+
+```js
+[ require("markdown-it-plugin"), plugin_param_0, plugin_param_1, ... ]
+```
+
 #### callback
 
 Type: `Function` taking (`Error`, `Object`)

lib/markdownlint.js

@@ -5,7 +5,7 @@
 const fs = require("fs");
 const path = require("path");
 const { URL } = require("url");
-const md = require("markdown-it")({ "html": true });
+const markdownIt = require("markdown-it");
 const rules = require("./rules");
 const shared = require("./shared");
 
@@ -289,7 +289,14 @@ function uniqueFilterForSortedErrors(value, index, array) {
 
 // Lints a single string
 function lintContent(
-  ruleList, name, content, config, frontMatter, noInlineConfig, resultVersion,
+  ruleList,
+  name,
+  content,
+  md,
+  config,
+  frontMatter,
+  noInlineConfig,
+  resultVersion,
   callback) {
   // Remove UTF-8 byte order marker (if present)
   content = content.replace(/^\ufeff/, "");
@@ -410,6 +417,7 @@ function lintContent(
 function lintFile(
   ruleList,
   file,
+  md,
   config,
   frontMatter,
   noInlineConfig,
@@ -420,8 +428,8 @@ function lintFile(
     if (err) {
       return callback(err);
     }
-    lintContent(ruleList, file, content, config, frontMatter, noInlineConfig,
+    lintContent(ruleList, file, content, md, config, frontMatter,
-      resultVersion, callback);
+      noInlineConfig, resultVersion, callback);
   }
   // Make a/synchronous call to read file
   if (synchronous) {
@@ -455,6 +463,12 @@ function lintInput(options, synchronous, callback) {
   const noInlineConfig = !!options.noInlineConfig;
   const resultVersion = (options.resultVersion === undefined) ?
     2 : options.resultVersion;
+  const md = markdownIt({ "html": true });
+  const markdownItPlugins = options.markdownItPlugins || [];
+  markdownItPlugins.forEach(function forPlugin(plugin) {
+    // @ts-ignore
+    md.use(...plugin);
+  });
   const results = newResults(ruleList);
   // Helper to lint the next string or file
   function lintNextItem() {
@@ -476,6 +490,7 @@ function lintInput(options, synchronous, callback) {
           ruleList,
           item,
           strings[item] || "",
+          md,
           config,
           frontMatter,
           noInlineConfig,
@@ -486,6 +501,7 @@ function lintInput(options, synchronous, callback) {
         lintFile(
           ruleList,
           item,
+          md,
           config,
           frontMatter,
           noInlineConfig,

package.json

@@ -36,6 +36,10 @@
     "glob": "~7.1.2",
     "istanbul": "~0.4.5",
     "js-yaml": "~3.12.0",
+    "markdown-it-for-inline": "~0.1.1",
+    "markdown-it-mathjax": "~2.0.0",
+    "markdown-it-sub": "~1.0.0",
+    "markdown-it-sup": "~1.0.0",
     "nodeunit": "~0.11.3",
     "rimraf": "~2.6.2",
     "toml": "~2.3.3",

test/markdownlint-test.js

@@ -4,6 +4,10 @@ const fs = require("fs");
 const path = require("path");
 const { URL } = require("url");
 const md = require("markdown-it")();
+const pluginInline = require("markdown-it-for-inline");
+const pluginMathjax = require("markdown-it-mathjax");
+const pluginSub = require("markdown-it-sub");
+const pluginSup = require("markdown-it-sup");
 const tv4 = require("tv4");
 const packageJson = require("../package.json");
 const markdownlint = require("../lib/markdownlint");
@@ -952,6 +956,7 @@ module.exports.readmeHeadings = function readmeHeadings(test) {
           "##### options.frontMatter",
           "##### options.noInlineConfig",
           "##### options.resultVersion",
+          "##### options.markdownItPlugins",
           "#### callback",
           "#### result",
           "### Config",
@@ -2451,3 +2456,79 @@ module.exports.customRulesDoc = function customRulesDoc(test) {
     test.done();
   });
 };
+
+module.exports.markdownItPluginsSingle =
+  function markdownItPluginsSingle(test) {
+    test.expect(2);
+    markdownlint({
+      "strings": {
+        "string": "# Heading\n\nText [ link ](https://example.com)"
+      },
+      "markdownItPlugins": [
+        [
+          pluginInline,
+          "trim_text_plugin",
+          "text",
+          function iterator(tokens, index) {
+            tokens[index].content = tokens[index].content.trim();
+          }
+        ]
+      ]
+    }, function callback(err, actual) {
+      test.ifError(err);
+      const expected = { "string": [] };
+      test.deepEqual(actual, expected, "Unexpected issues.");
+      test.done();
+    });
+  };
+
+module.exports.markdownItPluginsMultiple =
+  function markdownItPluginsMultiple(test) {
+    test.expect(4);
+    markdownlint({
+      "strings": {
+        "string": "# Heading\n\nText H~2~0 text 29^th^ text"
+      },
+      "markdownItPlugins": [
+        [ pluginSub ],
+        [ pluginSup ],
+        [ pluginInline, "check_sub_plugin", "sub_open", test.ok ],
+        [ pluginInline, "check_sup_plugin", "sup_open", test.ok ]
+      ]
+    }, function callback(err, actual) {
+      test.ifError(err);
+      const expected = { "string": [] };
+      test.deepEqual(actual, expected, "Unexpected issues.");
+      test.done();
+    });
+  };
+
+module.exports.markdownItPluginsMathjax =
+  function markdownItPluginsMathjax(test) {
+    test.expect(2);
+    markdownlint({
+      "strings": {
+        "string":
+          "# Heading\n" +
+          "\n" +
+          "$1 *2* 3$\n" +
+          "\n" +
+          "$$1 *2* 3$$\n" +
+          "\n" +
+          "$$1\n" +
+          "+ 2\n" +
+          "+ 3$$\n"
+      },
+      "markdownItPlugins": [ [ pluginMathjax ] ],
+      "resultVersion": 0
+    }, function callback(err, actual) {
+      test.ifError(err);
+      const expected = {
+        "string": {
+          "MD032": [ 8 ]
+        }
+      };
+      test.deepEqual(actual, expected, "Unexpected issues.");
+      test.done();
+    });
+  };