feat: add fenced-code-meta rule

README.md

@@ -89,6 +89,7 @@ export default defineConfig([
 | **Rule Name**                                                                  | **Description**                                                                                   | **Recommended** |
 | :----------------------------------------------------------------------------- | :------------------------------------------------------------------------------------------------ | :-------------: |
 | [`fenced-code-language`](./docs/rules/fenced-code-language.md)                 | Require languages for fenced code blocks                                                          |       yes       |
+| [`fenced-code-meta`](./docs/rules/fenced-code-meta.md)                         | Require or disallow metadata for fenced code blocks                                               |       no        |
 | [`heading-increment`](./docs/rules/heading-increment.md)                       | Enforce heading levels increment by one                                                           |       yes       |
 | [`no-bare-urls`](./docs/rules/no-bare-urls.md)                                 | Disallow bare URLs                                                                                |       no        |
 | [`no-duplicate-definitions`](./docs/rules/no-duplicate-definitions.md)         | Disallow duplicate definitions                                                                    |       yes       |

docs/rules/fenced-code-meta.md

@@ -0,0 +1,76 @@
+# fenced-code-meta
+
+Require or disallow metadata for fenced code blocks.
+
+## Background
+
+Fenced code blocks can include an info string after the opening fence. The first word typically specifies the language (e.g., `js`). Many tools also support additional metadata after the language (separated by whitespace), such as titles or line highlighting parameters. This rule enforces a consistent policy for including such metadata.
+
+## Rule Details
+
+This rule warns when the presence of metadata in a fenced code block's info string does not match the configured mode.
+
+Examples of **incorrect** code for this rule:
+
+````markdown
+<!-- eslint markdown/fenced-code-meta: "error" -->
+
+```js
+console.log("Hello, world!");
+```
+````
+
+## Options
+
+This rule accepts a single string option:
+
+- `"always"` (default): Require metadata when a language is specified.
+- `"never"`: Disallow metadata in the info string.
+
+Examples of **incorrect** code when configured as `"fenced-code-meta": ["error", "always"]`:
+
+````markdown
+<!-- eslint markdown/fenced-code-meta: ["error", "always"] -->
+
+```js
+console.log("Hello, world!");
+```
+````
+
+Examples of **correct** code when configured as `"fenced-code-meta": ["error", "always"]`:
+
+````markdown
+<!-- eslint markdown/fenced-code-meta: ["error", "always"] -->
+
+```js title="example.js"
+console.log("Hello, world!");
+```
+````
+
+Examples of **incorrect** code when configured as `"fenced-code-meta": ["error", "never"]`:
+
+````markdown
+<!-- eslint markdown/fenced-code-meta: ["error", "never"] -->
+
+```js title="example.js"
+console.log("Hello, world!");
+```
+````
+
+Examples of **correct** code when configured as `"fenced-code-meta": ["error", "never"]`:
+
+````markdown
+<!-- eslint markdown/fenced-code-meta: ["error", "never"] -->
+
+```js
+console.log("Hello, world!");
+```
+````
+
+## When Not to Use It
+
+If you aren't concerned with metadata in info strings, you can safely disable this rule.
+
+## Prior Art
+
+* [MD040 - Fenced code blocks should have a language specified](https://github.com/DavidAnson/markdownlint/blob/main/doc/md040.md)

src/rules/fenced-code-meta.js

@@ -0,0 +1,102 @@
+/**
+ * @fileoverview Rule to require or disallow metadata for fenced code blocks.
+ * @author TKDev7
+ */
+
+//-----------------------------------------------------------------------------
+// Type Definitions
+//-----------------------------------------------------------------------------
+
+/**
+ * @import { MarkdownRuleDefinition } from "../types.js";
+ * @typedef {"missingMetadata" | "disallowedMetadata"} FencedCodeMetaMessageIds
+ * @typedef {["always" | "never"]} FencedCodeMetaOptions
+ * @typedef {MarkdownRuleDefinition<{ RuleOptions: FencedCodeMetaOptions, MessageIds: FencedCodeMetaMessageIds }>} FencedCodeMetaRuleDefinition
+ */
+
+//-----------------------------------------------------------------------------
+// Rule Definition
+//-----------------------------------------------------------------------------
+
+/** @type {FencedCodeMetaRuleDefinition} */
+export default {
+	meta: {
+		type: "problem",
+
+		docs: {
+			recommended: false,
+			description: "Require or disallow metadata for fenced code blocks",
+			url: "https://github.com/eslint/markdown/blob/main/docs/rules/fenced-code-meta.md",
+		},
+
+		messages: {
+			missingMetadata: "Missing code block metadata.",
+			disallowedMetadata: "Code block metadata is not allowed.",
+		},
+
+		schema: [
+			{
+				enum: ["always", "never"],
+			},
+		],
+
+		defaultOptions: ["always"],
+	},
+
+	create(context) {
+		const [mode] = context.options;
+		const { sourceCode } = context;
+
+		return {
+			code(node) {
+				const lineText = sourceCode.lines[node.position.start.line - 1];
+				const fenceLineText = lineText.slice(
+					node.position.start.column - 1,
+				);
+
+				if (mode === "always") {
+					if (node.lang && !node.meta) {
+						const langIndex = fenceLineText.indexOf(node.lang);
+
+						context.report({
+							loc: {
+								start: node.position.start,
+								end: {
+									line: node.position.start.line,
+									column:
+										node.position.start.column +
+										langIndex +
+										node.lang.trim().length,
+								},
+							},
+							messageId: "missingMetadata",
+						});
+					}
+
+					return;
+				}
+
+				if (node.meta) {
+					const metaIndex = fenceLineText.lastIndexOf(node.meta);
+
+					context.report({
+						loc: {
+							start: {
+								line: node.position.start.line,
+								column: node.position.start.column + metaIndex,
+							},
+							end: {
+								line: node.position.start.line,
+								column:
+									node.position.start.column +
+									metaIndex +
+									node.meta.trim().length,
+							},
+						},
+						messageId: "disallowedMetadata",
+					});
+				}
+			},
+		};
+	},
+};